Define the term gas exchange.
Mayfly nymphs (Ephemera danica) rely on abdominal tracheal gills for gas exchange. Describe three structural features of these gills that adapt them for rapid and efficient gas exchange.
A group of students investigated the effect of water temperature on the ventilation rate of mayfly nymphs. They placed nymphs of the same body length in chambers of water at different temperatures. They measured the ventilation rate by counting the number of abdominal gill beats 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 |
|---|---|---|---|---|---|
| 8 | 28 | 32 | 29 | 31 | 30 |
| 12 | 54 | 51 | 55 | 52 | 53 |
| 16 | 76 | 73 | 79 | 76 | Y |
| 20 | 104 | 101 | 105 | 102 | 103 |
| 24 | 138 | 135 | 136 | 139 | 137 |
Calculate the missing average, YYY, for a water temperature of 16 ∘C16\text{ }^{\circ}\text{C}16 ∘C.
Explain how these results support the hypothesis that warmer water contains less dissolved oxygen than colder water.
The students selected nymphs of the same body length. Explain why this control is necessary to ensure a valid investigation.
Suggest two other variables that the students should have controlled in this investigation.
