HL questions Flashcards
- Explain the effect of light intensity and temperature on the rate of photosynthesis. 8 marks
light:
affects the light-dependent stage;
at low intensities insufficient ATP;
and insufficient NADPH + H+ produced;
this stops the Calvin cycle operating (at maximum rate);
temperature:
affects light-independent stage / Calvin cycle;
temperature affects enzyme activity;
less active at low temperatures / maximum rate at high temperatures;
but will then be denatured (as temperature rises further);
- Explain photophosphorylation in terms of chemiosmosis. 8 marks
chemiosmosis is synthesis of ATP coupled to electron transport and proton movement
photophosphorylation is the production of ATP with energy from light
light energy causes photolysis/splitting of watter
electrons energized (from chlorophyll)/photoactivation
photolysis provides (replacement) electrons for those lost from excited chlorophyll
photolysis provides protons/H+ (for thylakoid gradient)
electron transport (carriers on membrane of thylakoid)
causes pumping of protons/H+ across thylakoid membrane/ into thylakoid space
protons/H+ accumulate in thylakoid space/proton gradient set up
protons/H+ move down concentration gradient
into stroma
flow through ATPase/synthetase
leading to ATP formation
- Explain why the light-independent reactions of photosynthesis can only continue for a short time in darkness. 6 marks
- Explain why the light-independent reactions of photosynthesis can only continue for a short time in darkness. 6 mark
light independent reaction involve ATP/NADPH + H+ / intermediates which are made in light dependent reactions
supply of ATP/NADPH + H+ / intermediates used up / runs out in the dark
ATP and NADPH + H+
GP therefore not reduced / converted to triose phosphate
RuBP therefore not regenerated
carbon dioxide fixation therefore stops
GP accumulates
stomata close in the dark
carbon dioxide is therefore not absorbed
. Explain the role of water in photosynthesis. 4 marks
water is a substrate / reactant / raw material / for photosynthesis / equation for photosynthesis
water is a source of electrons
to replace those lost by chlorophyll / photosystem II
water is a source of H+ needed to produce NADPH + H+
photolysis / splitting / breaking of water
water for non-cyclic photophosphorylation / ATP production
Autotroph vs heterotroph
Autotrophs are known as producers because they are able to make their own food from raw materials and energy. Examples include plants, algae, and some types of bacteria. Heterotrophs are known as consumers because
