Transcript Genetics and Adaptation

Genetics and Adaptation
Higher Biology
Unit 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
5
4
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.
Chromatid
Centromere
Chiasma
(crossing over
point)
Exchanged pieces
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.
X X
X X
XX
XX
XX
XX
X X
XX
XX
Site of division
Pairing and movement of
chromosomes
MITOSIS
MEIOSIS
Occurs all over the body
In the sex organs
Chromosomes replicate
Homologous
then pair up singly on the chromosomes form pairs:
equator
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 2 identical daughter cells
produced
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 =
R
Wrinkled =
r
Yellow =
Y
Green =
y
Cross the true-breeding round yellow with
the true breeding wrinkled green:
To find the F2:
Resulting phenotypes:
Round and yellow = 9
Round and green = 3
Wrinkled and yellow = 3
Wrinkled 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
TT YY
TY
X
ty
Short Green
tt yy
ty
TY
TtYy
All offspring will be TALL and YELLOW
If two F1 plants are crossed:
TtYy
TY ty
x
TY
TtYy
TY ty
ty
TY
ty
3 Tall Yellow : 1 Short Green
Only 2 types of
gamete
possible
In reality, in the above cross, if 400
seeds grew from the F2 the ratio might
be:
292
Tall Yellow
:
7
Tall Green
:
6
:
Short Yellow
Recombinants
95
Short Green
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
B
C
A
B
C
a
b
c
a
b
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:
Recombinatio
n Frequency
number of F2 recombinants
COV =
x 100
total number of F2 offspring
In the example of the peas, the 400 F2
offspring:
292
Tall Yellow
:
7
Tall Green
:
6
:
Short Yellow
95
Short Green
Recombinants
13
Recombination =
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
DxE
AxE
AxD
ExB
BxA
Recombination
Frequency
8
6
2
12
6
The positions of the genes on the
chromosome are therefore as follows:
B
D
E
A
2
6
6
12
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
XX
X
X
Man
XY
X
X
Y
X
X
Y
Ratio of 1 boy : 1 girl
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
Xr
XR
F1 = red-eyed female 1
red-eyed male 1
Y
White-eyed female X Red-eyed male
XrXr
XRY
Xr
XR
Y
XR
Xr
F1 = red-eyed female 1
white-eyed male 1
Y
Haemophilia
Haemophilia is a disorder involving
defective blood clotting.
It is caused by a recessive gene on the
“X” chromosome and is therefore sexlinked.
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 husk
t
= no husk
At the locus (position) of this gene on the
chromosome are 3 separate genes
formed by a duplication mutation.
So:
T T
T T
T T
and
t t
t t
t t
will have complete husks
will have no husks
But intermediates such as:
TT
T t Will have
t t
or
T t partly
TT
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 population
2. Barrier divides population
3. Accidental mutations occur in both
halves of the population
4. Natural selection retains favourable
mutations
5. Each half of the population evolves
differently
6. Two species have evolved
Barriers may be:
Ecological
Geographical
Reproductive
(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 evolution
Evolution 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 betteradapted 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
Tiger – Eastern medicines
Black Rhino – dagger handles
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.
Californian Condor
Przewalski’s Horses - Mongolia
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 breeding
Desirable 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 genes
2.Transferring the genes
1. Locating the gene
• Four methods exist:
1. Chromosome mapping using cross over
values of linked genes.
2.Chromosome banding patterns
Irradiation 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
A
T
G
C
C
T
A
C
G
T
T
G
T
A
C
G
G
A
T
G
C
A
A
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.
Human DNA
Endonuclease site
Cut with
endonuclease
Cut with
endonuclease
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 Fusion
This 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
Transpiration
Rate
Wind speed
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
Transpiration
Rate
Humidity
• Explanation: High concentration of
water molecules in air outside leads to a
small concentration gradient. Therefore
diffusion is slow.
3. Temperature
Transpiration
Rate
Temperature
Explanation: Water evaporates from liquid
to vapour more quickly.
4. Light
Transpiration
Rate
Light
Explanation: Stomata are closed in
darkness and open gradually as light
levels rise.
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
C
B
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 pressure
The 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) Capillarity
Water rises up the inside of a thin xylem
tube because of adhesion between
water molecules and the wall of the
tube.
(c) Transpiration pull
D
C
B
A
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
Humid air builds up outside the
stomata
Rolled or hairy leaves
Stomata sunken in pits
Deep roots
Find water deep underground
Widespread surface
roots
Succulent tissues
Gather maximum rain after a
shower
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 airfilled 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.
4.
3.
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. Trout
Problem: 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. Cod
Problem: 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)Bees
When 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
Lion
Anteater
Prey
Search
Pursuit
Time Economics
Zebra
Short
time
Long
time
Must spend time
selecting an old or
weak individual
None
Cannot afford
time to be
selective – all ants
eaten
Ant
Long
time
(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 items
Small 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:
food
water
space
shelter
mates
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.
35
30
25
Rate of Process
20
15
10
5
0
Midnight
1
6
Shade
Midday
Sun
11
Respiration
Midnight
16
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 in
the day.
Coping with dangers
Plants
1. Ability to tolerate grazing by
herbivores
Plants can tolerate grazing if:
• Low growing points
• Leaves flat to the ground
• The ability to regenerate missing parts
25
20
present
Average number of plant species
Effect of grazing on species
diversity
15
10
5
0
0
Least
intense
1
2
3
Grazing Pressure by Rabbits
4
5
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 defences
Avoidance 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
DEFENCE
Physical
Claws and
teeth
ACTIVE DEFENCE - Chemical
ACTIVE
DEFENCE
Behaviour
Feigning death
Intimidation
PASSIVE
DEFENCE
Protective covering
of spines
PASSIVE
DEFENCE
Protective
covering
Shells
PASSIVE DEFENCE
Camouflage
Shape
Colour and
PASSIVE DEFENCE – Warning colouration
PASSIVE
DEFENCE
Mimicry
Pretending to
be ‘nastier’ than
you are
Animal defence mechanisms groups
Pupil note from Torrance Pg 215 – 216 on
Musk Ox, Quail & Baboon.