Genetics and Adaptation Higher Biology Unit 2. Variation Genes and Inheritance Shortly before a cell...

Genetics and Adaptation

Higher BiologyUnit 2

Variation

• Genes and Inheritance

Shortly before a cell divides, the appearance of its nucleus changes. Long threads become visible in the nucleus, these are the chromosomes.

The number of chromosomes, and their size and shape varies between species.

Organism Number of Chromosomes

Human 46

Kangaroo 12

Domestic Chicken 36

Daisy 4

Hermit Crab 254

Dog 78

When viewed under the electron microscope, each chromosome is seen to consist of many dark bands.

These are the genes, each of which is responsible for controlling one characteristic in an organism.

Cell Division

There are two types:1. Mitosis (normal cell division in

growing organisms)2. Meiosis (takes place in gamete

mother cells in the sex organs to produce gametes).

Mitosis

This is simple cell division forming new cells (daughter cells) containing the same number of chromosomes as the mother cell.

In mitosis the number of chromosomes stays the same (46 in humans). This is called the diploid number.

1 3

45

Meiosis

The genetic difference in gametes is the result of cell division in the sex cells called meiosis.

During meiosis each diploid gamete mother cell undergoes two divisions to produce four haploid gametes.

The diploid number (2n) is the full chromosome number (complement) in normal cells.

The haploid number (n) is half the diploid number. Only gametes have this number.

• In a diploid cell, chromosomes can be sorted into pairs which look the same, and contain genes for the same characteristics.

• These pairs are called homologous pairs.

• Haploid gametes contain one member of each homologous pair.

How meiosis increases variation

1. Crossing over

This takes place on the spindle during the first division of meiosis.

Small pieces are exchanged between the chromosomes of a homologous pair.

Exchanged pieces

Chromatid

Centromere

Chiasma(crossing over

point)

2. Independent Assortment

When homologous pairs of chromosomes line up at the equator of the spindle (during the first division of meiosis) the position of one pair is random in relation to any other pair.

XXX

XX X

XX X

XX

X

XX X

X XX

MITOSIS MEIOSIS

Site of division Occurs all over the body

In the sex organs

Pairing and movement of chromosomes

Chromosomes replicate then pair up singly on the equator

Homologous chromosomes form pairs: Chromosomes line up in pairs on the

equator

Exchange of genetic material

Chiasmata not formed. No crossing over.

Chiasmata formed, and crossing over occurs.

Number of divisions One division Two divisions

Number and type of cells produced

2 identical daughter cells

4 haploid gametes

Effect on chromosome number

Stays the same Halved

Effect on variety Does not increase variation

Increases variation

Genetics

Genetics is the study of patterns of inheritance from one generation to the next.

Monohybrid cross

Revision from Standard Grade/Int 2.

Dihybrid Cross

This is a cross involving the inheritance of two characteristics.

In pea plants the seeds (peas) can be either round or wrinkled, and either yellow or green.

Round and Yellow are the dominant alleles.

Round = RWrinkled = rYellow = YGreen = y

Cross the true-breeding round yellow with the true breeding wrinkled green:

To find the F2:

Resulting phenotypes:

Round and yellow = 9Round and green = 3Wrinkled and yellow = 3Wrinkled and green = 1

Linked genes

If two genes are on the same chromosome they are said to be linked.

Linked genes are transmitted together.

• e.g. In peas, the gene for plant height and seed colour are on the same chromosome (i.e. they are linked)

T = tall, t = short, Y = yellow, y = green

Tall Yellow X Short Green TT YY tt yy

TY ty

All offspring will be TALL and YELLOW

TYty TtYy

If two F1 plants are crossed:

TtYyx TtYy TY ty TY ty

3 Tall Yellow : 1 Short Green

TY ty

TY

ty

Only 2 types of gamete possible

In reality, in the above cross, if 400 seeds grew from the F2 the ratio might be:

292 : 7 : 6 : 95Tall Yellow Tall Green Short Yellow Short

Green

Recombinants

The “Tall green” and “Short yellow” plants are possible because of crossing over during meiosis.

This can “unlink” linked genes. The new forms are called recombinants.

Frequency of recombination

Chiasmata can occur at any point along the length of homologous chromosomes.

Genes that are further apart are more likely to be separated by crossing over than close genes. Recombinants gametes are therefore more likely to be formed.

