Author: Philip Colls
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Photosynthesis booklet revision questions    NAME:
Q1.
A student investigated the effect of different wavelengths of light on the rate of photosynthesis. She used the apparatus shown in Figure 1.
Figure 1
 
(a)     What measurements should the student have taken to determine the rate of photosynthesis?
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(1)
(b)     Other than temperature and pH, give two factors which should be kept constant during this investigation.
1. _________________________________________________________________
2. _________________________________________________________________
(2)
(c)     The student did not use a buffer to maintain the pH of the solution. 
Explain what would happen to the pH of the solution during this investigation.
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(2)

(d)     Figure 2 shows the student’s results.
Figure 2
 
Suggest and explain why the rate of photosynthesis was low between 525 nm and 575 nm wavelengths of light.
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________________________________________________________________ (2)
(Total 7 marks)
Q2.
The diagram shows the light-dependent reactions of photosynthesis.
 
(a)     In which part of a chloroplast do the light-dependent reactions occur?
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(b)     Name the substances in boxes A, B and C.
A ________________________________
B _______________ + _______________
C ________________________________					(3)
(c)     Use information in the diagram to explain
(i)      the role of chlorophyll in photolysis;
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(ii)     how the energy of light is converted into chemical energy in the light-dependent reactions.
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(d)     In an investigation, single-celled algae were kept in bright light and were supplied with carbon dioxide containing radioactive carbon atoms. After 300 seconds, the carbon dioxide supply was turned off. The graph shows how the concentrations of carbon dioxide, glycerate 3-phosphate (GP) and ribulose bisphosphate (RuBP) changed.
 
(i)      Explain why, between 0 seconds and 300 seconds, the concentration of radioactive GP remained constant.
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(ii)     Explain why, between 300 seconds and 380 seconds, the concentration of radioactive RuBP increased.
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(Total 15 marks)
Q3. During photosynthesis, carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate (GP). This reaction is catalysed by the enzyme Rubisco. Rubisco can also catalyse a reaction between RuBP and oxygen to form one molecule of GP and one molecule of phosphoglycolate. Both the reactions catalysed by Rubisco are shown in Figure 1.
Figure 1
 
(a)     (i)      Where exactly in a cell is the enzyme Rubisco found?
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(1)
(ii)     Use the information provided to give the number of carbon atoms in one molecule of phosphoglycolate.
 
(1)

(b)     Scientists investigated the effect of different concentrations of oxygen on the rate of absorption of carbon dioxide by leaves of soya bean plants. Their results are shown in Figure 2.
Figure 2
 
                                Concentration of oxygen / %
Use Figure 1 to explain the results obtained in Figure 2.
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(2)
(c)     Use the information provided and your knowledge of the light-independent reaction to explain why the yield from soya bean plants is decreased at higher concentrations of oxygen. Phosphoglycolate is not used in the light-independent reaction.
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(Extra space)________________________________________________________
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(Total 7 marks)
Q4. (a)     The concentrations of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours. Use your knowledge of photosynthesis to describe these changes and explain why they occur.

(5)
(b)     In the light-independent reaction of photosynthesis, the carbon in carbon dioxide becomes carbon in triose phosphate. Describe how.

(5)
(Total 10 marks)
Q5. The diagram represents some of the light-independent reactions of photosynthesis.
 
(a)     Describe the light-independent reactions of photosynthesis and explain how they allow the continued synthesis of hexose sugars.

(6)
(b)     Describe the role of electron transport chains in the light-dependent reactions of photosynthesis.

(6)
(c)     Explain why the increase in the dry mass of a plant over twelve months is less than the mass of hexose produced over the same period.

(3)
(Total 15 marks)
Q6. The percentage of light absorbed by an aquatic plant was measured when it was exposed to different wavelengths. The rate of photosynthesis was also measured at each wavelength of light. The results are shown in the graph.
 
