BiologyCode 9700
Photosynthesis as an energy transfer process
What this topic asks you to be able to do
- describe the link between chloroplast structure, as depicted in diagrams and electron micrographs, and the job it performs
- account for the way ATP and reduced NADP carry energy from the light-dependent stage into the light-independent stage (Calvin cycle) of photosynthesis, where that energy is used to build complex organic molecules
- state that, inside a chloroplast, the light-dependent stage takes place in the thylakoids (the thylakoid membranes and thylakoid spaces), stacked together as grana, while the light-independent stage takes place in the stroma
- describe what chloroplast pigments (chlorophyll a, chlorophyll b, carotene and xanthophyll) do when they absorb light inside thylakoids
- interpret the absorption spectra of chloroplast pigments plus the action spectra linked to photosynthesis
- describe and employ chromatography, which allows chloroplast pigments to be separated and identified, citing Rf values when identifying them
- state that the light-dependent stage of photosynthesis involves both cyclic and non-cyclic photophosphorylation
- account for the following in cyclic photophosphorylation: only photosystem I (PSI) takes part, chlorophyll undergoes photoactivation, and ATP is synthesised
- explain that non-cyclic photophosphorylation involves both photosystem I (PSI) and photosystem II (PSII), that chlorophyll is photoactivated, that the photolysis of water is catalysed by the oxygen-evolving complex, and that ATP and reduced NADP are both synthesised
- explain that, in photophosphorylation: energetic electrons give out energy as they move along the electron transport chain (the carriers' details are not expected); this energy is used to move protons across the thylakoid membrane; and the protons flow back out of the thylakoid space into the stroma by facilitated diffusion through ATP synthase, which provides energy to make ATP (ATP synthase need not be known in detail)
- outline the Calvin cycle's three main stages: carbon dioxide is fixed by rubisco, which catalyses its joining to ribulose bisphosphate (RuBP), a 5C compound, yielding two molecules of the 3C compound glycerate 3-phosphate (GP); GP is then reduced, in reactions needing ATP and reduced NADP, to triose phosphate (TP); and TP is used to regenerate RuBP, a step that also needs ATP
- state that intermediates of the Calvin cycle are used to make other molecules, limited to GP, from which some amino acids are made, and TP, from which carbohydrates, lipids and amino acids are made