Chloroplasts and the overall reaction of photosynthesisEdexcel A-Level Biology A: Mind map

Exam questions on Chloroplasts and the overall reaction of photosynthesis

1. A student examines an electron micrograph of a palisade mesophyll cell from a spinach leaf. Each chloroplast is about 5 µm long and is surrounded by two membranes. Inside, there are flattened membrane-bound sacs arranged in stacks, linked by thin membranes, in a surrounding fluid that contains starch grains and a small circular piece of DNA.
   Explain how the stacking of the thylakoids into grana is related to the role of the chloroplast in the light-dependent reactions.2 marks
2. Two experiments were carried out with the alga Chlorella. In experiment 1 the water supplied contained the heavy isotope oxygen-18 (¹⁸O), and the carbon dioxide contained only oxygen-16 (¹⁶O). In experiment 2 the water contained only ¹⁶O and the carbon dioxide contained ¹⁸O. In each experiment the algae were illuminated and the oxygen gas that was released was analysed to find which isotope it contained.
   Use the overall equation for photosynthesis to explain what these experiments show about the origin of the oxygen that is released and what happens to the hydrogen from water.2 marks
3. A biologist is preparing a talk on chloroplasts in the leaf cells of green plants. Chloroplasts are the site of photosynthesis, which uses light energy to make glucose from carbon dioxide and water.
   Describe the structure of a chloroplast.3 marks