ANSWERS 1 (68 Marks)
Higher level Biology Dulwich College Shanghai
Topic 3 (SL): Chemistry of Life
Topic 8 (HL): Respiration and Photosynthesis
3.8
3.8.1
3.8.2
3.8.3
3.8.4
3.8.5
3.8.6
3.8.7
3.8.8
8.2
8.2.1
8.2.2
8.2.3
8.2.4
8.2.5
8.2.6
8.2.7
8.2.8
Photosynthesis (SL)
State that photosynthesis involves the conversion of light energy into chemical energy.
State that light from the Sun is composed of a range of wavelengths (colours)
State that chlorophyll is the main photosynthetic pigment.
Outline the differences in absorption of red, blue and green light by chlorophyll
(students should appreciate that pigments absorb certain colours of light. The
remaining colours of light are reflected. It is not necessary to mention wavelengths or
the structure responsible for the absorption).
State that light energy is used to produce ATP, and to split water molecules (photolysis)
to form oxygen and hydrogen.
State that ATP and hydrogen (derived from the photolysis of water) are used to fix
carbon dioxide to make organic molecules.
Explain that the rate of photosynthesis can be measured directly by the production of
oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass.
Outline the effects of temperature, light intensity and carbon dioxide concentration on
the rate of photosynthesis (The shape of the graph is required).
Photosynthesis (HL)
Draw and label a diagram showing the structure of a chloroplast as seen in electron
microscope.
State that photosynthesis consists of light-dependent and light-independent reactions
(these should NOT be called ‘light’ and ‘dark’ reactions).
Explain the light-dependent reactions. (include the photoactivation of photosystem II,
photolysis of water, electron transport, cyclic and non-cyclic photophosphorylation,
photoactivation of photosystem I, and reduction of NADP+.
Explain photophosphorylation in terms of chemiosmosis.
Explain the light-independent reactions. Include the roles of ribulose bisphosphate
(RuBP), carboxylate, reduction of glycerate 3-phosphate (GP) to triose phosphate (TP),
NADPH + H+, ATP, regeneration of RuBP, and subsequent synthesis of more complex
carbohydrates.
Explain the relationship between the structure of the chloroplast and its function.
Limit this to the large surface area of thylakoids for light absorption, the small space
inside thylakoids for accumulation of protons, and the fluid stroma for the enzymes of
the Calvin cycle.
Explain the relationship between the action spectrum and the absorption spectrum of
photosynthetic pigments in green plants. (A separate spectrum for each pigment is
NOT required).
Explain the concept of limiting factors in photosynthesis with reference to light
intensity, temperature and concentration of carbon dioxide.
Paper 1
Multiple Choice (8 Marks)
1.
Which two colours of light does chlorophyll absorb most?
A.
Red and yellow
B.
Green and blue
C.
Red and green
D.
Red and blue
2.
What is needed in photosynthesis to convert carbon dioxide into organic molecules?
A.
Light and hydrogen from the splitting of water
B.
Light and oxygen from the splitting of water
C.
ATP and hydrogen from the splitting of water
D.
ATP and oxygen from the splitting of water
3.
How is the proton gradient generated in chloroplasts during photosynthesis?
A.
Flow of electrons from carrier to carrier in the thylakoid membrane causes
pumping of protons across the thylakoid membrane.
B.
Light causes protons to flow through protein channels in the thylakoid
membrane.
C.
Light splits water molecules in the stroma, causing the release of protons.
D.
Protons are pumped across the thylakoid membrane using energy from ATP.
4.
Why is the action spectrum for photosynthesis similar to the absorption spectra of
photosynthetic pigments?
A.
Photosynthetic pigments have the same optimum temperature as the enzymes
used in photosynthesis.
B.
Plants absorb the same photosynthetic pigments for use in photosynthesis.
C.
Only wavelengths of light absorbed by pigments can be used in
photosynthesis.
D.
The amount of energy absorbed by photosynthetic pigments is equal to the
activation energy for photosynthesis.
5.
Which of the following features is/are present in mitochondria but not in
chloroplasts?
I.
DNA and ribosomes
II.
Outer and inner membranes
III. Cristae
A.
I only
B.
II only
C.
III only
D.
I and III only
Which limiting factor of photosynthesis is shown below?
Rate of photosynthesis
6.
A.
B.
C.
D.
Increasing carbon dioxide concentration
Increasing temperature
Increasing light intensity
Increasing humidity
7.
Which two colours of light does chlorophyll absorb most?
A.
Red and yellow
B.
Green and blue
C.
Red and green
D.
Red and blue
8.
The diagram below summarizes the light-dependent reactions in photosynthesis.
What is occurring at X?
Electrons
X
Electrons
Light
Photosystem I
Light
Photosystem II
A.
C.
