Notes

4.7 Ecology

The Sun is a source of energy that passes through ecosystems. Materials including carbon and
water are continually recycled by the living world, being released through respiration of animals,
plants and decomposing microorganisms and taken up by plants in photosynthesis. All species live
in ecosystems composed of complex communities of animals and plants dependent on each other
and that are adapted to particular conditions, both abiotic and biotic.

These ecosystems provide
essential services that support human life and continued development. In order to continue to
benefit from these services humans need to engage with the environment in a sustainable way. In
this section we will explore how humans are threatening biodiversity as well as the natural systems
that support it. We will also consider some actions we need to take to ensure our future health,
prosperity and well-being.

4.7.1 Adaptations, interdependence and competition
4.7.1.1 Communities

Students should be able to describe:

• different levels of organisation in an ecosystem from individual
organisms to the whole ecosystem

• the importance of interdependence and competition in a
community.

Students should be able to, when provided with appropriate
information:

• suggest the factors for which organisms are competing in a
given habitat

• suggest how organisms are adapted to the conditions in
which they live.

An ecosystem is the interaction of a community of living organisms
(biotic) with the non-living (abiotic) parts of their environment.
To survive and reproduce, organisms require a supply of materials
from their surroundings and from the other living organisms there.

Plants in a community or habitat often compete with each other for
light and space, and for water and mineral ions from the soil.

Animals often compete with each other for food, mates and territory.
Within a community each species depends on other species for
food, shelter, pollination, seed dispersal etc. If one species is
removed it can affect the whole community.

This is called
interdependence. A stable community is one where all the species
and environmental factors are in balance so that population sizes
remain fairly constant.


Recording first-hand
observations of organisms.

Students should be able to extract and interpret information from
charts, graphs and tables relating to the interaction of organisms
within a community.


Extract and interpret
information from charts,
graphs and tables.

4.7.1.2 Abiotic factors
Content Key opportunities for
skills development

Students should be able to explain how a change in an abiotic
factor would affect a given community given appropriate data or
context.

Abiotic (non-living) factors which can affect a community are:
• light intensity
• temperature
• moisture levels
• soil pH and mineral content
• wind intensity and direction
• carbon dioxide levels for plants
• oxygen levels for aquatic animals.

Students should be able to extract and interpret information from
charts, graphs and tables relating to the effect of abiotic factors on
organisms within a community.

Extract and interpret
information from charts,
graphs and tables.

4.7.1.3 Biotic factors

Students should be able to explain how a change in a biotic factor
might affect a given community given appropriate data or context.
Biotic (living) factors which can affect a community are:

• availability of food
• new predators arriving
• new pathogens
• one species outcompeting another so the numbers are no
longer sufficient to breed.

Students should be able to extract and interpret information from
charts, graphs and tables relating to the effect of biotic factors on
organisms within a community.


Extract and interpret
information from charts,
graphs and tables.

4.7.1.4 Adaptations

Students should be able to explain how organisms are adapted to
live in their natural environment, given appropriate information.
Organisms have features (adaptations) that enable them to survive
in the conditions in which they normally live. These adaptations may
be structural, behavioural or functional.

Some organisms live in environments that are very extreme, such
as at high temperature, pressure, or salt concentration. These
organisms are called extremophiles. Bacteria living in deep sea
vents are extremophiles.

4.7.2 Organisation of an ecosystem
4.7.2.1 Levels of organisation

Students should understand that photosynthetic organisms are the
producers of biomass for life on Earth.
Feeding relationships within a community can be represented by
food chains.

All food chains begin with a producer which
synthesises molecules. This is usually a green plant or alga which
makes glucose by photosynthesis.

A range of experimental methods using transects and quadrats are
used by ecologists to determine the distribution and abundance of
species in an ecosystem.

In relation to abundance of organisms students should be able to:
• understand the terms mean, mode and median
• calculate arithmetic means
• plot and draw appropriate graphs selecting appropriate scales
for the axes.


Producers are eaten by primary consumers, which in turn may be
eaten by secondary consumers and then tertiary consumers.

Consumers that kill and eat other animals are predators, and those
eaten are prey. In a stable community the numbers of predators and
prey rise and fall in cycles.

Interpret graphs used to
model predator-prey cycles.

Students should be able to interpret graphs used to model these
cycles.

4.7.2.2 How materials are cycled
Content Key opportunities for
skills development

Students should:

• recall that many different materials cycle through the abiotic
and biotic components of an ecosystem
• explain the importance of the carbon and water cycles to
living organisms.

All materials in the living world are recycled to provide the building
blocks for future organisms.

The carbon cycle returns carbon from organisms to the atmosphere
as carbon dioxide to be used by plants in photosynthesis.

