The table below shows gas measurements from a school anaerobic digester. Food waste and animal manure were placed in the digester without oxygen. Fig. 1 sho...
Question 1 Report
The table below shows gas measurements from a school anaerobic digester. Food waste and animal manure were placed in the digester without oxygen. Fig. 1 shows the sealed tank and a pipe leading to a gas bag. The gas can be burned to heat water for washing equipment.
| day | methane collected / dm3 |
|---|---|
| 1 | 0.4 |
| 3 | 1.8 |
| 5 | 3.1 |
| 7 | 2.0 |
(a) When was the greatest volume of methane collected? [1]
(b) What is the main source of energy in the methane? [1]
(c) Describe one environmental advantage of using this methane rather than coal. [2]
The table below shows carbon stores measured in a restored peatland. Fig. 1 shows moss plants growing above waterlogged peat. The site manager blocked drainage channels in 2022 so that the peat remained wet. Carbon was measured in samples from the top 20 cm of soil.
| year | carbon in topsoil / kg m-2 |
|---|---|
| 2021 | 8.6 |
| 2022 | 8.8 |
| 2023 | 9.4 |
| 2024 | 10.1 |
(a) Describe the overall change in carbon stored from 2021 to 2024. [1]
(b) What gas is removed from the air by moss cells during photosynthesis? [1]
(c) Explain why keeping peat waterlogged can reduce the rate of decay. [2]
(d) Give one reason why repeating soil samples improves the reliability of the data. [1]
Answer Details
Labelled answer diagram:
Anaerobic digester
- The greatest volume of methane was collected on day 5, when 3.1 dm3 was collected. [1]
- The energy stored in methane is chemical energy. [1]
- Using methane uses waste that would otherwise decay. It can reduce fossil-fuel use, and its carbon was recently fixed by plants rather than released from long-stored fossil carbon. [2]
Peatland carbon store
- Carbon stored increased from 8.6 kg m-2 in 2021 to 10.1 kg m-2 in 2024. [1]
- Moss cells remove carbon dioxide from the air during photosynthesis. [1]
- Waterlogging limits oxygen availability. This reduces aerobic respiration by decomposers, slowing decay. [2]
- Repeating samples reduces the effect of anomalous samples and allows a mean to be calculated, improving reliability. [1]
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