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Transcript of Name: Form: Teaching Groupresources.hwb.wales.gov.uk/VTC/ngfl/2007-08/science... · a) There are...
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2
REVISION TIPS To be successful in your exams you must be well prepared. This
involves hard work both in and outside the classroom.
Listen carefully during the lesson and try not to be distracted.
To learn something you must understand it. So read through your work after each
lesson and ask for help if you are unsure of anything.
Set yourself a realistic time frame for revision. Work with small chunks of
time over a longer time span rather than hours on end at the last moment.
Get up and walk about whilst trying to learn something.
Avoid last a minute rush.
When you are revising have a copy of the syllabus, your notes, paper and
coloured pencils/highlighters. Check off the topic when you have fully
understood and learnt it.
In the exam, read the question carefully and make sure you answer the question being
asked. Some key question words are:
STATE means write the facts for the answer in a short concise way
EXPLAIN means to make known in detail or give the reason for something.
DESCRIBE means to state what the form or function of something is using words
or diagrams. For a graph it means to state what the graph shows or what pattern is
shown by the results. An explanation may be required eg if you are asked to
describe a process.
SUMMARISE means to give a brief statement of.
LIST means write facts one after the other
DISTINGUISH BETWEEN state the important differences between two things.
Remember to be precise and say which you are describing.
= revision tip
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BIOLOGY – topic check list 1. ADAPTATION AND COMPETITION
Why and how should organisms be classified?
Which organisms live here and how are they affected by others?
What features enable organisms to survive here?
What affects the numbers of organisms here?
Does pollution affect where organisms live?
2. VARIATION
Are all individuals in a species the same?
What causes variation?
What causes genes to alter?
What are the risks in the environment?
3. EVOLUTION
Do species change over time?
What is natural selection?
How does evolution work?
Is evolution still going on?
4. INHERITANCE
What are chromosomes made of and what is DNA?
What are genes and how do they affect cells?
What effect does cell division have on the genetic composition of cells?
What causes offspring to be male or female?
Are other features inherited in the same way?
How was the mechanism worked out?
Can some conditions be passed on in families?
5. GENE TECHNOLOGY
Why should anyone need genetically identical individuals?
Can genes be transferred between organisms artificially?
Why is this gene transfer carried out?
Are there any ethical issues surrounding this technology?
Is there a planning or control process surrounding the use of this technology?
6. HOMEOSTASIS
Why is the core temperature of the body always around 37 degrees?
How does the body keep the temperature constant? Structure of the skin.
Why should the level of glucose in the blood vary and how is it kept constant?
What happens when the control mechanism fails to work efficiently?
7. NERVOUS SYSTEM
How does the body check on its surroundings?
Why are some reactions very fast?
What is a reflex arc?
8. HEALTH
What is health?
What causes ill health?
How can ill health be treated? Production and trialling of medicines
Are there ethical issues involved with these treatments and how should decisions be
made
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1. ADAPTATION AND COMPETITION
Why and how should organisms be classified? Which organisms live here and how are they affected by others? What features enable organisms to survive here? What affects the numbers of organisms here? Does pollution? Candidates should: (a) know that organisms that have similar features and characteristics can be classified together in a logical way. Understand the need for a scientific system for identification and scientific as opposed to 'common' names. (b) use local first and/or second hand data/ICT simulation: to compare the variety of organisms which live in particular habitats; investigate how the organisms in an area are affected by other organisms. (w(i)a) (c) explore information about the morphological adaptations shown by organisms which enable them to survive in their environment. (d) know that individuals have a basic need for energy and resources from their environment the size of a population of individuals may be affected by competition, for food, space, light; predation, disease, pollution, availability of minerals. (e) examine how indicator species, changes in pH and oxygen levels may be used as signs of pollution in a stream examination of lichens as indicators of air pollution. (w(i)a)
During revision:
Highlight any topic that you have covered in lessons and have fully understood and learnt
Add any extra notes or „aides de memoir‟ below
5 1. Adaptation and competition
Key words
a) There are many visible differences between living things. Scientists use these
differences to „classify‟ or put living things into groups that have features in common.
With the advance in technology, the DNA of living things is also being used to make
classification more precise.
Carolus Linnaeus (1707-78) first introduced an organised system to classify living things
and it forms the basis of today‟s system. In his system living things are put into the
following groups.
o Kingdom
o Phylum (Division)
o Class
o Order
o Family
o Genus
o Species
Make up a mnemonic to help you remember the order, for example:
King Prawns Can Only Fill Giant‟s Stomachs
At species level, only members of the same species can mate to produce fertile offspring.
Every living thing is given two names (Latin) and so the system is called the ‘binomial’
system.
The FIRST NAME (written with a capital at the start) is the organism‟s GENUS The
second name (written with no capital) is the species name.
Canis familiaris = domestic dog, Homo sapiens = human
In text the binomial or scientific name is usually written in italics or is underlined
As we move down the groups,
there are more similarities and
fewer differences between the
members of the group.
• Environment
• Habitat
• Population
• Community
• Adaptation
• Competition
• Living things and physical features
• Place where plants and animals live
• Number of one type of living thing in a habitat
• Number of populations in a habitat
• Special feature that helps living thing survive
• When a number of living things fight for the same resource
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b) ADAPTATION – special features which make an organism particularly well suited to
where they live.
Even in our own back garden we see
adaptations. The blue tit can hold
itself on the edge of the feeder with
long claws and flexible legs. The
blackbird cannot do this but feeds in
an upright position on the table. What
other adaptations do they have?
