Biology PAG 8: Transport in and out of cells

Suggested Activity 2: Expanding Gummy Bears

Instructions and answers for teachers and technicians

These instructions cover the learner activity section which can be found on page 10. This Practical activity supports OCR GCSE Biology.

When distributing the activity section to the learners either as a printed copy or as a Word file you will need to remove the teacher instructions section.

This is a suggested practical activity that can be used as part of teaching the GCSE (9-1) Gateway Science (A) and Twenty First Century Science (B) specifications.

These are not controlled assessment tasks, and there is no requirement to use these particular activities.

You may modify these activities to suit your learners and centre. Alternative activities are available from, for example, Royal Society of Biology, Royal Society of Chemistry, Institute of

Physics, CLEAPSS and publishing companies, or of your own devising.

Further details are available in the specifications (Practical Skills Topics), and in these videos.

OCR recommendations:

Before carrying out any experiment or demonstration based on this guidance, it is the responsibility of teachers to ensure that they have undertaken a risk assessment in accordance with their employer’s requirements, making use of up-to-date information and taking account of their own particular circumstances. Any local rules or restrictions issued by the employer must always be followed.

CLEAPSS resources are useful for carrying out risk-assessments: (http://science.cleapss.org.uk).

Centres should trial experiments in advance of giving them to learners. Centres may choose to make adaptations to this practical activity, but should be aware that this may affect the Apparatus and Techniques covered by the learner.

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IntroductionOsmosis is the movement of water molecules from areas of high water concentration to areas of low water concentration, through a selectively permeable membrane.

The concept of osmosis, particularly the direction of water movement, is abstract and can be difficult for students to grasp. Especially when taught alongside diffusion. Visualising a change in mass should give pupils a concrete example of this scientific phenomena.

Most osmosis experiments use potatoes. The practical can be dull and therefore pupils often aren’t engaged. Making a simple change, using gummy sweets, can make the experiment more engaging, as students can observe the gummy bears, hearts, lips getting ‘fatter’ and ‘thinner’.

For observable results, the gummy sweets need to be left in solution for a period of time, ideally two days. Therefore, it is recommended that this practical lesson is carried out over two lessons. The first lesson explaining the theory, developing a hypothesis and setting up the experiment. The second lesson collecting and concluding results.

Calculating percentage change in mass is a required skill. With repeat tests, in different solutions, for some students the array of numbers can be overwhelming. With most osmosis experiments, students are expected to measure length and width of the solid they are using in addition to percentage change in mass. To keep percentage change in mass the mathematical focus, but enabling students to be able to see the change in size, it is recommended that students photograph the gummy sweets before and after (an example is given below). The use of technology may also students, but additionally they will have photo of the experiment to add to their notes. This will give them a visual to revise from, rather than just data.

Before osmosis example:

After osmosis example:

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DfE Apparatus and Techniques coveredThe codes used below match the OCR Practical Activity Learner Record Sheet (Biology / Combined Science) and Trackers (Biology / Combined Science) available online. There is no requirement to use these resources.

1 [1]: Use of appropriate apparatus to make and record a range of measurements accurately, including: iii [iii]) mass; iv [iv]) time; vi [vi]) volume of liquids

3 [3]: Use of appropriate apparatus and techniques for the: i) observation of biological changes and/or processes; ii) measurement of biological changes and/or processes

5 [5]: Measurement of rates of reaction by a variety of methods including: ii) uptake of water

8: Use of appropriate techniques and qualitative reagents to identify biological molecules and processes in more complex and problem-solving contexts including: i) continuous sampling in an investigation

AimsTo use appropriate techniques to observe the movement of water molecules

To use apparatus to measure mass, time and the volume of a liquid

To calculate the percentage change in mass

Intended class timeThis activity will take 90 - 120 minutes.

Links to Specifications: Twenty First CenturyB3.2.2a Explain how substances are transported into and out of cells through diffusion, osmosis and active transport.

B3.2.2b Describe practical investigations into the processes of diffusion and osmosis.

B3.2.3 Explain how the partially-permeable cells membranes of plant cells and prokaryotic cells are related to diffusion, osmosis and active transport.