(a)     Describe and explain the relationship between light absorption and the rate of photosynthesis for the wavelengths of light between 410 nm and 500 nm.
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(2)
(b)     Give one dependent variable you could measure in order to determine the rate of photosynthesis in an aquatic plant.
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(1)
(c)     Use the graph to identify the range of wavelengths of light that would be green in colour.
Give a reason for your answer.
Wavelengths __________ to __________ nm
Reason ____________________________________________________________
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(d)     A suspension of chloroplasts was isolated from an aquatic plant and a reagent was added. The reagent is blue when oxidised and is colourless when reduced.
(i)      The suspension of chloroplasts in blue reagent was exposed to sunlight. The blue colour disappeared. Use your knowledge of the light-dependent reactions of photosynthesis to explain why.
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(ii)     Another suspension of chloroplasts was set up as before. Small quantities of ADP and phosphate ions were added and then the tube was exposed to light. The blue colour disappeared more quickly. Explain why.
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(Total 9 marks)
Q7. A student isolated chloroplasts from spinach leaves into a solution to form a chloroplast suspension. He used the chloroplast suspension and DCPIP solution to investigate the light-dependent reaction of photosynthesis. DCPIP solution is blue when oxidised and colourless when reduced.
The student set up three test tubes as follows:
•   Tube 1 – 1 cm^3 of solution without chloroplasts and 9 cm^3 of DCPIP solution in light.
•   Tube 2 – 1 cm^3 of chloroplast suspension and 9 cm^3 of DCPIP solution in darkness.
•   Tube 3 – 1 cm^3 of chloroplast suspension and 9 cm^3 of DCPIP solution in light.
The student recorded the colour of the DCPIP in each of the tubes at the start and after the tubes had been left at 20 °C for 30 minutes.
His results are shown in the table.
 
Tube | Colour of DCPIP in tube
| At start | After 30 minutes
1 | blue | blue
2 | blue | blue
3 | blue | colourless

(a)     The solution that the student used to produce the chloroplast suspension had the same water potential as the chloroplasts. Explain why it was important that these water potentials were the same.
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(b)     Explain why the student set up Tube 1.
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(c)     Explain the results in Tube 3.
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(d)     The student evaluated the effectiveness of different chemicals as weed-killers by assessing their ability to prevent the decolourisation of DCPIP in chloroplast suspensions. He added different concentrations of each chemical to illuminated chloroplast suspensions containing DCPIP. He then determined the IC_50 for each chemical. The IC_50 is the concentration of chemical which inhibits the decolourisation of DCPIP by 50%.
Explain the advantage of the student using the IC_50 in this investigation.
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(e)     Explain how chemicals which inhibit the decolourisation of DCPIP could slow the growth of weeds.
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(Total 9 marks)
Q8.
Scientists investigated the effect of iron deficiency on the production of triose phosphate in sugar beet plants. They grew the plants under the same conditions with their roots in a liquid growth medium containing all the necessary nutrients. Ten days before the experiments, they transferred half the plants to a liquid growth medium containing no iron. The scientists measured the concentration of triose phosphate produced in these plants and in the control plants:
•        at the end of 6 hours in the dark
•        then for 16 hours in the light.
Their results are shown in the graph.
 
(a)     (i)      The experiments were carried out at a high carbon dioxide concentration. Explain why.
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(1)
(ii)     Explain why it was important to grow the plants under the same conditions up to ten days before the experiment.
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(1)
(iii)    The plants were left in the dark for 6 hours before the experiment. Explain why.
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(b)     Iron deficiency reduces electron transport. Use this information and your knowledge of photosynthesis to explain the decrease in production of triose phosphate in the iron-deficient plants.
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________________________________________________________________ (4)
(c)     Iron deficiency results in a decrease in the uptake of carbon dioxide. Explain why.
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_____________________________________________________(2) (Total 9 marks)
Q9. Beech trees have two types of leaves called sun leaves and shade leaves. Sun leaves grow on branches exposed to direct sunlight, shade leaves grow on branches exposed to light that has passed through leaves. An ecologist collected sun leaves and shade leaves from beech trees and determined the mean mass of each photosynthetic pigment in both types of leaf. His results are shown the table below.

