Explore, inspire, discover: practical work in science

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Practical Work in Science Explore… Discover… Inspire…

Transcript of Explore, inspire, discover: practical work in science

Page 1: Explore, inspire, discover: practical work in science

Practical Work in Science

Explore…

Discover…

Inspire…

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“Practical work mirrors the pioneering investigative and exploratory nature of science”Teacher response to SCORE questionnaire

Foreword

What do I really remember about doing science at school? Making a cardboard aeroplane in physics, colourful and explosive experiments in chemistry, looking at the intricate structure of plants and bodies down a microscope in biology. Above all, science is a practical subject. Most of what we know about how the world works was discovered, not by sitting in a chair and thinking hard, but by getting hands-on: pulling things apart, putting them back together, testing out ideas. Practical science is all about ‘learning by doing’. Students achieve a deeper level of understanding by finding things out for themselves, and by experimenting with techniques and methods that have enabled the secrets of our bodies, our environment, the whole universe – to be discovered.

So – brains on, hands on, get practical!

Dr Alice RobertsAnatomistUniversity of Bristol

Photograph by Dave Pratt

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Introduction

Activity grids

General health and safety guidance

Upper primary activities:Bone mystery: Living thingsMaking sandcastles: MaterialsBishops can fl y: Forces

Secondary biology experiments:No stomach for it: Modelling the effect of antacid medicationBiodiversity in your backyard: Fieldwork using your school playing fi eldGoing up in smoke: Collecting and analysing the products of burning tobaccoBrine date: Mating behaviour and sexual selection in brine shrimpsMicrobes ate my homework: Investigating how microbes help us to break down cellulose and recycle plant materialA window on the past: How stomatal density adapts in changing environments

Contents

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ChemistryBiology Physics

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Secondary chemistry experiments:A matter of balance: The combustion of iron woolRed cabbage indicator: Making a pH indicatorSoot surveys: Investigating air pollutionHydrogels in the home: Hair gel and disposable nappiesDiscovering the formula: Finding the formula of hydrated copper(II) sulfatePreparing perfumes: Making esters from alcohols and acids

Secondary physics experiments:Bolt from the blue:Timing a 100 m run accurately Feeling the pressure:Investigating the effects of atmospheric pressure Power from the Sun:What affects the output of a solar panel? Does the Earth move?Photographing the night sky Kicking up a force:Investigating the force used to kick a footballMaking sparks:Demonstrating the ionising effects of alpha radiation

Further information

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Introduction

Hands-on learning experiences are key to the development of skills and the tying together of practical and theory. Good quality practical work can not only engage students with the processes of scientifi c enquiry, but also communicate the excitement and wonder of the subject.

This booklet has been designed to illustrate a range of reasons why you might do practical work, and to direct you to sources of high quality practical activities for you to use in your classroom. Whilst the focus of this booklet is practical work in secondary science, a few primary level activities have also been included to highlight the importance of transition. Many secondary schools have links with colleagues in primary schools, and an understanding of each phase is important to be able to help students through the diffi cult transition from Key Stage 2 to 3.

There is a wide range of possible purposes for including practical work in science lessons. Any particular piece of work should have its purposes made explicit to pupils if they are to benefi t fully from it. If not, there is a danger of pupils seeing practical work merely as a break from the more routine activities of speaking, listening and writing.

The activities chosen here illustrate a range of purposes and highlight

different types of practical activity that could be used to teach various topics in the science curriculum. The selections are purely illustrative and we recommend that you take a look at the original sources (particularly www.practicalbiology.org, www.practicalchemistry.org and www.practicalphysics.org) for further examples, and use the directory at the back of the booklet to help you fi nd an activity to suit your needs.

The activities have been categorised into Upper Primary (age 8-11), Lower Secondary (age 12-14), Upper Secondary (age 15-16), and Post-16. Often, however, activities can be adapted for use with more than one age group. The activities have also been categorised by purpose, and as you will see in the table, many of the activities fall into more than one category: Investigations including teamwork, Extended enquiry, Challenging existing ideas, Out of the classroom, Use of ICT, The ‘messiness’ of real data, Stimulating demonstrations, and Developing skills.

We would encourage Heads of Science to look at what is being offered in terms of practical work within their own institutions and ensure that the full range of purposes are covered. A blank table has been provided that could be photocopied and completed by departments.

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“Science without practical is like swimming without water. ” Teacher response to SCORE questionnaire

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Primary Science

Bone mystery: Living things X X X X X

Making sandcastles: Materials X X X

Bishops can fl y: Forces X X X X

Biology

No stomach for it X X X

Biodiversity in your backyard X X X X X X X

Going up in smoke X X X X X

Brine date X X X X X

Microbes ate my homework X X X X X

A window on the past X X X X X

Chemistry

A matter of balance X X X

Red cabbage indicator X X X

Soot surveys X X X X X

Hydrogels in the home X X

Discovering the formula X X X

Preparing perfumes X X X X

Physics

Bolt from the blue X X X

Feeling the pressure X X X X

Power from the Sun X X X X

Does the Earth move? X X X

Kicking up a force X X X

Making sparks X X

Activities categorised by level and purpose

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Complete this table with your own activities, and assess their purposes

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General health and safety guidance

See the health and safety notes in each experiment. The following is general guidance. Health and safety in school and college science affects all concerned: teachers and technicians, their employers, students, their parents or guardians, as well as authors and publishers.

These guidelines refer to procedures in the United Kingdom. If you are working in another country you may need to make alternative provision.

Health & safety checkingAs part of the reviewing process, the experiments in this booklet have been checked for health and safety. In particular, we have attempted to ensure that:• all recognized hazards have

been identifi ed, • suitable precautions are suggested, • where possible, the procedures

are in accordance with commonly adopted model (general) risk assessments,

• where model (general) risk assessments are not available, we have done our best to judge the procedures to be satisfactory and of an equivalent standard.

AssumptionsIt is assumed that:• practical work is conducted in a

properly equipped and maintained laboratory,

• rules for student behaviour are strictly enforced,

• mains-operated equipment is regularly inspected, properly maintained and appropriate records are kept,

• care is taken with normal laboratory operations such as heating substances and handling heavy objects,

• good laboratory practice is observed when chemicals are handled,

• eye protection is worn whenever risk assessments require it,

• any fume cupboard used operates at least to the standard of Building Bulletin 88,

• students are taught safe techniques for such activities as heating chemicals, smelling them, or pouring from bottles,

• hand-washing facilities are readily available in the laboratory.

Teachers’ and their employers’ responsibilitiesUnder the COSSH Regulations, the Management of Health and Safety at Work Regulations, and other regulations, employers are responsible for making a risk assessment before hazardous procedures are undertaken or hazardous chemicals used or made. Teachers are required to cooperate with their employers by complying with such risk assessments.

However, teachers should be aware that mistakes can be made. Therefore, before carrying out any practical activity, teachers should always check that what they are proposing is compatible with their

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employer’s risk assessments and does not need modifi cation for their particular circumstances. Any local rules issued by the employer must always be followed, whatever is recommended here. However, far less is banned by employers than is commonly supposed.

Be aware that some activities, such as the use of radioactive material, have particular regulations that must be followed.

Reference materialModel (general) risk assessments have been taken from, or are compatible with:CLEAPSS Hazcards (see annually updated CLEAPSS Science publications CD-ROM)CLEAPSS Laboratory handbook (see annually updated CD-ROM)CLEAPSS Recipe cards (see annually updated CD-ROM)ASE Safeguards in the school laboratory 11th edition 2006ASE Topics in Safety 3rd edition, 2001

ProceduresClearly, you must follow whatever procedures for risk assessment your employers have laid down. As far as we know, almost all the practical work and demonstrations in this booklet are covered by the model (general) risk assessments detailed in the above publications. Therefore, in most schools and colleges, you will not need to take further action, other than to consider whether any customisation is necessary for the particular circumstances of your school or class.

Special risk assessmentsOnly you can know when your school or college needs a special risk assessment. But thereafter, the responsibility for taking all the steps demanded by the regulations lies with your employer.

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Upper primary activities

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“Practical work is doing things with stuff. ”11 year old pupil

IntroductionPractical work lies at the heart of primary science. Children need opportunities to develop practical and enquiry skills in order to engage with the world in a scientifi c way and to make sense of what they are learning about living things, the environment, materials and physical processes. Hands-on experience promotes curiosity and engagement and provides opportunities for the discussion and questioning which develop understanding. Practical work can take place inside or outside the classroom, and can happen at any point in a unit of work or lesson. It may be a fi ve minute demonstration, a short activity to practise using an unfamiliar piece of equipment or an extended enquiry. What it must be is a varied and integral part of the learning process which promotes thinking as well as doing.

Upper primary activities:Bone mystery: Living thingsMaking sandcastles: MaterialsBishops can fl y: Forces

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Bone mystery:Living things

IntroductionThis activity presents children with a mystery to be solved when a skeleton is discovered during renovation work at a local site of historical interest. It requires children to make decisions about what data to collect, to measure accurately and to fi nd patterns in their data. They will use their knowledge that the skeleton grows until adulthood.

Lesson organisation This activity takes place over two lessons: one for planning and obtaining data, the second for presenting the data and drawing conclusions.Measurements will need to be taken from children of different ages and from adults. Arrangements will need to be made with colleagues to ensure minimal disruption of lessons. Children work in pairs to make the measurements. You may wish them to work in larger groups when planning the investigation so that 2 or 3 pairs can combine their data into a larger total sample.

Equipment and materials• Letter / news report• Model skeleton or ICT / paper

images of a skeleton (see note 1)• Selection of rulers, metre sticks and

tape measures, enough to allow a choice for each pair of pupils. Calipers may also be useful if available.

• Spreadsheet or graphing software (optional)

Technical notes and safety1 If a model is not available an archaeologists report, with data about the skeleton, should be used.

Procedurea Introduce the activity with a letter or news report about the discovery of a skeleton buried at a local historical site. It is clearly ancient but, as yet, archaeologists have very little information about it. The task for the class is to try to determine what age the individual was when they died. In order to answer the question the children will need to make comparisons between the skeleton and people of various ages in their school. The bones have been disturbed and have not yet been reassembled into a whole skeleton so children will have to make measurements of individual bones. No measurements are available yet but assure the pupils that the archaeologists will send these by the time of their next lesson.b Using a model skeleton or suitable images discuss what measurements it would be possible to take from a living person in order to make comparisons with the skeleton. Pairs or groups of children decide what measurement to take and plan their investigation. They then make and record the measurements.

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c In the second lesson the data is presented as a bar chart grouped by class or age or as a scattergraph with age plotted against bone measurement. This can be done using ICT. Discuss patterns in the sets of data. d Reveal to the children that the archaeologist’s data about the skeleton has now arrived. This will either be in the form of measurements on a table or diagram or, if a suitably sized model skeleton is available, as a reconstruction of the actual skeleton.

Children compare the measurements of the skeleton with their own fi ndings and decide on the likely age range of the mystery individual. Older or more able children can use combined evidence from different measurements to report an overall conclusion to the archaeologist.

Teaching notesWhen planning their investigation you may want to prompt pupils to consider and justify some or all of the following decisions (depending on age and ability):

• What measuring equipment to use.• Where exactly to measure to and

from on each person. • Which year groups to sample –

do they need to choose all years to fi nd a pattern?

• How many people in each year group to measure.

• Whether they need the same numbers of boys and girls.

• How they will choose which children in a class to measure – the tallest, the shortest, a random selection.

• Which adults to measure.If doing this investigation for the fi rst

time, without a model skeleton, you will need to look at the data collected by your pupils in order to choose suitable measurements to include in the archaeologist’s report for the second lesson.

Children may also consider evidence that people in the past were, on average, shorter than we are now. How might this affect their conclusion?

The mystery can be further extended into cross curricula work by introducing evidence which allows children to draw further conclusions about when the person may have lived and who they might have been.

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Making sandcastles:Materials

Lesson organisation This activity could be completed in one lesson. It can be extended for older children to provide the time to explore and try different ideas for data collection. Children work in small groups (ideally not more than four).

Equipment and materialsEach group will need:• Tray of dry sand (see note 1)• Jug of water (more may be needed

if there is limited access to water)• Small containers for making

sandcastles• A range of equipment for

measuring volume e.g. beakers, measuring cylinders

• Other equipment such as a camera, timers / stopwatches and masses may also be requested by the children.

Technical notes and safety1 Fine sand may blow or be rubbed into the eyes. Sand should be handled sensibly and pupils should be reminded not to touch their eyes.2 Wash hands after the activity.

Procedurea Introduce the activity by attempting to demonstrate making a sandcastle using dry sand. Children should recognise that you are unsuccessful because you have

not added water. Ask the children how much water you need to add. There is unlikely to be a consensus so the challenge for the class is to investigate ‘What is the best mixture of sand and water for making sandcastles?’b Provide each group with a tray of sand and jug of water. Other equipment should be available for the children to choose. The group will need to discuss how they will judge / measure which is the most successful sandcastle. They will also need to consider how to present their fi ndings clearly to the rest of the class. c Compare the results from each group and discuss the reasons for any differences.

Teaching notesThe investigation question is open ended so it should stimulate discussion and allow groups of children to make their own decisions about what criteria they will use and what measurements or observations they will make.

Responses may range from a simple ranking of the sandcastles based on appearance, which could be recorded by sketching or using a digital camera, to measurements of how much weight each sandcastle can support. Some methods of data collection will be more successful than others and children should be encouraged to evaluate different methods suggested by the group.

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IntroductionIn this investigation children mix sand and water to fi nd the ideal proportions for making a sandcastle. It promotes discussion as they agree on their criteria for identifying the best mixture. The activity can be used across the primary age range: younger pupils can make observations and simple measurements in a familiar context while older children are challenged by fi nding more sophisticated ways to collect and present measured data.

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Lesson organisationThe introductory activity and exploration involve students working individually with their own paper model. This leads to an investigation where they work in small groups of not more than three.

Equipment and materials• A4 paper, several sheets per pupil• Scissors• Paper clips • Rulers

Technical notes and safetyIf students are investigating releasing their model from above their own height (not essential but may be part of exploratory activities) they should stand on PE or playground equipment and not classroom furniture. (Refer to Be Safe! p12)

Procedurea Setting the problemQuite simply the students are challenged to make a piece of A4 paper fl oat across the classroom. They are allowed to cut and fold the paper in any way they wish but are not allowed to apply any force when releasing the paper. The only forces that can act on the paper as it falls are gravity and the resistance caused by air particles. The students spend at least 5 minutes exploring a number of options but invariably admit they need help.b Making the model The students are shown how to make a Bishop’s hat by folding and cutting the paper to form an isosceles right angle triangle and then folding the hypotenuse twice inwards thinly like folding a scarf, before joining the ends to form a mitre or Bishop’s hat.

Bishops can fl y:Forces

IntroductionThe initial problem solving challenge to make a piece of A4 paper fl oat across the classroom leads to the systematic exploration of the physical and material phenomena of balance, friction, forces, gravity and the properties of common materials. The activity starts with a problem solving approach and then with further exploration leads to the identifi cation and testing of trends and patterns, followed by the communication of the processes used and tentative explanations developed.