B5.1.2 Explain how the partially-permeable cell membranes of animal cells are related to diffusion, osmosis and active transport.

B5.4.4 Explain the effect on cells of osmotic changes in body fluids.

GatewayB2.1a Explain how substances are transported into and out of cells through diffusion, osmosis and active transport.

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B3.3f Explain the effect on cells of osmotic changes in body fluids.

Mathematical Skills coveredM1a Recognise and use expressions in decimal form

M1c Use fractions, ratios and percentages

M2b Find arithmetic means

M2f Understand the terms mean, mode and median

M4c Plot two variables from experimental and other data

Twenty First Century IaS references covered IaS2.1 Present observations and other data using appropriate formats

IaS2.4 Be able to translate data from one form to another

IaS2.6 When processing data use an appropriate number of significant figures

Gateway Working scientifically references coveredWS1.2a - use scientific theories and explanations to develop hypotheses

WS1.2e - evaluate methods and suggest possible improvements and further investigations

WS1.3a – presenting observations and other data using appropriate methods

WS1.3b – translating data from one form to another

WS1.3c – carrying out and representing mathematical and statistical analysis

WS1.3e – interpreting observation and other data

WS1.4a – use scientific vocabulary, terminology and definitions

WS1.4c – use SI units

WS1.4f – use an appropriate number of significant figures in calculation

WS2a – carry out experiments to include due regard to the correct manipulation of apparatus, the

accuracy of measurements and health and safety considerations, and following written instructions

WS2b – make and record observations and measurements using a range of apparatus and

methods to include keeping appropriate records

WS2c – presenting observations using appropriate methods to include methods to include

descriptive, tabular diagrammatic and graphically

EquipmentPer group

4 gummy sweets 4 boiling tubes Boiling tube rack 40cm3 distilled water (tap water will work) 1 spatula of salt* 1 spatula of sugar*

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20cm3/50cm3 measuring cylinder Forceps Marker pen that will write on glass A4 sheet of paper

In the class

2dp mass balance Camera (iPad, phone, digital camera, flipcam)

NB/ Allowing students to add their own sugar/salt to make up solutions makes it easier for them to recall which is which, and know the difference in the solutions.

Sugar and salt will dissolve and make more effective solutions if the water is warm ~ 25-30oC, rather than using cold water.

Health and SafetyGummy sweets are usually made of gelatine, it is therefore advisable to speak with students who may have any objections to working with pork based products.

Method 1. Stand the 4 boiling tubes in a boiling tube rack

2. Using the marker pen, label the tubes as follows;a. Control – This tube DOES NOT need any water or solution added to itb. Distilled water (or tap water) c. Salt water d. Sugar water

3. Using the measuring cylinder, add 20cm3 of water to boiling tubes b, c and d.

4. Add 1 spatula of salt to c. Saltwater

5. Add 1 spatula of sugar to d. Sugar water

The solutions are now prepped to add the gummy sweets

6. Place the 4 gummy sweets on a A4 sheet of paper

7. Under each gummy sweet, write which boiling tube it will be added to (see image on next page)

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8. Measure the initial mass of each gummy sweet and note this on the A4 sheet

9. Place the gummy sweets in their allocated boiling tubes

10. Leave the gummy sweets overnight, to allow the process of osmosis to take place. Leave the A4 paper with the mass recordings with the experiments – this will be needed again

After a period of 24 - 48 hours

11. Using the forceps, collect each of the gummy bears out of the boiling tubes and place them back onto the A4 sheet in their allocated spaces

12. Using the scales, measure the final mass of the gummy sweets

13. Record the final mass on the A4 paper

14. Calculate the percentage change in mass, using the equation below

Percentage change in mass = (final mass – initial mass) ÷ initial mass x 100

NB/ You may get a negative result – that just indicates the mass has decreased.

15. Take a photo of the gummy sweets on the A4 sheet with the mass recordings

EXTENSION ACTIVITY: Place the gummy sweet that was in boiling tube b distilled water in to a clean boiling tube with 20cm3 water and 1 spatula with salt. Observe what happens after 24 hours.