Photosynthetic pigment

Mean mass of each pigment per m^2 of leaf area / μg
(± standard deviation)

| Sun leaves | Shade leaves
Chlorophyll a | 299.3 (± 2.1) | 288.9 (± 0.1)
Chlorophyll b | 290.7 (± 2.1) | 111.1 (± 0.1)
Chlorophyll c | 0.10 (± 0.01) | 0.07 (± 0.01)
(a)     Describe how you would present the data in the table as a graph.
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(2)
(b)     The ecologist collected shade leaves at random from a branch.
Suggest a method he could have used to collect shade leaves at random from a branch.
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(2)
(c)     The ecologist concluded that there is a significant difference between the amounts of chlorophyll b in sun leaves and shade leaves of beech trees.
Do you agree with this conclusion?
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(2)
(d)     Each type of chlorophyll is produced by a specific enzyme-controlled pathway.
Use this information to suggest how the same beech tree can produce more chlorophyll b in some leaf cells than others.
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(Total 8 marks)
Q10. Heat stress is a condition that often occurs in plants exposed to high temperatures for a prolonged period of time. Heat stress is a major factor in limiting the rate of photosynthesis.
(a)     Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction.
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(b)     Another effect of heat stress is a decrease in the activity of the enzyme rubisco. A decrease in the activity of an enzyme means that the rate of the reaction it catalyses becomes slower. A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis.
Explain why.
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(c)     Where precisely is rubisco found in a cell?
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Scientists investigated the effect of temperature on the activity of two enzymes isolated from the leaf cells of cotton plants.
•        Rubisco           •        Rubisco activase – an enzyme that activates rubisco
Figure 1 and Figure 2 show their results.

(d)     The scientists concluded that heat stress reduces the activity of rubisco in plant leaves by affecting rubisco activase.
Use all the information to evaluate their conclusion.
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(4)
(Total 9 marks)