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All the students are required to make a model that works. The model is held horizontally near the tail with the tail on the underside of the model and released. As it falls the Bishops hat will gently glide across the classroom. c Exploring the model and its fl ight patternTime needs to be spent making a range of Bishop’s hats exploring ways to improve the fl ight pattern, direction and distance, by changing the centre of balance, by adding paper clips or the fl ow of air, by folding the tail up and down. Following this exploration a discussion of what is involved when the paper fl oats across the room is conducted including: • Talking about the movement through

the air / and resulting air fl ow.• Identifying the manner in which

the model moves.• Identifying some questions

using the lead, I wonder what will happen if…?

• Making a list of questions that could be investigated.

• Identifying one that the whole class can complete.

d As a class investigate“I wonder what will happen to the fl ight pattern if I change the way the air fl ows over the tail by changing the shape of the tail?”

Depending on their experience the students, in small groups of no more than three, can plan a simple investigation to identify the effect changing the tail has on the fl ight pattern. It may be appropriate to introduce the notion of multiple testing when looking for patterns and the use of symbols to communicate what has been observed. For example the students could draw symbols to show the fold in the tail and a curve to show the glide path. The students will test their models a number of times and as a class build up a table to highlight patterns.

The teacher could use one group’s results and record them in pictorial form on the white board or large sheet of paper. (See example in teaching notes).

In a class discussion ask the student to identify inferences that can be drawn from these patterns that can retested or evaluated and then turn the inferences into explanatory statements such as “when the tail is folded down the fl ow of air is changed and it causes the fl ight pattern to change” or “with our models it makes the model fall directly down” If the students have not made the connection to aircraft and birds this would be a suitable time to link this experience to other similar situations.

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Tail shape Test 1 Test 2 Test 3 Test 4Exploring fl ight patterns / glide paths of Bishop’s hat when tail shape is changed

e Finally discuss the activity from a science perspective; ‘What makes this activity a science activity?’, ‘What conventions of science activity have been applied as we have completed this exploration?’.

For example, a scientifi c idea is an idea where the evidence supporting the idea has been tested and this testing can be replicated and scientist use symbols to record and communicate data and ideas.

Teaching notesExample results table:

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BiologyThe science of the life processes and habits of all living things, from tiny single cells to whole organisms and how they interact with each other and their environment.

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“Doing practical work is fun! We learn lots by trying things out and then explaining what we have found out to others. ”15 year old pupil

IntroductionStudents come to understand how living things behave through opportunities to engage in practical activities. Biology involves making sense of complex systems at the level of cells, organisms and whole ecosystems. Often biologists have to devise models that isolate individual processes for closer study, have to control the many variables in a system to see the effect of each more clearly, or have to study changes over long time scales. A successful biologist will master key ideas in chemistry and physics, and use mathematical tools for interpreting and analysing data. Much of what students learn in biology is directly applicable to their own lives, as a growing understanding of other living things helps them to learn about the human body and the wider environment.

Secondary biology experiments:No stomach for it: Modelling the effect of antacid medicationBiodiversity in your backyard: Fieldwork using your school playing fi eldGoing up in smoke: Collecting and analysing the products of burning tobaccoBrine date: Mating behaviour and sexual selection in brine shrimpsMicrobes ate my homework: Investigating how microbes help us to break down cellulose and recycle plant materialA window on the past: How stomatal density adapts in changing environments

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Lesson organisationOrganisation may depend on the number of pH probes and meters you have, or the range of antacids you want to try. Students working in pairs would each be able to investigate one or two antacids.

Apparatus and ChemicalsFor the class – set up by technician/ teacher:• Hydrochloric acid, dilute, 0.01 mol

dm-3, 100 cm3 for each antacid for each working group (refer to Hazcard 47A and note 1)

• Universal indicator solution, in dropping bottles (note 2)

• Antacids, with details of dosage from packaging

For each group of students:• Beaker, 100 cm3, 2 per antacid to

be tested• Mortar and pestle• Measuring cylinder, 100 cm3

Technical notes and safety1 Hydrochloric acid is described on Hazcard 47A as irritant at concentrations above 2.0M, causes burns and is irritating to the respiratory system. The acid used here is much

more dilute and presents a minimal hazard to students.2 Universal indicator – see Hazcard 31 and Recipe card 32. The bottled solution is highly fl ammable.

Procedure SAFETY: Take care when making up the dilute acid.Preparation by the teachera Make up the dilute hydrochloric acid by serial dilution (1 in 10, twice) from 1 mol dm-3 acid. (See note 1.)b Copy (and enlarge if necessary) the details of typical doses of antacids from the packaging.c Set up a few beakers of 50 cm3 of water with indicator to show what a neutral pH would look like.Investigationd Measure 50 cm3 of dilute acid into each of two beakers and add enough Universal indicator to get a clearly visible colour. (See note 2.)e Sit both beakers on a sheet of white paper. f Keep one beaker for comparison as small changes in the acid pH range can be hard to see.g Add a normal dose of antacid to the other beaker and watch the colour change. If the antacid is in

No stomach for it: Modelling the effect of antacid medication

IntroductionThis practical has been developed with support from the British Pharmacological Society and the Physiological Society. Pupils monitor the changing pH of a sample of dilute hydrochloric acid as doses of over-the-counter antacid preparations dissolve. Typical doses of a range of over-the-counter antacid preparations (powders, tablets and liquids) are added to a volume of dilute hydrochloric acid that models the volume and concentration of our stomach contents. Pupils monitor the changing pH, and compare the effects of different preparations and discuss the short and long-term consequences of using each medicine.

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tablet form, crush the tablet in a mortar with a pestle before adding to the acid.h Repeat with other antacids.i Decide which antacid is making the greatest change, or the quickest change. Record any other observations – such as effervescence.j If using a pH probe, plot a graph of pH against time over 10-15 minutes.

Teaching notesThe approximate relaxed volume of our stomach is 50 cm3, but it is able to expand to nearly 4 dm3. The lowest pH of secreted acid is about 0.8, but it is diluted in the stomach to an ideal pH of around 1.4. The stomach secretes acid to produce the optimum pH for the action of pepsin. An excess of acid is sometimes produced, which results in acid indigestion (in the short term) or could result in ulceration of the stomach lining (if high concentrations of acid persist). Antacids have been developed to treat short-term excesses. Other pharmaceuticals are used to treat long-term imbalance of acid production.

Students may be surprised how little the pH changes when the antacid is added.

It is interesting to compare liquids with powders, and to see just how slowly an uncrushed tablet reacts.

There are ingredients other than antacids in many over-the-counter preparations that have an effect on indigestion. Some include a mucilaginous component that coats the stomach lining and may protect

the lining tissue from damage by acid. This could lead into a more detailed exploration of the structure of the stomach and the different tissues that make up the organ.

Discuss the issues associated with long-term use of antacid preparations. Ideas are listed below.• Pepsin operates best at acid pHs,

so using antacids before meals, or immediately after, could reduce the rate of digestion.

• The body has many mechanisms that maintain balance. Is it possible that taking antacid medication regularly would, in fact, stimulate the gastric lining to make more acid to restore normal pH?

Further informationwww.rsc.org/education/teachers/learnnet/pdf/LearnNet/rsc/Kev51-60.pdf This is from the RSC’s ‘Classic Chemistry Experiments’ – a formal titration of preparations of indigestion tablets with hydrochloric acid. You could use this as a more quantitative extension activity linked to the above investigation.

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Lesson organisationStudents working in groups of three (or four) can each take a role in the survey. Depending on your students, it should be possible to carry out your survey of one or two areas of the school grounds in one lesson. Then, presenting and analysing the results could be completed in the next lesson. Collecting data to investigate hypotheses might be spread over several weeks. Each time the students survey the area, they will be more effi cient as they become more familiar with the technique and the species present.

Apparatus and ChemicalsFor the class – set up by technician/ teacher:• Tape measure, 20 m, 2 (or string

marked into metres)• Number cards, 1-20, in each of two

bags (or bowls or buckets)OR 20-sided dice, 2 (ask someone who plays war games or fantasy role-play games)

• Pinboard, or sheet of cardboard (for step 1) with sticky tape or pins to attach plants to the board

For each group of students:• Quadrat – a wire frame

0.25 m x 0.25 m, or 0.5 m x 0.5 m• Key to plants – see links• Clipboard, 1• Pencil, 1• Record sheet – devised by teacher

or students

Technical notes and safety1 Choosing your quadrat: A quadrat, not a ’quadrant‘, is a frame used for sampling an area and it is usually square. Smaller quadrats present a smaller number of species to be identifi ed. However, groups taking 10 samples each with 0.5 m x 0.5 m quadrats will collect information about a more signifi cant sample of the area.2 Refer to the supplementary risk assessment (SRA 08) dated October 2006 from CLEAPSS for more details of hazards and control

Biodiversity in your backyard: Fieldwork using your school playing fi eld

IntroductionIntroduce the core fi eldwork technique of random sampling with quadrats in your school grounds. Random sampling allows you to make an estimate of the populations of different species in any area. It should eliminate sampling bias introduced by the sampler selecting areas that look interesting or easier to count. Develop an understanding of plant biodiversity in the grassland typical of school playing fi elds. Use the Field Studies Council key Playing fi eld plants to identify the species that you fi nd. Students are often surprised by the biodiversity in an area they think of as ‘grass’. There is scope for students to develop and investigate hypotheses about plant distribution based on observations and measurements of factors such as soil, moisture, light intensity and wind speed. Observations of human or other animal activity in the area, and background information about the characteristics of common playing fi eld plants, provide further starting points for developing hypotheses to test over short or long time scales

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measures for working outdoors. This risk assessment advises that it is important to consider the following.a How students are likely to behave when working outdoors, and suggests that the normal ratio for classrooms or laboratories may not be adequate to ensure safe working outdoors.b Provision for hand washing needs to be readily available whenever plants and soil are handled. You might consider the use of alcohol gels or other hand sanitisers with paper towels.c The low risk of diseases such as toxoplasmosis and toxocariasis from plants and soil contaminated by cat or dog faeces. Covering any cuts and grazes and ensuring that children do not eat snacks or sweets while working outdoors as well as confi rming thorough hand washing reduce this risk. d The possibility of allergic reactions to substances encountered outdoors, such as pollen, plant sap, contact with leaves, insect bites and stings or some hairy caterpillars. Be alert to the development of any allergic reactions or asthma symptoms and deal with them according to your school’s normal policy.e The risk of sunburn on sunny summer days if exposed for more than 20-30 minutes.f Risks of injury when using and carrying tools or heavy loads of unfamiliar equipment which should be assessed for each individual in the specifi c environment.g Hazards such as building rubble, pot holes in the ground, unsafe

structures or items such as broken glass and other ‘litter’ that could be hidden in grass or soil. Check the area in advance and be aware of any such risks that could cause wounds or cause children to trip and fall. Remove the hazards or identify them with warning signs and keep children away from them.3 Sample size: You can test whether your sample size is big enough by comparing the results from two groups sampling the same area. If their results are very similar, your sample size is big enough to be a good estimate of the populations in the area.

Ethical issuesIt is useful to consider how the act of surveying the area and collecting plants might damage or change the environment surveyed. Although this is probably not an issue for a school playing fi eld (which is regularly mowed and trampled in normal use), it would certainly be an issue for a natural or ‘wild’ area.

Procedure SAFETY: Make a full risk assessment for the outdoor activity and put in place any necessary control measures.Preparationa Check the area where you will be working for hazards.

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b Make a preliminary survey yourself to identify the most common plants (other than grass). c Collect your equipment together and check it for hazards such as sharp edges. Consider attaching tags of brightly-coloured electrical tape to make it easier to locate equipment that gets ‘lost’ on the site.d Organise your students in groups of three (or four) and identify their roles in the group.Step 1: Preliminary observationsa Stand in the area to be surveyed and make a simple plan drawing of key features – the direction of north, any nearby buildings, large plants (trees and shrubs), favoured paths across the area, slopes etc. Include information about the use of adjacent land and think about whether the site is open and exposed or sheltered by a belt of trees or buildings. b Make a note of any clearly visible features in the ‘grassland’ vegetation, such as areas of fl owering plants, worn grass or darker vegetation.Step 2: Identifying what species are presentc Give the students a quadrat per group. Place the quadrat on the ground and ask students to look closely at the plants and see how many different plants they can see. d Develop vocabulary to describe the differences between plants – for example key botanical features such as leaf veins, sepals, or the arrangement of fl ower clusters, and the shapes of leaves, the patterns of attachment of leaves to stems, the habit of the plant (ground-hugging, creeping, rosette etc). The table on

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the inside of the FSC key Playing fi eld plants will guide such observations and allow students to use them to identify the main species of plants.e Collect samples of the fi ve most common plants (other than grass). Write their names on the board and ask each group to bring and attach a sample of each plant to the board.

Step 3: Sampling the area – a random samplef Lay out your tape measures (or marked string) at right angles along two edges of the area to survey. Lay the two bags of numbers near the point where the tapes meet.g With students working in threes, ask one student to hold the quadrat, a second to pick a number from the bag on one line, the third to pick a number from the other bag on the other line. Then, the students who have numbers should replace the numbers and walk to that number on their line. The student with the quadrat uses their colleagues as place markers and places the quadrat where it is in line with both of them. Then all three can work together to identify the species in their quadrat and record the results.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

12

34

56

78

910

1112

1314

1516

1718

1920

Put the quadratwhere you meet

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h Send two students back to the bags on the lines to pick more numbers and randomly select the next quadrat position. Repeat step g.

Count

Don’t count

i Each group should assess the contents of around 10 quadrats to get a reliable estimate of the species distribution.Step 4: What to recordj In a preliminary investigation, or with younger students, a presence or absence of each species in each quadrat may be enough information. You can then collate the results to show the percentage of quadrats in which each species was found, which will give you a relative abundance of each species.k With older students, or to provide data you can analyse with mathematical tools, you will need to estimate and record the number of plants of each species in each quadrat or the percentage cover of each species in each quadrat. Step 5: Analysing the resultsl Use a spreadsheet to analyse the results and produce bar graphs or other plots of the data collected.m The simplest analysis would be of the percentage of sample quadrats

that each species appears in. n If you have information about frequency (or percentage cover) you can calculate the average frequency (or average percentage cover) of each species for each area sampled.

Teaching notesIt can be very rewarding with younger students simply to open their eyes to the diversity of plant species under their feet. Developing observational skills and learning which features of plants are important when distinguishing one species from another are signifi cant basic skills.

The detail of the data you gather will depend on the investigation you are exploring.

A 20 m x 20 m survey area covers 400 m2. A 0.25 m quadrat covers one sixteenth of a square metre and a 0.5 m quadrat covers one quarter of a square metre. So, with 10 groups collecting data from 10 quadrats each (100 quadrats surveyed), the group will have sampled 6.25 m2 with 0.25 m quadrats (about 1.6% of the area) or 25 m2 with 0.5 m quadrats (6.25% of the area). (See note 3.)

A random sample will give you some descriptions that characterise an area. So it is useful if you want to compare two contrasting habitats. You could make random samples on two different areas of grassland in the school – such as the playing fi eld and any open areas that get less foot traffi c, or two different parts of the playing fi eld to see if there are any differences.

It is possible using the method here for selecting your random

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sample point that two groups of students will survey the same square metre. For introductory exercises this should not pose a problem, but for more thorough investigations you could keep track of the areas sampled and ensure you do not survey any sample square twice.

There are several methods of quantifying biodiversity – apart from comparing a simple list of the number of species identifi ed in each area. One measure is ‘species richness’. Others include ‘range-size rarity’ and ‘taxic richness’. See links below, or make a wider internet search.