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Technician Notes

60 gummy sweets (gummy bears will work best) 60 boiling tubes 15 x Boiling tube racks 300cm3 distilled water (tap water will work) – helps if water is warm to dissolve salt/sugar 15 spatulas of salt 15 spatulas of sugar 15 20cm3/50cm3 measuring cylinder (for measuring 20cm3 water) 15 Forceps 15 Marker pens that will write on glass 15 A4 sheets of paper

In the class

2dp mass balances (as many as possible, up to 15) Camera (iPad, phone, digital camera, Flipcam)

NB/ Sugar and salt will dissolve and make more effective solutions if the water is warm ~ 25-30oC, rather than using cold water.

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Answers - Learner activity – Hypothesis development Osmosis

The net movement of water across a partially permeable membrane from a high concentration of water to a low concentration of water.

Hypotonic

When a solution outside the cell contains a lower concentration of solute molecules than inside the cell.

Turgid

A plant cell fully swollen with water

Partially permeable membrane

The cell membrane has very small holes in it. Small molecules can pass through, but larger ones cant.

Isotonic

When a solution outside the cell contains the same concentration of solute molecules as inside the cell.

Flaccid

A plant cell that is limp through a reduction of pressure inside the cell.

Concentration gradient

The process of particles, which are sometimes called solutes, moving through a substance from an area with a higher number of particles to an area with a lower number of particles.

Hypertonic

When a solution outside the cell contains a higher concentration of solute molecules than inside the cell.

Plasmolysed

A plant cell that has lost water causing the cell membrane to be pulled away from the inside of the cell wall.

Equilibrium

A balanced state

Haemolysis/lysed

When a red blood cell bursts/has burst. This happens when the cell is placed in a hypotonic solution, such as pure water.

Lysis

Bursting an animal cell by osmosis.

This happens when the cell is placed in a hypotonic solution, such as pure water.

Example hypothesis

The gummy sweet in the distilled/tap water will have the greatest percentage change in mass. The water is a hypotonic solution. The solution outside the gummy contains a lower concentration of solute molecules than inside the gummy sweet. The water will move from a high to a low concentration, resulting in the gummy sweets mass increasing.

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Quiz – Answers 1. If the gummy sweet were a red blood cell what would happen if it were placed in pure water?

Explain why. Water is a hypotonic solution The concentration of water outside the cell is greater than the concentration inside

the cell The cell would expand Haemolysis

[4 marks]

2. If the gummy sweet were a plant cell, what would happen if it were placed in pure water? Why would the outcome be different?

Still in a hypotonic solution so would still expand Become turgid The cell would not burst, as it has a cell wall to maintain structure

[3 marks]

3. What type of solution was the salt water? Explain your answer, using ideas from the practical Hypertonic solution The gummy sweet decreased in mass Water moved out of the gummy sweet into the salt water/low to high concentration

[3 marks]

Document updatesv1 January 2018 Published on the qualification page

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Biology PAG 8: Transport in and out of cells

Suggested Activity 2: Expanding Gummy Bears

Learner Activity

IntroductionOsmosis is the movement of water molecules from areas of high water concentration to areas of low water concentration, through a selectively permeable membrane.

Osmosis occurs in cells.

Aims To use appropriate techniques to observe the movement of water molecules To use apparatus to measure mass, time and the volume of a liquid To calculate the percentage change in mass

Intended class time90 – 120 minutes

Learner activity – Hypothesis development (higher demand)

Find definitions for the key terms below

Osmosis Hypotonic Turgid

Use these ideas to construct a hypothesis. In which solution will you see the greatest percentage change in mass?

Hypothesis

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Learner activity – Hypothesis development

Osmosis

The net movement of ________ across a _____ _______membrane from a ____ concentration of water to a __ concentration of water.

Hypotonic

When a solution outside the cell contains a _______ __________ of solute molecules than inside the cell.

Turgid

A plant cell ___________________________

Partially permeable membrane

The _____ ______________ has very small _______ in it. Small molecules can pass through, but larger ones cant.

Isotonic

When a solution outside the cell contains the _______ __________ of solute molecules as inside the cell

Flaccid

A plant cell _____________________________

Concentration gradient

The process of particles, which are sometimes called _________, moving through a substance from an area with a ___________ number of particles to an area with a ___________ number of particles.

