A food chain is a sequence of organisms where each member feeds on the previous one, transferring energy. A food web shows the complex feeding relationships in an ecosystem. Energy flows from producers to primary, secondary, and tertiary consumers in trophic levels. Light provides initial energy for most communities. Energy is lost at each trophic level and transformations are never 100% efficient, usually being 10-20%. A pyramid of energy shows the decrease in available energy from lower to higher trophic levels. While energy enters ecosystems through light and leaves as heat, nutrients like carbon, nitrogen, and phosphorus must be recycled through decomposition.

1. Energy Flow

2. 5.1 Communities and
Ecosystems
5.1.4: Describe what is meant by a
food chain giving three examples,
each with at least three linkages
(four organisms).
• A food chain is a sequence of
relationships between trophic levels
where each member feeds on the
previous one.

3. 5.1 Communities and
Ecosystems
5.1.5: Describe what is meant by a
food web.
• A food web is a a diagram that
shows the feeding relationships in a
community. The arrows indicate the
direction of energy flow.

4. 5.1 Communities and
Ecosystems
5.1.6: Define trophic level.
• A trophic level is where an organism
is positioned on a food web.
– Producer
– Primary consumer
– Secondary consumer
– Tertiary consumer

5. 5.1 Communities and
Ecosystems
5.1.9: State that light is the initial
energy source for almost all
communities.
• Reference to communities that start
with chemical energy is not required.
Such as deep sea ocean vents.

6. 5.1 Communities and
Ecosystems
5.1.10: Explain the energy flow in a
food chain.
• Energy losses between trophic levels
include material not consumed or
material not assimilated, and heat
loss through cell respiration.

7. 5.1 Communities and
Ecosystems
5.1.11: State that when energy
transformations take place, including
those in living organisms, the
process is never 100% efficient,
commonly being 10–20%.

8. 5.1 Communities and
Ecosystems
5.1.12: Explain what is meant by a
pyramid of energy and the reasons
for its shape.
• A pyramid of energy shows the flow
of energy from one trophic level to
the next in a community. The units
of pyramids of energy are therefore
energy per unit area per unit time,
e.g. J/m2/yr.

9. 5.1 Communities and
Ecosystems

10. 5.1 Communities and
Ecosystems

11. 5.1 Communities and
Ecosystems
5.1.13: Explain that energy can enter
and leave an ecosystem, but that
nutrients must be recycled.
• Energy enters as light and usually
leaves as heat.
• Nutrients do not usually enter an
ecosystem and must be used again
and again. Nutrients such as Carbon
dioxide, Nitrogen, and Phosphorus

13. 5.1 Communities and
Ecosystems
5.1.14: Explain the role of
saprotrophic bacteria and fungi
(decomposers) in recycling nutrients.
• The digestive enzymes secreted by
saprophytes breaks down the organic
molecules in dead material releasing
the nutrients that were ‘locked up’