Qua

dra

t nu

mb

er

1

2

3

4

5

6

7

8

9

10

Species present

Numbers / percentages in each quadrat

Here is an example of a simple record sheet that you could use for your fi eld survey.

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You could survey to answer questions such as: Are there more daisies in mown or unmown grass? Is there more ribwort plantain where the grass is less trampled? Alternatively, after identifying differences in distribution of species between two areas, you can start to develop hypotheses that might explain the different distributions. These might depend on being able to collect further data about the areas. For example: Is the soil wetter where we fi nd more buttercups?

You could collect and collate information about the plants in the fi eld and maintain a database of distribution information (with photographs) over a number of years.

This kind of random sampling will probably not reveal any trends or changes across an area (such as differences near to or far from a regular walkway where plants are trampled). However, there are systematic sampling techniques that allow you to investigate changes along a line from one part of an area to another – such as a line transect or a belt transect. A good guide to ecological techniques will explain these techniques in more detail.

An example of a simple record sheet that you could use for your fi eld survey is shown.

Some questions to think about:1 What are the 5 main species in each area? 2 What do you think are the reasons for any differences?

3 How would you investigate these differences further?4 What has surprised you most about the diversity of plants on your school playing fi eld?

Further informationwww.fi eld-studies-council.org/publications/pubsinfoaspx?Code=OP97Details of the Field Studies Council key to Playing fi eld plants. This will be a great help in identifying the main plants and provides supplementary information about the plants to support hypothesis development and suggestions for further work. (Last accessed November 2008.)www.fi eld-studies-council.org/outdoorscience/diy.htmPart of the London Outdoor Science project – with details of how to make and use your own fi eldwork equipment. (Last accessed November 2008.)www.fi eld-studies-council.org/resources/index.aspxThe index to all the Field Studies Council on-line resources. (Last accessed November 2008.)http://internt.nhm.ac.uk/eb/homepage.shtmlThis is the homepage for a project called Exploring biodiversity (dated 2001) on the Natural History Museum (London) website. It includes interactive models that explain how to calculate species richness, range-size rarity and taxic richness. You will need to log in using Internet Explorer to view these pages. (Last accessed November 2008.)

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Going up in smoke: Collecting and analysing the products of burning tobacco

IntroductionDraw the smoke from a burning cigarette through apparatus that traps and analyses some of the components of the smoke. Establish the effect of unlit cigarettes on the apparatus by running the fi lter pump for 10 minutes. (There should be no effect.) Smoke at least two different cigarettes, and compare their effect on the white-coloured mineral wool and on the indicator solution. Discuss the differences between the cigarettes.

Lesson organisationThis procedure should be carried out in a fume cupboard as a teacher-led demonstration.

Apparatus and Chemicals(see fi gure 1 & 2 below)For the class – set up by technician/ teacher:This apparatus must be set up in a fume cupboard.Filter pump or hand-operated vacuum pump (see note 2)Clamp stand, boss and clamp, 2MatchesDishes to collect ash from cigarettesApparatus as in diagram 1 or diagram 2:• Conical fl ask, 250 cm3, 1 or 2• Glass tubes, bent to right angles, 2

or 4 (see note 3)

• T-piece, glass• Rubber bungs, two-holed, 1 or 2• Hard glass tube, shaped to hold

a cigarette, 1 or 2• White-coloured mineral wool,

superwool, glass wool or polymer wool for aquarist fi lters

Alternatives / additions:• connector to allow thermometer to

be held in the smoke stream near the cigarette

• U-tubes containing white-coloured mineral wool to replace tubes A and B

• hydrogencarbonate indicator (equilibrated with air) in place of Universal indicator.

Technical notes and safety1 Carry out the procedure in a fume cupboard.

topump

rubbertubing

direction of air flow

A

Universalindicator

Universalindicator

Universalindicator

lightedcigarette

cigaretteholder

cigaretteholder

cottonwool cottonwool cottonwoolrubbertubing

rubbertubing

A

lightedcigarette(type 1)

lightedcigarette(type 2)

B

direction of air flow

direction of air flow

topump

Fig. 1 Fig. 2

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2 If your water supply does not support a fi lter pump, use a hand-operated vacuum pump, or a syringe to draw air through the apparatus.3 Check that the tips of the longer glass tubes are below the surface of the indicator solution and the shorter glass tubes are well above the surface even if the liquid bubbles.4 Disassemble the apparatus in a fume-cupboard and avoid skin contact with the tars. This is essential. Wear protective gloves (preferably nitrile) and place the tar-soaked material in a plastic bag which is sealed before disposal with normal refuse. Wipe the glass with a paper towel soaked in a suitable solvent, such as ethanol (fl ammable) and dispose of the paper towel with the tarry wool. The apparatus is diffi cult to clean so re-use in future years. Store in a box or sealed plastic bag to contain the smell. (See CLEAPSS Laboratory Handbook, section 9.6.)

Procedure Cigarette packets carry health warnings and schools/ colleges are usually non-smoking premises on the grounds of the stated health risks of cigarette smoke. Set up the apparatus in a fume cupboard and avoid contact with the smoke and skin contact with the contents of the tubes at the end.

Parts of the apparatus near the cigarette may be hot at the end, so take care when disassembling to weigh the tubes.

Preparationa Find out the mass of tubes A and B and write the masses on paper associated with the apparatus.Investigationb This is often set up with one lit cigarette and the second unlit as a control. Consider running air through 2 unlit cigarettes (of different types) for 10 minutes to establish that this has no visible effect on the cotton wool or the indicator. Then you could use the apparatus to compare two different types of cigarette – for example normal and low tar, the same brand with and without its fi lter, packet cigarette vs hand-rolled.c Start the fi lter pump. Light the cigarette/s and run until the cigarette is nearly smoked. d Switch off the fi lter pump and see what happens to the fi nal few millimetres of cigarette. (This will be particularly interesting if you are comparing packet cigarette with hand-rolled as rolling tobacco contains fewer ingredients to keep it burning.)e Note the visible changes to the cotton wool and the indicator.f Find the mass of tubes A and B and calculate the increases in mass.g Disassemble the apparatus avoiding skin contact with the tar (see note 3).

Teaching notesThis demonstration makes a good starter activity for the subject of smoking. Students may be surprised at the amount of tar collecting in the mineral wool from just one cigarette. If you want to pass the wool around

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for children to smell (which can have a dramatic impact), remove it from the tube using a spatula and put it in a beaker to remove the risk of students touching the tar (note 4).

Cigarettes and smoking provide a rich context for ethical discussions. The fi rst reported research indicating links between lung cancer and cigarette smoking was published in 1950, and relatively recently in the UK smoking has been banned in public places. There is scope for debate about our rights to make risky lifestyle choices as well as the responsibility of government to promote public health. The commercial drive of tobacco companies and the tax revenue to government from tobacco sales are factors that could infl uence the reliability of information from different sources. It is hard to fi nd information presented impartially on the subject of smoking and cancer. It is worth trying to identify who has funded or supported any piece of reported ‘impartial’ or ‘scientifi c’ research.Effects of tobacco smoke on the body• Smoke from tobacco paralyses

cilia in the trachea and bronchi for approximately an hour after a cigarette has been smoked.

• Dry dust and chemicals in the smoke irritate the lungs causing more mucus to be secreted. Cilia normally sweep this mucus away, but smoke has paralysed them. Mucus builds up and if this becomes infected it can cause bronchitis.

• Tar is a dark brown, sticky substance, which collects in

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the lungs as the smoke cools. It contains carcinogens – chemical substances known to cause cancer.

• Carbon monoxide is a gas that combines with haemoglobin, the oxygen-carrying substance in the red blood cells, even more readily than oxygen does. So it reduces the oxygen-carrying capacity of the blood by as much as 15% in heavy smokers. Unlike the reaction with oxygen, the reaction is irreversible.

• Nicotine is the addictive drug that makes smoking such a hard habit to give up. It is responsible for the yellow staining on a smoker’s fi ngers and teeth. Nicotine can harm the heart and blood vessels too – it makes the heart beat faster, the blood pressure rise and the blood clot more easily.It is hard to fi nd information

presented without an agenda on the subject of smoking and cancer. There are links below to a range of sources of information.

As with many issues relating to health and lifestyle choices it is diffi cult to isolate the effects of any individual factor. Some of the reports indicate connections with socio-economic profi les that may also signifi cantly infl uence health.

There is scope to discuss the meaning of risk measurements and to try to track down original research papers in order to assess their methodology.

There is a link below to a report on the detailed analysis of the contents of the smoke from a range of brands. This is an independent analysis presented on the Tobacco Manufacturers site. It doesn’t connect

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the smoke contents to specifi c health risks, but it does mention using ISO conditions for smoking cigarettes (ISO 3308:2000). The idea of an ISO standard routine analytical cigarette smoking machine might interest some students. The smoking machine puffs with a puff volume of 35.0 ± 0.2 cm3 and with a 2.00 ± 0.02 second puff duration once every 60.0 ± 0.5 seconds.

The ISO standard machine makes a much more detailed analysis than the apparatus suggested above. The instructions for a smoking machine that would be acceptable for an ISO accredited test list 24 factors that must be controlled or measured by the machine. These include:• puff duration (the length of time

during which the port is connected to the suction mechanism – 2.00 ± 0.02 seconds)

• puff volume (the volume leaving the butt end of the cigarette and passing through the smoke trap)

• puff frequency (the number of puffs in a given time – one puff every 60.0 ± 0.5 seconds measured over 10 consecutive puffs)

• dead volume (the volume which exists between the butt end of the cigarette and the suction mechanism)

• draw resistance (negative pressure applied to the butt end under test conditions to sustain a volumetric fl ow of 17.5 cm3/ s, exiting the butt end when the cigarette is encapsulated in a measurement device to a depth of 9 mm)Ask students to evaluate your

apparatus compared to this list of

factors. What difference do you think it makes if the apparatus smokes continuously or puffs the cigarette? Why is it important that there is an internationally-recognised standard way of assessing cigarettes?

Some reports of cigarette analysis refer to NFDPM – which is nicotine free dry particulate matter, otherwise known as ‘tar’ . TPM stands for total particulate matter.

Further informationhttp://snipurl.com/7p46iThe UK Benchmark study report of an analysis of tobacco from cigarettes on the market in the UK. P5 of Part 1 of the report lists all brands tested and the components of their smoke.http://snipurl.com/7p47rThe Department of Health information about tobacco and health. www.ash.org.uk/Action on Smoking and Health (ASH).www.forestonline.org/Forest. http://snipurl.com/7rwhk Cancer Research UK, the leading funder of cancer research in the UK.www.beep.ac.uk/content/493.0.html The Bioethics Education Project, pages on tobacco and health risks and choices. http://snipurl.com/7rwhv Abstract from ‘The cumulative risk of lung cancer among current, ex- and never-smokers in European men’.http://snipurl.com/7rwi0 Abstract from ‘Estimate of deaths attributable to passive smoking among UK adults: database analysis’.

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Brine Date: Mating behaviour and sexual selection in brine shrimps

IntroductionThis procedure is adapted from the ideas in the Survival Rivals kits produced by the Wellcome Trust as part of the Darwin200 initiative and available for free from Spring 2009.

Pupils develop practical skills of scientifi c enquiry in an investigation of living brine shrimps – Artemia salina, and consider evidence that supports Darwin’s ideas about sexual selection.

Artemia salina (brine shrimps) kept in a brightly-illuminated aquarium provide an easily-observed and sustainable ecosystem for classroom-based ecological and behavioural studies by students at Key Stages 3 and 4 or Scottish Stages S1–S4 (Dockery and Tomkins, 2000).

The observable behaviours of brine shrimps allow students to investigate the phenomenon of sexual selection. Students will see the brine shrimps swimming and quickly distinguish between the sexes because mature animals swim together, in pairs, one male and one female. The females may choose the males they pair with. Once paired the males and females stay clasped together. A clasped pair may have mated or be yet to mate, but the clasping behaviour means the males guard the females which prevents other matings.

Lesson organisationBegin by observing the shrimps (as Darwin and other naturalists would have done). Lead a discussion of methods of investigating the phenomenon of mate-guarding which will generate hypotheses for students to test – such as ‘larger females pair with larger males’. Test the hypotheses in subsequent lessons.

There are opportunities here for students to work in groups with each taking a different role in the team. Collecting the data in a spreadsheet and generating different kinds of plot to search for relationships allows development of ICT skills. Completing the investigation could include communicating their results and conclusions to the class and evaluating their method and fi ndings.

Apparatus and ChemicalsFor the class – set up by technician/ teacher:• Brine shrimps – Artemia salina –

in a well-lit aquarium of salt water (notes 1-4)

• Clean salt water (35 g dm-3) – the best concentration for the shrimps

For each group of students:• Pipettes to withdraw shrimps

(note 5)• Beakers (100 cm3) to hold shrimps

withdrawn from the aquarium (note 5)• Glass slide, 1 (note 6)• Acetate measuring grid (note 6)

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Technical notes and safety1 Use a very clean plastic or glass vessel for your aquarium. An open tank of 1-5 litres is fi ne. Cover the bottom of the container with a layer of sand or limestone (oyster shell grit from pet stores is quite suitable) to provide a surface on which microorganisms can fl ourish. Fill the aquarium with water containing salt at a concentration of 35 g dm-3 (see note 7). Use plain sea salt (solar salt) or ‘artemia salt’ from an aquarium store. The latter includes minerals and algae that help newly-hatched shrimp to thrive. It may also contain microorganisms that contribute to starting off a more natural ecosystem for the shrimp. Iodine and anti-coagulants in table salt are bad for the shrimps! Use bottled mineral water, or de-ionised water, or tap water that has been left to rest for 48-72 hours to allow the chlorine to escape from it.2 Hatch eggs of Artemia salina in a Petri dish containing a little of the salt water from the aquarium, ideally at 25 °C, but no cooler than 20 °C. After hatching, transfer the Artemia to the larger aquarium (note 1). The shrimp will grow if the aquarium is placed on a warm well-lit windowsill. The lower the temperature, the longer Artemia will take to hatch. At 26-28 °C a nauplius hatches within 24-48 hours, gets pubescent in 8-14 days and lives up to 5 weeks, depending on the concentration of salt. The more salt, the less the life expectancy. You don’t need to illuminate your aquarium constantly.

3 Feeding: In an open aquarium, when the population density of brine shrimps is low there is abundant food and you will see a defi nite green colour in the water. The shrimp population will increase until competition for food (the green colour of the water disappears) halts further expansion. If you want to encourage larger populations for this investigation, feed with algae powder from aquarium suppliers once a week. Add algae only if the water is very clear and do not feed too much! If the water gets cloudy and green, there is too much food. After some time you may see some white/ yellow fl uffy stuff at the bottom of the aquarium. This is a brown diatom, which Artemia can and will eat. If it gets plentiful, you’re probably feeding too much. Diatoms produce oxygen, so it’s positively useful in the aquarium at low levels. You can keep Artemia in a closed drinks bottle aquarium (see diagram below).