Notes (a) CLASSIFICATON
Notes (b) ADAPTATIONS
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c) Examples of adaptation
• PHYSICAL (morphological) eg webbed feet of a frog, camouflage
• SEASONAL – overwintering organ eg bulb, migration, hibernation
• BEHAVIOURAL – huddling, nocturnal, crepuscular
DESERT – hot + dry
o Small body – larger surface area
o large ears increases heat loss
o stay in burrow in day – avoid predators, keep cool
o nocturnal – avoids high daytime temperatures
o large eyes – see in the dark
POLAR – cold, little food and water
o large body – smaller surface to lose heat
o thick fur – reduces heat loss
o thick fat layer under skin – reduces heat loss
o small ears – lose less heat
Eg Fennec fox
Eg polar bear
How is a camel adapted to
survive in its environment?
Remember to name or
describe the adaptation
and say HOW it helps the
living thing to survive.
Notes (c) EXAMPLES OF ADAPTATION in animals
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Plants have adaptations to live in hot or dry conditions. Water is mainly lost from the
underside of the leaf by transpiration.
The adaptations include:
o thick waxy layer - to reduce water loss
o formation of spines - leaf surface area reduced
o extensive superficial and deep root system - to maximise water uptake
o fleshy tissue eg in stem of cactus - water storage
o leaves curled in - to protect lower surface and so reduce water loss
CACTUS CONIFER
Notes (c) EXAMPLES OF ADAPTATION in plants
MARRAM GRASS
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d) living things have basic needs to stay alive
Living things may fight or compete for these basic essentials for life.
• Animals compete with one another for: shelter, food, water and a MATE
• Plants compete for light, water and nutrients
The size of a population may be affected by the availability of the essentials above
together with other factors including: predators, disease, pollution.
Eg male Robins will fight for the
Territory in the garden
LIVING THINGS
• COMPETITION WITHIN A SPECIES
• Plants compete for space light, water +
nutrients
• Animals may compete for a mate,
nesting spot, food
• The strongest will survive
• COMPETITION BETWEEN DIFFERENT
SPECIES
• The resources competed for can be the
same as competition within a species
• Often living things occupy slightly
different parts of a habitat or have a
varied diet
Think of some examples
that you know to help
you remember these
Eg different garden birds eat different
food and so can all survive in the garden
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PREY
• Are hunted and eaten by predators
• Most have eyes at the side of their head
• Alert and easily startled
• May crowd and live in groups
• Often have acute hearing and a good sense
of smell
• May have armour, spines or method to deter
predator
• Well camouflaged
• Many are nocturnal
Think of a predator
and a prey that you
know to help you
remember the
features of each
• PREDATORS
• Catch + kill prey
• Eyes point forward
• Good eyesight
• Excellent sense of smell
• Sharp claws, beaks or teeth
• Often camouflaged or good at hunting
by stealth
Notes (d) competition + populations
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e) POLLUTION INDICATORS
Certain living things can tolerate pollution better than others. Which living things are
present can be used to indicate or show how much pollution is present.
Air pollution indicator species are lichens. Lichens are a fungus and an algae living
together. Lichens are sensitive to the amount of sulphur dioxide present in the air.
Generally speaking in high levels of sulphur dioxide, there will be no lichens. The less
pollution, the bigger the lichens.
Water pollution indicator species are sensitive to the amount of oxygen present in the
water. Some examples are shown below.
These animals are found in clean water: Mayfly Nymph (6mm)
Stone fly nymph (14mm)
Salmon trout (40cm)
These animals are found in slightly polluted water:
Freshwater shrimp(4mm)
Caddis fly larvae (10mm)
Snail (20mm)
These animals are found in very dirty water:
Water louse (12mm)
Blood worm (16mm)
Rat-tailed maggot (10mm)
High air pollution Low air pollution
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Notes: (e) POLLUTION INDICATORS
13 2. VARIATION
Are all individuals in a species the same? What causes variation? What causes genes to alter? What are the risks in the environment? Candidates should: (a) examine the variation in height/length in individuals of the same species by collecting and analysing data and know that variation may be due to environmental or genetic causes. (w(i)a) (b) know that sexual reproduction leads to offspring that are genetically different from the parents unlike asexual reproduction where genetically identical offspring called clones are produced from a single parent. Sexual reproduction therefore gives rise to increased variation. (c) understand that new genes result from changes, mutations, in existing genes and that mutations occur naturally at random. Mutations may be beneficial or harmful and are increased by exposure to radiation and some toxic chemicals. (d) variation is the basis of evolution.
a) Variation is slight differences between living things. It is important to help a
species survive. This is because it will be more likely that at least a few of the species
will survive if conditions become difficult.
There are 2 types of variation:
CONTINUOUS – this is when the data has a continuous sequence of values eg, height,
weight
DISCONTINUOUS – this is when the data has discrete values eg right or left handed,
pierced ears, blood groups – the values are one or the other
We are all humans but we are all different!
We get all our characteristics or features in one of three ways
• INHERITED from our parents
• ENVIRONMENTAL or picked up from the environment
• A MIXTURE of inheritance and the environment
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c) MUTATIONS
Mutations are changes in the structure of the DNA molecule. This can result in a change
in a gene, the arrangements of the genes on a chromosome, or the number of
chromosomes in a cell. They can be passed on to daughter cells through cell division.
