A respirometer is apparatus used to measure the respiration rate of living tissue, such as germinating peas.
A simple respirometer is shown in Fig. 6.1.
A student investigated how temperature affects the respiration rate of germinating peas.
The student assembled the respirometer as in Fig. 6.1 and put it in a water-bath at $10^\circ\text{C}$. After five minutes, the student used the syringe to move the coloured liquid on the right-hand side of the U-shaped tube until it was level with $0\ \text{cm}$ on the ruler. The timer was started immediately. As the germinating peas used up oxygen, the coloured liquid in the U-shaped tube moved. The student measured how far the coloured liquid moved after 20 minutes. The experiment was repeated at $20^\circ\text{C}$, $30^\circ\text{C}$, $40^\circ\text{C}$ and $50^\circ\text{C}$.
(a)[1]
State the role of the potassium hydroxide solution in this investigation.
(b)[2]
Suggest how the validity of the results could be judged.
(c)[1]
Explain why the respirometer was kept in the water-bath for five minutes before the experiment began.
(d)[2]
Table 6.1 shows the rate of movement of the coloured liquid in the U-shaped tube, calculated from the results. Plot a graph of the results in Table 6.1 on the grid in Fig. 6.2. Draw a curved line of best fit.
(e)[3]
The rate at which the coloured liquid moves is linked to the respiration rate. Explain the effect of temperature on the respiration rate shown in Table 6.1 and Fig. 6.2.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Removes carbon dioxide released by the peas” …