Topic: Photosynthesis

light: rate of photosynthesis increases as light intensity increases photosynthetic rate reaches plateau at high light intensities CO2: rate of photosynthesis increases as carbon dioxide concentration increases photosynthetic rate reaches plateau at high carbon dioxide concentrations temperature: rate of photosynthesis increases with increase in temperature up to optimal level / maximum high temperatures reduce the rate of photosynthesis Some of the above points may be achieved by means of annotated diagrams or graphs.

CO2 + H2O –> (CH2O)n + O2/ suitable photosynthesis equation amount of CO2 absorbed (per unit time) can be measured increase in biomass (per unit time) can be measured O2 excretion (per unit time) can be measured methods for measuring the above: volume of O2 (bubbles) produced per unit time can be measured dry mass can be measured increase in starch concentration in leaves (as measured by iodine) use of pH indicator can monitor CO2 uptake in water the rate of photosynthesis measured is relative because some of the CO2 is produced by the plant internally through respiration the rate of photosynthesis measured is relative because some of the carbohydrates are used internally by the plan for respiration

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 water is transparent so photosynthesis can take place underwater / light can penetrate to chloroplasts

both light and temperature can be limiting factors; other factors can be limiting; graph showing increase and plateau with increasing light / description of this; graph showing increase and decrease with increasing temperature / description of this; 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); Award 5 max if only one condition is discussed.

(chlorophyll/antenna) in photosystem II absorbs light; absorbing light/photoactivation produces an excited/high-energy/free electron; electron passed along a series of carriers; reduction of NADP / generates NADPH + H+ ; absorption of light in photosystem II provides electron for photosystem I; photolysis of water produces 2 H /O ; called non-cyclic photophosphorylation; in cyclic photophosphorylation electron returns to chlorophyll; generates ATP by H+ diffusing across thylakoid membrane / by chemiosmosis / through ATP synthetase/synthase;

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 water 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

chlorophyll / photosystem absorbs light electron raised to higher energy level / photoactivated splitting of water/photolysis replaces electron passing of excited electrons between chlorophyll molecules in photosystems electron passed from photosystem II to carriers (in thylakoid membrane) production of ATP in this way is called photophosphorylation electron causes pumping of protons into the thylakoid proton gradient used by ATPase to drive ATP production electron passes to photosystem I at end of carrier chain electron re-excited and emitted by photosystem I electron passed to / used to reduce NADP+ NADPH + H+ / reduced NADP produced cyclic photophosphorylation using photosystem I electron and ATPase only Accept any of the above points if clearly drawn and correctly labelled in a diagram.

Award 1 mark for any of the below; up to a maximum of 8 marks) reactions take place in the stroma carbon dioxide reacts with RuBP catalysed by RuBP carboxylase GP formed GP converted to triose phosphate reduction reaction involving use of NADPH + H+ energy from ATP also needed from this conversion triose phosphate converted to glucose(phosphate)/starch RuBP regenerated from triose phosphate Calvin cycle

Award 1 mark for any of the below; up to a maximum of 6 marks) 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

light-independent reaction fixes CO2 to make glycerate 3-phosphate to triose phosphate / phosphoglyceraldehyde /glyceraldehyde 3-phosphate using NADPH ATP needed to regenerate RuBP ATP is made in light-dependent reactions light causes photoactivation / excitation of electrons flow of electrons causes pumping of protons into thylakoid membrane electrons are passed to NADP/NADP+ NADPH produced in the light dependent reactions

light-dependent reaction: 3 max chlorophyll absorbs light (energy)/photons electron activated/excited electron passed down electron carriers ATP produced NADP+ reduced/ reduced NADP produced/ NADPH produced light-independent reaction: 3 max CO2 fixed by/reacts with 5C molecule (RuBP) rubisco/ribulose bisphosphate carboxylase/RuBP carboxylase catalyses reaction (two) 3C molecules/ glycerate 3-phosphate/GP produced reduced NADP and ATP used to reduce glycerate 3-phosphate/GP triose phosphate/TP produced

similarities: both are double membrane organelles both contain DNA both contain ribosomes both have an electron transport chain both produce ATP by chemiomosis both contain ATP synthase /ATPase 3 max for labelled diagrams without the similarities stated chloroplast: site of photosynthesis third membrane system / thylakoid membranes photosynthetic pigments/chlorophyll to absorb light light generated ATP production H+ gradient across thylakoid membrane mitochondrion: site of respiration ATP production by oxidation of organic molecules / fats / amino acids H+ gradient across inner membrane