1. A student placed a plant in the dark for 2 days to ensure that no starch would be present in the leaves. After this time, she cut leaf discs from the plant. She put three leaf discs in each of eight transparent plastic syringes with 10 cm3 of water. In addition, each syringe contained 10 m3 of gas, either air containing carbon dioxide or nitrogen with carbon dioxide. Four syringes were placed in the light and four in the dark. The table below shows the conditions used in each syringe.
After 24 hours the student tested the leaf discs for the presence of starch. The table below shows the results.
The student removed the pigments from the leaves before testing for starch. Describe how the student could test a decolourised leaf for starch.
Answer
She could add iodine solution (in KI). If starch is present, it will turn blue-black.
2. Explain the results for syringes A-D.
Answer
In all these syringes, starch is produced through photosynthesis (since CO2 is present and light is available). In syringe A, ATP from respiration can be used to convert glucose solution into starch.
3. Explain the results for syringes E-H.
Answer
Leaves in syringe E use ATP from respiration to make starch from the glucose solution. Leaves in syringe F have no oxygen, so they cannot use ATP from respiration to store starch, even though glucose is present. Leaves in syringes G and H cannot photosynthesise and have no glucose to convert into starch.
4. The figure below summarises the main features of photosynthesis and respiration. Name the part of the cell where stage B, stage D and stage E take place.
Answer
stage B - stroma of the chloroplast,
5. Name molecules P, Q and S.
Answer
P = water,
6. Name gas X and stage D.
Answer
gax X = oxygen,
7. Explain the importance of molecule R in the process of photosynthesis.
Answer
Reduces GP (glycerate-3-phosphate) to TP (triose phosphate) in light independent stage.
8. The enzyme succinic dehydrogenase converts succinate to fumarate in the Krebs cycle. Malonate inhibits the enzyme succinic dehydrogenase. The structure of malonate and succinate are shown in the figure below. Identify what kind of inhibitor malonate is.
Answer
Malonate is a competitive inhibitor. It has a similar shape to succinate and fits into the active site of succinic dehydrogenase, preventing the enzyme from binding to its normal substrate.
9. Complete the table below.
Answer