Mutations can be caused by:
- Ionising radiation (UV, X-rays , cosmic rays)
- Radioactive substances (in Earth‟s crust)
- Certain chemicals
b) REPRODUCTION
There are two forms of reproduction:
• ASEXUAL REPRODUCTION – there is no fusion or joining of cells and only ONE
parent is needed. All the offspring are identical or CLONES
• SEXUAL REPRODUCTION – involves the fusion or joining of special sex cells
called GAMETES. The offspring are a mixture of genetic information from 2
parents and so are all different or show VARIATION
INHERITED
Shape of nose, eye colour,
blood group, gender
MIXTURE
Height, weight, health,
ENVIRONMENTAL
Language spoken, scars,
piercings, tattoos
Think of things you have
inherited from your
parents, have picked up in
life or a mixture of each
Hair colour from mum
Make up a table of differences between sexual and asexual
reproduction
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Effects:
- Mostly harmful
- Causes death or abnormality in reproductive cells
- Causes cancer in body cells
- Some CAN be neutral or even beneficial (e.g. the peppered moth)
The differences in an individual caused by a mutation leads to VARIATION. This can be
the raw material in natural selection
Notes: MUTATIONS
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3. EVOLUTION
Do species change over time? What is natural selection? How does evolution work? Is evolution still going on? Candidates should: (a) examine evidence and interpret data about how organisms and species have changed over time. Suggest reasons why species may become extinct. (w(i)a,b) (b) consider how individuals with characteristics adapted to their environment are more likely to survive and breed successfully. Consider the uses and limitations of modelling to illustrate the effect of camouflage colouring in prey and predator relationships. (c) know that the genes which have enabled these better adapted individuals to survive are then passed on to the next generation. This is natural selection. (w(i)c) (d) consider the process of data collection, creative interpretation and deduction that lead Charles Darwin to propose the theory of evolution. Discuss the controversy surrounding the acceptance of the theory. Discuss evidence that evolution is ongoing such as data on Warfarin resistance in rats.
a) Charles Darwin (1809-1882)
Darwin travelled to the Galapogos Islands in the HMS
Beagle and observed the plants and animals there. His key
observations:
1) All living things produce more offspring than survive to
adulthood
2) In spite of this, population sizes remain roughly constant
3) Variation exists among species
4) Characteristics can be passed on from one generation to the next.
b) Living things that have features that are best suited to their habitat are more
likely to survive. This is clearly seen in species that are camouflaged. The
peppered moth is a well known example. The moth has two forms, one dark the
other light. The dark dominate in areas where the background is darkened due to
pollution, and the lighter version in the less polluted lighter backgrounds.
Dark moth stands
out on the lighter
background and is
more likely to be
eaten
Lighter moth stands
out on the darker
background and is
more likely to be
eaten
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c) This idea can be modelled in a laboratory. This method has limitations and care
must be taken because in the natural situation the following factors play a part.
The size of the population is a significant factor. It must be large enough for the
results to be valid
Living things of reproductive age may not successfully produce offspring
Immigration or emigration may take place
Random mutations may occur
Colour may not only effect predation rates. For example a darker shell may absorb
more heat from the sun and so affect the chance of survivial.
C ) Natural Selection.
This was first suggested by Darwin but now has a more detailed scientific basis.
It can explain selection of simple features that have appeared by mutation, for example
colour, but cannot explain how complex features, for example, an eye, has appeared. For
this to have appeared, many mutations would have to occur all at once to form the eye
that works
Modern day examples of natural selection in action include antibiotic resistance and
warfarin resistance in rats
(NB. The idea of evolution as described by Darwin, the controversy around it and
alternative ideas are on the Higher paper)
The four main stages in natural selection are outlined below:
a) Variation – some strains of bacteria are resistant and some aren‟t.
b) Competition – The non-resistant bacteria are killed by the penicillin
c) Survival of the fittest – the resistant bacteria survive.
d) Passing on of genes – the resistant bacteria reproduce and pass on
their adaptations to their offspring.
The main evidence for this is from fossil records.
• There is no record of the origins of life on Earth, it is a puzzle that can never be
completely solved.
• Scientists must try to keep an open mind and make judgements based on fact and
not belief. Scientists must not try to make facts fit their ideas !!
• One source of information is fossils. These are the remains of plants and animals
that were around in the past !
Resistant bacteria Non resistant bacteria
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• The fossil record is not complete and can only provide a small piece of evidence.
Some of the aging techniques are also unreliable.
• The theory of evolution tells us that all species of living things alive today have
evolved from the first simple life forms that existed on the earth.
• There are a number of different ideas about how life has become what we see
today. None can be proven scientifically.
