(a) (i) State the word equation for photosynthesis.
(ii) State the name of the green pigment that is needed for photosynthesis.
(b) A student investigated the rate of photosynthesis at different temperatures in potato plants.
Fig. 1.1 shows the results of the investigation.
Using the information in Fig. 1.1:
(i) State a temperature when the rate of photosynthesis is 30 arbitrary units.
(ii) State the rate of photosynthesis when the temperature is 15°C.
(iii) Describe the effect of increasing temperature on the rate of photosynthesis in potato plants.
(c) (i) Potato cells contain starch. State one use of starch in potato cells.
(ii) Starch is a large molecule made from many glucose molecules. State the name of one other carbohydrate that is found in plants and is made from glucose molecules.
(iii) Glucose can be combined with ions to make amino acids in plants. State the name of the ions needed to make amino acids.
(d) Photosynthesis is one process of the carbon cycle. State two other processes of the carbon cycle.
▶️ Answer/Explanation
Ans:
(a)(i) The word equation for photosynthesis is: \[ \text{carbon dioxide + water} \rightarrow \text{glucose + oxygen} \]
(a)(ii) The green pigment required is chlorophyll, which absorbs light energy.
(b)(i) From the graph, photosynthesis reaches 30 units at 17°C and 35°C.
(b)(ii) At 15°C, the rate is 21 ± 0.5 arbitrary units.
(b)(iii) The rate increases up to an optimum (24°C), then declines due to enzyme denaturation.
(c)(i) Starch acts as an energy store in potato cells.
(c)(ii) Another glucose-based carbohydrate is cellulose (for cell walls).
(c)(iii) Nitrate ions are combined with glucose to form amino acids.
(d) Other carbon cycle processes include respiration and combustion.
(a) Fig. 3.1 shows the apparatus used in an investigation to determine the effect of carbon dioxide on photosynthesis. Soda lime and potassium hydroxide solution both absorb carbon dioxide from the air.
Using the information in Fig. 3.1, predict which plant, A or B, will have the lowest rate of photosynthesis. Explain your prediction.
(b) Explain why a student used iodine solution to show that photosynthesis had occurred in a leaf.
(c) Fig. 3.2 shows the effect of light intensity on the rate of photosynthesis.
Using the information in Fig. 3.2:
(i) Identify the highest rate of photosynthesis.
…………………………….. arbitrary units
(ii) Calculate the difference in the rate of photosynthesis between 1 and 2 arbitrary units of light intensity.
…………………………….. arbitrary units
(iii) Identify the lowest light intensity that gives the maximum rate of photosynthesis.
…………………………….. arbitrary units
(iv) Explain why the graph rises as light intensity increases from 0 to 2 arbitrary units.
(d) Carbon dioxide is one of the raw materials needed for photosynthesis. State the other raw material.
(e) State the name of the cell structure where photosynthesis occurs.
(f) In another investigation, a student investigated the rate of photosynthesis at two temperatures in three different species of plant. The results are shown in Table 3.1.
(i) Calculate the percentage increase in the rate of photosynthesis for species 1 between 20°C and 30°C. Give your answer to three significant figures.
(ii) Tick (✓) one conclusion that can be made from the data in Table 3.1.
▶️ Answer/Explanation
(a) Plant A will have the lowest rate of photosynthesis because soda lime absorbs carbon dioxide, and carbon dioxide is essential for photosynthesis. Without sufficient CO2, the rate decreases.
(b) Iodine solution is used to test for starch, which is a product of photosynthesis. If the leaf turns blue-black, it confirms the presence of starch, indicating photosynthesis occurred.
(c)(i) The highest rate of photosynthesis is 210 arbitrary units (peak of the graph).
(c)(ii) The difference between 1 and 2 arbitrary units is 60 arbitrary units (150 at 2 units – 90 at 1 unit).
(c)(iii) The lowest light intensity for maximum rate is 4.0 arbitrary units (where the curve plateaus).
(c)(iv) The graph rises because light provides energy for photosynthesis. More light increases the rate until another factor (e.g., CO2) becomes limiting.
(d) The other raw material is water (H2O).
(e) Photosynthesis occurs in the chloroplast.
(f)(i) Percentage increase for species 1:
\[ \frac{42 – 26}{26} \times 100 = 61.5\% \quad (\text{to 3 s.f.}) \]
(f)(ii) The correct conclusion is: “The rate of photosynthesis increases with temperature for all three species.” (✓)