Unit 3 Life on Earth Mr Gravellx

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Transcript Unit 3 Life on Earth Mr Gravellx

National 5 Biology Course Notes
Unit 3 : Life on Earth
Part 1 :
Biodiversity and distribution
of life
Biodiversity is the number of different types of organisms in an area – the more different species there are, the
greater the biodiversity.
What affects biodiversity?
Biodiversity is affected by:
• Biotic factors
• Abiotic factors
• Human influences
Biotic factors
Biotic factors are related to living organisms. Biotic factors can affect the number of other living organisms in an
area and where they are found.
Examples of biotic factors are:
• Predators
• Grazing
• Disease
• Availability of food
• Competition between organisms
Abiotic factors
Abiotic factors are non-living features of an area that can affect the number of different species (biodiversity) and
where the organisms are found (distribution).
Examples of abiotic factors are:
• Temperature – e.g. many animals and plants could not survive in a desert
• Light – e.g. plants cannot grow in the absence of light
• pH – e.g. many plants cannot grow in acidic soil, fish are killed when acid rain lowers the pH of the water
Human influences
Examples of human influences that reduce biodiversity are:
Habitat destruction – e.g. felling tropical rainforests
Over-grazing of farm animals leading to soil erosion
Human activities that help to maintain biodiversity are:
• Setting up conservation areas
• Captive breeding programmes for endangered species
Biomes are regions of the earth that have their own characteristic plants (flora) and animals (fauna) and
their own climate.
Examples of biomes are:
• Desert
• Grassland
• Tropical rainforest
• Polar
• Marine (sea)
• Aquatic (freshwater)
Biomes and abiotic factors
Which biomes occur in which parts of the earth (the global distribution of biomes) is affected by the abiotic
factors in that area, for example tropical rainforest occurs only where there is high rainfall and high
temperature whereas deserts are found where the temperature is high but the rainfall low.
Habitat and community
An organism’s habitat is the place where it lives.
The community is all the organisms (plants and animals) in an area.
An ecosystem consists of all the organisms in an area and their non-living environment (all the abiotic factors in
the environment.
The word niche describes an organism’s role within it’s community. This includes which other organisms it eats,
it’s predators, organisms it competes with, its parasites and the abiotic factors that affect it.
Revision of meaning of terms
The variety of different species in an area
Biotic factor
Abiotic factor
A factor related to living organisms that affects the number and distribution of living
things in an area, e.g. predators, disease
A factor that is not living but affects the number of living things and where they are
found (their distribution), e.g. temperature, pH
A large region of the earth with its own characteristic plants and animals and its own
characteristic climate, e.g. deserts, tropical rainforests
The place where a plant or animal lives
All the plants and animals in an area
The plants and animals (community) and their physical environment (habitat)
The role an organism plays in it’s ecosystem including it’s predators, prey, parasites,
competitors and the abiotic factors that affect it
National 5 Biology Course Notes
Unit 3 : Life on Earth
Part 2 :
Energy in Ecosystems
Food chain
A food chain shows how energy is passed from an organism that is eaten to the organism that eats it
The arrows show the direction of energy flow.
Energy stored in the grass passes to the rabbit when the rabbit eats the grass.
Energy stored in the rabbit passes to the fox when the fox eats the rabbit.
Energy losses
Most of the energy that the rabbit gets from the grass is not passed to the fox.
Only energy stored in the rabbit’s body passes to the fox.
By the time the fox eats the rabbit, the energy it got from the grass has been lost by:
• The rabbit producing heat
• The rabbit using energy to move
• Energy lost from the rabbit's body as undigested food.
In any food chain, only 10% of the energy is passed to the next level.