A

A

a

a

B

B

b

b

C

C

c

c

Low frequency of

recombination

Higher frequency of

recombination

The distance between a pair of linked genes is therefore indicated by the percentage number of F2 recombinants produced during a cross involving these genes.

This percentage is called the recombination frequency and is calculated as follows:

number of F2 recombinants

COV = x 100

total number of F2 offspring

Recombination Frequency

In the example of the peas, the 400 F2 offspring:

292: 7 : 6 : 95

Tall Yellow Tall Green Short Yellow Short Green

Recombinants

13Recombination = x 100 = 3.25 %Frequency 400

Chromosome maps

Chromosome maps are used to show the position of genes on a chromosomes relative to one another.

A large recombination frequency means that genes are far apart; a small frequency means that they are close together.

For example: Crosses involving 4 linked genes (ABDE) gave the following Recombination frequencies:

Genes Recombination Frequency

D x E 8

A x E 6

A x D 2

E x B 12

B x A 6

B D EA

26

612

The positions of the genes on the chromosome are therefore as follows:

Sex Determination

Diploid human body cells have 46 chromosomes.

These are made up of 22 normal homologous pairs (called autosomes) and one pair of sex chromosomes.

The sex chromosomes in woman are two similar “X” chromosomes.

In men there is one “X” chromosome and a smaller “Y” chromosome.

XX XY

The “X” chromosomes carry many genes (unrelated to sex). The “Y” carries no genes.

In a man, the genes on the “X” chromosome have no allele on the “Y”.

These are called sex-linked genes and will always express themselves.

Inheritance of sex

Woman Man XX XYX X X Y

Ratio of 1 boy : 1 girl

X X

X

Y

Sex linkage

A monohydrid cross involving a sex-linked gene does not give a typical 3:1 ratio in the F2 generation.

This is because the “Y” chromosome does not carry the sex-linked gene and therefore cannot provide dominance.

e.g. The gene for eye colour in Drosophilia flies is sex linked:Red-eyed female X White-eyed male

XRXR XrY XR Xr Y

F1 = red-eyed female 1

red-eyed male 1

Xr Y

XR

White-eyed female X Red-eyed maleXrXr XRY

Xr XR Y

F1 = red-eyed female 1

white-eyed male 1

XR Y

Xr

Haemophilia

Haemophilia is a disorder involving defective blood clotting.

It is caused by a recessive gene on the “X” chromosome and is therefore sex-linked.

Queen Victoria was a carried of the gene (XHXh) and passed it onto many of her descendants in other European royal families

Mutations

Mutations

Occurrence of mutations

Mutagenic Agents

Chromosome mutations:

Change in chromosome number:

Polyploidy

Changes in chromosome structure

Gene mutations

Deletion:

“Please stay where you are”

“Please say where you are”

Cystic fibrosis is caused by a deletion of three nucleotides.

Inversion

“Guerrillas sending arms to aid rioters”

“Guerrillas sending rams to aid rioters”

Insertion

“

Substitution

“Flossie now arriving by air from new york”

“Flossie not arriving by air from new york”

Karyotype

A karyotype is a display of a complement of chromosomes showing their number, form and size.

Non-disjunction of chromosome pair 21 leads to an extra copy of chromosome 21 in the embryo. This causes Down’s Syndrome.

An example of duplication: podcorn and popcorn.

Relevant pair of alleles:T (dominant) = with huskt = no husk

At the locus (position) of this gene on the chromosome are 3 separate genes formed by a duplication mutation.

So:T TT T will have complete husksT T

andt tt t will have no huskst t

But intermediates such as:T T T t Will havet t or T t partlyT T T t formed

husks

Duplication therefore increased variation in this feature.

So how did we get from life forming to modern humans?

Genesis: Creation

Evolution

• Evolution

Evolution is a theory which states that the organisms alive today have arisen by a process of gradual change (over millions of years) from simple ancestors.

Charles Darwin

(1802 – 1882)

Published the “The Origin of the Species”

Introduced the idea of “Natural Selection”

The mechanism of evolution

The best explanation for evolution is provided by Darwin’s theory of Natural selection.