35% salt solution

Sand / limestone granules

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An aquarium like this can develop into a self-supporting, closed ecosystem. The brine shrimps should never need feeding and should never run out of oxygen because the algae on which they feed carry out photosynthesis, grow and multiply by asexual reproduction. The algae never run out of carbon dioxide, water or mineral salts because they are recycled. Microorganisms in the water cause decay of dead algae, dead shrimps, shrimp droppings and dead microorganisms. Stir the substrate and water from time to time to mix in the nutrients from decayed organisms.4 With an open tank, replace some water (about 20%) every two weeks or so to keep ammonia, ammonium, nitrite and nitrate ion levels low, so that hazardous bacterial populations have no chance to develop and do harm to the Artemia. 5 Catching shrimps: Use a sieve with a mesh of 2-3 mm, such as a tea strainer which will catch only adults. Use soft plastic pipettes with an inside bore of 3-5 mm with the pointed end cut off. This should be wide enough for adult shrimp to enter when sucked up. The animals are robust in water and should not be handled outside this medium, but should not be distressed by drawing into a pipette like this. Return the animals to their tank after 5 minutes.6 Observing and measuring shrimps: Water has a high surface tension and will restrain the shrimp in the water drop. Any detergent on the slide (or in the water) will prevent the blob from forming. Photocopy a sheet of

graph paper, with millimetre squares, onto an overhead transparency acetate sheet. A piece of this on or under your glass slide will provide a measure ideal for shrimp observations with a hand lens (x10) or a microscope on low power (x40).7 Sodium chloride is described as low hazard on CLEAPSS Hazcard 47b.8 Observe good laboratory hygiene after handling aquarium water.

Procedure SAFETY: Ask students to wash their hands after handling the aquarium water.Preparationa Set up a population of brine shrimps in a salt water aquarium about 4 weeks before the investigation begins.b Spend part of one lesson observing the behaviour of the brine shrimps as an introduction to developing hypotheses. c Practice catching and measuring the shrimps for the rest of the lesson.Catching shrimps to measured Remove shrimps from the aquarium by fi shing them out with a fi ne sieve. Don’t let them dry up in the sieve. Lower them into a small beaker of aquarium water and allow them to swim free. e Pick up the shrimps from this water using a pipette that is wide enough for adult shrimp to enter when sucked up. f Return the animals to their tank after 5 minutes.

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Measuring shrimpsg Take a clean glass slide and gently rub it dry and shiny. Put just a few drops of water with a shrimp onto the slide from the pipette (below). Suck up any excess water so that the shrimp is confi ned in a blob of water (note 6).h Add one drop of water every minute or two so that the shrimp does not dry out.i Use a hand lens (magnifi cation x10) or a microscope on low power (x40) to observe the shrimps and measure them against a scale (note 6).Investigation 1: Pair choice experimentsj Students will have developed their own hypotheses to investigate, but could investigate pair choice by providing shrimps of different sexes with a choice of mate of different sizes and observing their behaviour. To develop the investigation students will need to make decisions for themselves about the details of what to look for and how to interpret different behaviours.Investigation 2: Measuring relative sizes of paired individualsk Students will have developed their own hypotheses to investigate, but could investigate the effect of size on pairing choices by measuring the relative sizes of pairs. This would involve capturing pairs of shrimps, measuring relative sizes and analysing data to look for correlations between sizes of males and females in pairs.

Teaching notesTeachers should be careful to introduce these animals in a way that promotes a good ethical attitude towards them and not a simply instrumental one. Although they are simple organisms that may not ‘suffer’ in the same way as higher animals, they still deserve respect. This would be particularly true of any experiments that established the limits of parameters favoured by the shrimps. Animals should be returned promptly to the holding tank after being examined. This supports ethical approaches that are appropriate to fi eld work where pond animals are returned to their habitat after observations have been made.

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Charles Darwin proposed two principal ideas to account for the diversity of life on earth. While the Origin of Species was mostly concerned with natural selection, Darwin noted briefl y in that book that sexual selection by mates was also a force for evolutionary change. He wrote:

“And this leads me to say a few words on what I call Sexual Selection. This depends, not on the struggle for existence, but on a struggle between the males for the possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring. [1]” [On the origin of species, First edition, 1859, Chapter IV]

By 1871 Darwin had expanded those few words to take up the greater part of his second book on evolution: The descent of man and selection in relation to sex. Sexual selection, he suggested, was largely responsible for human diversity – a conclusion with which many of today’s modern evolutionary biologists would agree.

Teenagers fi nd the social arrangement between the males and females inherently interesting to investigate!

34

Brine shrimps are herbivores in their ecosystem, feeding on algae and bacteria. In a natural salt-lake ecosystem there are no fi sh predators, but birds such as avocet and fl amingos feed on the shrimps. There is an opportunity here to develop the concept of energy fl ow and material transfer between trophic levels. Natural selection operates in this ecosystem as brine shrimps compete with one another for food.

Brine shrimps exhibit sexual dimorphism and pair for mating – male with female. The special case of sexual selection also operates. Males are competing with one another for larger females that produce more offspring. Females may be selecting male partners that are larger and stronger and help them to swim faster and so gather more food for eggs. Sexual selection would thus favour larger male shrimps. However, larger shrimps will be captured more easily from the water by fl amingos.

Different selection pressures operate on a living organism in its environment. The result of selection pressures is adaptation of a species to suit the situation almost perfectly.

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Further informationwww.survivalrivals.orgBrine Date is one of the Wellcome Trust’s experiments to celebrate Darwin 200. A kit containing everything needed to run this practical in school is available free to all state schools across the UK in 2009. Details on this website. (Last accessed November 2008. Full website not available at that time.)www.britishecologicalsociety.org/articles/education/resources/curriculum/brineshrimpDetails of how to get hold of, and access to downloadable sample material from, an invaluable book, published by the British Ecological Society, describing the culturing and use of brine shrimps – Brine Shrimp Ecology by Michael Dockery and Stephen Tomkins ISBN 1900579103. Price £14.50, including post and packing. This includes a starter kit with a substrate that includes the necessary microorganisms to colonise the salt water and start off a self-contained ecosystem. (Last accessed November 2008.)

http://www.captain.at/artemia/Captain’s Universe provides information about Artemia salina – video clips, photographs, culture details etc (Last accessed November 2008.)www.aquaculture.ugent.beVery high level information about culturing Artemia on a very large scale from the Artemia reference centre, University of Ghent. (Last accessed November 2008.)

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Microbes ate my homework: Investigating how microbes help us to break down cellulose and recycle plant material

IntroductionInvestigate the effects of cellulose-digesting enzymes in microbes on different kinds of paper. This long-term activity allows students to explore the role of microbes in decomposing organic waste and their place in the carbon cycle.

This practical investigates how quickly different kinds of paper decompose under the action of soil microbes. Soil microbes are unusual in the natural world in that they contain cellulases – enzymes that can digest cellulose the fi brous substance that helps to provide plants with a rigid structure. Without these cellulase enzymes in soil microbes, plant material would not decay and the elements such as carbon contained in the material would not be recycled for use by other living things.

Paper is made from woody plants and cellulose makes up 40-50% of the mature plant cell wall therefore paper is largely made of cellulose. In this investigation you will fi nd out how microbes in the soil can break down paper over a few weeks. This demonstrates how paper and plant material is broken down in the compost bin.

Cellulase-producing microbes are found in the strangest of places from termites’ stomachs through to the soil surrounding volcanoes. Scientists are genetically modifying cellulase-producing microbes to get them to produce larger quantities of cellulase. These microbes are being used commercially to produce biofuels from non-food stuff. Currently, most biofuels are made by fermenting edible plant material to produce ethanol. This means using plant products that could be used as food to make fuel instead. If we could produce ethanol from cellulose, we would be able to make use of a huge amount of non-edible plant waste instead, such as stalks from farmland, sawdust and wood chips from forestry operation.

Cellulase-producing bacteria in the guts of herbivores (for example, in the rumen of ruminants and the appendix of rabbits) help those animals to survive by breaking down cellulose so that the animals can use it as a source of energy.

Cellulase-producing microbes therefore play a key role in the carbon cycle, breaking down carbon compounds and releasing methane and carbon dioxide which are of enormous importance in their effects on global climate change.

Lesson organisationEach group will set up six tubes containing different paper/ card samples with nutrient broth containing soil microbes. The practical work in the ‘set-up’ session will take around 30 minutes and

each review session will take about 20 minutes. You need to leave at least one week (and up to 3 weeks) between set up and fi rst review and a further 1-3 weeks to each subsequent review. Each review will take only 10-15 minutes.

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Apparatus and ChemicalsFor the class – set up by technician / teacher:• Sterile nutrient broth

(50 cm3 per group) (see note 2)• Soil• Paper samples

For each group of students:• Sterile 5 cm3 graduated pipette

and fi ller, 1• Clean test tubes with aluminium foil

caps or cotton wool plugs, 6• Clean conical fl ask (250 cm3), 1• Test tube rack, 1 (to support the

tubes for up to 6 weeks)• Sterile nutrient broth, 50 cm3

• Soil, 5 g• Samples of different types of paper

in 1 cm x 2 cm strips (for example, fi lter paper, tissue paper, unprinted newspaper, heavily printed newspaper, glossy magazine covers, thin cardboard)

• Marker pen, 1

Technical notes and safety1 Before embarking on any practical microbiological investigation carry out a full risk assessment. For detailed safety information on the use of micro-organisms in schools and colleges, refer to Basic Practical Microbiology – A Manual (BPM) which is available, free, from the Society for General Microbiology (email [email protected]) or go to the safety area of the SGM website (www.microbiologyonline.org.uk/safety.html) or refer to the CLEAPSS Laboratory Handbook, section 15.

2 Make sterile nutrient broth by rehydrating tablets (more expensive) or powder according to manufacturer’s instructions. Make just enough (with a little extra for mistakes). (See BPM p6 for more details.)3 Suitable disinfectants include sodium chlorate(I) (hypochlorite) at concentrations providing 1000 ppm available chlorine for general surface cleaning, or 2 500 ppm chlorine for discard pots, or VirKon at 1% (follow manufacturer’s instructions). 4 Cultures and contaminated equipment and materials must be autoclaved at 121ºC for 15 minutes before disposal. After sterilisation, all materials can be disposed of with normal waste. Take care to package glass to prevent injury.

Procedure SAFETY: See Basic Practical Microbiology – a Manual for more information about hazards and risk control measures. Preparationa Make up sterile nutrient broth (note 2).b Collect soil sample (5 g per working group). Avoid areas where cats may have buried faeces. c Sterilise the pipettes.

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d Make cotton wool plugs for the test tubes.e Set up discard beakers with appropriate disinfectant fl uid (note 3).Investigationa Label 6 test tubes A - F, together with your name and date. b Use a graduated pipette and fi ller to place 5 cm3 of nutrient broth in tube A. Carefully drop in a 1 cm x 2 cm sample of fi lter paper.c Place 5 g of soil and 30 cm3 of nutrient broth in the conical fl ask. Swirl the contents to form a suspension. Allow this to settle for a

minute to avoid blocking the pipette.d Pipette 5 cm3 of the supernatant of the nutrient broth / soil suspension into each of the fi ve remaining tubes. Put the pipette into a discard beaker.e Into tube B, carefully drop in a 1 cm x 2 cm sample of fi lter paper.f Put a 1 cm x 2 cm sample of a different kind of paper or card into each of the other four tubes C – F.g Stopper each of the tubes with either cotton wool or loosely cover with aluminium foil.h Record the contents of each of the six tubes in a table.

i Leave the tubes at room temperature for at least a week.j Before reviewing the tubes, give each a tap with your fi nger. Carefully observe what happens to the paper strip. Do not take out the cotton wool stoppers.k Record your results in the table.l Dispose of the soil suspension immediately after the fi rst lesson and the contents of the tubes safely at the end of the investigation (note 4).

Tube Treatment Appearance after … weeks

Appearance after … weeks

A Nutrient broth (sterile) + fi lter paperB Nutrient broth + soil + fi lter paperC Nutrient broth + soil +D Nutrient broth + soil +E Nutrient broth + soil +F Nutrient broth + soil +

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Teaching notesCellulose is a fi brous substance that helps to provide plants with a rigid structure. It makes up 40-50% of the mature plant cell wall and is the most abundant carbohydrate. The molecules are very large and very long and contain carbon, hydrogen and oxygen. In wood, forest and agricultural wastes, and in waste paper, cellulose occurs in a complex mixture with lignin (another plant polymer) called lignocellulose.

The microbes that can decompose and thus recycle it are extremely important in maintaining the turnover of organic matter in the carbon cycle. On land, the major decomposers of cellulose are fungi aided by a few bacteria. Cellulolytic bacteria include species of Cellulomonas, Pseudomonas and Ruminococcus. Cellulolytic fungi include Chaetonium, Fusarium, Myrothecium and Trichoderma. Ask students to locate the position of soil microbes on a diagram of the carbon cycle.

Cellulose is not soluble in water, so microbes cannot absorb it into their cells. They secrete cellulase enzymes which partly digest cellulose and break it down to soluble sugar molecules that can be absorbed and used. Higher organisms do not make cellulases which means that herbivores cannot digest cellulose themselves. They depend on cellulolytic bacteria in their intestinal tracts to do the job for them. This can be a complicated process – for example involving regurgitation, chewing and swallowing in ruminants,

or re-ingestion of faecal pellets in rabbits. This is an interesting opportunity for students to carry out some research into different methods of digesting cellulose. Humans cannot digest cellulose at all, so all the cellulose we eat passes through our digestive system unchanged. This is called ‘dietary fi bre’.

Students are often very aware of issues associated with recycling and may be interested to think about the length of time paper of different sorts would sit in landfi ll before rotting if it is not recycled. This may also introduce discussion about how different paper treatments make them harder to recycle.

If you have access to a compost bin or wormery, you could compare the results of this investigation with the rate (and manner) of decomposition of similar paper samples in the compost bin and wormery. Be aware of the risks posed by mould spores in compost. If you choose to work with material in a domestic compost bin, make sure no cooked food or meat products go into the compost, and that there is no evidence of rodent activity around the bin. Practise good personal hygiene after handling compost.

There is scope for higher level investigations using this and related techniques such as:• exploring the effect of temperature

on the activity of cellulolytic microbes or cellulases (from school science suppliers),

• exploring the cellulolytic activity of microbes from different soils,

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Further informationwww.microbiologyonline.org.ukSociety for General Microbiology – source of Basic Practical Microbiology, an excellent manual of laboratory techniques and Practical Microbiology for Secondary Schools, a selection of tried and tested practicals using microorganisms. These booklets are available free of charge. (Last accessed November 2008.)www.microbiologyonline.org.uk/misacMiSAC (Microbiology in Schools Advisory Committee) is supported by the Society for General Microbiology (see above) and their websites include more safety information and a link to ask for advice by email. (Last accessed June 2008.)www.ncbe.reading.ac.uk/NCBE/PROTOCOLS/pracbiotech.htmlThe NCBE is a rich source of up-to-date protocols and practical equipment for biotechnology practicals in schools. These notes (from 1993) show two more protocols for assessing cellulase activity – by digesting cellulose in an agar plate (similar methodology to the starch and protein methods on the Practical Biology site) and by measuring the change in viscosity of wallpaper paste in syringe barrels! (Last accessed July 2008.)

• exploring the effect on cellulolytic activity of adding nutrients to the soil samples,

• exploring whether fungi or bacteria are more important in terms of cellulolytic activity in particular types of soil.