90% of the energy is lost in these three ways:
1. As heat
2. In movement
3. As undigested material
Producers and consumers
Producer – A green plant that is able to produce its own food – food chains begin with a producer
Primary consumer - An animal that feeds on (consumes) the producer
Secondary consumer – An animal that feeds on (consumes) the primary consumer
Tertiary consumer – An animal that feeds on the secondary consumer
e.g. Algae
Water flea
(primary consumer)
(secondary consumer)
(tertiary consumer)
Pyramids of numbers, biomass and energy
For most food chains, the number of organisms, their biomass (total mass of all the organisms) and the energy
stored in all the organisms decrease at each level of the food chain.
i.e. there are more producers than primary consumers, more primary consumers than secondary consumers and
more secondary consumers than tertiary consumers
The producers have a greater total biomass and more stored energy than the primary consumers, the primary
consumers have a greater biomass and more energy than the secondary consumers and the secondary consumers
have a greater biomass and more energy than the tertiary consumers
The decrease in these three features
• Number or organisms
• Biomass
• Energy
at each level of the food chain can be represented as a pyramid of numbers, a pyramid of biomass or a
pyramid of energy:
Pyramid of biomass
Pyramid of numbers
Tertiary consumers
Secondary consumers
Tertiary consumers
Secondary consumers
Primary consumers
Primary consumers
Pyramid of energy
Tertiary consumers
Secondary consumers energy
Primary consumers
Pyramid of numbers that don’t have the usual pyramid shapes
The pyramid of numbers is shaped like this:
Secondary consumer
Primary consumer
When the producer is a large
plant like a tree that has many
primary consumers feeding on it
The pyramid of numbers is shaped like this:
Tertiary consumer
When the food chain includes a parasite as the
secondary or tertiary consumer e.g.
Secondary consumer
Primary consumer
Even when the pyramid of numbers have
these unusual shapes, the pyramids of
biomass and of energy for the same food
chains still have the usual pyramid shape
The pyramid is this shape since many parasites can feed
on a single animal
Since the biomass and total energy stored both decrease
at each higher level for all food chains including these
Nitrogen cycle
Plant and animal proteins contain nitrogen.
Plants get nitrogen from nitrate absorbed from the soil.
This nitrogen is used to produce protein. Animals get protein by eating plants so their protein also depends on nitrate
absorbed by plants.
Organisms involved in the nitrogen cycle and what they do
These include soil fungi and bacteria. They decompose proteins in dead organisms and nitrogen compounds in animal
wastes to produce ammonium and nitrate.
Nitrifying bacteria
Nitrifying bacteria change ammonium into nitrite and nitrite into nitrate.
This is called nitrification.
Nitrification by nitrifying bacteria
Nitrogen fixing bacteria
These bacteria are able to use nitrogen gas in the air.
Some nitrogen fixing bacteria live in the soil, they change nitrogen gas into nitrate. – this is called nitrogen fixation.
Other nitrogen fixing bacteria live in swellings
called root nodules in the roots of a particular
group of plants called legumes.
(This group of plants includes clover, beans and
Legume root
Nitrogen fixing bacteria in root nodules change nitrogen gas into
a form that can be used by the plant to make protein.
Nitrogen gas can also be changed to soil nitrates during lightning storms
Denitrifying bacteria
Denitrifying bacteria change soil nitrates into nitrogen gas which escapes into the atmosphere – this
process is called denitrification.
Summary of nitrogen cycle
Nitrogen gas
(in the air)
fixation by
nitrogen fixing Plant protein (made
bacteria (free
using nitrogen atoms
living in soil and
in nitrate
in root nodules
of legumes
Absorbed by plant roots
eat plants
Animal protein
Dead bodies of plants and animals
broken down by decomposers,
e.g. bacteria and fungi
Summary of processes in the nitrogen cycle
Organisms involved
Decomposers, e.g. soil bacteria
and fungi
Nitrifying bacteria
Nitrogen fixation
Nitrogen fixing bacteria
Denitrifying bacteria
Reactions involved in the process
nitrogen gas
nitrogen gas
Competition between organisms occurs when they need the same resources, for animals they might feed on the same
prey, for plants they compete for light and soil water.
Interspecific competition
This is competition between animals or plants from different species for the same resources.
For example, lions and cheetahs belong to different species but they both feed on gazelle.
Intraspecific competition
Intraspecific competition is animals or plants belonging to the same species competing with each other, for example two
cheetahs competing with each other.
This competition is more intense because members of the same species need exactly the same resources, whereas
members of different species use different resources.
Members of the same species can show behaviour that reduces competition, e.g.
Territorial behaviour – male members of the species establish territories where they do not allow other males to feed –
this can be seen in gardens with male blackbirds
Pecking order – for animals that live in groups, dominant individuals get first choice of resources.
