A sealed research habitat contains algae and is kept in light. Before animals are added to the main habitat, scientists place the same number of animals in test chambers containing gas from the habitat.
The table shows the results after the animals had been in each test chamber for 24 hours.
| Day gas was collected | Oxygen in the gas in % | Animals still alive after 24 hours in % |
|---|---|---|
| 12 | 6.5 | 20 |
| 18 | 8.4 | 90 |
Explain why the results support waiting until day 18 before adding animals to the main habitat.
Explain how the percentage of carbon dioxide in the main habitat is expected to change between day 12 and day 18.
79 exam-style questions on AQA GCSE Chemistry 9.1 The composition and evolution of the Earth's atmosphere, covering 9.1.1 The proportions of different gases in the atmosphere, 9.1.2 The Earth's early atmosphere, 9.1.3 How oxygen increased, and 9.1.4 How carbon dioxide decreased. Each one has a worked solution and a mark scheme showing where the marks go.