Fig. 1 shows a simplified biomass pyramid from a freshwater pond. A student dried samples of organisms before calculating biomass, so that the measurements ...
Question 1 Report
Fig. 1 shows a simplified biomass pyramid from a freshwater pond. A student dried samples of organisms before calculating biomass, so that the measurements were not affected by different amounts of water in their cells. Each rectangle represents the biomass available at one trophic level.
(a) State the biomass of water fleas shown in Fig. 1. [1]
(b) Explain why organisms were dried before biomass was measured. [2]
(c) Describe the trend in biomass from algae to heron. [2]
(d) Explain two reasons for this trend. [3]
Answer Details
(a) The biomass of water fleas is 96 g m−2. [1]
(b) Water has mass, and different organisms can contain different amounts of it. Drying removes this variable water mass, so biomass comparisons represent dry organic material. [2]
(c) Biomass decreases at every higher trophic level, from 820 g m−2 in algae to 2 g m−2 in herons. [2]
(d) Not all organisms, or all their parts, are eaten. Of material that is eaten, some is not digested and is lost in faeces. Organisms also use energy in respiration and movement, losing energy as heat, so less material is available to make biomass at the next level. [3]
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