These questions will help students to focus their observations and think about the purpose of the practical procedure.1 In this investigation, what is the purpose of the tube containing fi lter paper with sterile nutrient broth and no soil?2 Why is it important not to take out the cotton wool stoppers?3 How have the papers changed as a result of the action of microbes from the soil?4 Which paper has decomposed the least?5 What would you do to develop this investigation to give you more information about soil microbes and cellulose? How could you improve it?

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Lesson organisationDemonstrate the technique and give students an opportunity to practise the skill of making epidermal peels or impressions. Supply students with plants kept for several weeks under controlled conditions (such as varying CO2 level, water supply, humidity, temperature or light intensity) or offer this as the groundwork for a longer-term self-directed investigation for students.

Apparatus and ChemicalsFor the class – set up by technician/ teacher:• Plants to investigate (note 1 and note 2)

For each group of students:• Microscope with eyepiece

graticule (calibrated for different magnifi cations) or stage graticules on microscope slides to allow simple measurement of fi eld of view (note 6)

• Nail varnish and sellotape OR• Germolene ‘New skin’ to take

impressions from the epidermis

Technical notes and safety1 Plants with hairy leaves are not suitable for taking impressions. Spider plants (Chlorophytum comosum) work well in this procedure. Red hot poker (Kniphofi a) is a common garden plant and an easy to study monocotyledonous example as you can peel its epidermis and view it directly under a microscope. Grey willow (Salix cinerea) has been studied in modern and fossil forms. Also useful are the Mexican hat plant (Kalanchoe diagremontiana), and Arabidopsis thaliana (a popular model organism for plant biology and genetics which has one of the smallest plant genomes and was the fi rst plant genome to be fully sequenced). Pot geranium (Pelargonium) is also easy to study and you can tear sections of epidermis for direct viewing. Variegated Tradescantia leaves can be used for direct viewing of stomata in the regions with little or no chlorophyll.2 Grow plants under clear domes taped to a bench or tray so you

IntroductionThese notes describe how to measure the density of stomata on a leaf epidermis. You can use the method to collect data about stomatal density from a range of species of plants, or from plants that have been grown in a range of conditions. The technique is straightforward, but requires care to achieve good results.

Stomatal density usually varies between the upper and lower epidermis of any leaf, will vary from species to species and may change with carbon dioxide concentration in the surrounding atmosphere, and with light intensity. Any change will take several weeks to occur, so there is an opportunity here for a long term, self-directed investigation. Mathematical analysis of the data gathered may be a challenge for some students – but is simplifi ed with a spreadsheet such as the one attached.

A window on the past: How stomatal density adapts in changing environments

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can control the atmosphere around them. You could use a large plastic water container, a plastic garden bell cloche or a laboratory bell jar. Include a thermometer in each dome so you can monitor temperature. Reduce humidity levels by including a desiccant such as silica gel or calcium chloride (note 3). Increase humidity levels by including an open vessel of water (such as a deep Petri dish), and topping it up regularly before the liquid evaporates fully. Reduce light levels by covering domes with increasing numbers of layers of fi ne fabric or horticultural fl eece. The level of carbon dioxide in normal atmospheric air is low, but plants will produce some from their metabolic processes. You could increase the carbon dioxide level by breathing into the dome, or adding a boiling tube with a few marble chips (calcium carbonate) and 10-20 cm3 of dilute hydrochloric acid (approximately 0.1M). You could reduce carbon dioxide levels by including a carbon dioxide absorber such as soda lime (note 4). 3 Desiccants: Silica gel (see Hazcard 86), for users in year 7 advises wearing gloves and to beware of dust from blue (self-indicating) silica gel. The advantage of blue moisture-indicating gel (containing < 0.5% cobalt(II) chloride) is that it can be reheated and used again. The risk to health from cobalt(II) chloride is very low. Calcium chloride (see Hazcard 19A) is an irritant as a solid. Wash hands immediately if any gets on the skin and wear eye protection when handling the powder or granules.

4 Carbon dioxide: Calcium carbonate is described as low hazard on Hazcard 19B. Hydrochloric acid (Hazcard 47A) at low concentrations presents a minimal hazard to students, and will be neutralised as the marble chips react with it. Soda lime is described as corrosive on Hazcard 91. Ensure that students do not handle the soda lime and wear eye protection if there is any risk of getting soda lime in their eyes. Be aware of the necessary fi rst aid response if any soda lime should get into anyone’s eyes. 5 Make an epidermal impression by spreading a thin layer of nail varnish on the leaf and leaving it to dry. Remove the layer of varnish by attaching clear sticky tape to it, peeling it from the leaf surface and sticking it to the slide. You could try Germolene ‘New skin’ as an alternative to nail varnish. It has slightly different elastic properties and may make a clearer impression. You won’t need to use sticky tape with ‘New skin’.6 Graticules printed on plastic are available at reasonable prices – around £20 for 10 – if your microscopes are not already equipped with them (see Suppliers section).

Procedure SAFETY: Plant sap can be irritating to the skin. Students may have allergic reactions to nail varnish or Germolene ‘New skin’. Be alert to any students suffering allergic responses to the materials handled. Offer gloves as skin protection if necessary and make

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sure students wash their hands thoroughly at the end of the procedure.Preparationa Grow plants in different conditions for 4-6 weeks. Useful varieties of plants are suggested in note 1. Ideas for creating different conditions for the plants are suggested in note 2.b Make sure students know what stomata look like, and understand something about their function in the plant.Investigationc Collecting epidermal evidence: The epidermis will peel from some leaves quite readily. First cut the leaf. Use your fi ngernails to catch hold of and peel off the epidermis, or use a sharp razor blade to peel off the epidermis. Mount the peel in a drop of water on a microscope slide with a coverslip. Alternatively, make an epidermal impression with nail varnish (or another clear substance) and place that on a microscope slide to view it (note 5). d Discuss and decide how many impressions or epidermal samples should be taken, and from where on each plant, to get a representative sample. Try to be consistent about which part of the leaf to use.e View the epidermal impressions using a calibrated microscope fi tted with an eyepiece graticule (note 6).f Calculate the true area of the fi eld of view. You can calculate this using the formula area = πr2 when you have measured the true radius of the fi eld of view (r). (See also table overleaf.)g Count the stomata visible in each of three areas of the impression.

h Calculate the stomatal density for each impression. (See table overleaf.)i Analyse average density for each impression and for each plant. (See table overleaf.)j Plot a graph of average stomatal density against light intensity.

Teaching notesStomata control the movement of gases and vapours into and out of a leaf. They are often discussed primarily in the context of controlling loss of water from a leaf – as shortage of water is a common stress experienced by plants. The stomata of wilting plants close which minimises further water loss from the leaf.

However, closed stomata will also reduce the availability of carbon dioxide for a photosynthesising leaf. So at low concentrations of carbon dioxide, in light conditions, stomata are stimulated to open wide which permits photosynthesis to continue. In low light conditions, carbon dioxide concentration is not a limiting factor for photosynthesis and stomata can be closed without affecting carbon dioxide uptake.

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Over short time scales, reducing the size of the aperture in each stoma reduces the loss of water vapour from a leaf, but also reduces the amount of carbon dioxide that the plant can absorb. Therefore, at high light intensities (which are often accompanied by high temperatures and low water levels) reducing water loss has the concomitant effect of limiting photosynthesis.

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(See the link to Annals of Botany below.)

There are potentially commercial implications when stomatal density changes in plants grown under artifi cial light or with additional atmospheric CO2 to improve crop production. This is because stomatal reaction to high light intensity or high CO2 levels could result in plants having altered water requirements

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and hence incurring additional costs for supplying water to that crop.

If students are struggling with the calculations, a spreadsheet with these headings and formulae to ‘fi ll’ the spreadsheet would be useful.

Some species of plant have stomata on both sides of the leaf, and others have stomata only on the lower epidermis. The shape of stomata (and the mechanisms for controlling the size of the aperture) differ between monocotyledonous plants (such as grasses) and dicotyledonous plants.

Some species seem to respond to prolonged ambient levels of light intensity and carbon dioxide by developing leaves with an altered density of stomata. For example, at high CO2 levels, a lower density of stomata will not limit the rate of photosynthesis, but will reduce water loss and at higher light intensities, a higher density of stomata will maximise the rate of photosynthesis, but with the risk of enhanced water loss.

Interaction between factors is complex and varies from species to species. A literature search will fi nd many suggestions of factors already investigated which could promote ideas for further work in the school/ college laboratory.

Studies of stomatal density of plant samples up to 300 years old in botanical libraries have been used alongside evidence of recent changes in carbon dioxide levels in

the atmosphere. Studies of stomatal density in fossils has been correlated with information from ice cores to give evidence of how carbon dioxide levels in the atmosphere have affected plants in the past.

Further informationwww-saps.plantsci.cam.ac.uk/docs/post16/article2.pdf This link is to an 8-page booklet published by SAPS (‘Seeing without eyes – how plants learn from light’ by Stephen Day) that explains how phytochromes in plants react to light intensity and provide a mechanism by which plants can respond to light.www.plantscienceimages.org.ukThe SAPS plant science images database which includes images of stomata from dicotyledonous plants such as Kalanchoe lower epidermis and Arabidopsis thaliana.http://aob.oxfordjournals.org/cgi/content/abstract/76/4/389Link to abstract of Annals of Botany 76: 389-395, 1995 – an article entitled Stomatal Density and Index of Fossil Plants Track Atmospheric Carbon Dioxide in the Palaeozoic by Jennifer C. McElwain and William G. Chaloner. This research correlates the stomatal density of forest tree species collected over the last 200 years with changes in carbon dioxide levels in the atmosphere. It goes on to link stomatal density in fossil specimens from the Palaeozoic with carbon dioxide levels as deduced from ice cores.

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ChemistryThe science of materials, their structure, physical and chemical properties, and how they interact.

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IntroductionChemistry is about the study of atoms, how they interact, the structures they form and the materials they make. Practical activities provide opportunities for students to explore the chemistry of materials, and observe patterns in reactions. They can also be used to demonstrate the applications of chemistry, increasing its relevance to students. Practical work is vital in the development of students’ skills of manipulating and handling apparatus and data, working with others, and scientifi c enquiry. They can also provide opportunities for students to collect their own data and use this to apply and develop mathematical skills. Chemistry demonstrations should be exciting and stimulating and some of the most memorable experiences that students will take from science.

Secondary chemistry experiments:A matter of balance: The combustion of iron woolRed cabbage indicator: Making a pH indicatorSoot surveys: Investigating air pollutionHydrogels in the home: Hair gel and disposable nappiesDiscovering the formula: Finding the formula of hydrated copper(II) sulfatePreparing perfumes: Making esters from alcohols and acids

www.practicalchemistry.org 47

“Practical work mirrors the pioneering investigative and exploratory nature of science. Teaching is not about simply passing on what we (think we) know but the thrill of the chase”Teacher response to SCORE questionnaire

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A matter of balance: The combustion of iron wool

IntroductionIron wool is heated in air on a simple ‘see-saw’ balance. The increase in mass is seen clearly.

Lesson organisationThis demonstration takes around 5 minutes once it has been set up.

Apparatus and chemicalsFor one demonstration:• Eye protection • Bunsen burner• Heat resistant mat• Wooden metre rule (see note 1)• Aluminium cooking foil, about

10 cm x 10 cm• Retort stand, boss and clamp• Plasticine, few grams• Knife edge, triangular block or

something similar• Steel wool (Low hazard), about 4g

Technical notes and safetySteel wool (Low hazard) Refer to CLEAPSS Hazcard 55A1 A shallow groove cut across the width of the ruler at the 50 cm mark will help when balancing it on the knife edge. Cover the end of the meter ruler with foil to protect it from the Bunsen burner.

Procedurea Cover one end of the metre ruler with foil to protect it from the Bunsen burner. Take about 4 g of steel wool and tease it out so that the air can get around it easily. Use a few of the strands to attach it to the end of the ruler.b Balance the ruler on a knife edge or triangular block at the 50 cm mark. Weight the empty end with plasticine until this end is just down (see the diagram). This part is critical.

Before

After

Steel wool

Foil to protect ruler

Knife edge

Plasticine

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c Place a heat resistant mat underneath the steel wool.d Wear eye protection. Light the Bunsen burner and heat the steel wool from the top with a roaring fl ame. It will glow and some pieces of burning wool will drop onto the heat resistant mat. Heat for about a minute by which time the meter ruler will have over-balanced so that the iron wool side is down.

Teaching notesAs you are setting up, ask the students whether they think the iron wool will go up, down or remain the same. Many will predict a weight loss.

If fi ne steel or iron wool is used then it may be possible to light it using a splint.Equation:Iron + oxygen iron oxide2Fe(s) + 3/2 O2(g) Fe2O3(s)This demonstration could be complemented by a class experiment such as ‘The change in mass when magnesium burns’ which can be found at www.practicalchemistry.org.

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Red cabbage indicator:Making a pH indicator

IntroductionA pH indicator is a substance which has one colour when added to an acidic solution and a different colour when added to an alkaline solution. In this experiment pupils make an indicator from red cabbage.

Lesson organisationThe experiment is in two parts. The fi rst part involves boiling some red cabbage in water. In the second part the students test their indicator. Between the two parts the mixture must be allowed to cool. The fi rst part takes about 10 to 15 minutes. The cooling takes about 15 minutes and the testing less than 5 minutes.

The cooling period could be used as an opportunity to discuss the background to the experiment – see Teaching notes below.

Apparatus and chemicals• Eye protection for allEach working group will require:• Beaker (250 cm3)• Bunsen burner• Tripod• Gauze• Heat resistant mat• Test-tubes, 3 (see note 1)• Test-tube rack • Dropping pipette• Several pieces of red cabbageAccess to (see notes 2 and 3):• Dilute hydrochloric acid, 0.01

mol dm-3 (Low hazard at this concentration)

• Sodium hydroxide solution 0.01 mol dm-3 (Low hazard at this concentration)

• De-ionised or distilled water

Beaker

Water

Tripod

Bunsen burner

Pieces of red cabbage

Gauze

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Technical notes and safetyDilute hydrochloric acid, 0.01 mol dm-3 (Low hazard at concentration used). Refer to CLEAPSS Hazcard 47ASodium hydroxide solution 0.01 mol dm-3 (Low hazard at concentration used). Refer to CLEAPSS Hazcard 911 Small test-tubes of capacity about 10 cm3 are ideal.2 Each group of students will need access to the hydrochloric acid and sodium hydroxide solutions. Dropper bottles are ideal. Alternatively small beakers (100 cm3) with dropper pipettes could be used. Students need to be able to pour the acid and alkali solutions easily and safely into test-tubes. 3 Provide similar containers for de-ionised or distilled water. Label the containers ‘Acid’, ‘Alkali’ and ‘Water’.4 A good tip is to attach a pipette to each bottle with an elastic band, to avoid cross-contamination.

ProcedureSAFETY: Wear eye protection throughout. Consider clamping the beaker.a Boil about 50 cm3 of water in a beaker. b Add 3 or 4 small (5 cm) pieces of red cabbage to the boiling water. c Continue to boil the red cabbage in the water for about 5 minutes. The water should turn blue or green.d Turn off the Bunsen burner and allow the beaker to cool for about 15 minutes.e Place 3 test-tubes in a test-tube rack. Half-fi ll one of the test-tubes with acid, one with alkali, and one with distilled or de-ionised water. Label the test-tubes.

f Use a dropper pipette to add a few drops of the cabbage solution to each test-tube. Note the colour of the cabbage solution in each of the three test-tubes.

