What is meant by the term gas exchange?
Fish use gills as a gas exchange surface. Suggest three ways in which fish gills are adapted for efficient gas exchange.
Students investigated the effect of water temperature on the breathing rate of goldfish. They placed fish of the same mass in tanks of water at different temperatures. They measured the breathing rate by counting the number of opercular (gill cover) movements per minute.
The results are shown in the table below:
| Water temperature (∘C^{\circ}\text{C}∘C) | Trial 1 | Trial 2 | Trial 3 | Trial 4 | Average |
|---|---|---|---|---|---|
| 5 | 12 | 10 | 11 | 11 | 11 |
| 10 | 22 | 25 | 24 | 25 | 24 |
| 15 | 41 | 38 | 39 | 42 | X |
| 20 | 62 | 59 | 60 | 63 | 61 |
| 25 | 86 | 84 | 85 | 85 | 85 |
Calculate the missing average, XXX, for a water temperature of 15∘C15^{\circ}\text{C}15∘C.
Explain how these results support the hypothesis that warmer water contains less dissolved oxygen than colder water.
The students controlled the mass of the fish. Explain why this is needed to ensure a valid investigation.
Suggest two other factors that the students should have controlled in this investigation.
16 exam-style questions on Edexcel IGCSE Biology Gas exchange. Each one has a worked solution and a mark scheme showing where the marks go.