The nature of ecosystems and samplingEdexcel A-Level Biology B: Mind map

Exam questions on The nature of ecosystems and sampling

1. In a woodland, one oak tree supports about 2000 caterpillars. The caterpillars are eaten by about 20 blue tits, and the blue tits are eaten by one sparrowhawk. A student draws a pyramid of numbers for this food chain.
   A pyramid of dry biomass is often used instead of a pyramid of fresh mass. Explain one advantage and one disadvantage of using dry biomass.2 marks
2. A student investigates how the abundance of creeping buttercup changes across a school field, moving from a damp hedge bottom into the open, drier field. She also needs a method for grass in the same field, where individual plants cannot easily be told apart.
   Explain why percentage cover is more suitable than counting individuals for the grass.2 marks
3. A student estimates the population of snails in a pond margin by mark-release-recapture. She collects 48 snails and marks the shell of each with a small spot of non-toxic paint. She releases them at the place of capture. After 24 hours she collects 40 snails, of which 12 are marked.
   Calculate the estimated population size of the snails.3 marks