Teaching notesDiscussion points could include any or all of the following.

Many plant colouring materials in berries, leaves and petals act as indicators.

Some of these will not dissolve in water easily. A solvent other than water (e.g. ethanol) could be used, but it may be fl ammable. Discuss how the risk of fi re can be reduced by using a beaker of hot water to heat the mixture.

Possible variations on this experiment might include using beetroot, blackberries, raspberries, copper beech leaves, or onion skins in place of the red cabbage.

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Soot surveys: Investigating air pollution

IntroductionThis experiment is adapted from a series of activities from a Field Studies Council project ran between 2005-07 called London Outdoor Science. The investigation looks at whether the levels of particulates vary in urban green spaces.

It is often diffi cult to measure air pollution, as sophisticated equipment and long-term monitoring are usually needed to obtain worthwhile data. In this investigation, on the other hand, particulate pollution (i.e. soot) adhering to tree bark can rapidly be measured using nothing more complicated than sticky tape.

Lesson organisationThe complete investigation will take about three lessons, and pupils will need a basic understanding of the key pollutants before they begin. Because there are a variety of measurements to be taken, it is best if pupils work in groups and are assigned roles; i.e. recorder, distance measurer, sampler, noise pollution monitor. If groups start taking their measurements at different points along the transect this will give them more room to work.

The location and transect should be carefully identifi ed in advance, and could be determined by the teacher, or chosen by students during planning. An ideal transect for this investigation would use a row of trees (about 8 or more) of the same species and similar age, that start at a road and move progressively into a green space.

If time permits, the class could be taken outside to a local site before designing the method, to be shown the basic techniques. If time is limited, the distances between the trees along the transect could be measured prior to the lesson and the trees marked using site numbers.

Apparatus and chemicalsFor fi eldwork, each working group will require:• Clipboard, 1 • Plain paper to record results,

about 3 sheets• Sticky tape, 1 roll• Scissors, or sellotape dispenser• Tape measure, 1 • Trundle wheel, 1• Tree identifi cation key (see note 1)• Microscope slides (optional), 1 for

each site studied • Noise sensor / datalogger (optional) • Air pollution sensors – ozone, CO2,

SOx, NOx (optional)• Key to lichens (optional)For analysis of results, each working group will require:• Hand lens, 1• Mini-quadrats (see note 2)• Microscope, 1

Technical notes and safety1 The Tree Name Trail is a tree identifi cation key available from the Field Studies Council, and can be bought online. (www.fi eld-studies-council.org/publications/pubsinfo.aspx? Code=OP51)

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2 Mini-quadrats are small square frames used for sampling. Mini-quadrats can be made by photocopying graph paper onto acetate sheets (See Fig. 2).3 An appropriate risk assessment specifi c to the site being used, and in line with school policy, must be carried out. It is important that pupils are always properly supervised when working near roads. Risks to pupils on out-of-school activities make it vital that all trips which take pupils any distance away from school are planned carefully and well in advance. The leader of the fi eld trip has particular responsibilities which must be taken seriously. Most local authorities will have regulations and guidance for the conduct of out-of-school activities and complying with these is essential.

Hazards need to be identifi ed in advance and precautions taken; pupils must be warned and supervised with these hazards in mind.

Refer to CLEAPSS Laboratory Handbook Chapter 17: Monitoring in the Field and Laboratory.

ProcedureLesson 1a Introduce the area to be studied. This research could be carried out and presented by pupils as a preparatory task. The internet can be used to fi nd relevant sites that list pollution data for the region. Students should be introduced to lichens as air pollution bio-indicators at this stage.b Provide students with knowledge of the basic techniques for taking measurements and samples, including use of the datalogger if applicable. The detailed planning of the investigation could then be left to them allowing for a variety of methods to be discussed and evaluated later.c Ask students to make a prediction: e.g. ‘The amount of pollution will decrease further from the road,

Site 3Site 2Site 1

Fig. 1: Use of sticky tape for sampling Fig. 2: Mini-quadrats, for use under a microscope, placed over each strip of sticky tape.

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into the middle of the park’, and consider how it will be measured. d Put students into small

groups to write the method for their investigation, and assign roles to all members of their group.Lesson 2e On arriving at the site, demonstrate taking a sample on the bark using sticky tape. Place a 3 cm length of sticky tape fi rmly onto the bark of the tree, leave for 10 seconds, and then remove it. Soot and other particles from the air will have adhered to the tape, along with debris such as loose bark and moss from the tree (Fig. 1).f Ask students to get into their groups. Give them their starting points along the transect, and begin taking and recording measurements. - Distance: Measure the distance from the road to the fi rst tree and to subsequent trees using a trundle wheel, or tape measure. Each tree should be numbered, starting from the road as ‘site 1, site 2, site 3… etc’. - Samples: Take two samples from the bark of each tree using sticky tape, 1 m from the base of the tree. Stick the samples onto plain paper and label it with the site. If time, a third sample can be taken and placed onto a labelled microscope slide. - Tree species: Use a suitable identifi cation chart and record the tree species.

- Tree age: Measure the girth of the tree trunk using a tape measure held at shoulder height. The tree age can be estimated by dividing the tree girth (in cm) by 2.5. - Noise (optional): A data logger / sensor may be used to record noise levels at each site. - Bio-indicators (optional): Observe and record the presence of lichens on the tree. - Other pollutants (optional): If sensors are available, use these to measure the levels of other pollutants e.g. CO2, SOx, NOx. Lesson 3g Look at the microscope slide from site 1 under a microscope to observe in detail the types of items that are found on tree bark.h Lay a mini-quadrat (acetate grid) over the fi rst pollution sample (sticky tape stuck to paper) for site 1. Randomly select a small (1 mm) square to look at, using random coordinates. Estimate the percentage of that square that is covered with black particulates and record your estimate. Only black particles of soot should be recorded; ignore bark and moss. A hand lens may be useful.i Repeat this 15 to 20 times, each time randomly selecting another small square, and estimating the percentage of that square that is covered with black particulates. j Calculate an average percentage cover of particulates for the sample site, by adding together the estimated values and dividing by the number of repeats.

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k Repeat steps h to j for the second sample from site 1 and calculate an overall average. Record the overall average for site 1. l Repeat steps g to k for all sample sites. m Put the data into a spreadsheet to be analysed, or plot a graph by hand, with distance from the road along the x-axis and average percentage cover of particulates along the y-axis. If applicable, plot a second graph over the fi rst, with the sound reading, or concentration of other pollutants on the y-axis. n Analyse and evaluate the results. Consider the variables that were diffi cult to control, and how secondary data could be used to assess the reliability of the experimental results.

Teaching notesThe investigation could be put into a context, suitable for the location, such as ‘Investigate the most suitable site for a café in the park by collecting and analysing the deposition of airborne particulates on trees, and noise levels.’

A discussion of validity will be valuable, before and after the fi eldwork. The discussion could begin with ‘do particles on the sticky tape actually indicate air pollution?’ Repetition and standard procedures are important, e.g. taking measurements at the same height from the ground each time, and either always from the same aspect or from all round the circumference of the tree. Using the same type of tape

and technique for applying the same pressure each time is important.

The investigation has many interesting areas to consider and highlights the way scientists work in the ‘real world’. Pupils can go on to consider primary data collected by nearby pollution monitoring stations (available on the internet) and observe how these data vary on a daily and seasonal basis.

An alternative method for investigating levels of air pollution by using lichens as indicators has been developed by the Natural History Museum. See www.nhm.ac.uk/jdsml/nature-online/lichen-id-guide/

Further informationThe original investigation and other fi eldwork activities can be found at www.fi eld-studies-council.org/outdoorscience.

Secondary data can be found at:www.defra.gov.uk/noisemappingwww.airquality.co.uk/archive/index.phpwww.research-tv.com/stories/health/airpollution/bb/

Activity adapted from:Melissa Glackin’s activities at London Outdoor Science (www.fi eld-studies-council.org/outdoorscience). Contactable at [email protected]

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Hydrogels in the home: Hair gel and disposable nappies

IntroductionIn this pair of activities students investigate hydrogels – polymeric smart materials. They are found in many commonly available products including disposable nappies and cheap hair gel. The practical work is fun to do and the results are sudden and dramatic.

Lesson organisation To do all the practical work takes about 30 mins. The hair gel experiment is a good quick introduction to hydrogels, while the nappy experiment is more detailed.

If time is available, it is worth considering combining this experiment with another experiment with hydrogels, using plant water crystals. This experiment can be found at www.practicalchemistry.org

It is a good idea to ask students to make detailed observations of each part of the experiment.

Apparatus and chemicals• Eye protection

Hair gel – each group requires:• Hair gel (see note 1)• Salt• Petri dish or lid• Teaspoon or similar – an ordinary

spatula is a bit small

Nappies – each group requires:• A disposable nappy (see note 2) • Scissors• A large ice cream tub or similar

container (see note 3)• Dessert spoon or similar measure• Stirring rod

• Large beaker or plastic tub to hold at least 600 cm3

• Plastic gloves for those with sensitive skin

Access to:• Distilled water, about 500 cm3

per group (see note 4)• Salt

Technical notes and safety1 For the hair gel the cheaper and nastier the better. Allow about one large teaspoonful per group.2 Pampers Baby Dry® nappies work well, but any ultra absorbent disposables should be fi ne. As an alternative to using nappies and extracting the hydrogel, it is possible to order sodium polyacrylate (Low hazard) from Sigma Aldrich.3 The ice cream tub is for collecting the inside of the nappy and is safer than collecting it over newspaper or similar. If tubs are in short supply, large zip-lock bags can be used. Students put the nappy in the bag, zip it up and manipulate it until all the hydrogel is extracted and then proceed as per the directions.4 If distilled water is not available, tap water can be used but the results are not so spectacular.

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ProcedureSAFETY: Wear eye protection

Hair gela Put a blob of hair gel onto the petri dish lid. A large teaspoonful is fi ne.b Gently sprinkle salt from a spatula over the hair gel.

Disposable nappya Cut the middle section out of the nappy – the thicker piece that is designed to absorb the urine. Discard the other piece.b Make sure the ice cream container is completely dry – wipe it with a paper towel if necessary. Any moisture in the tub stops the experiment from working properly.c Put the centre piece of the nappy into the ice cream container and gently take it apart. Small white grains should start coming away and this is what you are trying to collect. Keep gently pulling the nappy apart until you have collected as many of the grains as you can. Do not do this roughly or you will lose your product and put a lot of dust and fl uff into the air. Avoid breathing in any of the dust.

d Remove and dispose of all the fl uff and other parts of the nappy, keeping the grains in the bottom of the tub. They are heavier and fall to the bottom, which makes it easier to separate them out.e Estimate the volume of the grains.f Pour them into the large beaker and add about 100 cm3 of distilled water. Stir. Keep adding distilled water, 100 cm3 at a time, until no more can be absorbed and stir between each addition. Estimate the fi nal volume of the hydrogel.g Add a dessert spoonful of salt and stir.

Teaching notes This activity can be used to enhance the teaching of ionic and covalent bonding, or hydrogels can be considered as an interesting polymer as well as an example of a smart material. Hydrogels are smart materials because they change shape when there is a change in their environment – in this case it is the change in the concentration of ions.

Students need to have some knowledge and understanding of ionic and covalent bonding, reversible reactions, and acids and bases to understand what is happening.

O

O

H2O+

n

H

O

O

H3O++

n

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Hydrogels are polymers that can retain many times their own weight in water. They are often polymers of carboxylic acids that ionise in water, leaving the polymer with several negative charges down its length. This has two effects. First, the negative charges repel each other and the polymer is forced to expand. Secondly, polar water molecules are attracted to the negative charges. This increases the viscosity of the resulting mixture still further as the polymer chain now takes up more space and resists the fl ow of the solvent molecules around it.

The polymer is in equilibrium with the water around it, but that equilibrium can be disturbed in a number of ways. If the ionic concentration of the solution is increased – e.g. by adding salt – the positive ions attach themselves to the negative sites on the polymer, effectively neutralising the charges. This causes the polymer to collapse in on itself again. Adding alkali removes the acid ions and moves the equilibrium to the right; adding acid has the opposite effect.

There are a large number of hydrogels and they are sensitive to different pHs, temperatures and ionic concentrations. By using a mix of monomers to create the polymer these characteristics can be fi ne-tuned.

The hydrogels that are commonly available and are used in this practical activity are sensitive to salt concentration, but do not show much change across the pH range that can be readily investigated in the classroom. However, they do

lend themselves very well to a range of investigative practical work. For example, their volume in different amounts of water or in different salt concentrations can be measured. For this type of investigation it is best to use either plant water crystals or to order sodium polyacrylate from Sigma Aldrich – this has a smaller crystal size and gives faster results.

Students should make detailed notes on their experiments, noting changes in volume, colour and any other observations. Some expected observations could include:

Hair gelThe hair gel shrinks in size very quickly when the salt is added. After a couple of minutes all that is left is some liquid in the petri dish.

Disposable nappyAbout 10 cm3 of hydrogel can be extracted from the nappy core. (Exactly how much depends on the make and the size of the nappy.) The hydrogel swells up extremely quickly (much quicker than with plant water storage crystals). It absorbs about 500 cm3 of distilled water giving a very viscous mixture. When salt is added, the viscosity immediately reduces and the mixture is easier to stir. The hydrogel releases the water and settles on the bottom of the beaker.

Further informationInspirational chemistry on Learnnet has more information about hydrogels. www.chemsoc.org/networks/learnnet/inspirchem.htm

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Lesson organisationThis is a class experiment suitable for students who already have a reasonable understanding of the mole concept.

The degree to which the mole calculations need to be structured will depend on the ability and mathematical competence of the class. The outline structure given in the Procedure below is intended for students with reasonable mathematical competence and experience of mole calculations.

Given adequate access to top-pan balances, and skill in their use, students should be able to complete the experimental work in 30-40 minutes.

Apparatus and chemicals• Eye protection

Each working group will require:• Crucible (see note 1)• Crucible tongs (see note 2)• Tripod• Pipe-clay triangle• Bunsen burner• Heat resistant mat

Access to: • Top-pan balance (± 0.01 g)• Hydrated copper(II) sulfate (Harmful, Dangerous for environment), 2 - 3 g (see note 3)

Discovering the formula: Finding the formula of hydrated copper(II) sulfate

IntroductionIn this experiment, a known mass of hydrated copper(II) sulfate is heated to remove the water of crystallisation. The mass of water is found by weighing before and after heating. This information is used to fi nd x in the formula CuSO4.xH2O, using mole calculations.

CrucibleCopper sulfate

Tripod

Bunsen burner

Pipe clay triangle

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Technical notes and safetyHydrated copper(II) sulfate (Harmful, Dangerous for environment) Refer to CLEAPSS Hazcard 27C1 Crucibles may be of porcelain, stainless steel or nickel, of capacity about 15 cm3, and should sit safely in the pipe-clay triangles provided. Lids should not be used.2 Crucible tongs should have a bow in the jaws of the right size to pick up the hot crucibles safely.3 The copper(II) sulfate should be provided as fi ne crystals. If large crystals are used, these should be ground down before use by students.

