26
OCR Photosynthesis Questions
OCR
Photosynthesis
Questions
20
© OCR 2008
6 (a) The rate of photosynthesis is determined mainly by environmental limiting factors. These are light intensity, the availability of carbon dioxide and temperature. Water supply has indirect effects by influencing the availability of carbon dioxide.
(i) Define the term limiting factor.
...........................................................................................................................................
..................................................................................................................................... [1]
(ii) Explain how water shortage could have an indirect effect on photosynthesis by influencing the availability of carbon dioxide.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [2]
(b) Some plants, such as wood sorrel, Oxalis acetosella, nearly always grow in shade where light intensity is commonly a limiting factor for photosynthesis. They are known as shade plants. Plants that live in open habitats, for example the daisy, Bellis perennis, are called sun plants.
Fig. 6.1 shows the net rate of photosynthesis of sun and shade plants in response to increasing light intensity. The net rate of photosynthesis is defined as:
mass of CO2 fixed in photosynthesis minus mass of CO2 produced in respiration, per unit time
light intensity
sun plant
shade plant
40
20
0
net rate ofphotosynthesis /
CO2 uptakemg cm–2 h–1
Fig. 6.1
21
[Turn over© OCR 2008
Using Fig. 6.1, describe the responses of sun and shade plants to increasing light intensity.
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
............................................................................................................................................. [2]
(c) Leaves of wood sorrel have been shown to have very low respiration rates per unit leaf area. Fig. 6.2 shows sections through the leaves of typical sun and shade plants.
upper epidermis
palisade mesophyll
spongy mesophyll
sun shade
Fig. 6.2
(i) With reference to Fig. 6.2, suggest why the leaves of wood sorrel have low rates of respiration.
..................................................................................................................................... [1]
(ii) Explain why a low rate of respiration in leaves is an adaptation to low light intensities.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [3]
22
© OCR 2008
(d) A large number of seedlings of common orache, Atriplex patula, were grown for several weeks in different environmental conditions as follows:
• group 1 – high light intensities
• group 2 – intermediate light intensities
• group 3 – low light intensities.
When fully grown, the net rate of photosynthesis at different light intensities was measured for each group. The results obtained are shown in Fig. 6.3.
light intensity
net rate ofphotosynthesis /
CO2 uptakemg cm–2 h–1
40
30
20
10
0A
xx x x xx
x
x
x
x
x
x
xx x
high light[group 1]
intermediate light[group 2]
low light[group 3]
Fig. 6.3
(i) State the net rate of photosynthesis for plants in groups 1 and 3 at light intensity A on Fig. 6.3.
group 1 ..............................................................................................................................
group 3 ........................................................................................................................ [2]
(ii) Suggest how adaptation to light intensity is controlled in A. patula.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [3]
[Total: 14]END OF QUESTION PAPER
10
© OCR 2008
3 (a) Fig. 3.1 is a summary of the light independent reactions of photosynthesis (Calvin cycle).
G D
E
C
6 ribulose bisphosphate (RuBP) + 6CO2 12 glycerate 3–phosphate (GP)
6 ribulose phosphate (RuP) 12 triose phosphate (TP)
hexose sugars
rearrangement of C atoms of 10 triosephosphate to generate 5 carbon sugars
F
Fig. 3.1
(i) Name the two products of the light dependent stage of photosynthesis that are required in the Calvin cycle.
1 ........................................................................................................................................
2 ................................................................................................................................... [2]
(ii) Using Fig. 3.1, state the letters of the two steps where chemicals named in section (a)(i) are required.
1 ........................................................................................................................................
2 ................................................................................................................................... [2]
(iii) State two possible fates of the hexose sugars shown in Fig. 3.1.
1 ........................................................................................................................................
...........................................................................................................................................
2 ........................................................................................................................................
...................................................................................................................................... [2]
(iv) State where in the chloroplast the light independent stage of photosynthesis takes place.
