AQA GCSE Biology (8461), Higher tier · Ecology › Trophic levels in an ecosystem
Practise Pyramids of biomass. 13 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Complete the sentences. Choose answers from the list. 1 · 3 · biomass · number · water A pyramid of biomass shows the relative amount of ....................... at each trophic level of a food chain. Trophic level ....................... is always at the bottom of the pyramid.
biomass; 1
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
{fig} shows a pyramid of biomass for a food chain.
[object Object]
(a) Which organism in {fig} is the producer?[1]
(b) What does the width of each bar in a pyramid of biomass show?[1]
(c) Why is each bar smaller than the bar below it? Tick (✓) one box.[1]
Biomass is lost between trophic levels
Organisms at higher trophic levels are smaller
There are more predators than prey
Producers do not photosynthesise
(d) At which trophic level are the grass snakes?[1]
Show the answer and mark scheme
(a)Answer: Grass
grass
(b)
the (relative) biomass / mass of living material at that trophic level
(c)Answer: Biomass is lost between trophic levels
(d)Answer: Level 4 (tertiary consumers)
4 / tertiary consumers
Question 2Medium6 marks
Students want to construct a pyramid of biomass for this food chain in a meadow: grass → grasshoppers → spiders
Describe how the students could collect and process the data needed to construct an accurate pyramid of biomass for this food chain, and how they should draw the pyramid.[6]
Show the answer and mark scheme
place several quadrats (e.g. 1 m²) at random positions in the meadow, so the sample is representative
collect the grasshoppers and spiders from the area of each quadrat, e.g. with a sweep net or pooter, before cutting all the grass in the quadrat at ground level
sort the organisms into the three trophic levels
dry each sample in an oven at a low temperature (e.g. about 80 °C) and reweigh it until its mass stops changing (constant mass), to find the dry mass
dry mass is used because the amount of water in organisms varies
calculate the mean dry mass per m² for each trophic level
draw a bar for each trophic level, to scale (bar width proportional to the biomass), with the producer (grass) at the bottom and the spiders at the top
only small samples should be taken, because the organisms are killed when they are dried
Marked with levels of response: the full level descriptors are in the app.
Question 3Hard9 marks
One oak tree can support thousands of caterpillars. The caterpillars are eaten by a few birds.
(a) To construct pyramids of biomass, scientists usually measure dry mass. Describe how the dry mass of a sample of caterpillars could be found.[3]
(b) Explain why dry mass is used rather than fresh mass.[1]
(c) A sample of 50 caterpillars had a total dry mass of 4.0 g. The oak tree supports about 75 000 caterpillars. Estimate the total dry mass of all the caterpillars on the tree. Give your answer in kg.[2]
(d) The dry mass of the oak tree is about 2500 kg. Explain why the pyramid of biomass for this food chain is pyramid-shaped, even though there are many more caterpillars than oak trees.[2]
(e) Give one disadvantage of measuring dry biomass.[1]
Show the answer and mark scheme
(a)
heat the caterpillars in an oven (e.g. at 80–100 °C) to evaporate the water
weigh them, then heat and weigh again repeatedly
until the mass stays constant (all the water has been removed)
(b)
the water content of organisms varies, so dry mass gives a more accurate / comparable measure of biomass
(c)Answer: 6.0 kg
4.0 ÷ 50 = 0.08 g per caterpillar / 75 000 ÷ 50 = 1500
0.08 × 75 000 (or 1500 × 4.0) = 6000 g = 6.0 (kg)
(d)
one oak tree has a very large biomass compared with one caterpillar / the total biomass of the caterpillars (about 6 kg) is much smaller than the biomass of the tree (2500 kg)
(because) only a small part of the tree is eaten / biomass is lost between trophic levels, so the caterpillar bar is narrower than the tree bar