Mark schemes
Q1.
(a)     Oxygen production / concentration and time.
Accept: oxygen volume / concentration
Reject: oxygen uptake
Neutral: reference to carbon dioxide uptake
1
(b)     1.      Intensity of light;
Accept: distance from light
2.      Amount / number / mass / species of algae / photosynthesising cells;
3.      Carbon dioxide (concentration / partial pressure);
4.      Time.
2 max
(c)     1.      (pH) increases;
Neutral: becomes more alkaline / less acidic
2.      As (more) carbon dioxide removed (for photosynthesis).
2
(d)     1.      Less absorption / (more) reflection (of these wavelengths of light);
Reject: no absorption or cannot absorb unless in context of green light.
Note: no green light absorbed or green light reflected = 2 marks.
2.      (Light required) for light dependent (reaction) / photolysis
Accept: for excitation / removal of electrons (from chlorophyll)
3.      (Represents) green light / colour of chlorophyll.
2 max
[7]
Q2.
(a)     Grana / thylakoids / lamellae;
1
(b)     A = oxygen / O_2
B = ADP and phosphate / P_i  / phosphoric acid / correct formula;
C = reduced NADP; ALLOW NADPH / NADPH_2 / NADPH + H^+
3
(c)     (i)      Absorbs light / energy;
Loses electrons / becomes positively charged / is oxidised;
Accepts electrons from water / from OH^– which causes more water 
to dissociate / pulls equilibrium to the right;
3
(ii)     Electrons raised to higher energy level / electrons excited;
Use of electron carriers / cytochromes / acceptors;
For production of ACT
[REJECT ‘energy production’]
3
(d)     (i)      GP formed from RuBP + CO_2;
GP → TP / sugar-phosphate / sugar / to RuBP;
GP formed at same rate as it is used;
3
(ii)     No CO_2 to combine with / not enough CO_2 to combine with RuBP
RuBP not changed into GP / TP RuBP reformed from GP / TP;
2
[15]
Q3.
(a)     (i)      Stroma (of chloroplasts);
Reject: stoma
1
(ii)     2;
1
(b)     1.      As oxygen (concentration) increases less Rubisco / RuBP reacts / binds with carbon dioxide;
1. Accept - as oxygen (concentration) increases more Rubisco / RuBP reacts / binds with oxygen
1. Accept – less GP / more phosphoglycolate formed as oxygen (concentration) increases
2.      Competitive inhibition / competition between oxygen and carbon dioxide for rubisco / enzyme / active site (therefore) less RuBP formed / regenerated (to join with carbon dioxide);
2. Accept oxygen and carbon dioxide are complementary to active site
2
(c)     1.      Less glycerate 3-phosphate / GP produced;
1. Accept one GP formed rather than two GP
2.      (Less) triose phosphate to form sugars / protein / organic (product) / any named photosynthetic product;
3.      Less RuBP formed / regenerated;
3. Accept RuBP takes longer to form
3
[7]
Q4.
(a)     1.      High concentration of carbon dioxide linked with night / darkness;
Accept: converse of low in day
2.      No photosynthesis in dark / night / light required for photosynthesis / light-dependent reaction;
Ignore references to rate of photosynthesis in day / night
Accept day = light
3.      (In dark) plants (and other organisms) respire;
Must be a reference to plants or all organisms
4.      In light net uptake of carbon dioxide by plants / plants use more carbon dioxide than they produce / rate of photosynthesis greater
than rate of respiration;
Do not allow converse for this point
Accept description of compensation point
5.      Decrease in carbon dioxide concentration with height;
Accept: converse of increase closer to ground
6.      At ground level fewer leaves / less photosynthesising
tissue / more animals / less light;
5 max
(b)     1.      Carbon dioxide combines with ribulose bisphosphate / RuBP;
2.      To produce two molecules of glycerate 3-phosphate / GP;
3.      Reduced to triose phosphate / TP;
4.      Requires reduced NADP;
5.      Energy from ATP;
This mark scheme is based on specification content. Accept alternate names such as NADPH
Credit relevant diagrams
Accept: description of ‘reduced’
5
[10]
Q5.
(a)     1       5C / RuBP combines with CO_2;
2       to form 3C compound / TP / GP;
3       using ATP;
4       and reduced NADP / eq;
5       2 molecules of 3C compound / TP / GP form hexose;
6       all RuBP is regenerated;
7       10 molecules of 3C / TP / GP form 6 molecules of 5C / RuBP;
6 max
(b)     1       electron transport chain accepts excited electrons;
2       from chlorophyll / photosystem;
3       electrons lose energy along chain;
4       ATP produced;
5       from ADP and Pi;
6       reduced NADP formed;
7       when electrons (from transport chain) and H^+ combine with NADP;
8       H^+ from photolysis;
6 max
(c)     1       some hexose / biomass / eq. used in respiration;
growth cancels this point
2       CO_2 produced (is lost to air);
3       some parts of the plant are eaten / some parts lost to decomposers
/ in leaf fall;
3
[15]
Q6.
(a)     the more light absorbed, the greater the rate of photosynthesis;
light provides the energy for light dependent reactions / photolysis / 
light independent reactions / production of reduced NADP / 
exciting electrons in chlorophyll;
(do not give credit if energy is used in photosynthesis)
2
(b)     count the number of bubbles / measure the volume of gas / measure the 
change in pH / carbon dioxide / hydrogen carbonate ions;