Hypertonic

When a solution outside the cell contains a _______ ____________ of ____________ molecules than inside the cell.

Plasmolysed

A ________ cell that has _______water causing the cell ________ to be pulled away from the inside of the cell wall.

Equilibrium

A ___________ state

Haemolysis/lysed

When a _____________ bursts/has burst. This happens when the cell is placed in a _________ solution, such as pure water

Lysis

__________ an animal cell by osmosisThis happens when the cell is placed in a ___________ solution, such as pure water

(standard demand)

Fill in the keywords in the definitions below

Hypothesis

The gummy sweet in the ________ water will have the greatest percentage change in mass.

The water is a _______________ solution.

The solution outside the gummy contains a __________ concentration of solute molecules than inside the gummy sweet.

The water will move from a _______ to a ______ concentration, resulting in the gummy sweets mass increasing.

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EquipmentPer group

4 gummy sweets 4 boiling tubes Boiling tube rack 40cm3 distilled water (tap water will work) 1 spatula of salt* 1 spatula of sugar* 20cm3/50cm3 measuring cylinder Forceps Marker pen that will write on glass A4 sheet of paper

In the class

2dp mass balance Camera (iPad, phone, digital camera, Flipcam).

Method 1. Stand the 4 boiling tubes in a boiling tube rack

2. Using the marker pen, label the tubes as follows;a. Control – This tube DOES NOT need any water or solution added to itb. Distilled water (or tap water) c. Salt water d. Sugar water

3. Using the measuring cylinder, add 20cm3 of water to boiling tubes b, c and d.

4. Add 1 spatula of salt to c. Saltwater

5. Add 1 spatula of sugar to d. Sugar water

The solutions are now prepped to add the gummy sweets

6. Place the 4 gummy sweets on a A4 sheet of paper

7. Under each gummy sweet, write which boiling tube it will be added to (see image on following page)

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8. Measure the initial mass of each gummy sweet and note this on the A4 sheet

9. Place the gummy sweets in their allocated boiling tubes

10. Leave the gummy sweets overnight, to allow the process of osmosis to take place. Leave the A4 paper with the mass recordings with the experiments – this will be needed again

After a period of 24 - 48 hours

11. Using the forceps, collect each of the gummy bears out of the boiling tubes and place them back onto the A4 sheet in their allocated spaces

12. Using the scales, measure the final mass of the gummy sweets

13. Record the final mass on the A4 paper

14. Calculate the percentage change in mass, using the equation below

Percentage change in mass = (final mass – initial mass) ÷ initial mass

NB/ You may get a negative result – that just indicates the mass has decreased.

15. Take a photo of the gummy sweets on the A4 sheet with the mass recordings

EXTENSION ACTIVITY: Place the gummy sweet that was in boiling tube b distilled water in to a clean boiling tube with 20cm3 water and 1 spatula with salt. Observe what happens after 24 hours.

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ResultsAdd you result from the A4 sheet in to the table 1 below;

TABLE 1

Solution Initial mass (g) Final mass (g) Change in mass (g)

Percentage change in mass

(%)Control (a)

Distilled Water (b)

Salt Water (c)

Sugar Water (d)

Compare your results with peers, by sharing results in table 2

TABLE 2

Solution

Percentage change in mass (%)

Your results Group 1 Group 2 Average (mean)

Control (a)

Distilled Water (b)

Salt Water (c)

Sugar Water (d)

ConclusionUse scientific knowledge about osmosis to write a paragraph to explain your data. Was your hypothesis correct?

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Quiz – test your knowledge and understanding 1. If the gummy sweet were a red blood cell, what would happen if it were placed in pure water?

Explain why. [3 marks]

2. If the gummy bear were a plant cell, what would happen if it were placed in pure water? Why would the outcome be different? [3 marks]

3. What type of solution was the salt water? Explain your answer, using ideas from the practical. [3 marks]

DfE Apparatus and Techniques coveredIf you are using the OCR Practical Activity Learner Record Sheet (Biology / Combined Science) you may be able to tick off the following skills:

Biology Combined Science1-iii 1-iv 1-vi 1-iii 1-iv 1-vi3-ii 5-ii 8-i 3-ii 5-ii

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