National 5 Biology Course Notes
Unit 3 : Life on Earth
Part 3 :
Sampling techniques and
measuring abiotic factors
A quadrat is a square frame divided into smaller squares
It is used to sample the abundance of plants or very slow moving animals in an
The number of squares containing the organism is counted to give a measure of
its abundance.
The quadrat must be thrown at random and the results from several quadrats are taken and an average
taken to make the result more reliable.
Pitfall trap
A pitfall trap is a container, for example a plastic cup which is
buried in the soil with it’s rim level with the soil surface.
It is used to collect and sample invertebrates crawling on the soil
Several pitfall traps should be set up to make the result more
Errors may occur when using pitfall traps because:
• Insects that can fly may escape from the traps
• Some predators that are trapped may eat other trapped
Measuring abiotic factors
Abiotic factor
Instrument used to measure
abiotic factor
Light intensity
Light meter
Soil moisture
Moisture meter
pH meter
Soil pH
Steps taken to reduce error when measuring
Hold the meter away from your body to ensure
you are not shading the meter
Wipe the meter probe dry after each
Make sure the probe is deep enough in the soil
Clean the meter probe between readings
National 5 Biology Course Notes
Unit 3 : Life on Earth
Part 4 :
Adaptation, natural selection
and the evolution of species
A mutation is a change to an organism’s genetic material.
Mutations are random.
They are the only way in which new alleles can arise in a population.
Mutations are usually harmful but some mutations can result in genes that give characteristics that give an
individual a survival advantage.
Mutations are rare but the frequency with which they happen can be increased by mutagenic agents- these
include radiation, e.g. X-rays and UV radiation, and some chemicals, e.g. mustard gas.
An adaptation is an inherited characteristic that makes an organism more able to survive in it’s environment.
e.g. adaptations of camel to survival in the desert
Adaptations of a cactus to survival in the desert
Can drink up to 30% of its body weight when it
finds water (200L in 3 minutes)
Low levels of sweat
Low volume of urine
Copes with 30% water loss
(most animals die at 10%)
Leaves are spines to reduce water loss.
Fat in hump releases
water when broken
Can tolerate body
temperature changes
more than 3 times level
that would kill us
Can store large amounts of water in the gut
Stores water.
Thick waxy cuticle reduces water loss
Extensive roots to absorb as much water as possible
Natural selection
Most organisms produce more offspring than the environment can sustain.
Since there is variation within a species, some individuals have characteristics that make them better able to
survive than others, e.g. taller individuals might see predators sooner, faster individuals may be more able to
outrun predators, individuals with a certain colour may be better camouflaged.
The best adapted individuals have a selective advantage and are more likely to survive, breed and pass on the
genes that gave them the best characteristics to the next generation.
This process where the best adapted survive at the expense of the others (survival of the fittest) is called natural
Examples of natural selection
1. The peppered moth
There are two forms of the moth:
a light coloured speckled form
a dark form
These differences are caused by two different alleles of a gene
Peppered moths are active at night and during the day rest on surfaces such as tree trunks.
The moths are eaten by birds.
In unpolluted areas, the tree trunks are covered by light coloured lichens that
camouflage the light forms – in these areas, the light forms have a selective
advantage so less are eaten and more survive and pass on the light gene.
Light moth
Dark moth
On lichen covered
tree trunk
In polluted areas, the lichens are killed and tree trunks are stained with
soot – in these areas dark moths are camouflaged and given a selective
advantage so more dark moths survive and pass on the dark gene.
Dark moth
Light moth
On soot covered
tree trunk
Examples of natural selection
2. Antibiotic resistance
When an antibiotic is applied to a population of bacteria, most are killed but some will have genes that make them
resistant to the antibiotic.
The resistant bacteria survive antibiotic treatment and pass on the resistance genes to offspring.
Since bacteria reproduce quickly and asexually (needing only one parent and producing offspring genetically identical
to the parent), antibiotic resistance spreads quickly.
Overuse of antibiotics has led to many bacteria becoming resistant.+
Speciation is the formation of one or more new species from an already existing species.
The first step in speciation is a population being isolated from the rest of the species.