(credit oxygen produced)
1
(c)     530 – 630 nm;
(any values within this range)
limited absorption of light / (green) plants reflect green light / 
limited photosynthesis at these wavelengths of light;
(allow references to no light absorbed or no photosynthesis)
2
(d)     (i)      chlorophyll excited / reduced NADP formed;
electrons from chlorophyll / reduced NADP changes the dye colour;
2
(ii)     ADP and phosphate needed to produce ATP / ATP is a product of 
the light dependent reactions;
ADP levels are a limiting factor;
(must explain the idea of limiting factors – do not credit answers like more ADP causes more photosynthesis) 
2
[9]
Q7.
(a)     1.      Osmosis does not occur;
2.      Chloroplast / organelle does not burst / lyse / shrivel / shrink;
1.      Accept: osmosis would occur if water potentials were not the same.
1 and 2, Accept: correct reference to osmotic lysis for 2 marks.
2.      Accept: chloroplast would burst / lyse / shrivel / shrink if water potentials were not the same.
2.      Reject: ‘cell bursts/shrivels’
2.      Ignore: damage to chloroplasts on its own is not enough for a mark.
3.      Reject: becomes turgid / flaccid.
2
(b)     1.      To show light does not affect DCPIP;
2.      To show chloroplasts are required;
Ignore: comparison with other tubes.
2
(c)     1.      Reduction of DCPIP by electrons;
2.      (From) chlorophyll / light dependent reaction;
1.      Accept: hydrogen / H for electrons but not protons / hydrogen ions / H* on their own.
2.      Accept: from chloroplasts / photosystems / water.
2
(d)     Provides a standard / reference point
OR
Can compare different chemicals/weed-killers
OR
Can compare different concentrations of chemicals / weed-killers;
Accept: decolourises quicker than 100% or saves time waiting for complete decolourisation.
Note: comparisons must be qualified.
Accept: find the most effective weed-killer or the most effective concentration.
Accept: answers relating to cost effectiveness.
1
(e)     1.      Less / no ATP produced;
2.      Less / no reduced NADP produced;
3.      Less / no GP reduced / converted to TP;
2, Accept: less / no NADPH / NADPH_2 / NADPH + H
2 max
[9]
Q8.
(a)     (i)    So it / CO_2 is not a limiting factor (on growth / photosynthesis);
Accept: CO_2 is a limiting factor
1
(ii)     So any difference is due to iron (deficiency);
Accept: iron is the variable
1
(iii)    Amount of triose phosphate / TP will be similar / same / low (at start);
Accept: to allow triose phosphate to stabilise / become constant
Reject: so all triose phosphate is used up
Reject: so no triose phosphate
1
(b)     1.      (Less) ATP produced;
Accept: alternatives for reduced NADP ie NADP with hydrogen / s attached
2.      (Less) reduced NADP produced;
3.      ATP / reduced NADP produced during light-dependent reaction;
4.      (Less) GP to triose phosphate / TP;
4
(c)     1.      Less triose phosphate converted to RuBP;
Accept: less triose phosphate so less RuBP
2.      CO_2 combines with RuBP;
2
[9]
Q9.
(a)     1.      Bar chart;
2.      Error bars to represent standard deviation (of mean);
3.      Photosynthetic pigment on x axis and mass of pigment on y axis;
Accept suitable sketch
2 max
(b)     1.      Number leaves on the branch;
2.      Use random number table / calculator / pick numbers from bag to determine which leaf to pick;
Accept use of random number generator
OR
3.      Collect large number of leaves;
4.      Pick out of bag with some idea of randomness;
2
(c)     No (no mark)
1.      No stats test carried out;
2.      Standard error / 95% confidence interval calculation identified;
If awarded, student scores 2 marks – for points 1 and 2
Yes (no mark)
3.      No overlap shown by the standard deviations;
4.      Ranges around mean stated;
88.6-92.8 and 111.0-111.2 (1 × SD) or 86.5-94.9 and 110.9-111.3 
(2 × SD)
2 max
(d)     In shade leaves:
1.      Greater amount of enzyme / enzyme activity (for production of chlorophyll b);
2.      Greater gene expression / transcription of the gene / more mRNA produced / gene switched on;
3.      Greater translation;
4.      Enzyme / substrate is light sensitive – faster rate of reaction with lower light;
2 max
[8]
Q10.
(a)     1.      (Less/no) ATP;
2.      (Less/no) reduced NADP;
Accept NADPH, NADPH + H, NADPH_2 NADPH + H^+
Reject reduced NAD, NADH etc,
2
(b)     1.      (Less/no) carbon dioxide (reacts) with RuBP;
2.      (Less/no) GP;
2
(c)     1.      Stroma (of/in chloroplast);
Reject: stoma
Reject stroma of cytoplasm/chlorophyll
Reject stroma of mitochondrion
Ignore references to Calvin cycle or the light-independent reaction
1
(d)     1.      Rubisco activity increases with temperature
OR
Rubisco optimum temperature is above (rubisco activase);
2.      (Rubisco) activase activity decreases at high temperatures (allow any temperature above 25 ºC.)
OR
(Rubisco) activase optimum (allow in range) 25 to 30 ºC.;
Accept denatures at high temperature (allow any temperature above 25 ºC)
3.      (Results/graphs suggest) activase cannot/does not affect activity of rubisco;
4.      (Results are) only for cotton;
Accept may not be the same in other species/types of plant
Ignore: only one study
5.      (Results are) for isolated enzymes;
6.      No stats test;
4 max
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