• The 4 main ideas are: Darwin, Lamarck , Intelligent Design and Creation
EXTINCTION is the permanent loss of all the members of a species from the face of
the Earth. Causes of extinction:
Change in climate
• Meteorites
• New predator
• New disease
• Competition
One fossil record – the horse
Modern horse
Equus 1.6m
Pliohippus 5 million
years ago
1.0m
Merychippus 25 million
years ago
1.0m
Mesohipus 37 million
yers ago
0.6m
Hyracotherium 55 million
years ago
0.4m
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4. INHERITANCE
What are chromosomes made of and what is DNA? What are genes and how do they affect cells? What effect does cell division have on the genetic composition of cells? What causes offspring to be male or female? Are other features inherited in the same way? How was the mechanism worked out? Can some conditions be passed on in families? Candidates should: (a) know that chromosomes are strands of DNA. DNA contains coded information that determines how cells function due to the types of proteins coded for. DNA can be extracted from cells, such as Kiwi fruit. (b) know that DNA can be analysed by 'genetic fingerprinting' which can be used to show the similarity between two DNA samples, for instance in criminal and paternity cases. (w(iv)a) (c) assess the issues surrounding 'gene ownership' as a result of DNA analysis and consider whether the ethical issues involved are a matter for society and beyond the scope of science to solve. (w(i)d;(iv)a,b) (d) understand the significance of mitosis and meiosis. (e) know that genes are sections of DNA molecules that determine inherited characteristics and are in pairs. Genes have different forms, called alleles. (f) know that in human body cells, one of the pairs of chromosomes carries the genes which determine sex, XX or XY. These separate and combine randomly at fertilisation. (g) consider the scientific process of experimentation, observation and deduction that led Gregor Mendel to propose the mechanism of inheritance. Discuss why the significance of the work was not recognised and validated by scientists for many years. (w(i)a,b;(iv)c) (h) be able to complete Punnet squares and explain the outcomes of monohybrid crosses. (i) understand that some mutations cause conditions which may be passed on in families, as shown by the mechanism of inheritance of cystic fibrosis, and be able to interpret family trees
Notes: evolution
Note the main points for
each idea. Note the
strengths and weakness of
each idea.
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The DNA molecule looks like a spiral staircase
Pairs of „bases‟ form the steps
of the staircase
DNA is made up of ‘nucleotides‟
a) + e)
A gene can have different forms
these are called ALLELES
The gene for eye colour has alleles for brown, blue, green etc.
Our chromosomes hold all the information we inherit. Different living things have
different numbers of chromosomes
We have 46 chromosomes made up of 23 pairs. .One of each pair has come from our
mother and the other from our father
Kiwi fruit, like other living things, contains DNA. It can be used to extract DNA which
can than be studied. Other living material can also be used!
Proteins are made up of amino acids.
The order of the amino acids determine which protein it is.
3 bases „code‟ for one amino acid. So the order of the bases
determines the order of the amino acids
This is called „protein synthesis‟.
cell membrane
cytoplasm
Nucleus with chromosomes A chromosome
A section of a chromosome = a gene
The bases always match
up in the same pairs: A
with T and C with G
The sequence of the
bases will determine
the protein that is
made.
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T C A A A C T G G T C A
RIBOSOME
b) Our DNA is unique to us!! It can make us stand out in a crowd. This can be good for
some of us but bad for the „baddies‟!! Genetic fingerprinting can be used to identify a
criminal or a dead body. Only a small amount of blood, saliva, hair or semen is needed.
Our DNA is very similar to our parents.
Genetic fingerprinting can be used to determine who is the father, or mother, of a child.
d) In a recent murder hunt, the police obtained blood samples from more than 5,000
people for genetic fingerprinting. The Home Office is considering creating a data
base which will contain everyone‟s genetic prints.
Do you think that this would be a good idea?
• Give reasons for your answer.
d) When we grow or have to repair damage done to our body, new cells have to be made.
These cells must be the same as the ones they are replacing. However, when our sex cells
(gametes) are made, the number of chromosomes has to be halved. Each gamete is
slightly different to all the others that are made by the same person.
= amino acid
Make up a list of uses for DNA or „genetic
fingerprinting‟. For each give a reason why it
is right and why it might be wrong to use it
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There are two ways that cells can divide: mitosis and meiosis. Each type of cell division is
outlined below:
f) In humans there are 23 pairs of chromosomes. One of these pairs are called the sex
chromosomes because they carry the genes that will determine if we are male or female.
This pair will separate by meiosis during the formation of the gametes (sex cells) and
then combine randomly at fertilisation. The sex chromosomes are named „X‟ and „Y‟.
A female is „XX‟ and a male is „XY‟.
All our body cells have 23 pairs, or a total of 46 chromosomes
Our sex cells (gametes), the egg (ovum) and sperm have only 1 set of chromosomes – 23 in total
mum dad
fertilisation
46 chromosomes
The number of chromosomes is halved to make the gametes
Mitosis:
• Used for growth and repair of cells
• Used in asexual reproduction
• Cells with identical number of
chromosomes and genetic information
are produced
Meiosis:
• Used to produce gametes for
sexual reproduction
• Each daughter cell has half the
number of chromosomes of the
parent
• One copy of each chromosome is
in each daughter cell. They are
all GENETICALLY different.
This brings in VARIATION
between individuals
Makes ‘ME’
‘MY TOES IS’ made this
way!
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This can also be shown in a Punnett square
gametes X Y
X XX XY
X XX XY
The Punnett square was first used in 1905 by R C Punnett who used it to predict genetic
crosses. The male alleles go across the top, and the female down the side.
Key words:
chromosome Strands of DNA
DNA DeoxyriboNucleic Acid
gene Section of DNA (chromosome) that determine inherited
characteristics
allele Alternative form of a gene eg blue or brown alleles of
the gene for eye colour
gamete Sex cell – egg(ovum) or sperm
zygote Formed when an egg is fertilised by a sperm
Male is XY Female is XX
MOTHER = XX FATHER = XY
meiosis meiosis
fertilisation
female female male male 50% chance of a boy
50% chance of a girl
gametes
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dominant If present, this allele will be expressed
recessive The characteristic of this allele will only be seen if no
dominant gene is present
homozygous The two alleles present are the same
heterozygous The two alleles present are different
phenotype Physical appearance of an individual
genotype Genetic make up of an individual
Gregor Mendel is the father of modern genetics because of the
work he did on pea plants in 1865.
He chose pea plants because they had characteristics that were
easy to see and they were easy to grow.
