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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.