This document discusses key ecological concepts including trophic levels, energy flow through ecosystems, and nutrient cycling. It defines producers as autotrophs that obtain energy from sunlight or chemicals, and consumers as heterotrophs that obtain energy by eating other organisms. The five main trophic levels are described as primary producers, primary consumers, secondary consumers, tertiary consumers, and detritivores/saprotrophs. Photosynthesis, food chains, and energy and matter cycling are also summarized.

1. Stage 1 Biology
Ecology: Energy & Relationships

2. Important Terms
• Autotroph (producer) – an organism that makes
organic molecules from inorganic molecules using
light or chemical energy. Eg. algae, grass.
• Heterotroph (consumer) – an organism which
needs to eat other organisms to obtain energy &
large organic molecules. Eg. humans, sheep.
• Detritivore – organisms that ingest dead organic
material. Eg. earthworms.
• Saprotroph – an organism that feeds on dead
organic matter using extracellular digestion. Eg.
fungi, bacteria.

3. Trophic Levels
• A trophic level is the level of the food chain at which
an organism is found.
• Ecologists divide the species in a community or
ecosystem into different trophic levels based on their
main source of nutrition.
There are five main trophic levels:
1.Primary producers
– autotrophs eg. plants
2.Primary consumers
– herbivores eating autotrophs eg. rabbits

4. 3. Secondary consumers
– carnivores eating
herbivores
eg. lions
4. Tertiary consumers
– carnivores eating
other
carnivores
eg. eagles
5. Detritivores &
Saprotrophs
– eg. bacteria, fungi

5. Energy from the Sun
• Light is the initial source of energy for nearly all
communities.
• Light energy is captured by producers and
converted into chemical energy by the process of
photosynthesis.
• Chemical energy (such as ATP or glucose) can be
used by consumers to carry out processes such as
active transport and the synthesis
(making) of macromolecules like protein.

6. Photosynthesis
• Photosynthesis is the process of making
carbohydrates from simple raw materials:
Light energy --> Chemical energy
CO2 + H2O --> C6H12O6 + O2
• All living things depend on photosynthesis, which
provides the input of energy necessary for the
functioning of ecosystems.
• The rate of photosynthesis can be measured
directly by the production of oxygen or the uptake of
carbon dioxide or indirectly by the increase in biomass
(i.e. increase in plant weight due to sugar production).

7. Very Basic!

8. Factors Affecting Rate of
Photosynthesis
• Many factors influence the rate of photosynthesis
such as temperature, light intensity and CO2
concentration.
• Without enough light a plant can’t photosynthesise
very quickly. Increasing the light intensity will make
photosynthesis occur faster.
• Even if there is plenty of light a plant cannot
photosynthesise if it has run out of CO2.
• If it gets too cold the rate of photosynthesis will
slow right down; equally, plants cease to be able to
photosynthesise if it gets too hot.

9. Effects on Rate of Photosynthesis
•Additional factors include: colour of light, amount
of water available, enzyme presence and amount
of chlorophyll.

10. Energy Flow
• Energy enters an ecosystem via the autotrophs
(photosynthesis).
• This energy is then used or changed into other
forms of energy before leaving the ecosystem.
• When energy is transformed, the process is never
100% efficient. For example when energy is
transferred from one trophic level to another.
Grass  Grasshopper  Frog

11. • Only about 10 – 20% of
the energy obtained by
the Grasshopper from
the Grass can be used
by the Frog for growth.
• The rest is used in the
Grasshopper’s own
metabolic activities or
lost as heat.
• This efficiency depends
on a number of
physiological and
behavioural factors.

13. Energy Pyramids
• Energy pyramids are diagrams that show how
much energy flows through each trophic level in a
community.
• The width of each level represents the number of
organisms at that level.
• Energy is lost at each trophic level, so less
remains for the next trophic level.
0.1 %
1 %
10 %
100 %

14. • Energy absorbed by living organisms is only available
to the next trophic level if it remains as chemical
energy in the growth of the organism.
Energy is ‘lost’ in various ways:
1. Lost as heat through cell respiration
2. Death before being eaten
3. Indigestible parts or not all parts eaten

15. Example:

16. Energy is lost…

17. Food Chains
• A food chain is the transfer of the sun’s energy
from producers to consumers as organisms feed
on one another.
• Ie. The linear chain of organisms to show feeding
relationships.
• Arrows show flow of energy i.e. who eats whom.
• Can be shown in words or pictures.
• The number of organisms in each ‘group’
decreases as the food chain progresses.
• Energy is lost as heat in each exchange in the
food chain.

18. Examples:
OR:
Grass → Grasshopper → Frog → Snake → Hawk

19. A food chain generally follows this order:

20. Food Webs
• In most ecosystems, there is more than one
primary consumer, and animals often eat more than
one thing.
• To show the complex feeding interactions in an
ecosystem we use a food web.
• A food web is basically a whole heap of food chains
linked together to form the web.
• The complexity of the food web is what gives the
ecosystem it’s stability.
• Ie. a food web is more stable than a food chain as
it can cope with the removal of one species…

22. Your Turn:
Identify the:
• Producers
• Primary Consumers
• Secondary
Consumers
• Herbivores
• Carnivores
• Omnivores

23. Recycling
• We already know that energy is not recycled.
• Energy enters ecosystems in the form of light,
flows through food chains and is lost as heat.
• Matter remains and therefore needs to be recycled.
• Materials such as carbon, hydrogen, oxygen,
water, phosphorus and nitrogen cycle through
ecosystems again and again – they are not lost nor
are they made.
• These materials move from the physical
environment (air, rocks, soil) into the bodies of
organisms and back again.

24. Carbon Cycle
• Carbon enters food chains through photosynthesis.
• Plants in land ecosystems absorb carbon dioxide
gas into their leaves from the air & convert it to
organic matter, which accumulates as plant tissue
(biomass).
• The carbon is then passed along food chains as
organic matter.
• Output of carbon from food chains back into the
atmosphere is through cellular respiration.

26. Water Cycle
• Water is essential for life (our bodies are approx.
95% water).
• Most water (97%) is in the oceans and thus easily
available to marine organisms.
• Organisms on land depend on water cycling
between the oceans and the atmosphere.
• Water evaporates from oceans, moves in the
atmosphere over land and falls as precipitation.
• Some water evaporates again, some becomes
stored in lakes, glaciers or underground, but most
eventually runs off into rivers & returns to oceans.

28. Depleting water
resources?
• Presently, there is much talk over the water crisis,
particularly in Australia.
• What is important to remember however is that we
have not lost any water on Earth.
• Water does not get “used up”, nor does it simply
disappear. We also cannot make more.
• Currently we are in a drought in Australia because
not much water has fallen here, however in a
global sense there is no less water!
• This doesn’t mean you can have 30 min showers,
we still have a severe water shortage.