3.8 & 8.2 Photosynthesis Answers

ANSWERS 1 (68 Marks)
Higher level Biology Dulwich College Shanghai
Topic 3 (SL): Chemistry of Life
Topic 8 (HL): Respiration and Photosynthesis

8. Photosynthesis (SL)
1. State that photosynthesis involves the conversion of light energy into chemical energy.
2. State that light from the Sun is composed of a range of wavelengths (colours)
3. State that chlorophyll is the mainphotosynthetic pigment.
4. Outline the differences in absorption of red, blue and green light by chlorophyll (students should appreciate that pigments absorb certain colours of light. The remaining colours of light are reflected. It is not necessary to mention wavelengths or the structure responsible for the absorption).
5. State that light energy is used to produce ATP, and to splitwater molecules (photolysis) to form oxygen and hydrogen.
6. State that ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.
7. Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass.
8. Outline the effects oftemperature, light intensity and carbon dioxide concentration on the rate of photosynthesis (The shape of the graph is required).

2. Photosynthesis (HL)
1. Draw and label a diagram showing the structure of a chloroplast as seen in electron microscope.
2. State that photosynthesis consists of light-dependent and light-independent reactions (these should NOT be called ‘light’ and ‘dark’reactions).
3. Explain the light-dependent reactions. (include the photoactivation of photosystem II, photolysis of water, electron transport, cyclic and non-cyclic photophosphorylation, photoactivation of photosystem I, and reduction of NADP+.
4. Explain photophosphorylation in terms of chemiosmosis.
5. Explain the light-independent reactions. Include the roles of ribulose bisphosphate(RuBP), carboxylate, reduction of glycerate 3-phosphate (GP) to triose phosphate (TP), NADPH + H+, ATP, regeneration of RuBP, and subsequent synthesis of more complex carbohydrates.
6. Explain the relationship between the structure of the chloroplast and its function. Limit this to the large surface area of thylakoids for light absorption, the small space inside thylakoids for accumulation ofprotons, and the fluid stroma for the enzymes of the Calvin cycle.
7. Explain the relationship between the action spectrum and the absorption spectrum of photosynthetic pigments in green plants. (A separate spectrum for each pigment is NOT required).
8. Explain the concept of limiting factors in photosynthesis with reference to light intensity, temperature and concentration of carbondioxide.

Paper 1
Multiple Choice (8 Marks)
1. Which two colours of light does chlorophyll absorb most?
A. Red and yellow
B. Green and blue
C. Red and green
D. Red and blue

2. What is needed in photosynthesis to convert carbon dioxide into organic molecules?
A. Light and hydrogen from the splitting of water
B. Light and oxygen from the splitting of water
C. ATPand hydrogen from the splitting of water
D. ATP and oxygen from the splitting of water

3. How is the proton gradient generated in chloroplasts during photosynthesis?
A. Flow of electrons from carrier to carrier in the thylakoid membrane causes pumping of protons across the thylakoid membrane.
B. Light causes protons to flow through protein channels in the thylakoid membrane.C. Light splits water molecules in the stroma, causing the release of protons.
D. Protons are pumped across the thylakoid membrane using energy from ATP.

4. Why is the action spectrum for photosynthesis similar to the absorption spectra of photosynthetic pigments?
A. Photosynthetic pigments have the same optimum temperature as the enzymes used in photosynthesis.
B. Plants...