Natural Selection

1. Overproduction of offspring means that they cannot all survive, so there is:

2. Competition between the offspring

3. Variation exists between the offspring because of:

• Meiosis (independent assortment and crossing over)

• Mutation• Fertilisation of gametes (a random

process)

4. Best suited offspring will survive longer and breed more

5. Favourable alleles will therefore be passed on, and increase in the population.

Species and speciation

A species is a group of organisms which have similar appearance and can interbreed to produce fertile offspring.

They share the same range of genes, which are called the gene pool.

Speciation

Speciation is the formation of new species by natural selection.

Speciation takes place when an existing species is split into two (or more) groups by a barrier which prevents interbreeding and exchange of genes.

1. Single population2. Barrier divides population3. Accidental mutations occur in both

halves of the population4. Natural selection retains favourable

mutations5. Each half of the population evolves

differently6. Two species have evolved

Barriers may be:EcologicalGeographicalReproductive

(a) Ecological barriers

These might be caused by rainfall, temperature, soil pH etc.

e.g. The effect of temperature on a population of alpine plants

(b) Geographical barriers

These include sea, rivers, deserts, mountains.

e.g. The effect of a mountain range on a population of tiger beetles.

(c) Reproductive barriers

These might include:• Changes in courtship patterns• Changes in breeding seasons

which can result in one part of a population being unable to breed with one another.

Adaptive radiation

Adaptive radiation has taken place when several different species have evolved from one common ancestor.

This might happen when a feature of an organism evolves to fill a number of different niches.

An organism’s niche is the precise way in which it fits into its environment.

Adaptive radiation is shown well by the beak shapes of Darwin’s Finches on the Galapagos Islands.

This process is well shown by “Darwin’s finches” on the Galapagos Islands.

Darwin’s Finches

Make your own notes of adaptative radiation from Torrance

High speed evolutionEvolution normally takes place very

slowly, but occasionally can be seen taking place much more rapidly. This is high speed evolution.

Two examples are:• Melanic Peppered moths• Antibiotic resistant bacteria

• Make your own notes of this topic from Torrance

2. Resistance to antibiotics

Extinction of species

As evolution proceeds new and better-adapted species evolve.

Natural selection results in the disappearance (extinction) of their ancestors.

The natural (slow) rate of species extinction has recently been greatly accelerated by man’s activities.

Main threats:1. Over-hunting

Black Rhino – dagger handles

Tiger – Eastern medicines

Blue whales – food and research

2. Habitat destruction

Orang-utan – Forest clearance Giant Panda – forest clearance

Conservation of species

Genetic diversity (variety) is essential for natural selection.

It is also important for selective breeding of organisms under man’s control.

Man uses a variety of methods to ensure this genetic diversity is maintained:

• Wildlife reserves• Captive breeding• Cell banks

1. Wildlife reserves are natural areas where habitat is managed and protected for the benefit of rare species

RSPB Reserve at Culbin Sands.

Ngorongoro Crater, Tanzania

2. Captive breeding involves taking animals from the wild and breeding them in secure conditions until they can be re-introduced to their natural habitat.

Przewalski’s Horses - Mongolia

Californian Condor

3. Cell and seed banks contain collections of living gametes or seeds which can be preserved in controlled temperature and humidity.

Artificial Selection

Artificial selection is the deliberate selection by humans of organisms with characteristics useful to mankind.

(a)Selective breedingDesirable features (perhaps not

successful in the wild) are selected by man, and organisms showing these features are bred together.

(i) Wild Cabbage

Common ancestor – Wild Sea Cabbage

(ii) Dogs

(b) Inbreeding and hybridisation

Inbreeding: Breeding is allowed between two individuals possessing a desirable feature.

Advantages: Next generation retains desired feature.

Disadvantages: Increased chance of offspring which are homozygous recessive for a harmful allele.

Hybridisation: Breeding between two genetically different varieties of the same species.

Superior offspring may be produced by combining the good features of two parents. This is hybrid vigour.

Heterozygous offspring will have harmful recessive alleles masked by the dominant allele.

(c) Genetic engineering

This is the creation, by man, of new combinations of genes from more than one species.

It involves the transfer of genes from the genome (haploid gene set) of one organism (e.g. Human) to the genome of another organism (e.g. Bacterium).

Two stages are involved:1.Locating the genes2.Transferring the genes

1. Locating the gene• Four methods exist:1.Chromosome mapping using cross

over values of linked genes.2.Chromosome banding patternsIrradiation of chromosomes (resulting in

gene deletion mutations) can be followed by genetic crosses to identify unusual offspring characteristics.