...................................................................................................................................... [1]
11
[Turn over© OCR 2008
(v) Describe and explain what will happen to the concentrations of ribulose bisphosphate (RuBP) and glycerate 3-phosphate (GP) if carbon dioxide concentrations fall.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [2]
(b) The rate of photosynthesis is limited by environmental factors.
List three environmental limiting factors of photosynthesis.
1 ................................................................................................................................................
2 ................................................................................................................................................
3 ........................................................................................................................................... [3]
(c) The rate of carbon dioxide uptake was determined for a maize plant during a warm sunny day. Readings were taken at two-hourly intervals. The results are shown in Table 3.1.
Table 3.1
time of daycarbon dioxide uptake /
cm3 m–2 h–1
07.00 1.209.00 3.811.00 2.513.00 1.815.00 1.217.00 2.2
With reference to limiting factors, suggest an explanation for the decrease in carbon dioxide uptake between 9.00 and 15.00.
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
.............................................................................................................................................. [4][Total: 16]
16
© OCR 2009
7 The light-dependent stage of photosynthesis takes place on the thylakoids of the chloroplast. Fig. 7.1 represents a section through a thylakoid to show some of the components involved in the light-dependent stage.
2e–
2H+ + ½O2
2e–
P Q2e–
R
2e–
thylakoid lumen
thylakoid
stroma
light light
H2O H+H+
H+
H+ NADP+ H+
NADPreduced
S
ADP+ Pi
ATP
Fig. 7.1
(a) Identify the structures labelled P, Q, R and S.
P ....................................................................
Q ....................................................................
R ....................................................................
S .................................................................... [4]
(b) Atrazine is a widely used herbicide (weedkiller). It binds to a chloroplast protein involved in electron transfer between photosystems.
(i) Explain how atrazine works as an effective herbicide.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [5]
17
© OCR 2009
(ii) Maize plants are insensitive to atrazine.
The cytoplasm of maize plant cells contains a tripeptide which binds to atrazine. The product is then transported to the vacuole.
Explain why maize plants are insensitive to atrazine.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [2]
(iii) Suggest how this insensitivity to atrazine can be of benefit to maize farmers.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [2]
[Total: 13]
END OF QUESTION PAPER
2
© OCR 2009
Answer all the questions.
1 Absorption of light and the generation of hydrogen atoms in the light dependent stage of photosynthesis can be demonstrated by using isolated chloroplasts. A chloroplast suspension is prepared by grinding up leaves in an ice cold buffer solution that has the same water potential as the stroma of the chloroplasts. The mixture is filtered, centrifuged and the supernatant decanted and discarded. The chloroplasts are resuspended in fresh, cold buffer solution. A sample of this suspension rapidly reduces a dilute solution of DCPIP (dichloro-phenolindophenol).
The DCPIP is blue when oxidised and colourless when reduced.
chloroplast suspension in lightoxidised DCPIP reduced DCPIP
(blue) (colourless) (a) (i) Name two pigments found in a chloroplast that are involved in light absorption.
1 ........................................................................................................................................
2 .................................................................................................................................. [2]
(ii) Outline how hydrogen atoms are generated in the light dependent stage of photosynthesis.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [2]
(iii) State the name of the hydrogen acceptor found in chloroplasts that is replaced by DCPIP in the experiment described above.
..................................................................................................................................... [1]
(iv) Explain why the chloroplasts are suspended in an ice cold buffer solution that has the same water potential as the stroma.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [4]
3
Turn over© OCR 2009
(b) An investigation was performed on the chloroplast suspension by setting up the following mixture in a colorimeter tube:
• 0.5 cm3 chloroplast suspension • 4 cm3 buffer solution • 1 cm3 DCPIP solution.
This tube was placed in a colorimeter and the disappearance of the blue colour of the oxidised DCPIP was determined by taking readings at two-minute intervals. The results of this and of a similar tube in which the chloroplast suspension had previously been boiled and cooled are shown in Fig. 1.1.