ADP + phosphate  ATP
+
+
NADP  NADPH + H
2–
+
H2O  O + 2H
D.
+
+
NADPH + H  NADP
B.
Rate of photosynthesis /  l CO2 min
Π1
Paper 2
Section A
Data Analysis (10 marks)
1.
There are many abiotic factors that affect the rate of photosynthesis in
terrestrial plants. Wheat is an important cereal crop in many parts of the world.
Wheat seedlings were grown at three different concentrations of carbon dioxide
(in parts per million) and the rate of photosynthesis was measured at various light
intensities.
50
40
30
key:
20
1300 ppm CO2
500 ppm CO2
280 ppm CO2
10
0
0
5
10
15
20
Light intensity / ? 10 3 lumen m Π2
[Source: Adapted from J P Kimmins, 1997 Forest Ecology, (2nd edition) page 161]
(a)
Describe the relationship between the rate of photosynthesis and light intensity
for wheat seedlings grown at a CO2 concentration of 500 ppm.
(2)
rate of photosynthesis increases (rapidly) /
directly proportional;
rate of photosynthesis levels off /
–2
increases slightly after 10000 lumen m ;
(b)
Outline the effect of CO2 concentration on the rate of photosynthesis of the
wheat seedlings.
maximum photosynthetic rate is highest with highest
CO2 concentration;
at low light levels, higher CO2 slightly increases the
photosynthetic rate;
at low CO2 / 280 ppm, the photosynthetic rate reaches its
maximum at low light levels / constant over most light intensity /
at 280 ppm CO2 concentration limits photosynthesis;
at 500 and 1300 ppm CO2 the curve is the same shape
but with different maximum rates /
each higher light intensity requires a higher CO2 concentration
to reach maximum rate;
maximum rate of photosynthesis from 280 to 500 ppm /
increases 5 to 6 times
while 500 to 1300 ppm increases 1.5 times;
(3)
(c)
The normal atmospheric concentration of CO2 is 370 ppm. Deduce the effect of
doubling the CO2 concentration to 740 ppm on the growth of wheat plants.
(2)
the rate of photosynthesis will increase (over the rate at 370 ppm);
the photosynthetic rate will at least double (but less than 5–6 times);
not linear;
bigger plants / more growth / more grain / greater yield;
Leaf area and chlorophyll levels were measured in sun leaves and shade leaves of
Hedera helix (English Ivy) and Prunus laurocerasus (Cherry Laurel). Sun leaves
developed under maximal sunlight conditions while shade leaves developed at
reduced sunlight levels in the shadow of other leaves.
Species
Leaf Type
Chlorophyll/
Leaf Area/
-1
2
mg ml
cm
Ivy
Shade
4.3
72.6
Sun
3.8
62.9
Laurel
Shade
4.7
38.7
Sun
4.2
25.7
[Source: D Curtis, Plant Ecology independent project, 1990]
(d)
Calculate the percentage increase in the amount of chlorophyll in shade leaves of
ivy compared to sun leaves of ivy.
(1)

(e)
4.3  3.8
 100  13.16% (Accept 13.2%)
3.8
Suggest a reason for the differences in chlorophyll concentration and leaf area in
sun and shade leaves in these two species.
(2)
shade leaves receive less light than sun leaves;
to capture sunlight, shade leaves produce more chlorophyll;
to capture sunlight, shade leaves have greater leaf area;
Paper 2
Section A
Short Structured (36 Marks)
1.
Explain the reasons for
(a)
a large area of thylakoid membrane in the chloroplast.
more chlorophyll / photosystems;
so more light absorbed;
2.
(2)
(b)
low rates of photosynthesis in plants growing beneath trees, where the light has
already passed through the trees’ leaves.
(2)
insufficient light / poor absorption hence low rate of photosynthesis;
higher leaves absorb majority of red and blue wavelengths;
only green / orange / yellow wavelengths available for lower leaves;
(c)
large amounts of RuBP carboxylase in the chloroplast;
catalysis of reaction in the Calvin cycle;
RuBP carboxylase not very effective so much needed / reference
to photorespiration;
used for carbon fixation;
carbon fixation is vital to the plant / carbon dioxide needed
for photosynthesis;
During photosynthesis in plants, light energy is absorbed by chlorophyll. This energy
is then used to carry out photolysis, which supply substances that are needed to
convert carbon dioxide into organic molecules such as glucose.
(a)
State the names of two products of photolysis in photosynthesis.
oxygen;
+
hydrogen / reduced NADP (NADPH) / H / protons;
ATP;
(2)
(2)
(b)
Explain briefly one method for measuring the rate of photosynthesis in a plant. (2)
measure oxygen production over a fixed period of time / rate;
collect bubbles of oxygen (from water plant);
or
measure carbon dioxide uptake over a fixed period of time / rate;
measure (colour) change of pH indicator / other method over a fixed
period of time / rate;
or
measure increase in biomass / height / leaf size etc over a fixed period of
time / rate;
harvest replicate samples at time intervals for biomass determination;
(c)
The rate of photosynthesis is affected by light intensity. Draw a line on the graph
below to show the relationship between light intensity and the rate of
photosynthesis.
