Topic: Photosynthesis Flashcards
Outline the effect of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis. 6 marks
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.
Explain how the rate of photosynthesis can be measured. 7 marks
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
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
water is transparent so photosynthesis can take place underwater / light can penetrate to chloroplasts
Explain the effect of light intensity and temperature on the rate of photosynthesis. 8 marks
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.
Outline the light-dependent reactions of photosynthesis. 6 marks
(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;
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 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
Explain the reactions involving the use of light energy that occur in the thylakoids of the chloroplast. 8 marks
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.
Outline the light-independent reactions of photosynthesis. 8 marks
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
Explain why the light-independent reactions of photosynthesis can only continue for a short time in darkness. 6 marks
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
Explain how the light-independent reactions of photosynthesis rely on light-dependent reactions. 8 marks
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
Outline the formation of carbohydrate molecules in photosynthesis starting from the absorption of light energy. 6 marks
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
Compare the structure of a chloroplast and a mitochondrion in relation to function. 8 marks
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