3. Gene probes

• Take the protein (e.g. Hormone or enzyme) and identify the amino acid sequence. The base sequence of the genetic code can then be worked out.

• Make single stranded DNA with the identified bases. This is the gene probe, It is labelled radioactively.

alanine

leucine

proline

serine

ATGCCTA CGTT G

TACGGAT GCAA C

Gene probe

• Select the relevant chromosome from the nucleus and break it into fragments.

• Mix probe and fragments. The probe attaches to the fragment carrying the required gene.

(4) Genome sequencing (Human Genome Project)

The entire human genome has been sequenced – which means the order of the bases are known. Computer programmes can then be used to identify the position of genes based on their similarity to known genes in other organisms.

2. Transferring the gene

Once located, the gene is cut from the chromosome using the enzyme endonuclease,

The gene is then inserted into a bacterial plasmid (small circular chromosome) using the enzyme ligase.

Endonuclease site

Cut with endonuclease

Cut with endonuclease

Human DNA

An application of this technology

The gene for the human insulin protein can be inserted into the bacterium E. coli (Escherichia coli).

The bacteria containing the plasmid are then grown in large numbers and made to express (produce) the insulin protein which can then be purified.

(d) Somatic FusionThis technique is used to produce new,

improved crop species.Two different species cannot

interbreed successfully. At best a cross between them will produce a sterile hybrid.

However new techniques are enabling scientists to overcome this problem of sexual incompatibility.

1. Suitable cells from two plant species are selected.

2. The cells walls are digested away using cellulase. Forming a protoplast.

3. Somatic fusion induced by electric current. Forming a somatic cell hydrid.

4. Cell wall formation is induced.5. Cell division occurs producing a

mass of un-differentiated cells.6. Cells treated with hormones to

produced a hybrid plant.

Animal and Plant Adaptations

Higher Biology

This section covers:

• Water balance in plants• Water balance in animals• How animals obtain food• Living in social groups

Water balance in plants

• Revision from S-Grade:

??? ??? sop.hyll ??? ??? mesophyll ,

Transpiration

Transpiration is the loss of water by evaporation from the leaves of a plant.

The transpiration stream is the flow of water up through the plant from the roots to the leaves.

Evidence for transpiration

A ____________ plant was put in a bag with a humidity sensor.

The experiment proved that transpiration happens as the humidity in the bag with the plant was greater than the humidity of the room.

The rate of transpiration

Over a period of _____ hours the plant has lost ________ of water which represents a rate of loss of ______ ml/hour.

Comparing transpiration rates

Transpiration can be measured using a potometer.

The plant was then subjected to normal conditions, windy conditions and more humid conditions.

The windy conditions were generated using a fan.

The humid conditions were created by a bag.

Factors affecting the rate of transpiration

1. Wind

Wind speed

Transpiration

Rate

Explanation: Wind blows water vapour as it leaves the leaf. Therefore a steep concentration gradient exists between the inside and outside of the leaf. Leading to rapid diffusion.

2. Humidity

Humidity

Transpiration

Rate

• Explanation: High concentration of water molecules in air outside leads to a small concentration gradient. Therefore diffusion is slow.

3. Temperature

Explanation: Water evaporates from liquid to vapour more quickly.

Temperature

Transpiration

Rate

4. Light

Explanation: Stomata are closed in darkness and open gradually as light levels rise.

Light

Transpiration

Rate

In summary, transpiration is increased by:

• Increase in wind speed• Decrease in humidity• Increase in temperature• Increase in light intensity.

Stomata

Stomata (stoma = singular) are found in the lower epidermis of the leaf.

Purpose: Allow entry of carbon dioxide for photosynthesis.

Problem: Water vapour escapes from the leaf through the pore.

Mechanisms to reduce water loss:1. Stomata are on underside of leaf

(cool and shaded)2. Stomata close in darkness (no need

for carbon dioxide)

How stomata open

The opening of stomata depends on the turgor of the guard cells.

If they are turgid (much water in them) then the pore opens.

If they are flaccid (water has moved out) then the pore closes.

The transpiration stream

This is the flow of water through a plant from the root to the leaves.

It replaces the losses due to transpiration.