(2)
straight line increase;
followed by a plateau at high light intensities;
3.
4.
(d)
State two factors in the environment of a plant, apart from light intensity, that can
affect the rate of photosynthesis in the plant.
(2)
temperature;
carbon dioxide concentration;
water / humidity;
(a)
State where, in the chloroplast, the enzymes of the Calvin cycle are located.
stroma
(b)
Explain how the proton gradient in the chloroplast is generated by chemiosmosis.(3)
electron transport causes protons to be pumped inside the thylakoid;
ATPase located in the thylakoid membrane
(lets protons across the membrane);
protons go down the concentration gradient;
protons move from the thylakoid to the stroma;
energy is used to synthesize ATP;
(c)
Explain the relationship between the position of a leaf on a tree and the
photosynthetic rate of the leaf.
photosynthetic rate is dependent on light intensity and wavelength;
leaves lower in the tree will have a lower photosynthetic rate /
or vice versa;
leaves lower in the tree will receive filtered light /
light of reduced number of wavelengths /
contains less violet / blue and / or red light / or vice versa;
leaves lower in the tree will receive more light consisting of
yellow and green light / or vice versa,
(a)
(b)
(1)
(2)
Draw and label the structure of the chloroplast as seen in the electron microscope.
(3)
Award [1] for each of the following structures clearly
drawn and correctly labelled.
thylakoid membrane / grana;
double outer membrane / envelope;
ribosomes; circular DNA;
lipid globules / starch granules;
stroma;
Explain the relationship between the structure of the chloroplast and its function.
(2)
large surface area of thylakoids for light absorption / photosynthesis;
(small) space in the thylakoids to accumulate protons;
fluid stroma for enzymes of the Calvin cycle /
light independent reaction;
5.
The graph below shows the effect of light intensity on photosynthesis at 0.1%
carbon dioxide concentration.
Key:
0.01% CO2
0.1% CO2
Rate of
photosynthesis /
arbitrary units
Light intensity / arbitrary units
(a)
On the graph above, draw the results obtained at 0.01% carbon dioxide.
(1)
(b)
Outline the fate of the oxygen and hydrogen which are produced in the photolysis
of water during photosynthesis.
(2)
Oxygen:
released / waste product (through stomata) / used in respiration / specific
reference to where used in respiration;
hydrogen:
used in production of organic molecules / sugars / to fix / combine with
carbon
dioxide / specific reference to where used in photosynthesis;
(c)
The energy produced in photosynthesis can enter a food chain. Explain how this
energy can be lost before it reaches the last link in the chain.
NB Action verb is “explain” so reasoning must be given for each marking point.
material not consumed because of death;
material not eaten (eg bones / hair);
material not assimilated is defecated;
heat loss through respiration;
excretion of organic molecules eg urea;
(2)
6.
(a)
Compare the structure of a mitochondrion with a chloroplast.
Award [1] for each row of structural features.
mitochondrion
chloroplast
both contain DNA and RNA;
both contain ribosomes;
both have double membranes;
no pigments
contains pigments;
matrix
stroma;
inner membrane folded (cristae)
no folds (cristae) /
/
thylakoids;
no thylakoids
both have electron transport system
does not have NADPH
has NADPH
(3)
(b)
(3)
Explain the role of chemiosmosis in oxidative phosphorylation.
ADP is phosphorylated to ATP through addition of inorganic phosphate;
by enzyme ATP synthetase / synthase;
when H+ ions (protons) diffuse;
through channels in ATP synthetase / synthase;
from high H+ concentration in mitochondrial intermembrane space;
to low H+ concentration in mitochondrial matrix;
Section B
Extended Response (14 Marks)
1.
Explain how the light-independent reactions of photosynthesis rely on light-dependent
reactions.
(8)
light-independent reaction fixes CO2;
to make glycerate 3-phosphate;
glycerate 3-phosphate / GP / phosphoglyceric acid becomes reduced;
to triose phosphate / phosphoglyceraldehyde / glyceraldehyde 3-phosphate;
using NADPH;
using ATP;
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;
ATP formation when protons pass back across thylakoid membrane;
+
electrons are passed to NADP / NADP ;
NADPH produced in the light dependent reactions;
2.
Outline the effect of temperature, light intensity and carbon dioxide concentration on
the rate of photosynthesis.
(6)
light:
rate of photosynthesis increases as light intensity increases;
photosynthetic rate reaches plateau at high light levels;
CO2:
photosynthetic rate rises as CO2 concentration rises;
up to a maximum when rate levels off;
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.