13. Photosynthesis
13.1 Photosynthesis as an energy transfer process
Light energy absorbed by chloroplast pigments in the light dependent stage of photosynthesis is used to drive reactions of the light independent stage that produce complex organic compounds. Chromatography is used to identify chloroplast pigments and was also used to identify the intermediates in the Calvin cycle.
describe the relationship between the structure of chloroplasts, as shown in diagrams and electron micrographs, and their function
explain that energy transferred as ATP and reduced NADP from the light-dependent stage is used during the light-independent stage (Calvin cycle) of photosynthesis to produce complex organic molecules
state that within a chloroplast, the thylakoids (thylakoid membranes and thylakoid spaces), which occur in stacks called grana, are the site of the light-dependent stage and the stroma is the site of the light-independent stage
describe the role of chloroplast pigments (chlorophyll a, chlorophyll b, carotene and xanthophyll) in light absorption in thylakoids
interpret absorption spectra of chloroplast pigments and action spectra for photosynthesis
describe and use chromatography to separate and identify chloroplast pigments (reference should be made to Rf values in identification of chloroplast pigments)
state that cyclic photophosphorylation and non-cyclic photophosphorylation occur during the light-dependent stage of photosynthesis
explain that in cyclic photophosphorylation:
• only photosystem I (PSI) is involved
• photoactivation of chlorophyll occurs
• ATP is synthesised
explain that in non-cyclic photophosphorylation:
• photosystem I (PSI) and photosystem II (PSII) are both involved
• photoactivation of chlorophyll occurs
• the oxygen-evolving complex catalyses the photolysis of water
• ATP and reduced NADP are synthesised
explain that during photophosphorylation:
• energetic electrons release energy as they pass through the electron transport chain (details of carriers are not expected)
• the released energy is used to transfer protons across the thylakoid membrane
• protons return to the stroma from the thylakoid space by facilitated diffusion through ATP synthase, providing energy for ATP synthesis (details of ATP synthase are not expected)
11. outline the three main stages of the Calvin cycle:
• rubisco catalyses the fixation of carbon dioxide by combination with a molecule of ribulose bisphosphate (RuBP), a 5C compound, to yield two molecules of glycerate 3-phosphate (GP), a 3C compound
• GP is reduced to triose phosphate (TP) in reactions involving reduced NADP and ATP
• RuBP is regenerated from TP in reactions that use ATP
12. state that Calvin cycle intermediates are used to produce other molecules, limited to GP to produce some amino acids and TP to produce carbohydrates, lipids and amino acids
Structure of a chloroplast
Light dependent stage
Light independent stage
13.2 Investigation of limiting factors
Environmental factors influence the rate of photosynthesis. Investigating these shows how they can be managed in protected environments used in crop production.
state that light intensity, carbon dioxide concentration and temperature are examples of limiting factors of photosynthesis
explain the effects of changes in light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis
describe and carry out investigations using redox indicators, including DCPIP and methylene blue, and a suspension of chloroplasts to determine the effects of light intensity and light wavelength on the rate of photosynthesis
describe and carry out investigations using whole plants, including aquatic plants, to determine the effects of light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis