At a coastal education centre, visitors monitored a small brackish-water enclosure for 30 days. Fig. 1 shows one feeding route observed in the enclosure. An...
Question 1 Report
At a coastal education centre, visitors monitored a small brackish-water enclosure for 30 days. Fig. 1 shows one feeding route observed in the enclosure. An arrow points from the organism that is eaten to the organism that eats it. Table 1 gives the energy becoming new biomass at each stage during the survey. The centre is considering whether fish from similar ponds could be used as food for people.
Table 1
| Organism | Energy becoming new biomass in 30 days / kJ |
|---|---|
| algae | 48 000 |
| water fleas | 5 800 |
| sticklebacks | 620 |
| heron | 45 |
(a) Name the producer in Fig. 1. [1]
(b) Describe what the arrows in Fig. 1 show. [2]
(c) Use Table 1 to calculate the percentage of water-flea biomass energy transferred to stickleback biomass. Give your answer to the nearest whole number. [2]
(d) Explain why much of the energy in water fleas does not become stickleback biomass. [3]
(e) Suggest why growing edible algae for human food could provide more usable food energy per area than growing sticklebacks. [3]
(f) Describe the likely effect on the heron population if disease caused a large fall in the number of water fleas. [2]
Answer Details
(a) The producer is algae. Producers make biomass using energy from sunlight. [1]
(b) The arrows show feeding relationships, or transfer of food energy. Each arrow points from the organism that is eaten to the consumer that eats it. [2]
(c) \[\frac{620}{5800}\times100=10.69\ldots\%\] To the nearest whole number, the transfer is 11%. [2]
(d) Sticklebacks use energy in respiration, and energy is released as heat. Energy is also used for movement and maintaining body processes. Some food is not digested and is lost in faeces, while some is lost in excretion. Any three relevant losses explain why only a small fraction becomes biomass. [3]
(e) If people eat algae, fewer trophic transfers are needed than if they eat sticklebacks. Energy is lost through respiration and waste at every transfer. Therefore more original energy becomes available as human food, so less area is needed for the same usable food energy. [3]
(f) A large fall in water fleas reduces food available to sticklebacks, so stickleback numbers are likely to fall. Herons then have less stickleback food, reducing survival or reproduction, so the heron population is also likely to fall. [2]
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