100
75
50
25
00 4 8 12 16 20
time / min
24 28 32 36 40
percentageof oxidised
DCPIPpresent
tube with boiledchloroplast suspension
tube with unboiledchloroplast suspension
Fig. 1.1
(i) State the colour of the chloroplast suspension in the two tubes after 40 minutes.
boiled .................................................................................................................................
unboiled ....................................................................................................................... [2]
(ii) Explain the difference in the results obtained for the boiled and unboiled chloroplast suspensions.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [4]
[Total: 15]
12
© OCR 2010
5 The light dependent stage of photosynthesis takes place on thylakoid membranes in chloroplasts. These membranes surround the thylakoid space (lumen) and are arranged into stacks known as grana. Fig. 5.1 summarises the processes that take place at the thylakoid membrane.
thylakoidmembrane
stroma
thylakoidspace(lumen)
H2O 2H+ + O2
H+
H+
H+ H+
H+
H+
H+
H+
H+
P680P680
2e2e–
P680
light
2e–
E
1–2
light
F
2e–
2e–
P700
NADP
ATPADP + Pi
NADPredATPsynthase
G
Fig. 5.1
(a) State the general name of the pigment complexes shown as E and F on the diagram.
.............................................................................................................................................. [1]
(b) Name the pigment represented by P680 and P700.
.............................................................................................................................................. [1]
(c) Name the type of molecule represented by G.
.............................................................................................................................................. [1]
(d) State, using the information in Fig. 5.1, why the pH of the thylakoid space (lumen) is lower than that of the stroma.
.............................................................................................................................................. [1]
(e) Explain the function of this pH gradient.
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
13
Turn over© OCR 2010
...................................................................................................................................................
...................................................................................................................................................
.............................................................................................................................................. [3]
(f) Herbicides (weedkillers), such as diquat and paraquat, act on the chloroplast thylakoids.They interfere with electron transport by accepting electrons and preventing the light dependent stage of photosynthesis from taking place.
Explain how this causes plants to die.
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
.............................................................................................................................................. [5]
(g) Some weed species are not killed when herbicides are applied.
Suggest why.
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
.............................................................................................................................................. [2]
[Total: 14]
4
© OCR 2010
2 A cell suspension of a species of Chlorella, a photosynthetic protoctistan, was supplied with carbon dioxide, initially at a concentration of 3%. The concentration of carbon dioxide was reduced to 1% after 100 seconds, and then to 0.03% after a further 200 seconds.
The suspension was illuminated with a bench lamp and kept at a temperature of 25°C. The levels of ribulose bisphosphate (RuBP) and glycerate 3-phosphate (GP) present were determined at intervals.
The results are shown in Fig. 2.1.
2
1
00 50 100 150 200 250
time / s
concentration/ arbitraryunits
300 350 400 450 500
RuBP
GP
3% CO2 1% CO2 0.03% CO2
Fig. 2.1
(a) (i) State two distinguishing features of organisms classified in the kingdom Protoctista.
1 ........................................................................................................................................
2 ................................................................................................................................... [2]
(ii) Suggest an advantage of using Chlorella, rather than whole leaves from a plant, when carrying out experiments such as the one used to obtain the results shown in Fig. 2.1.
...........................................................................................................................................
...................................................................................................................................... [1]
(iii) Name the biochemical pathway that involves the chemicals RuBP and GP.
...................................................................................................................................... [1]
(iv) State where this pathway occurs in the chloroplasts of Chlorella.
...................................................................................................................................... [1]
5
Turn over© OCR 2010
(b) With reference to Fig. 2.1,
(i) describe the changes in the concentrations of RuBP and GP when the carbon dioxide concentration is reduced from 3% to 1% and then to 0.03%;
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [3]
(ii) explain the change in the concentration of RuBP during the 85 seconds immediately after the carbon dioxide concentration is reduced to 0.03%.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [4]
(c) Photosynthetic protoctistans such as Chlorella often form ‘blooms’ in ponds and lakes. These blooms are caused by rapid population growth. In the United Kingdom, these blooms often occur in May and June.
Suggest why rapid population growth can occur in May and June.
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
.............................................................................................................................................. [3]
[Total: 15]
