Biology 9700 · AS & A Level · Investigation of limiting factors
Investigation of limiting factors — practice question
Experiments were performed to investigate how light intensity affects the rate of photosynthesis in a species of the unicellular protoctist, $\textit{Chlorella}$. A suspension of $\textit{Chlorella}$ cells was used.
Carbon dioxide uptake was taken as a measure of the rate of photosynthesis.
• The $\textit{Chlorella}$ suspension was illuminated at a light intensity of 3 lux for 20 seconds.
• At the end of the 20 second illumination period, the carbon dioxide uptake by $\textit{Chlorella}$ was measured.
• The experiment was then repeated at 6 lux, 9 lux, 12 lux and in a dark room.
• Throughout the experiment, the suspension was kept at a temperature of $20\,^\circ\text{C}$.
Table 7.1 presents the experimental results.
(a(i))[1]
Use Table 7.1 to calculate the rate of photosynthesis at a light intensity of 6 lux. Enter your calculated value in the space provided in Table 7.1.
(a(ii))[3]
Plot a graph of the data in Table 7.1 on the grid in Fig. 7.1 to show how light intensity affects the rate of photosynthesis. Draw a curve and extend it to show what the rate of photosynthesis would be if the experiment were done at $18\ \text{lux}$.
(a(iii))[2]
Suggest an explanation for the shape of your curve from $12\ \text{lux}$ to $18\ \text{lux}$.
(b)[4]
In photophosphorylation, photoactivation of chlorophyll leads to ATP synthesis. Describe how photoactivation of chlorophyll results in the synthesis of ATP in photophosphorylation.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “rates correctly worked out from CO$_2$ uptake data” …