The water cycle provides fresh water for plants and animals on land
before draining into the seas. Water is continuously evaporated and
precipitated.

Students are not expected to study the nitrogen cycle.

Students should be able to explain the role of microorganisms in
cycling materials through an ecosystem by returning carbon to the
atmosphere as carbon dioxide and mineral ions to the soil.

Interpret and explain the
processes in diagrams of
the carbon cycle, the water
cycle.

There are links with the
water cycle to GCSE
Chemistry The Earth's early
atmosphere.


4.7.3 Biodiversity and the effect of human interaction on ecosystems
4.7.3.1 Biodiversity


Biodiversity is the variety of all the different species of organisms on
earth, or within an ecosystem.

A great biodiversity ensures the stability of ecosystems by reducing
the dependence of one species on another for food, shelter and the
maintenance of the physical environment.

The future of the human species on Earth relies on us maintaining a
good level of biodiversity. Many human activities are reducing
biodiversity and only recently have measures been taken to try to
stop this reduction.


Explain how waste,
deforestation and global
warming have an impact on
biodiversity.

4.7.3.2 Waste management

Rapid growth in the human population and an increase in the
standard of living mean that increasingly more resources are used
and more waste is produced. Unless waste and chemical materials
are properly handled, more pollution will be caused.

Pollution can occur:
• in water, from sewage, fertiliser or toxic chemicals
• in air, from smoke and acidic gases
• on land, from landfill and from toxic chemicals.

Pollution kills plants and animals which can reduce biodiversity.

5.9.3.1 Atmospheric
pollutants from fuels.

4.7.3.3 Land use

Humans reduce the amount of land available for other animals and
plants by building, quarrying, farming and dumping waste.

The destruction of peat bogs, and other areas of peat to produce
garden compost, reduces the area of this habitat and thus the
variety of different plant, animal and microorganism species that live
there (biodiversity).

The decay or burning of the peat releases carbon dioxide into the
atmosphere.

Understand the conflict
between the need for cheap
available compost to
increase food production
and the need to conserve
peat bogs and peatlands as
habitats for biodiversity and
to reduce carbon dioxide
emissions.

There are links within this
section to Global warming
(page 65).

4.7.3.4 Deforestation
Content Key opportunities for
skills development

Large-scale deforestation in tropical areas has occurred to:
• provide land for cattle and rice fields
• grow crops for biofuels

Evaluate the environmental
implications of
deforestation.

Students should be able to describe some of the biological
consequences of global warming.
Levels of carbon dioxide and methane in the atmosphere are
increasing, and contribute to ‘global warming’.

Understand that the
scientific consensus about
global warming and climate
change is based on
systematic reviews of
thousands of peer reviewed
publications.


Explain why evidence is
uncertain or incomplete in a
complex context.

4.7.3.6 Maintaining biodiversity

Students should be able to describe both positive and negative
human interactions in an ecosystem and explain their impact on
biodiversity.

Scientists and concerned citizens have put in place programmes to
reduce the negative effects of humans on ecosystems and
biodiversity.

These include:
• breeding programmes for endangered species
• protection and regeneration of rare habitats
• reintroduction of field margins and hedgerows in agricultural
areas where farmers grow only one type of crop
• reduction of deforestation and carbon dioxide emissions by
some governments
• recycling resources rather than dumping waste in landfill.

Evaluate given information
about methods that can be
used to tackle problems
caused by human impacts
on the environment.

Explain and evaluate the
conflicting pressures on
maintaining biodiversity
given appropriate
information.

4.8 Key ideas

The complex and diverse phenomena of the natural world can be described in terms of a small
number of key ideas in biology.

These key ideas are of universal application, and we have embedded them throughout the subject
content. They underpin many aspects of the science assessment.

Key ideas in biology:
• life processes depend on molecules whose structure is related to their function

• the fundamental units of living organisms are cells, which may be part of highly adapted
structures including tissues, organs and organ systems, enabling living processes to be
performed effectively

• living organisms may form populations of single species, communities of many species and
ecosystems, interacting with each other, with the environment and with humans in many
different ways

• living organisms are interdependent and show adaptations to their environment
• life on Earth is dependent on photosynthesis in which green plants and algae trap light from
the Sun to fix carbon dioxide and combine it with hydrogen from water to make organic
compounds and oxygen

• organic compounds are used as fuels in cellular respiration to allow the other chemical
reactions necessary for life

• the chemicals in ecosystems are continually cycling through the natural world

• the characteristics of a living organism are influenced by its genome and its interaction with
the environment

• evolution occurs by a process of natural selection and accounts both for biodiversity and how
organisms are all related to varying degrees.