7.4 Trophic Levels in an Ecosystem

What are producers and what trophic level are they?

• Plants and algae that make their own food.

• 1

What are primary consumers and what trophic level are they?

• Herbivores that eat plants/algae.

• 2

What are secondary consumers and what trophic level are they?

• Carnivores that eat herbivores

• 3

What are tertiary consumers and what trophic level are they?

• Carnivores that eat other carnivores

• 4

What are apex predators?

Carnivores with no predators

How do decomposers break down dead plant and animal matter?

• Secreting enzymes into the environment

• Small soluble food molecules diffuse into microorganism

What is the order of tropic levels?

level 1 (producers) → level 2 (primary consumers) → level 3 (secondary consumers) → level 4 (tertiary consumers)

Label this pyramid of biomass.

• A — 4

• B — 3

• C — 2

• D — 1

Producers are mostly ________ and ________ which transfer about 1% of the incident _________ from light for ______________.

• plants

• algae

• energy

• photosynthesis

What percentage of biomass from each trophic level is transferred to the level above it?

10%

What are losses of biomass due to? (3)

• Not all ingested material is absorbed — some is egested as faeces

• Some absorbed material is lost as waste — e.g:

  • carbon dioxide and water in respiration

  • urea in urine

• Not all biomass can be eaten — e.g. bones, claws, teeth etc.

Large amounts of _________ are used in repiration.

glucose

How do you calculate the efficiency of biomass transfers?

efficiency = (biomass available after transfer ÷ biomass available before transfer) × 100

• A food web contains several food chains.

• Figure 9 shows a food web.

• The animals in Figure 9 get their energy by eating other organisms

Describe how the algae get energy. [2 marks]

• From light

• Absorbed by chlorophyll

• A food web contains several food chains.

• Figure 9 shows a food web.

Name one primary consumer in Figure 9. [1 mark]

Krill

• A food web contains several food chains.

• Figure 9 shows a food web.

Name one producer in Figure 9. [1 mark]

Algae

• A food web contains several food chains.

• Figure 9 shows a food web.

• The different food chains in Figure 9 have different numbers of organisms.

Complete Figure 10 to show a food chain in Figure 9 with five organisms, including the human. [1 mark]

Figure 10

1. _________________________

2. _________________________

3. _________________________

4. _________________________

5. Human

1. Algae

2. Krill

3. Squid

4. Mackerel

• A food web contains several food chains.

• Figure 9 shows a food web.

• Figure 9 shows that mackerel eat krill and squid.

• The biomass of mackerel is much less than the combined biomass of krill and squid.

• One reason for this is that the mackerel cannot digest all parts of the krill and squid.

Give two other reasons. [2 marks]

• Non-eaten parts

• Respiration