Other benefits are:1.Minerals (nutrient ions) are

transported in solution in the water.2.Evaporation of water cools the

plants’ leaves.

1. How water enters the root

Water enters root hair cells on the root epidermis.

Root hairs provide a large surface area for water uptake.

A

B

C

Water enters the root and crosses the cortex to the xylem in two ways:

1. Soaking along the cell walls of the cortex cells.

2. By osmosis. Soil water has a higher water concentration than the cytoplasm of the root hair cell (Cell A). Water therefore enters the cell by osmosis. Cell A now has a higher water concentration than Cell B, so water moves from A in to B, and so on till it reaches the xylem.

2. How water moves up the xylem

(a) Root pressureThe force with which water crosses the

root and enters the xylem by osmosis is enough to push water a short distance up the xylem vessels.

(b) CapillarityWater rises up the inside of a thin

xylem tube because of adhesion between water molecules and the wall of the tube.

(c) Transpiration pull

A

BC

D

As water evaporates from the leaves it creates a tension (pulling force).

Cohesion forces between water molecules mean that they will attract each other and so the tension pulls the water column up the xylem vessel.

Adaptations to environmental conditions

Mesophytes: are normal plants which grow where water is easily available and excessive transpiration is not a problem (e.g. Dandelion, buttercup).

Specialised plants

1. Xerophytes are plants which are adapted for life in habitats where the transpiration rate is high and/or water is hard to get

e.g. Hot, dry deserts – cacti Exposed, windy hills - heather

Adaptation Explanation

Fewer stomata Reduces water loss

Thick leaf cuticle Prevents evaporation through the cuticle

Rolled or hairy leaves Humid air builds up outside the stomataStomata sunken in

pits

Deep roots Find water deep underground

Widespread surface roots

Gather maximum rain after a shower

Succulent tissues Store water

Short life cycle Survive dry conditions as a seed

Reversed stomatal rhythm

Open at night when it’s cool, close during the hot day

2. Hydrophytes are plants which live partly or totally submerged in water (e.g. Pondweed, water lily).

They show the following adaptations:

Air spaces• Possesses an extensive system of

air-filled cavities. Instead of escaping into the surrounding water, much of the oxygen is stored in these spaces and used for respiration when required.

• The presence of such aerated tissue also gives a submerged plant buoyancy keeping its leaves near the surface for light.

Reduction of xylem• Any xylem present is normally found

at the centre of the stem. This allows the stem maximum flexibility in response to water movements while at the same time enabling it to resist pulling strains.

Specialised leaves• A hydrophyte’s submerged leaves

are narrow in shape or finely divided. This helps them avoid being torn by water currents.

Water balance in animals

Osmoregulation is the process by which animals keep the water concentration of their body fluids constant.

1.

2.

3.

4.

In groups discuss the structure of the kidney. (1) Identify the numbered structures. (2) Be able to describe exactly what happens in each of the numbered structures. (3) What is filtered out of the blood? (4) What is reabsorbed? One person from the class will be expected to stand at the board and describe the function of the kidney – so be sure every in the group knows what they are talking about.

1. Osmoregulation in freshwater fish

e.g. TroutProblem: The tissues of the fish are

hypertonic (lower water concentration) to the river water.

Water therefore enters by osmosis through the gills and intestines.

Solution:(a)Many large glomeruli in kidney(b) High filtration rate of blood(c) Large volume of dilute urine(d) Chloride secretory cells in the gills

absorb salts from water by active transport.

2. Osmoregulation in saltwater fish

e.g. CodProblem: Sea water is hypertonic to

the tissues of the fish, so the fish loses water by osmosis.

Solution:(a) Sea water is drunk.(b) Chloride secretory cells excrete

salt.(c) Few, small glomeruli in kidney(d) Low filtration rate.(e) small volume of concentrated

urine.

3. Adaptations of migratory fish

e.g. Salmon or eels

Make your own notes from p172 Q3 (a) and (b)

4. Water conservation by desert rats

Problem: Since there is little rainfall in the desert and high daytime temperatures (with low night time temperatures) desert mammals, such as the kangaroo rat, have only a limited supply of water available to them.

To survive they have to be able to practise rigorous water conservation.