The isolated population gradually becomes totally different from the rest of the species because:
1. Different mutations occur in the two groups so their gene pools become more and more different
2. Since they live in different environments, their selection pressures are not the same so the genes
that give survival advantage and are passed on are different for the two groups.
Eventually the two groups become so different they can no longer interbreed to produce fertile
offspring – the isolated group has now become a new species.
An example of speciation – Galapagos island finches
These finches arrived from mainland South America and
were isolated from the main population by the sea.
A number of new species developed from the ancestral
seed eating finches to fill niches occupied by other bird
species on the mainland.
Their beaks became adapted to eat different food sources
as shown on the diagram.
National 5 Biology Course Notes
Unit 3 : Life on Earth
Part 5 : Human impact on the
Increasing human population
The graph shows the human population explosion that has taken place
in recent centuries.
This increase in population leads to a need to produce more and more
The use of fertilisers to supply necessary plant nutrients and of
pesticides to destroy pests that damage crops helps to produce high
crop yields.
However, these chemicals can cause damage to ecosystems.
How fertilisers can damage ecosystems
Fertilisers can be washed by rain from farm fields into lakes where
they increase the growth of surface microscopic plants called algae.
The increase in growth of these algae leads to large numbers of
them coating the water surface in what are called algal blooms
When the algae die, they provide food for bacteria which
rapidly multiply and use up oxygen leading to the death of
aquatic animals, like fish
Algal bloom on a lake surface
The flow chart outlines this process:
Fertiliser is leached into the water
Fertiliser causes increased growth
of algae (algal bloom)
Bacteria feed on dead algae and
use up oxygen in the water
Water animals such as fish die due
to lack of oxygen
Accumulation of pesticides in food chains
Pesticides are sprayed on crops to kill pests like insects that
damage the crops.
Predators of these pests eat a lot of them and so accumulate
pesticides in their bodies.
This trend continues along a food chain with predators at each
level accumulating more pesticides in their bodies.
The problem is made worse by the fact that organisms often
cannot get rid of the pesticide and store it in their bodies.
Predators at the top of the food chain can have levels of
pesticide that are damaging or lethal.
The diagram shows the accumulation of the now banned
insecticide DDT in an aquatic food chain in concentrations of
parts per million (ppm) after it had been washed into water
from farmland,
Accumulation of pesticide (DDT) in a food chain
Indicator species
Indicator species are organisms whose presence or absence from an area indicates the level of pollution.
For some organisms, e.g. bloodworms in water, the fact that they are present indicates pollution while for others,
e.g. lichens, the fact that they are absent from trees indicates air pollution.
Rivers can be polluted with organic waste, e.g. sewage. Bacteria feed on this and use up oxygen causing death of
other organisms such as fish. Some of the invertebrate indicator species whose presence indicates polluted or
clean water are shown below:
Indicator species present
Level of pollution
Very low
Stonefly or mayfly
Absence from water indicates pollution
level of
Freshwater shrimp
Water louse
Presence in water indicates pollution
Very high
Rat-tailed maggot
Indicators of Air Pollution
Lichens are plants that grow in exposed places such as tree bark.
Tree trunk covered
in lichens
Air pollutants like sulphur dioxide from burning fossil fuels
dissolves in rainwater and damages lichens preventing them
from growing.
This makes lichens natural indicators of air pollution.
In places where no lichens are growing, this is often a sign
that the air contains pollutants such as sulphur dioxide.
Tree trunk stained
with soot and
having no lichens
due to pollution
Biological control
Biological control is a way of controlling pests that doesn’t use pesticides.
Instead, natural predators of the pest are used to kill them.
For example aphids (also called greenfly) feed on crops and garden plants
damaging them and killing them.
Ladybirds are natural predators of aphids and can be put on infected
plants to control the aphid population
Myxomatosis in rabbits
Ladybirds feeding on aphids
Myxomatosis is a fatal virus disease of rabbits.
It has been used to control the rabbit population in countries such as Australia.
However those rabbits surviving the disease had genetic resistance and
resistance in rabbit populations has been growing
GM crops
GM crops can be genetically modified to contain genes that produce chemicals
lethal to pests so that pesticides do not have to be used or to produce crops
that don’t need as much fertiliser.