Hyndland Secondary
CfE Biology Unit 3b: Life on Earth
Content:
Mutation
Page 2
Adaptation
Page 3
Variation
Page 4
Natural Selection
Page 4
Speciation
Page 5
Human Impact
Page 6-7
Indicator Species
Page 8
Biological control & GM
Page 9
1
Mutations

A mutation is a completely random change to the genetic information of a species.
This can be a change to a single base in the genetic sequence, section or whole
chromosomes containing many genes.

Mutations may be neutral, confer an advantage or a disadvantage.
•
•
•

Where a neutral mutation occurs this may be passed on but would not give
the organism any selective advantage.
An organism that has a mutation that causes a disadvantage rarely survives
to reproductive age and does not pass on the mutated gene.
An organism that has an advantageous mutation has a selective advantage
over other organisms and has a better chance of surviving and reaching
reproductive age, passing on the beneficial mutated gene.
Mutations are the only source of new alleles in a population. Without mutation, all
organisms would be the same for all genes and no variation would exist.
•
The only way a species can adapt and evolve is by random mutations that
give that organism a better chance of survival than any other. (selective
advantage)
Mutagenic agents

Mutations happen at random, are spontaneous and occur at a low rate, however
certain environmental factors can increase this rate of occurrence.
•
•
Radiation eg. U.V light and X-rays
Chemicals eg. Mustard gas
2
Adaptation
An adaptation is an inherited characteristic that makes an organism well suited to survive in its
environment.
Some adaptations involve the structure of the organism’s body (physiological); others depend on
the way the organisms behaves in response to environmental stimuli (behavioural).
Eg.
The lion has examples of both physiological and behavioural adaptations.
•
•

Their coat colour gives them excellent camouflage in the long dry grasses of
the savannah.
Lions have adapted an excellent hunting strategy where they work as a team
and ambush their pray.
Both of these adaptations help the lion to catch its prey and therefore increase its
chance of survival.
Cacti grow and thrive in very hot dry conditions.
•
•

Their leaves have been reduced to spines and stems have thick cuticles,
helping to reduce water loss.
They have vast root systems that either spread across the surface to absorb
moisture from the cool night air or deep root systems that penetrate far into
the soil to reach deep water sources.
These adaptations allow the plant to survive long periods of drought.
3
Variation
•
•
Variation within a population makes it possible for that population to evolve over
time in response to changing environmental conditions.
The greater the variation within a species the greater the chance of some of the
species surviving should selective pressures change
• eg.
• Climate change,
• predator pressures,
• disease resistance.
Natural Selection
•
Natural selection or survival of the fittest occurs when more offspring are produced
than the environment can sustain, leading to a struggle for surtvival. Many offspring
die before reaching reproductive age as a result of factors such as:



•
Competition (food/space)
Inability to escape or hide from predators
Lack of disease resistance
Only the best adapted/suited individuals survive to reproduce, passing on the genes
that confer the selective advantage. Members of the same species are not identical
to one another but show phenotypic variation in many characteristics. Much of this
variation is inherited and key to the process of natural selection.
4
Speciation
A species is a group of similar organisms that can interbreed to produce fertile offspring.
They have;
•
•
•
•
The same chromosome complement
Share the same gene pool
Have similar anatomy & physiology
Speciation occurs after a population becomes isolated. Isolating mechanisms
include:
• geographical (mountain ranges, oceans, habitat clearing)
• ecological (climate change, increase temperature, pH change)
• reproductive (timing of breeding season, physiology)
•
Isolating mechanisms create a barrier to gene exchange and separate the gene pool.
•
•
Random mutations occur within each sub species
Natural selection favours those individuals more suited to occupy a particular
niche (exploit a particular food source or habitat)new alleles are passed on.
The genotype of each sub species changes over a period of time until they are no
longer genetically similar or share the same chromosome complement as the other
sub-species. They evolve into different species
Eg. Darwins Finches
I GER M Naturally
5
Human impact on the environment
Increasing human population requires an increased food yield.
Food shortage is becoming a serious issue for the ever growing human population.
Farmers increase food yield by:
Clearing land for agricultural purpose;
Huge areas of woodland and rainforest have been cut down (deforestation) and wetland or
marshlands drained to increase areas for crop production or grazing. This can cause loss of
habitat, food sources and isolation between groups of organisms.
Using fertilisers;
Adding or replacing nitrates that have been lost from the nitrogen cycle when the plants are
harvested and removed from the area. Fertilisers can leach into nearby freshwater sources
causing algal blooms. Other aquatic plants living under the surface of the water cannot
source sufficient light and die. Bacteria feed on the decaying matter and increase in number.
Bacteria use oxygen during aerobic respiration, reducing the concentration of dissolved
oxygen in the water. Most organisms cannot survive in the low oxygen concentrations and
die out, increasing decomposition.
6
Using pesticides; (insecticide and fungicide),
These chemicals kill species that are eating or affecting the growth of crops. They are often
indiscriminate and kill all insects. Neonicotinoids are often blamed for the decreasing honey
bee population. Pesticides can accumulate in the bodies of organisms over time. As they
are passed along the food chain they increase in toxicity and can reach fatal levels.
Eg. DDT was widely used as an insecticide up until the 1980s in the UK when it was
confirmed to be toxic to many aquatic animals and fish. It cannot be broken down
once ingested and increases in concentration as it is passed up the food chain,
accumulating in bird of prey species and was a major contributor to the decline of
birds of prey due to thinning egg shells.
7
Indicator species
Some species can only thrive well under certain environmental conditions such as very clean air,
highly polluted water etc. These species are known as indicator species as, by their presence or
absence in a particular area, indicate environmental quality or levels of pollution.
Examples of freshwater indicators;
Indicators of air pollution
8
Alternative Farming Methods
Biological control and GM crops may be alternatives to mitigate the effects of intensive
farming on the environment.
Biological Control
Biological control is the reduction of a pest population by the deliberate introduction of one
of its natural enemies such as a predator or parasite. The use of ladybirds to clear greenfly
from plants is an example of biological control. The predator acts as the control agent and
specifically targets the pest. No environmental pollution occurs and no chemicals persist or
accumulate in food chains. Careful considerations should be made to ensure the introduced
species does not carry disease or have a negative impact on the ecosystem in any other
way.
Genetically Modified Crops
Genetically modified or genetically engineered refers to organisms whose genetic
information has been altered, usually by the addition of a useful gene from another
organism. Some species of maize has been developed that produces a built in toxin. These
GM crops are able to resist pests and disease and do not need to be sprayed with pesticide.
Other species may produce greater crop yields or additional nutrients such as ‘Golden rice’
that was developed to combat vitamin A deficiency in developing countries.
9