Obtaining water: In its natural habitat, the kangaroo rat does not drink water at all. It is able to obtain all its water from its food (“dry” seeds) and remain in water balance as the following diagram shows:

Ways of conserving water

Physiological adaptations:• Mouth and nasal passages tend to be

dry, thereby reducing water loss during expiration.

• Bloodstream contains a high level of anti-diuretic hormone.

• Kidney tubules possess very long loops of Henle (kidney tubules). These adaptations promote water reabsorption so effectively that it can produce urine 17 times more concentrated than its blood.

• It does not sweat.• Its large intestine is extremely

efficient at reabsorbing water from waste material and producing faeces with a very low water content.

Behavioural adaptations:• Remains in its underground burrow

during the extreme heat of the day.• Inside the burrow the air is cooler

and more humid. Thus the air being inhaled by the rat is almost as damp as the air being exhaled and minimum water loss occurs.

• It has no need to produce sweat as it is active at night.

Obtaining food

Most animals are mobile and actively search for and/or pursue food.

A few animals (e.g. Barnacles) are sessile (fixed in one place) and depend on filtering food from water.

Forms of nutrition

1. Auxotrophic nutrition is used only by green plants. They employ photosynthesis to make complex organic substances from simple inorganic molecules.

2. Heterotrophic nutrition is used by animals and fungi. They depend on plants for ready-made organic materials.

Foraging for food

• When animals go foraging for food, they show distinct behaviour patterns organised to gain maximum energy.

Foraging behaviour in colonial insects

(a)BeesWhen a worker bee locates a good

source of food it returns to the hive and “dances”. This gives information on the location of the food to other workers.

Bee clip

(b) Ants

Use pg 190 of text-book to make notes.

Make a copy of the diagram on pg 190.

Economics of foraging behaviour

Net loss of energy will result if the energy obtained from an animals food is less than the energy spent foraging for it.

Animals must consume food items which give them the best return for time and energy spent.

Three factors affect this:

(a) Time

Predator Prey Search Pursuit Time Economics

Lion Zebra Short time

Long time

Must spend time selecting an old

or weak individual

Ant-eater

AntLong time

None

Cannot afford time to be

selective – all ants eaten

(b) Quality of the food

Worst quality food is found very quickly but the energy reward is poor.

Best quality food takes a long time to find but the energy reward is high.

Intermediate quality food doesn’t take too long to find and has a reasonably good energy reward – this is the optimum energy value approach in a poor ecosystem.

(c) Size of prey itemsSmall prey items require little energy

to find and kill, but contain little energy reward.

Large prey items require a lot of energy to find and kill, and contain a large energy reward.

Medium sized prey items don’t require too much energy to find and kill, and contain a reasonably good energy reward – this is the optimum energy value approach.

Competition

If resources are scarce, animals may compete for:foodwaterspacesheltermates

Types of competition

Interspecific competition takes place between members of different species.

For example, English Crayfish are being exterminated from English rivers by introduced American Crayfish.

Intraspecific competition takes place between members of the same species.

This is more intense because the animals have identical requirements and are also competing for mates.

For example, Red deer stags compete fiercely for females during the autumn rut.

Competition often leads to adaptations which ensure the survival of the fittest individuals.

Living in social groups

(a)Dominance heirarchy (e.g. peck order among hens)

In a dominance hierarchy animals organise themselves in an order from strongest to weakest. This order is maintained largely by threat.

Benefits are:• Survival of the fittest individuals are

ensured.• Experienced leadership is

guaranteed.• Little fighting takes place, so injury is

avoided and energy is saved.

Individuals often display behaviours to indicate dominance or submission.

2) Co-operative hunting

Some predatory mammals, such as killer whales, lions, wolves and wild dogs, rely on co-operation between members of the social group to hunt their prey.

• Ambush strategy• Employed by lions involves some

predators driving prey towards others that are hidden in cover and ready to pounce.

• Running down• Dogs and wolves take turns at

running down a solitary prey animal to the point of exhaustion and then attack it.

Advantages of co-operative hunting

• More effective hunting strategies can be employed

• A group can kill larger prey than a lone individual

• Weaker individuals will get some food

Food sharing will only occur if the reward for sharing exceeds the reward for foraging individually.

Territorial behaviour

A defended territory provides food for an animal, it’s mate and it’s offspring.

Factors affecting territory size:• Large enough to supply requirements• Small enough to defend effectively• Larger when food is in short supply

than when food is plentiful.