Two plants were taken, one which is pure-bred for tallness and one
pure-bred for shortness, and Mendel crossed them:
All the plants produced were tall.
Two of these plants were crossed and 3 out of every 4 plants were tall.
Learn these well.
They will help you to understand the
questions and so be able to answer it.
Cross 1
Cross 2
X
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I‟‟m 1 in 2,000
This led Mendel to hypothesise that “for every characteristic there must be two
determiners”. He labelled one „dominant‟ and the other as „recessive‟.
The significance of Mendel‟s work was not recognised until the early 1900‟s because no
one had seen a chromosome.
Mendel‟s unit of inheritance was named a „gene‟ in 1910.
Punnett squares can be used to show Mendel‟s experimental crosses with peas.
Cross 1: Pure bred (homozygous) tall plant x pure bred (homozygous) short plant
Let T = tall (dominant), t = short (recessive)
Parents: TT x tt
gametes T T
t Tt Tt
t Tt Tt
Cross 2: Now if two of the F1 plants are crossed: Parents: Tt x Tt
gametes T t
T T T T t
t Tt tt
The ratio is 3 tall : 1 short
If the genotype of an individual is not known, a test cross is done. In this the unknown
individual is crossed with a known homozygous recessive.
i) Family trees or „pedigrees‟ have been used to trace characteristics through family
trees for hundreds of years
Cystic fibrosis is a genetic disorder. It cannot be caught like other illnesses, it can only
be inherited.
Cystic fibrosis causes the airways to produce a thick
sticky mucus that prevents the respiratory system
working properly. A sufferer has to have physiotherapy
to remove this mucus. It also effects how the pancreas works.
The person has to take certain digestive enzymes as tablets before
eating.
Cystic fibrosis is caused by a faulty recessive allele.
This means that both parents must be carriers (heterozygous) for
the condition if a child is to be born with cystic fibrosis. This is shown in
the Punnett square below.
All the offspring (F1) are
heterozygous tall
The offspring (F1) are:
1 homozygous tall
2 heterozygous tall
1 homozygous short
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Always give the letter of the
dominant allele as the capital and
then the recessive allele as the
lower case of the SAME letter
Let the normal allele = N and the allele for cystic fibrosis = n
Both parents must be carriers (heterozygous):
Nn x Nn
There is a 25% or 1 in 4 chance of a child having cystic fibrosis
A family tree is often used to show how a genetic condition is passed on to successive
generations
gametes N n
N NN Nn
n Nn nn
The offspring (F1) are:
1 homozygous normal
2 heterozygous normal
1 homozygous cystic fibrosis
Children have CF even
though parents do not.
The gene for CF must
therefore be recessive and
the parents are carriers
Notes: Inheritance
There‟s quite a lot to learn in this section.
Learn the jargon and this will help you
understand what is being asked. Work through
a number of examples using a Punnett square
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5. GENE TECHNOLOGY
Why should anyone need genetically identical individuals? Can genes be transferred between organisms artificially? Why is this done? Are there any ethical issues surrounding this technology? Is there a planning or control process surrounding the use of this technology? Candidates should: (a) know the commercial applications of clones of plants and animals. (w(iv)a) (b) know that genes can be transferred artificially from one organism to another, and understand that the introduction of genes from resistant plants into Soya bean plants, so increasing their resistance to herbicides, may increase the crop yield. (w(iv)a) (c) critically assess the issues surrounding this GM crop technology and how decisions are made, including the need to plan scientifically valid, suitable trials to assess the possible effects in order to inform the debate: for the scientific community, government policy departments, wider public opinion. (w(i)a;(iv)b,c)
a) When we grow or replace damaged and worn out cells, our cells can divide to produce
new, identical cells. This is called cell division (mitosis).
Some living things can reproduce a whole organism without making sex cells. These are
mainly plants. We can use this when we grow plants from cuttings. All the resulting
plants are identical to the parents and are called CLONES. This can be done on a
commercial scale.
Micro propagation or tissue culture.
This is a technique used in plants.
A stem from a desirable plant is cut into many pieces, each
piece has a bud. Each piece is sterilised to remove pathogens.
It is then put into a pot with growth medium and rooting
hormones. A plantlet grows which can then be potted up,
grown and sold. This method is fast and needs little space.
The plants are all genetically identical, disease free and can be
grown all the year round.
Cloning in animals is much more controversial.
Embryo transplants/cloning. Eggs are taken from the
best cows and fertilised with sperm from the best bull
in a petri dish. This is called in vitro fertilisation. The
fertilised egg divides to make a ball of cells. These
cells can be separated and each one is grown into a new
embryo. Each embryo will grow into an individual that
will be genetically identical - they will be clones. The
embryos are put into less desirable 'host' or
'surrogate' cows, which will free up the best cows for
further egg production.
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Sheep A
Sheep B
Adult udder
cell
Mature
ovum
Nucleus
removed
Empty ovum
Nucleus removed
Mild
electric
shock
Nucleus +
ovum fuse
Embryo implanted
in sheep C
Lamb is a clone of Sheep A
ADULT CELL
CLONING
You must be able to describe how
animals are cloned and which type
of reproduction is involved
Notes: Cloning
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b) Genes can be taken from one organism and transferred to another. This is called
‘genetic engineering’. It can be used to produce certain proteins that can then be
collected and used by humans. One example of this is the production of insulin (the
function of insulin is in section 6 homeostasis)
This technology can also be used to put in a herbicide resistant gene into crops such as
soya. This may increase the yield and so produce more food for humans and other
animals. These are called „genetically modified‟ or „GM‟ crops.
