1. Explain what a pyramid of biomass is.
Answer
A graphical way of representing the relative amount of biomass in each level of a food chain. (Trophic level 1 is at the bottom of the pyramid.)
2. What are primary consumers ?
a) herbivores that eat plants or algae
b) carnivores that feed on herbivores
c) decomposers that recycle nutrients from dead matter
d) omnivores that feed on both plants and animals
Answer
a) herbivores that eat plants or algae
3. What are carnivores ?
Answer
Animals that eat herbivores or other carnivores.
4. What are apex predators and where are they found in a food chain ?
Answer
Carnivores with no predators that are the final organism in a food chain.
5. Describe some ways that biomass can be lost between trophic levels.
Answer
Not all ingested material is absorbed; some is egested as faeces. Some of the absorbed material is lost as waste, such as carbon dioxide and water during respiration, or water and urea in urine.
6. The figure below shows the flow of energy from the sun to humans via various food chains. Which of these pathways make the most eficient use of solar energy ?
Answer
More energy from the sun is transferred to man if there are fewer trophic levels in the food chain. Since there are only two trophic levels in the food chain "rice ➜ man", it is the most efficient transfer of energy to man.
7. The flowchart below shows the flow of organic compounds and carbon dioxide in an ecosystem. P, Q , R and S represent different groups of organisms. What role does each group of organism play in this ecosystem ?
Answer
Organism P represents decomposers such as fungi and bacteria which play the role of releasing organic compounds from dead organisms back into the soil where the plants can absorb as nutrients. Organism Q is the producer as it is the only one that takes in carbon dioxide. This means that organism R is the primary consumer and organism S is the secondary consumer.
8. Sardines have a greater biomass than tuna. Explain why a greater proportion of biomass is passed to humans if they eat sardines rather than tuna.
Answer
Eating sardines would mean that there are fewer trophic levels and so less biomass would be lost in faeces, urine or carbon dioxide. Large amounts of glucose are used in respiration, so there would be less respiratory losses.
9. Why do plants and algae transfer only about 1% of the energy from light into glucose during photosynthesis ?
Answer
Some light is reflected by the leaf, not absorbed by chlorophyll, or transmitted through the leaf.