The energy gained from the food in the territory must exceed the energy needed to defend it.

Obtaining Food - Plants

Unlike animals, which are mainly mobile, plants are sessile, which means they cannot move around.

Plants must therefore obtain their food, water and minerals from the soil and air around them.

Competition between plants

Plants compete for:• Water• Light• Soil minerals

Plants of same species often grow together, so competition is intraspecific and therefore intense.

Compensation Point

This is the level of light intensity at which the rates of photosynthesis and respiration are equal.

The plant is making and using carbohydrate at the same rate.

0

5

10

15

20

25

30

35

1 6 11 16

Shade Sun Respiration

Midnight Midday Midnight

Rat

e of

Pro

cess

Sun and shade plants

Sun plants (e.g. Dandelion) live only in bright habitats. They achieve the compensation point slowly but go on to photosynthesise very rapidly later in the day.

Shade plants (e.g. Primrose, Wood Anemone) live in shady places. They achieve compensation point very rapidly but never receive enough light for a fast rate of

photosynthesis later inthe day.

Coping with dangers

Plants1. Ability to tolerate grazing by

herbivoresPlants can tolerate grazing if:• Low growing points

• Leaves flat to the ground

• The ability to regenerate missing parts

Effect of grazing on species diversity

0

5

10

15

20

25

0 1 2 3 4 5

Grazing Pressure by Rabbits

Ave

rage

num

ber

of

plan

t sp

ecie

s

pres

ent

Least intense

Most intense

No grazing: Vigorous grasses thrive and shade out most wild flowers which cannot survive the competition.

Heavy grazing: Grasses and “wild flowers” are eaten. Only plants which grow from the base (grass, daisy) can survive.

Moderate grazing: Vigorous grasses are kept in check and a good variety of wild flowers can grow.

Plant defences

(1)Chemical defences:(a)Stings (e.g. nettles). Each sting hair

takes the form of a thin capillary tube ending in a spherical tip.

When an animal touches a hair, its tip breaks off leaving a sharp edge. This penetrates the skin allowing the liquid irritant to be injected into the animal.

(b) Cyanogenesis (e.g. Clover)

Hydrogen cyanide is produced in clover leaves in response to being nibbled by slugs. It is formed by an enzyme acting on a non-toxic chemical called glycoside.

(2) Physical defences(a)Thorns – a thorn is a sharp side

branch.(b)Spines – a spine is a sharp pointed

leaf.

Animal defencesAvoidance behaviour: is an instinctive

response by an animal to avoid danger e.g.

• Running away• With drawing into a shell• Hiding in a burrow

Habituation

Habituation is a short term change in behaviour when an animal stops responding to a stimulus which is proving harmless.

This:• Allows the animal to keep feeding• Conserves energy• Is specific to one stimulus

Habituation is temporary. After a short time the original avoidance behaviour will return.

Fan worms are stimulated by shadows as they are the prey of fish, but if it is sea weed floating on the surface the worm will retreat back into its tube, but if it continues and proves harmless it will stop retreating for a short time.

Learning to avoid danger

Learning involves a long term modification of an animals behaviour. In order to learn something you need to be able to remember.

1. Learning to avoid poisonous food

Pupil notes from Torrance Pg 211-212 on Toad and Bee example.

2. IMPRINTING

Newly hatched ducklings and goslings quickly learn to follow the first large object they see if it moves and makes sounds – normally this would be their mother.

This can only happen during a brief period of early life and is called imprinting.

It is a behavioural adaptation of survival value because it provides a mean by which they can avoid danger.

Ducklings can become wrongly imprinted on humans if they are the first things they see.

Animal defence mechanisms - individuals

ACTIVE DEFENCEPhysical

Claws and teeth

ACTIVE DEFENCE - Chemical

ACTIVE DEFENCEBehaviour

Feigning death

Intimidation

PASSIVE DEFENCE

Protective coveringof spines

PASSIVE DEFENCEProtective covering

Shells

PASSIVE DEFENCECamouflage

Colour and Shape

PASSIVE DEFENCE – Warning colouration

PASSIVE DEFENCEMimicry

Pretending tobe ‘nastier’ than

you are

Animal defence mechanisms - groups

Pupil note from Torrance Pg 215 – 216 on Musk Ox, Quail & Baboon.