Gene for insulin
is „cut‟ out using
an enzyme
Bacterial DNA, in the
form of a circular
„plasmid‟ is removed.
Chromosome with insulin gene
Plasmid cut open using an enzyme
Insulin gene put into bacterial
plasmid using an enzyme The bacterial plasmid is put back into the
bacteria. The bacteria is then put in a
large container with plenty of food and
oxygen and multiplies rapidly.
The bacteria produce the insulin along with their own proteins. This can
then be collected, purified and used by diabetics.
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b) The growth and use of GM crops is very controversial. Any trials must be
done scientifically with suitable controlled trials. This evidence could then
be used to inform the debate between scientists, government and the public.
For GM crops Against GM crops
Could be an answer to global
hunger. Crops with resistance to
drought and frost could increase
the areas of food production
Resistance to herbicides in GM
crops could pass out into the „wild‟
population and form „super weeds‟
which would be difficult to control
Introduced genes are not harmful
because they are digested as
other food materials into harmless
sub units.
The effect of „foreign‟ genes
outside the initial population has
not been fully researched nor is it
fully understood
Less use of artificial chemicals in
farming and less fertilizers if
genes to increase nitrate uptake
are introduced
GM crops will probably lead to
„super‟ farms and so destroy many
habitats and reduce biodiversity.
Many ethical issues arise from this new technology.
Who owns the new or „recombinant‟ DNA?
Should imperfect genes be replaced in an embryo or an embryo discarded if an
undesirable gene is found?
Be prepared to put forward
arguments for and against
such questions.
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6. HOMEOSTASIS
Why is the temperature of the body always around 37 degrees? How does the body keep it constant? Why should the level of glucose in the blood vary and so needs to be kept constant? What happens when the control mechanism fails to work efficiently? Candidates should: (a) understand that animals need to regulate the conditions inside their bodies to keep them relatively constant and protected from harmful effects. (b) recognise and label a simplified given diagram of a vertical section through the skin and understand its role in temperature regulation (c) use data to draw conclusions about the relationship between glucose and insulin levels in the blood and understand that glucose levels need to be kept within a constant range. (w(i)a) (d) know that diabetes is a condition in which a person's blood glucose may rise to a fatally high level because the body does not produce enough insulin. It can be diagnosed by the presence of glucose in the urine. (e) plan and carry out testing of artificial urine samples for glucose.
a) Homeostasis is the regulation of the conditions inside our body. Hundreds of chemical
reactions take place in our body and in our cells. For these to work correctly certain
conditions such as temperature, water content, pH and glucose levels must be kept within
a certain range. If this changes then our chemical reactions do not take place as they
should and so our body doesn‟t function as it should. This can result in illness and even
death if not corrected.
b) Our body temperature must stay at 37oC.
Our internal body temperature is detected by the thermoregulatory centre in the brain.
Our skin is the main organ that regulates our body temperature.
Normal 37o C
Too high and the chemical
reactions will go too fast and
the enzymes that control them
may be denatured or destroyed.
Too low will result in the
chemical reactions going too
slow to keep our body
working properly and alive
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Too hot Too cold
Sweat glands release sweat onto the
surface of the skin. This cools the
body down by heat loss during
evaporation of the sweat
Sweat glands do not release sweat
Blood capillaries dilate and blood flow
near the surface increases. Heat is
lost by radiation from the skin.
Blood capillaries constrict so blood flow
near surface is reduced. Heat loss is
also reduced
Hairs lay flat against the skin Hairs pulled upright by erector
muscles. This traps a layer of air and
so reduced heat loss.
No shivering Involuntary contractions of the
muscles (shivering) generates heat
energy.
c) The glucose level in the blood is detected by the pancreas.
Blood glucose levels will
increase when food is eaten.
How quickly this happens
depends on the type of food
eaten.
Glucose is used in energy
production by respiration and
so its levels will fall during
exercise.
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Too much glucose in circulation can lead to health problems including blindness and poor
circulation. The pancreas releases 2 hormones (chemical messengers) to control the level
of glucose – insulin and glucagon.
Glucose cannot be stored but can be changed into glycogen which can be stored. The flow
chart above shows how this takes place.
d) Excess glucose will pass out in the urine and this, together with excessive thirst and
the increase need to go to pass urine are sign of a diabetic. Diabetes has a number of
causes: Juvenile diabetes (type 1)– either insulin is not produced or is not detected.
Diagnosed early in life. This is also known as type 1 diabetes and is controlled by
insulin injections. It is thought to be an auto immune condition.
• Maturity onset diabetes (type 2)– confined to overweight, older people. Too little
insulin produced to meet demands of the body. This is also known as type 2
diabetes and can usually be controlled by diet.
• Stress diabetes – may occur during pregnancy or when under other physical or
mental stress. This is usually temporary and can be controlled by diet.
GLUCOSE
GLYCOGEN
glucagon insulin
When the glucose is „‟igh‟ (i)
Insulin is released
When the ’gluc has gone’
(low glucose levels)
„gluc-a-gon’ is released!!
Notes: Homeostasis
34 7. NERVOUS SYSTEM
How does the body check on its surroundings? Why are some reactions very fast? What is a reflex arc? Candidates should: (a) know that sense organs are groups of receptor cells, which respond to specific stimuli: light, sound, touch, temperature, chemicals, and then relay this information as electrical signals, called nerve impulses, to the brain. (b) know that some responses in animals are reflex actions. These reactions are fast, automatic and some are protective, as exemplified by the withdrawal reflex. (c) know that a reflex arc involves stimulus � receptor � coordinator � effector. Recognise and label a given diagram of a reflex arc to show: receptor, sensory nerve cell, connecting nerve cell in spinal cord, motor nerve cell, effector, synapses. (d) plan and carry out practical work on sensitivity and reaction times.
a) The nervous system enables us to react to our surroundings and coordinate our
behaviour.