Procedurea Weigh the empty crucible, and then weigh into it between 2 g and 3 g of hydrated copper(II) sulfate. Record all weighings accurate to the nearest 0.01 g.b Support the crucible securely in the pipe-clay triangle on the tripod over the Bunsen burner.c Heat the crucible and contents, gently at fi rst, over a medium Bunsen fl ame, so that the water of crystallisation is driven off steadily. The blue colour of the hydrated compound should gradually fade to the greyish-white of anhydrous copper(II) sulfate. Avoid over-heating, which may cause further decomposition, and stop heating immediately if the colour starts to blacken. If over-heated, toxic or corrosive fumes may be evolved. A total heating time of about 10 minutes should be enough.d Allow the crucible and contents to cool. The tongs may be used to move the hot crucible from the

hot pipe-clay triangle onto the heat resistant mat where it should cool more rapidly.e Re-weigh the crucible and contents once cold.f Calculation:• Calculate the molar masses of

H2O and CuSO4 (Relative atomic masses: H=1, O=16, S=32, Cu=63.5).

• Calculate the mass of water driven off, and the mass of anhydrous copper(II) sulfate formed in your experiment.

• Calculate the number of moles of anhydrous copper(II) sulfate formed.

• Calculate the number of moles of water driven off.

• Calculate how many moles of water would have been driven off if 1 mole of anhydrous copper(II) sulfate had been formed.

• Write down the formula for hydrated copper(II) sulfate.

Teaching notesRemind students to zero the balance before each weighing.

Students will probably also have to be reminded about the need to allow the crucible and contents to cool thoroughly before weighing.

Metal crucibles (stainless steel or nickel) are more robust than porcelain crucibles.

Further informationAn alternative version of this experiment, illustrated with video-clips, can be found at: http://dwb4.unl.edu/chemistry/smallscale/SS041c.html (This website is intended for teacher use.)

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Lesson organisationAs a class experiment this can be organised, if desired, as a class-cooperative investigation of the ability of a range of alcohols to react with a range of organic acids. Working groups could compare their results with others to build a general overview of this route to the formation of esters, with an interesting variety of smells.

Depending on the actual way the lesson is organised, this may be designed to take from 15 minutes to an hour.

Apparatus and chemicalsEach working group will require:• Eye protection• Glass specimen tubes, 4 (see note 1)• Plastic dropping pipettes, access to

adequate supply • Beaker (100 cm3)• Test-tubes, 4• Test-tube rack• Bunsen burner• Heat resistant mat• Tripod and gauze• Crucible tongs

Access to the following alcohols – about 10 drops of each required (see note 2)• Methanol (Highly fl ammable, Toxic)• Ethanol (Highly fl ammable,

Harmful)

• Propan-1-ol (Highly fl ammable, Irritant)

• Butan-1-ol (Harmful)One or more other alcohols, as available, from:• Propan-2-ol (Highly fl ammable,

Irritant)• Butan-2-ol (Irritant)• 2-Methylpropan-1-ol (Highly

fl ammable, Harmful) (see note 2)

• Ethanoic acid, pure (Corrosive), about 2 cm3

• Benzoic acid (Harmful), about 0.2 g• Propanoic acid (Corrosive) (if

available), about 2 cm3

• Concentrated sulfuric acid (Corrosive), 5 - 10 drops (see note 3)

• Sodium carbonate solution, 0.5 mol dm-3 (Low Hazard at concentration used), about 10 cm3 per ester

Technical notes and safety• Methanol (Highly fl ammable, Toxic)

Refer to CLEAPSS Hazcard 40B• Ethanol (Highly fl ammable,

Harmful) Refer to CLEAPSS Hazcard 40A

• Propan-1-ol (Highly fl ammable, Irritant) Refer to CLEAPSS Hazcard 84A

• Butan-1-ol (Harmful) Refer to CLEAPSS Hazcard 84B

• Ethanoic acid, pure (‘glacial’) (Corrosive) Refer to CLEAPSS Hazcard 38A

Preparing perfumes: Making esters from alcohols and acids

IntroductionIn this experiment students investigate the reactions between a range of alcohols and acids on a test-tube scale, to produce small quantities of a variety of esters quickly.

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• Benzoic acid (Harmful) Refer to CLEAPSS Hazcard 13A

• Propanoic acid (Corrosive) Refer to CLEAPSS Hazcard 38B

• Propan-2-ol (Highly fl ammable, Irritant) Refer to CLEAPSS Hazcard 84A

• Butan-2-ol (Irritant) Refer to CLEAPSS Hazcard 84B

• 2-Methylpropan-1-ol (Highly fl ammable, Harmful) Refer to CLEAPSS Hazcard 84B

• Concentrated sulfuric acid (Corrosive) Refer to CLEAPSS Hazcard 98

• Sodium carbonate solution (Low hazard at concentration used) Refer to CLEAPSS Hazcard 95A and Recipe Card 61

1 The essential requirements for these tubes are: • neutral borosilicate glass• a wide fl at base, so that they are

stable when stood in a beaker. If not available, small test-tubes could be used instead, standing in a larger (250 cm3) beaker.

2 The alcohols and acids may be best provided as a central resource, away from fl ames, with a supply of

plastic pipettes for each. Ideally each pipette is held on to each bottle with an elastic band.3 For younger students, prepare the specimen tubes by adding one drop of concentrated sulfuric acid to each. This minimises the risks involved with such students handling this substance. Advanced students may be reliable enough to prepare their own tubes in this way.

ProcedureSAFETY: Wear goggles throughouta Add 10 drops of ethanoic acid (or propanoic acid) to the sulfuric acid in the specimen tube.b Add 10 drops of ethanol (or other alcohol) to the mixture.c Put about 10 cm3 of water into the 100 cm3 beaker. Carefully lower the tube into the beaker so that it stands upright.d Heat the beaker gently on a tripod and gauze until the water begins to boil, then stop heating.e Stand for 1 minute in the hot water. If the mixture in the tube boils, use the tongs to lift it out of the water until boiling stops, then return it to the hot water.f After 1 minute, using tongs, carefully remove the tube and allow it to cool on the heat resistant mat.g When cool, pour the mixture into a test-tube half-full of 0.5 M sodium carbonate solution. There will be some effervescence. Mix well by pouring back into the specimen tube – repeat if necessary. A layer of ester will separate and fl oat on top of the aqueous layer.

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h Smell the product by gently wafting the odour towards your nose with your hand – do not put your nose near the top of the tube!i Repeat this procedure for up to three more different esters.

Compare the odours of the different esters prepared by your group and by other groups. Write word equations for each reaction, and (for advanced students) chemical equations using structural formulae.

For solid acids, the procedures in steps 1 and 2 need to be changed:j Add 1 cm3 of methanol (or other alcohol) to the sulfuric acid in the specimen tube.k Weigh out 0.2 g of benzoic acid (or another solid acid, such as salicylic (2-hydroxybenzoic) acid (Harmful – refer to CLEAPSS Hazcard 52) and add it to the tube. Then proceed as above. Yields from solid acids are not as great, but odours are detectable and distinctive.

Teaching notesThis method is an updated version of the traditional test-tube scale approach to ester preparation, which minimises the risks involved in handling the reagents involved. For further information about this method of ester preparation, consult CLEAPSS Guidance Leafl et PS67-07 ‘Making esters’.

This method is only suitable for preparing small samples for characterisation by odour. Advanced students could scale up the quantities using larger test-tubes, but this would still not give suffi cient product for isolation, characterisation by boiling point, or calculation of percentage yield.

Do NOT be tempted to use butanoic (butryric) acid, because of its very unpleasant odour (of rancid butter).

Further informationFor a broad review of esters, and interesting details of their odours and some uses, go to: http://en.wikipedia.org/wiki/Esters

Another site which looks extensively at the odours and uses of esters in fl avours and perfumes is: www.hartnell.cc.ca.us/faculty/shovde/chem12b/esters.htm

And for information from a manufacturer of an amazingly wide range of esters for uses from fl avourings and perfumes to lubricants and paints, go to:www.esterchem.co.uk/index.htm

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The science of matter and its motion, as well as space and time. Concepts such as force, energy, mass and charge, and learning to understand how the world around us behaves.

Physics

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“Practical work is doing things with different types of materials” Teacher response to SCORE questionnaire

IntroductionPractical work in physics is important in showing things to learners, as well as giving them an experience or feeling of a phenomenon, particularly an abstract one such as momentum. Experiments can sharpen students’ powers of observation, stimulate questions, and help develop new understanding and vocabulary. Practical work plays a particularly important role in developing pupils’ understanding of the physical world around them. Everyone remembers a number of dramatic practical activities from school – often demonstrations or activities with unexpected outcomes. These vivid memories of dramatic events can help students to retain scientifi c knowledge.

Secondary physics experiments:Bolt from the blue:Timing a 100 m run accuratelyFeeling the pressure:Investigating the effects of atmospheric pressurePower from the Sun:What affects the output of a solar panel?Does the Earth move?Photographing the night skyKicking up a force:Investigating the force used to kick a footballMaking sparks:Demonstrating the ionising effects of alpha radiation

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Bolt from the blue:Timing a 100 m run accurately

IntroductionThis is an exploration of issues of measurement, such as precision, range of values, uncertainty or ‘error’, repeat measurements and mean values.

Apparatus and materialsFor each student or student group:• Stopwatch or stopclock • String • Statistics board (see note 1) • Masses (50 g), 5 or 6 • Cones/Track markers, 10 (optional) • Video camera (optional)• Tape measure, long (at least 10 m)

(optional)

Technical notes and safety1 A statistics board is made from a piece of wooden board about 0.5 m square. 10 slotted channels are glued to it and metal (or other suitable material) discs are cut so that they fi t into the channels. The board is supported vertically. Assign values

to each channel. Students drop in a disc for the value they achieve. The distribution of results grows as results are added.2 If working outside, students must be appropriately supervised. 3 If a trolley is used in the lab, ensure that the trolley cannot land on anyone’s feet or legs.

Procedurea One student runs a distance of 100 metres. You, and other students, all independently time the run. b Compare all of the measurements. What is their range (the difference between the highest and the lowest values)?

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c What is the mean of all the measurements? A mean is a kind of average. Work this out by adding them all together and then dividing by the number of measurements. d Did everybody make measurements with the same precision? For example, did everybody make measurements using tenths of seconds (0.1 second is a tenth of a second) or hundredths of seconds (0.01 seconds is a hundredth of a second). e How certain can you be about the actual time taken for the run? You can’t be perfectly certain! There must be some uncertainty in the measurements. The mean measurement could be 14.8 seconds. Perhaps you think that the ‘true’ time for the run is in between 14.6 seconds and 15.0 seconds. Then you can say that the uncertainty is ± 0.2 seconds.

Teaching notesThe times can be collated as lists of numbers or, using a computer, as bar charts, or using a statistics board. Bar charts enable students to understand range, mean and error visually.

Statistical treatment plays a very important part in science. In advanced experiments students are expected to treat errors with some statistical care. In kinetic theory the steady pressure of a gas is recognised as an average of innumerable individual bombardments.

Statistical methods are used to delve into details of molecular speeds or sizes. In atomic physics statistical views are of prime importance. So

you might well make a gentle start now by showing how scientists look at a number of measurements of the same thing.

It is worth pointing out that there is such a thing as too much precision in a quoted value. A student who uses a stopwatch and gives a time of 14.77 seconds is crediting the timing process with more precision than it has. Answers of 15 seconds or 14.8 seconds may be acceptable (depending on the procedure and the stopwatch).

‘Mean’ is here used to indicate a particular kind of average – that found by dividing the sum of values by the sample size.

In more advanced work, uncertainty is conventionally called ‘error’. Here, the word uncertainty more clearly describes the concept. You could repeat the activity for a different motion, such as for a trolley pulled across a metre distance on a table, or the fall of a mass.

Again, all students should measure the time for the same motion. Range, mean, precision and uncertainty can be compared with those for the student’s 100 metre run.

You may want to compare timings for real sports races. Information on sporting records can be found on the Internet. For example see Usain Bolt’s record breaking 100 m run in the 2008 Olympics www.youtube.com/watch?v=YFE1ctdRc88. Precision of measurement in different sports can be compared, and students can discuss the idea of uncertainty in the values.

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How Science Works extension: This experiment already covers many of the areas relating to accuracy and reliability of data, as well as experimental errors. The scope could be increased further, as follows: • Arrange pairs of students every

5 m or 10 m apart along the 100 m running path. Use some kind of signal (e.g. dropping a raised arm) to start both the runner and everyone’s timers. As the runner passes each student, they stop their timer and record the time taken to reach them.

• Students then plot this data graphically (distance against time). This will make it easier for students to understand average speed and get a feel for the variation in measurements. A ‘true’ velocity can be calculated from the gradient of the best fi t line.

• If you placed cones/markers along the track, you might be able to video each student running, with a stopclock also in the camera view. This would generate a second set of results that could be compared numerically or graphically to the class set. Students could comment on whether this method improves on the previous one.

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Feeling the pressure: Investigating the effects of atmospheric pressure

IntroductionIt is not always easy to get students to understand the effects of atmospheric pressure, but here are a couple of simple activities to challenge existing ideas and allow the development of a more sophisticated understanding of this concept.

Lesson organisationAlthough these can readily be done as demonstrations, the simplicity of the equipment allows the activities to be done individually or in small groups as well.

Apparatus and materialsEach group/individual will need:• Two straws• A plastic cup of water• A clear plastic bottle up to 1 litre

in size• A clear plastic bottle up to 1 litre

in size, with a small hole on its base• 2 well stretched balloons• A drawing pin to make a hole in

a straw

Technical notes and safetyEach student who tries the two straws activity should use fresh straws and used straws should be thrown away.

ProcedureActivity 1 – atmospheric pressure and suction1 Put a straw in the clear cup of water.2 Hold a second straw outside the cup as shown.3 Try sucking the water up through the straw.4 Now make a small hole in one of the straws with the drawing pin about 3 cm from the top and try drinking through it.

Plastic bottle

Balloon

Small holePlastic cup

Water

Suck here

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Activity 2 – balloon in a bottle1 Place a balloon inside each bottle; spread its neck over the top of the bottle.2 Try blowing up the balloon in each case – only with the bottle with a hole in will it work.3 Air will exit the bottle via the small hole in the base of the bottle. Quickly seal the hole with your thumb and the balloon will stay infl ated.4 By slowly allowing air to enter the bottle, the balloon will defl ate under your command.

Teaching notesBoth activities can be run after some discussion to encourage students to make predictions and attempt explanations that use the idea of a pressure difference to explain what happens.

Activity 1The student will fi nd it impossible to drink if one of the straws is outside the glass.

If both straws are placed in the mouth it is diffi cult to maintain a suffi ciently low pressure to cause the water to be sucked up, because air enters the mouth through the second straw. In order for the water to be forced into your mouth, the pressure outside (atmospheric pressure) needs to be greater than the pressure inside your mouth. This means that no matter how you suck, a straw won’t work if air can get into your mouth.

A similar effect is achieved by making a small hole in a straw about 3 cm from the top and putting this straw in the water.

Extension activities could include exploring how many straws put IN the water can drink be sucked through – increasing the surface area makes it harder.

By joining straws together fi nd the longest straw it is possible to drink through.

Activity 2 Discuss why it is not possible to blow up the balloon without the hole in the bottle and why the balloon stays infl ated when the hole in the bottle is covered. Encourage students to use the idea of pressure differences in their answers.

Putting the lid on the bottle, or tape over the hole, can leave the balloon infl ated.

