Fig. 1 shows a city park food web. Fallen leaves are eaten by earthworms and decomposed by microorganisms. Blackbirds feed on earthworms. The park team meas...
Question 1 Report
Fig. 1 shows a city park food web. Fallen leaves are eaten by earthworms and decomposed by microorganisms. Blackbirds feed on earthworms. The park team measured the mean number of earthworms in soil samples before and after leaves were removed from one area. Table 1 shows the data.
| sampling time | mean earthworms per 0.25 m2 |
|---|---|
| before leaf removal | 18 |
| six weeks after removal | 7 |
(a) What is the decrease in mean number of earthworms? [1]
(b) Describe how removing leaves could affect the number of blackbirds. [1]
(c) Explain why dead leaves are important in the carbon cycle. [2]
(d) Give one reason why the team should take samples from several places in each area. [1]
Fig. 1 shows a woodland log with brackets of fungus growing from it. Rangers estimated the amount of dead wood remaining in two woodland areas over one year. One area was shaded by dense evergreen trees and the other was open. Table 1 shows the percentage decrease in dry mass of similar logs.
| woodland area | decrease in log dry mass / % |
|---|---|
| dense evergreen shade | 11 |
| open woodland | 24 |
(a) What organism in Fig. 1 is a decomposer? [1]
(b) Describe the difference between the two woodland areas. [1]
(c) Give two reasons why the open area could have a faster rate of decay. [2]
Answer Details
Labelled answer diagram:
Leaves, earthworms and carbon cycling
- \[18-7=11\] The decrease is 11 earthworms per 0.25 m2. [1]
- Blackbird numbers may decrease because fewer earthworms are available as food. [1]
- Dead leaves contain carbon that was fixed by photosynthesis. As decomposers break leaves down and respire, carbon is returned as carbon dioxide to the air, or transferred into soil carbon compounds. [2]
- Several samples are needed because soil organisms are unevenly distributed. This improves reliability. [1]
Decay of logs
- Fungus, or fungi, is the decomposer. [1]
- Logs in open woodland lost a greater percentage of dry mass: 24% compared with 11% in dense evergreen shade. [1]
- The open area could have a faster decay rate because it is warmer, receives more rain or is wetter, has more oxygen reaching the logs, or has conditions that favour microorganism growth. Any two are accepted. [2]
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