There are 4 types of nerve cells:
RECEPTOR – an impulse starts in response to a stimulus
SENSORY NEURONE – carries the impulse from the receptor into the central nervous
system (CNS)
RELAY NEURONE – carries the impulse in the CNS (the brain + spinal cord)
MOTOR NEURONE – carries the impulse from the CNS to the effector
The EFFECTOR then causes a response.
The nervous system uses electrical
impulses that travel along our nerve
cells (neurones).
The neurones are found inside our
nerves, a bit like spaghetti in a packet.
Nerve cells can only carry an impulse in
one direction.
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The sequence along the different neurones is shown below:
STIMULUS RECEPTOR SENSORY RELAY MOTOR EFFECTOR RESPONSE
CELL NEURONE NEURONE NEURONE MUSCLE
orGLAND
1) Receptors in the eye
detect the stimulus of
the moving ball
2) The impulse is
carried by SENSORY
NEURONES (in the
optic nerve) to the brain
3) The brain decides to
move away the hand
4) This impulse is sent by
MOTOR NEURONES to the arm
muscles (the effectors) via the
spinal cord…
6) Which then moves the
hand towards the moving ball
to catch it
This is a
VOLUNTARY
REACTION
EARS
sensitive
to sound
EARS sensitive to
sound +
changes in position
SKIN sensitive to
touch, pressure,
pain + temperature EYES sensitive
to light
NOSE + TONGUE
sensitive to
chemicals
The RECEPTOR CELLS
are found in sense organs
Make up a neumonic
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The nerve cells are not joined up directly to the
next one. There are gaps called SYNAPSES. The
electrical impulse cannot jump the gap. A chemical is
released that crosses the gap to the next neurone
b) Automatic actions, that you do without thinking are called REFLEX ACTIONS. These
are faster than a voluntary reaction.
Reflexes are important because they help you avoid danger and control actions in your
body like breathing.
c) The reflex arc is the name given to the sequence that takes place in a reflex action.
The sequence is shown in the diagram below:
Stimulus Receptor (i.e. the thing that detects the stimulus)
Effector (i.e. the thing that will do the reaction)
Response (i.e. action taken)
Bright light Eye (iris) Iris (muscle) Muscles contract
so pupil gets
smaller
Sour taste tongue Muscles in mouth Spit it out
Losing balance ears Muscles in legs Put foot out to
keep balance
Sit on a
drawing pin
Skin on bottom Muscles in legs Stand up quickly
Notes: Nervous System
37 8. HEALTH What is health? What causes ill health? How can ill health be treated? Are there ethical issues involved with these treatments and how should decisions be made? Candidates should: (a) know that health is affected by a variety of factors and that science and technology may provide the answer to some health problems. (b) know that some conditions can be prevented and that some can be treated by drugs or by other therapies. (c) know that gene therapy has been tried but there are difficulties in targetting the appropriate cells. It has been used to alleviate symptoms in Cystic Fibrosis sufferers but is not a cure for the underlying genetic condition and there may be side effects. (w(iv)a) (d) discuss the implications of genetic counselling and the ethical problems posed by an individual's prior knowledge of a genetic trait. (w(iv)a,b) (e) discuss: • the ethical issues surrounding, and • how decisions are made about the use of animals for testing drugs (w(iv)a,b) (f) investigate experimentally the comparative energy content from burning food and understand that energy from food, which is in excess, is stored as fat by the body. (g) explore and discuss available data, e.g. from ICT searches and food labelling, about the energy and additives in highly processed and less processed foods and the implications, particularly for health. (w(i)a;(iv)a) (h) know that some conditions are due to lifestyle choices and use information/data to explore the effects that alcohol, nicotine and drug abuse have on the chemical processes in peoples' bodies. Discuss how the attitudes to smoking have changed over time as scientific evidence about its effects has accumulated. (w(iv)a,c)
a) Good health is not just the absence of illness or disease.
GOOD HEALTH
Physical fitness
contentment
Absence of illness
Positive living +
enjoyment mental fitness
Happiness
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POOR HEALTH
Lack of exercise
discontentment
Illness
Poor living conditions
Smoking
Stress + worry
Excess alcohol Genetic disorder
Poor diet
Poor health can be due to our life style, environment of genetic make up
b) We cannot control all the factors that cause poor health. We can help reduce the
effect of ill health with:
1. Gene therapy and genetic screening
2. Drugs (medicines – legal drugs)
3. Life style choices.
c) Gene therapy is a new area of technology where a faulty or missing gene is replaced
by a healthy one.
The sequence of all our genes and their position on the chromosomes are known. This
is as a result of an international project known as the „Human Genome‟ project.
A persons chromosomes can be screened. This can be done in an adult or in an embryo.
Genetic disorders can be detected.
There are 3 main ways to add new healthy genes:
1. Use viruses to carry genes into cells
2. Healthy genes are put into an aerosol which is inhaled. It is hoped the healthy gene
will replace the defective gene. This is used in treating cystic fibrosis.
3. Genes are treated so that they can target certain cells. They are then injected
into the bloodstream and activate the target cells. This could be used in the
treatment of skin cancer.
