(1) Ecology is the branch of biology that deals with the relationships between organisms and their environments. (2) Key topics in ecology include energy flow through ecosystems, levels of ecological organization, and recycling of nitrogen. (3) Candidates should be able to define ecological terms like habitat, niche, population, community, ecosystem, and explain concepts such as trophic levels, food chains, food webs, and the role of nitrogen-fixing and nitrifying bacteria in nutrient cycling.

1. ECOLOGY
AS BIOLOGY

2. TOPICS
A Cell Structure
B Biological Molecules
C Enzymes
D Cell Membranes and Transport
E Cell and Nuclear Division
F Genetic Control
G Transport
H Gas Exchange
I Infectious Disease
J Immunity
K Ecology

3. CONTENT
• Energy flow through ecosystems
• Levels of ecological organization
• Recycling of nitrogen

4. Candidates should be able to:
Learning Outcomes
(a) define the terms habitat, niche, population, community
and ecosystem and be able to recognize examples of each;
(b) explain the terms autotroph, heterotroph, producer,
consumer and trophic level in the context of food chains and
food webs;
(c) explain how energy losses occur along food chains and
discuss the efficiency of energy transfer between trophic
levels;
(d) describe how nitrogen is cycled within an ecosystem, including the
roles of nitrogen-fixing bacteria (e.g. Rhizobium) and nitrifying bacteria
(Nitrosomonas and Nitrobacter);

5. (e) use the knowledge gained in this section in new situations
or to solve related problems.

6. Terminologies:
ēˈkäləjē/
Ecology-the branch of biology that deals with the relations
of organisms to one another and to their physical
surroundings.
Ecosystem -includes all the organisms living in a particular
area and all the non-living (abiotic) conditions.
An ecosystem is a community of living organisms (plants,
animals and microbes) in conjunction with the nonliving
components of their environment (things like air, water
and mineral soil), interacting as a system.

8. Habitat – The place where an organism lives
Population – A group of organisms belonging to the same
species
Community – All the populations of different organisms
living and interacting in the same space at the same time
Abiotic – The physical and chemical features of the
environment
Biotic – The biological features of the environment (living)
Niche – A species role within it’s habitat
Adaptation – A feature that members of a species have to
increase their chance of survival

9. The main route by which energy enters an ecosystem is
photosynthesis.
(Some energy enters sea ecosystems when bacteria use
chemicals from deep sea vents as an energy source.)
During photosynthesis plants convert sunlight energy into a
form that can be used by other organisms
- plants are called producers (because they produce organic
molecules using sunlight energy).
Energy is transferred through the living organisms of an ecosystem
when organisms eat other organisms, e.g. producers are eaten by
organisms called primary consumers.
Primary consumers are then eaten by secondary consumers and
secondary consumers are eaten by tertiary consumers.

10. Each of the stages (e.g. producers, primary
consumers) are called trophic levels.
Food chains and food webs show how energy is transferred
through an ecosystem
Food chains show simple lines of energy transfer
Food webs show lots of food chains in an ecosystem and how
they overlap.

15. Energy that get locked up in the things that cant be eaten e.g.,
bones and faeces get recycled back into the ecosystem by
microorganism called decomposers -they break down dead or
undigested material.

16. Not energy is transferred to the next energy level
Not all the energy (e.g. from sunlight or food) that's available
to the organisms in a trophic level is transferred to the next
trophic level - around 90% of the total available energy is lost
in various ways.
Some of the available energy (60%) is never taken in by the organisms in
the first place. For example:
•Plants can't use all the light energy that reaches their
leaves, e.g. some is the wrong wavelength, some is reflected,
and some passes straight through the leaves.
•Some sunlight can't be used because it hits parts of the
plant that can't photosynthesize, e.g. the bark of a tree.

17. •Some parts of food, e.g. roots or bones, aren't eaten by
organisms so the energy isn't taken in.
•Some parts of food are indigestible so pass through
organisms and come out as waste, e.g. faeces.
The rest of the avail able energy (40%) is taken in (absorbed)
- this is called the gross productivity. But not all of this is
available to the next trophic level either
•30% of the total energy available (75% of the gross productivity)
is lost to the environment when organisms use energy produced from
respiration for movement or body heat. This is called respiratory loss.
•10% of the total energy available (25% of the gross productivity)
becomes biomass (e.g. it's stored or used for growth) - this is called
the net productivity.

18. Net productivity is the amount of energy that's available
to the next trophic level.