By sucking air through the hole in the bottom of the bottle it is possible to infl ate the balloon.

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Power from the Sun:What affects the output of a solar panel?

IntroductionThis experiment is copyright of Gatsby Science Enhancement Programme, and is reproduced with permission.

A solar power system for a house is not always going to give the same power output. It will depend on the time of day, the season, the weather, and so on. In this activity, the factors that affect the power output of a solar panel are looked at, and may lead to an investigation of quantitative aspects of some of these factors.

Lesson organisationThis can be done in small groups as a qualitative activity to get a feel for the factors that affect the output of a solar panel, in which case the activity may only take up part of a lesson.

If this is followed by a quantitative investigation of one of the factors, then this might be done in pairs and will take longer.

The class could be organised so that different groups each look at a different factors in more detail, and then report back to the whole class. Students should be asked to explain how their results relate to real conditions with the Sun, and if there is an opportunity, they could take the panel outside and look at the effect of tilting the panel, of partially covering the panel or using different kinds of fi lters.

Apparatus and materialsEach group will need:• Solar panel unit• Small motor unit• Desk lamp• Digital multimeter (or voltmeter)• Plug-plug leads (red), 2• Plug-plug leads (black), 2• Metre rule• Piece of cardboard• Translucent sheets (e.g. tracing

paper) cut a suitable size to cover the solar panel

• Coloured fi lters• Clamp stand

V=A=

V

Fig. 1: A solar panel connected to an electric motor

Fig. 2: A solar panel connected to an electric motor and a voltmeter

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Technical notes and safetyDesk lamps with metal shades can get very hot and care needs to be taken when moving them.

Procedure1 Connect a solar panel to an electric motor (see Fig. 1). Shine a desk lamp on the panel so that the motor turns.2 Next, connect a voltmeter to the solar panel (see Fig. 2).The voltmeter can be used to get an idea about the output of the solar panel. A voltmeter does not measure power (power = voltage x current), but the voltage can be used to make comparisons.3 Explore the effects of:• moving the lamp closer and

further away• partially covering and uncovering

the solar panel• tilting the panel backwards and

forwards• putting a translucent sheet between

the lamp and the panel• putting different coloured fi lters

between the lamp and the panel.

Teaching notesIn this activity, students will get the opportunity to use a range of investigative skills, including the identifi cation of different kinds of variable, the tabulation of data and drawing different kinds of graphs and charts.

The activity works best if done in a room with blackout or low light levels as ambient light may overwhelm the variations in light levels being observed.

Students should fi nd that the maximum output is given with a high light intensity and the biggest surface area, and with no tilt in relation to the light source. The translucent sheet and coloured fi lters reduce the power output.

This investigation could be used as a starting point for further investigations, such as fi nding out how the voltage across the panel is affected by the distance of the lamp. A suitable range of distances is from 10 to 25 cm (if using just the motor); with the voltmeter, a suitable range of distances would be from 10 to 50 cm. To help students to measure the distance of the lamp from the panel, it is helpful to make a mark on the lamp casing level with the centre of the light bulb.

Another factor that would be worth investigating is the relationship between the area of the panel exposed and the voltage. Students could also try other factors of their own, such as putting glass, clear plastic sheet, white paper, etc over the solar panel.

v

Clamp stand

Lamp

Solar panel

Half metre rule

Voltmeter

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Students should be asked to relate their results to answer the question ‘If you were using this solar panel outside with the Sun, what factors would affect its power output?’ Even on a clear day, much of the radiation from the Sun is absorbed or scattered as it passes through the atmosphere; clouds will obviously reduce the radiation still further. We can’t control the amount of radiation coming from the Sun, but we can tilt the panel to make the best use of it. If a panel is mounted horizontally, the maximum output would be produced at noon, when the Sun is highest in the sky. When the Sun is low, the radiation is

spread over a larger area of the panel. (In addition the radiation is reduced because it travels a further distance through the atmosphere thus leading to greater absorption and scattering.) At the equator, the Sun is overhead at noon, but at other latitudes, the best output is achieved by tilting the panel (in the northern hemisphere, towards the south). The optimum angle of tilt depends on the latitude. Even better, is to have a panel that is able to track the position of the Sun and which can move so that it is always perpendicular to the radiation, though this adds considerably to the cost of the system.

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Does the Earth move? Photographing the night sky

IntroductionThis demonstration uses a time exposure photograph to illustrate the apparent motion of the stars.

Apparatus and materialsTripod, or other means of holding camera still during exposure Camera with B (open shutter) setting.

Technical notes and safetyIt is a good idea to cool down the camera by leaving it outside for some time before the exposure is set up, so that no condensation forms inside the camera.

The photograph will be more impressive if the picture includes the silhouette of the school building or of well-known trees near by. Avoid doing this at a time of month near a full moon.

To get a B (Bulb) setting (open shutter) on a digital camera, you need to have your camera on manual setting and then decrease shutter speed. You will also need a cable release that you can lock. Otherwise the shutter only stays open as long as you keep your fi nger down on the button!

Have the lens aperture as wide open as possible so that you photograph more than just the brightest stars.

A digital camera or colour fi lm will show the different colours of the stars.

Use a torch when setting up the camera and tripod. If students do this at home, they should make arrangements with parents or guardians to do it in a safe place.

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Procedurea Take a photograph of the night sky by exposing a fi lm in a rigidly fi xed camera for two hours or more, and make it available for discussion. b Encourage students who are interested to make a photograph themselves. To take such a photograph, attach a simple camera with an ordinary lens (not telephoto) to a fi rm stand or tripod. Point it towards the Pole Star, open the shutter on a setting that keeps it open indefi nitely, (though the aperture will usually have to be found by trial), and leave undisturbed for the period chosen (at least 2 hours, preferably 4 to 8 hours).

6 November at 11 p.m. 6 December at 11 p.m.

Betelgeuse

RigelOrion

Betelgeuse

Rigel

Orion

Procyon

Sirius

Aldebaran

A view of the stars through a window in Britain at the same time of night, but one month apart. Can you explain why the stars appear to have moved in this case?

Teaching notes1 The photograph will show arcs of a circle as the stars appear to revolve around the Pole Star. The length of the arc, as a fraction of the circumference of the circle of which it forms a part indicates the time for the exposure as a fraction of 24 hours. 2 For the southern hemisphere, there is no bright star close to the celestial pole. The southern polestar, Sigma Octantis, is only of the 5th magnitude, so the direction to point the camera will have to be judged from other stars.

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Apparatus and materials• Scaler, or electronic timer,

accurate to 0.001 s • Round football

(rugby type not suitable) • Flexible leads, 30 cm• Crocodile clips, 2 • Stopwatch or stop clock • Balance (to measure mass of ball) • Aluminium foil square,

15 cm by 15 cm • Aluminium foil square,

7.5 cm by 7.5 cm • Sellotape • Plasticene

Technical notes and safetyTake care that the football is aimed so that it does not cause damage, and there is no danger of the timer being knocked off the bench.

The large foil is Sellotaped to the football: the small foil is taped to the toe of the kicker’s foot.

Connections to the foil are made with crocodile clips. The other ends of the leads should be a loose fi t in the ‘timer input’ sockets so that they will come out easily in the event of an accident. It is sensible to have a student holding the timer on the bench.

Providing that the fl exible leads are arranged so that the period of contact takes place before the ball pulls the foil away from the crocodile-clip contact, no diffi culties should arise. You should obtain consistent results.

It is possible to get a value for the time of fl ight of a ball kicked with medium force down a 10 m corridor (or even a 5 m laboratory).

Kicking up a force:Investigating the force used to kick a football

IntroductionThis demonstration uses impact time and change of momentum of a football to measure the force needed to kick the ball.

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Procedurea Place the ball on three small lumps of plasticene to stabilize it. b Kick the ball in a horizontal direction from a standing position on a laboratory table, with only medium force. More vigorous kicks can be used out of doors to show the longer time of contact. c Find the time of contact of the ball with the foot from the scaler or timer, t, seconds. d Find the mass of the ball, m kg, using a balance.

Teaching notes1 Measure how far the ball travels horizontally before it hits the fl oor, s, then s = vT. The time of fl ight, T, can be found from the height of the table, h = 1/2 gT2. The acceleration due to gravity = 10 ms-2 T2 = 2h/gT = √2h/g.

Substituting in the equation v = s/T gives a value for the initial velocity of the ball. Therefore using Ft = (mv) the force, F, on the ball can be calculated.

Alternatively, fi lm the fl ight of the ball using a camcorder, and use frame by frame playback mode to calculate its speed. Multifl ash photography creates successive images at regular time intervals on a single frame, and further details can be found on www.practicalphysics.org. 2 Once students have learnt about the conservation of momentum in a collision then a different method can be used to calculate the force. The football is kicked into a cardboard box which is fi xed to roller-skates or a skateboard.

or

by multiflash photo

toscaler

h

s

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The box should be made massive so that it moves slowly enough for the time of motion to be measured with a stopwatch. The fl aps on the box should trap the ball. All the momentum of the ball is shared with the box. The momentum of the box is calculated from its mass and velocity (= distance travelled in the measured time). This is equal to the initial momentum of the ball after it is kicked. Using Ft = (mv) then the force can be calculated if the time of contact is measured on the scaler.

Cardboard box

Door flaps trap the ball

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Making sparks: demonstrating the ionising effects of alpha radiation

IntroductionThe spark counter demonstration is a highly visible (and audible) way of showing and counting ionisation of the air caused by alpha radiation (or a match). It is a useful step towards understanding the Geiger-Müller tube.

Apparatus and materials• Power supply, EHT, 0-5 kV

(with option to bypass safety resistor)

• Spark counter • Sealed source of radium, 5 µC

(if available) • or sealed source of americium-241,

5 µC • Holder for radioactive source

(e.g. forceps) • Connecting leads

Technical notes and safetyThe spark counter is a special piece of apparatus (see image below). It consists of a metal gauze with a wire running underneath. Philip Harris call it a Spark discharge apparatus.

Any kink or bend in the wire in the counter is liable to cause a spark discharge at that point. If that happens the wire should be replaced.

A continuous spark (which will very soon damage the wire) shows the voltage is too high.

The spark counter should be dust free. Dust around the stretched wire can usually be blown away.

The gauze on top is connected to the earth on the EHT supply as a safety precaution.

Radium is a source of alpha, beta and gamma radiation. Beta and gamma radiations do not cause enough ionisation of the air to start a spark.

Refer to CLEAPSS for further guidance on managing radioactive materials in schools.

A school EHT supply is limited to a maximum current of 5 mA which is regarded as safe. For use with a spark counter, the 50 MW safety resistor can be left in circuit so reducing the maximum shock current to less than 0.1 mA.

Metal gauze

Wire beneath metal gauze

Spark discharge apparatus

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Although the school EHT supply is safe, shocks can make the demonstrator jump. It is therefore wise to see that there are no bare high voltage conductors; use female 4 mm connectors where required.

ProcedureSetting up a Connect the positive, high voltage terminal of the spark counter to the positive terminal of the EHT supply without the 50 MW safety resistor. (The spark counter’s high voltage terminal is joined to the wire that runs under the gauze.) b Connect the other terminal on the spark counter to the negative terminal of the power supply and connect this terminal to earth.

c Turn the voltage up slowly until it is just below the point of spontaneous discharge. This is usually at about 4,500 V. Carrying out d Use forceps to hold a radioactive source over the gauze. You should see and hear sparks jumping between the gauze and the high voltage wire underneath each time an alpha source is brought near to the counter. e Move the source slowly away from the gauze and note the distance at which it stops causing sparks.

Teaching notes1 Draw attention to the random nature of the sparks and hence of the radiation. By counting sparks you are counting the number of alpha particles emitted.

+

+

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2 You should fi nd that the range of the alpha particles is about 5 cm. 3 You could mention that this is alpha radiation which is the most ionising of the three main types of radiation. 4 The sparks are similar to those produced by the Van de Graaff. The alpha particles ionise the air forming positive and negative ions. When these ions recombine to form neutral atoms then blue light is emitted. The noise of the spark is due to warming the air in the narrow region of the avalanche current producing a sound wave just like in a lightning strike. 5 A thin sheet of tissue paper or gold foil held between the spark counter and the source will show a reduced range for the alpha particles or even prevent them getting to the counter.

6 A version of this apparatus can be seen in the CERN visitor centre (if you happen to be passing). It detects cosmic rays and makes them visible using a 3D array of wire meshes with high voltages between them. The paths of rays can be seen by the trail of sparks that they leave as they ionise the air between the wire meshes. This type of 3D array of high voltage meshes is the principle used to detect the paths of particles produced in the collision experiments at CERN. 7 Before you use the spark counter showing ionisations from an alpha source, you could use the spark counter to count matches (as in ‘Counting matches with an EHT supply’ available on www.practicalphysics.org).

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Further information

GeneralCLEAPSS: www.cleapss.org.ukSSERC: www.sserc.org.ukASE: www.ase.org.ukASE Upd8: www.upd8.org.ukSciCast: www.planet-scicast.comField Studies Council (FSC): www.fi eld-studies-council.orgGatsby Science Enhancement Programme: www.sep.org.ukScience Learning Centres: www.sciencelearningcentres.org.ukTriple Science Support Programme: www.triplescience.org.ukEarth Science Education Unit: www.earthscienceeducation.com Earth Learning Idea: www.earthlearningidea.com

Primary scienceASE Primary Upd8: www.primaryupd8.org.ukCREST STAR Investigators: www.the-ba.net/the-ba/ccaf/CRESTStarInvestigators/

BiologyPractical Biology: www.practicalbiology.orgBioEthics Education Project (BEEP): www.beep.ac.ukScience and Plants for Schools (SAPS): www-saps.plantsci.cam.ac.ukSurvival Rivals: www.survivalrivals.orgGreat Plant Hunt: www.thegreatplanthunt.org

ChemistryPractical Chemistry: www.practicalchemistry.orgNuffi eld Re:Act: www.chemistry-react.org RSC Classic Chemistry Demonstrations: www.rsc.org/education/teachers/learnnet/classic.htmRSC Classic Chemistry Experiments: www.rsc.org/education/teachers/learnnet/classic_exp.htmRSC Microscale Chemistry: www.rsc.org/education/teachers/learnnet/microscale.htmRSC Video material for teachers of chemistry: www.rsc.org/education/teachers/learnnet/videoclips.htm

PhysicsPractical Physics: www.practicalphysics.orgPhysics & Ethics Education Project (PEEP): www.peep.ac.ukTeaching Advanced Physics (TAP): www.iop.org/activity/education/Teaching_Resources/Teaching%20Advanced%20Physics/page_8325.htmlDemonstrating physics – forces: www.teachers.tv/video/2505Demonstrating physics – radioactivity: www.teachers.tv/video/27400

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This booklet has been produced by

SCORE partners:

Association for Science EducationBiosciences FederationInstitute of BiologyInstitute of PhysicsRoyal SocietyRoyal Society of ChemistryScience Council

in association with:

CLEAPSSField Studies CouncilNuffi eld Curriculum CentreThe Wellcome Trust

Supported by Department for Children, Schools and Families and The Gatsby Charitable Foundation.

SCORE – Science Community Representing Education6-9 Carlton House TerraceLondon SW1Y 5AGemail [email protected] +44 (0)20 7451 2205web www.score-education.org

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without prior permission in writing of the publishers, or in the case of reprographic reproduction, only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organisation outside the UK. P

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