This is a new area of treatment and there may be side effects as well as the benefits
of alleviating the symptoms. However the underlying genetic cause of certain
conditions eg cystic fibrosis will still be present.
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d) Knowing the position of genes on our chromosomes can now allow us to find
information about ourselves that we couldn‟t until recent times. For example we can
be screened for „markers‟ for certain conditions such as certain cancers, heart disease
and diabetes. This would then give us the opportunity to change our lifestyle or to
seek medical tests to prevent the disease affecting us.
However, many people are concerned about finding out this information for a number
of reasons.
1. If we knew that we were going to get cancer it would completely dominate
our lives and those around us.
2. Life and even travel insurance companies would want to be given this
information and this could affect how much we pay for these.
3. This information may even affect our chances of a job!
This is a new technology and great care needs to be taken as its use expands.
e) Drugs. Conventional drugs take many years to produce. Research to find a drug has to
take place. Then the new drug has to go through a number of stages before it can be
used on humans. One of these stages involves using animals to test the drugs on. This is
an area of concern for many who disagree with the use of animals in this way. Great care
has to be taken to treat the animals used humanely and minimise suffering.
The drug testing has to be completed on a large enough sample. It also has to be checked
by scientists who will not gain financially from its production.
There have sadly been examples of where a drug tested for one use has been used for
another purpose. An example of theis is the drug „thallidomide‟. It was given to pregnant
woment o combat morning sickness and hadn‟t been tested for this use. The result was
severe limb deformities in many children whose mothers had take n the drug.
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Building larger
molecules from
smaller ones For muscles
to contract
Keeping our body
warm when cold
Active transport
of materials into
and out of cells
e) Life style choices.
Different foods contain different amounts of energy. The energy value is clearly put
onto food packets so we know how much energy it contains.
In a school laboratory the following apparatus can be used to find out how much
energy is in different foods.
The food sample needs to be dry so it burns well and the water content won‟t affect the
results. The tin can will reduce the amount of heat energy that is lost to the air around.
The same amount of water must be used and the starting temperature must be the same.
The amount of energy stored in the food can be calculated per gram of food. Energy is
measured in Joules or kilo Joules.
We need to have food to supply our body with energy. The energy in our food is
eventually released by respiration and is used in our body in the following ways:
We need a certain amount of energy to carry out our life processes and so stay alive. The
amount of energy we need will depend on our age, gender, weight and also our day to day
activities.
41
• TOO MUCH
• Overweight - fat
• Arthritis
• Diabetes
• High blood pressure
• Heart disease
• TOO LITTLE
• Underweight – thin
• Muscles waste away
• Immune system doesn‟t work very well
• Periods become irregular and may stop
If our energy input, through eating, is greater than the energy we use, during our day to
day activities, the excess energy will be stored in our body as fat. This will lead to a
person becoming overweight and obese.
• A balanced human diet contains:
• CARBOHYDRATES – needed to provide energy
• PROTEIN – needed for growth, repair and replacing cells
• FAT – needed for storage of energy and cell membranes
• VITAMINS AND MINERALS – needed in small amounts for the correct functioning
of our body
• FIBRE – adds bulk to our food and gives bowels something to push against – avoids
constipation
•
Our diet should be balanced, not containing too much or too little of any of the main food
groups.
Problem Linked with
Heart disease Too much fat in diet
Diabetes (type 2) Too much sugar
Tooth decay Too much sugar
High blood pressure Too much salt
Bowel cancer Too little fibre
Obesity Too much fat and carbohydrate
INPUT OUTPUT
GETTING THE BALANCE RIGHT
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g) Additives and preservative are put into processed food. These can affect our
health and some food colours have been linked to a change in the behaviour of young
children and teeagers. Processed food loses a lot of its nutritional value, particulary
vitamins as these can be destroyed by heating.
h) Our lifestyle choices can affect our health. Lack of exercise has an effect on the
health of our heart and circulatory system. Other factors such as smoking, alcohol and
drug abuse also affect our short term and long term health.
SMOKING:
Attitudes to smoking has changed since it was first introduced.
It has gone from being a sign of wealth, to one of sophistication to one now of disgust.
This has been mainly due to scientific research that has revealed what a burning
cigarette releases into a person and what harm those chemicals can cause. Smoking
related illnesses cost the NHS millions every year. However, the Government makes
millions from the sale of cigarettes through taxes.
The main harmful chemicals are:
Nicotine – addictive and increases blood pressure
Tar – contais over 4000 different chemicals, about 60 of which are known to be cancer
causing (carcinogens). Tar also stops the lung cleaning system of cilia from working.
Carbon monoxide – reduces the ability of red blood cells from carrying oxygen.
As well as the effects in the diagram, smoking also causes: emphysema, bronchitiis,
problems in pregnancy – reduced birth weight, arterial and heart disease, lung and other
cancers
Feeling of sickness, vomiting,
happiness or depression
Increased respiration
Increased blood
pressure
Increased
stomach
secretions
Reduced blood flow
to extremities
Increased cholesterol
levels
Increased adrenaline
release
Trembling in
heavy smokers
Increased gut movement
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ALCOHOL
Alcohol contains the chemical ethanol.
Alcohol is a depressant and it causes reactions to slow down.
Alcohol can lead to a lack of self control and if taken to an excess can lead to
unconsciousness, coma and even death.
Alcohol is a toxin to our body and is broken down by the liver.
Excess alcohol can lead to permanent liver damage.
Alcohol can become addictive and can cause brain damage.
OTHER DRUGS
NOTES: Drugs