A persistent pesticide, known as compound Z, was sprayed onto farmland near a lake to control insect pests. Compound Z is not broken down easily and is not ...
Question 1 Report
A persistent pesticide, known as compound Z, was sprayed onto farmland near a lake to control insect pests. Compound Z is not broken down easily and is not excreted by animals once it enters their bodies. Some time later, scientists measured the concentration of compound Z in the lake water and in each of the organisms of the food chain shown in the diagram. Their measurements, in parts per million (ppm), are given in the table.
| Component of food chain | Concentration / ppm |
|---|---|
| Lake water | 0.001 |
| Algae | 0.04 |
| Small fish | 0.5 |
| Large fish | 4.0 |
| Fish-eating bird | 32.0 |
(a) State what is meant by the term food chain. [2]
(b) Using the table, describe how the concentration of compound Z changes along this food chain. [2]
(c) Explain why the concentration of compound Z increases at each higher trophic level. [3]
(d) Calculate how many times greater the concentration in the fish-eating bird is than the concentration in the algae. [2]
(e) Suggest two harmful effects that the high concentration of compound Z could have on the fish-eating birds. [2]
(f) Name the top consumer in this food chain. [1]
Answer Details
(a) What is meant by a food chain [2]. A sequence showing the feeding relationships between organisms [1], showing the flow of energy from a producer through a series of consumers [1].
(b) How the concentration of compound Z changes along the chain [2]. The concentration increases along the chain [1], from the algae up to the fish-eating bird, that is from 0.04 ppm to 32.0 ppm [1].
(c) Why the concentration increases at each higher level [3]. Compound Z is not broken down and not excreted [1], so it is stored and builds up in the tissues of each organism [1]; each consumer eats many organisms from the level below, so the compound accumulates and becomes more concentrated at each step (bioaccumulation/biomagnification) [1].
(d) How many times greater the bird's concentration is than the algae's [2].
\[\frac{32.0}{0.04}=800\]So the concentration in the bird is 800 times greater than in the algae: \(\dfrac{32.0}{0.04}\) [1] \(=800\) times [1].
(e) Two harmful effects on the birds [2]. Any two of: death or reduced numbers; reduced breeding success/thin eggshells; general poisoning or illness [2], because the highest, most toxic concentration builds up in the top consumer.
(f) The top consumer [1]. The fish-eating bird [1], as nothing in this chain feeds on it.
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