A level Biology B · Edexcel 9BI0 · Topic 5C
Photosynthesis
Key points
- Chloroplasts have thylakoids stacked in grana (light-dependent reactions) surrounded by the stroma (light-independent reactions).
- Light-dependent reactions: light excites electrons in chlorophyll in photosystems; photolysis of water replaces them, releasing O; electron flow makes ATP (photophosphorylation) and reduced NADP.
- Calvin cycle: RuBisCO fixes CO with RuBP to make two GP; GP is reduced to GALP using ATP and reduced NADP; most GALP regenerates RuBP, the rest makes glucose and other molecules.
- Limiting factors: light intensity, CO concentration and temperature; the factor in shortest supply limits the rate.
- Chromatography separates photosynthetic pigments; = distance moved by pigment ÷ distance moved by solvent.
- Accessory pigments absorb different wavelengths, widening the range of light used.
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Photosynthesis converts light energy into chemical energy stored in organic molecules. It happens in two linked stages in the chloroplast: the light-dependent reactions make ATP and reduced NADP, and the light-independent reactions use them…
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