C1.3 Photosynthesis
Practice exam-style IB Biology questions for Photosynthesis, aligned with the syllabus and grouped by topic.
Question 1
What energy transformation occurs during photosynthesis when carbon compounds are produced?
A.
Thermal energy is converted into kinetic energy in carbon dioxide.
B.
Chemical energy in water is converted into electrical energy in glucose.
C.
Chemical energy is converted into light energy stored in oxygen.
D.
Light energy is converted into chemical energy stored in carbon compounds.
Question 2
In oxygenic photosynthesis, what is the source of the oxygen released as a by-product?
A.
Oxygen atoms removed from chlorophyll pigments
B.
Glucose molecules broken down in chloroplasts
C.
Water molecules split during photosynthesis
D.
Carbon dioxide molecules reduced in the Calvin cycle
Question 3
What occurs when a photosynthetic pigment absorbs a photon of a suitable wavelength?
A.
A carbon dioxide molecule is split to release oxygen.
B.
A glucose molecule is converted directly into ATP.
C.
An electron in the pigment is excited to a higher energy level.
D.
A proton is converted into an electron in the pigment.
Question 4
What is a photosystem?
A.
A group of glucose molecules stored as starch in chloroplasts
B.
A soluble enzyme in the stroma that fixes carbon dioxide
C.
A pore in the leaf epidermis that allows gas exchange
D.
A membrane-bound array of pigments and proteins with a reaction centre
Question 5
State the simple word equation for photosynthesis with glucose as the product.
[1]
State the source of the hydrogen used to convert carbon dioxide to glucose.
[1]
Question 6
In a paper chromatogram of leaf pigments, the solvent front moved 80 mm from the origin and a pigment spot moved 48 mm from the origin. What is the Rf value of the pigment?
A.
0.38
B.
128
C.
0.60
D.
1.67
Question 7
What distinguishes an action spectrum from an absorption spectrum for photosynthesis?
A.
An action spectrum shows rate of photosynthesis at different wavelengths.
B.
An action spectrum shows the mass of each separated pigment.
C.
An action spectrum shows the distance moved by a pigment in chromatography.
D.
An action spectrum shows only wavelengths reflected by chlorophyll.
Question 8
A student investigates the effect of sodium hydrogencarbonate concentration on the rate of photosynthesis in pondweed. What is the independent variable?
A.
Temperature of the water surrounding the pondweed
B.
Rate of oxygen production by the pondweed
C.
Concentration of sodium hydrogencarbonate solution
D.
Species and length of the pondweed shoot
Question 9
In a FACE experiment, carbon dioxide is released around field-grown plants. What is a suitable controlled variable?
A.
Plant species grown in control and enriched plots
B.
Growth response caused by added carbon dioxide
C.
Photosynthesis rate measured after enrichment
D.
Carbon dioxide concentration around the enriched plots
Question 10
What is an advantage of having different types of pigment molecules arranged in a photosystem?
A.
They replace the need for carbon dioxide in the Calvin cycle.
B.
They prevent any electrons from being emitted by the reaction centre.
C.
They make photosynthesis independent of membranes.
D.
They absorb a wider range of wavelengths and transfer excitation energy to the reaction centre.
Question 11
What are the products of photolysis of water in photosystem II?
A.
Glucose, oxygen and reduced NADP
B.
RuBP, GP and protons
C.
Carbon dioxide, ATP and electrons
D.
Oxygen, protons and electrons
Question 12
What must NADP accept to become reduced NADP during photosynthesis?
A.
Two phosphate groups and one electron
B.
One carbon dioxide molecule and ATP
C.
Two electrons and one hydrogen ion
D.
One oxygen molecule and two protons
Question 13
Rubisco catalyses carbon fixation in the Calvin cycle. What are its substrates?
A.
Carbon dioxide and ribulose bisphosphate
B.
Glucose and ATP
C.
Oxygen and glycerate 3-phosphate
D.
Triose phosphate and reduced NADP
Question 14
Oxygen produced by photosynthesis in an aquatic plant can be seen as bubbles.
State the process that produces this oxygen.
[1]
Outline why oxygen is described as a by-product of photosynthesis.
[1]
Question 15
Chlorophyll appears green when viewed in white light.
State what is meant by a pigment.
[1]
Explain why chlorophyll appears green.
[1]
Question 16
Outline the structure of a photosystem.
[1]
State where photosystems are located in photosynthetic eukaryotes.
[1]
Question 17
A student separated photosynthetic pigments from a spinach leaf using paper chromatography.
| Item | Colour | Pigment | Distance from origin / cm |
|---|---|---|---|
| Origin line | -- | -- | 0.0 |
| Band 1 | yellow-green | chlorophyll b | 2.4 |
| Band 2 | blue-green | chlorophyll a | 3.8 |
| Band 3 | yellow | xanthophyll | 5.6 |
| Band 4 | orange-yellow | carotene | 7.2 |
| Solvent front | colourless | -- | 8.0 |
Identify the pigment with the largest Rf value.
[1]
Calculate the Rf value of the blue-green pigment.
[1]
Suggest one reason why the origin line should be drawn in pencil rather than ink.
[1]
Question 18
Pondweed was placed at different distances from a lamp. Oxygen production was measured for 5 min at each distance.
Identify the independent variable.
[1]
Describe the trend in oxygen production as distance from the lamp increases.
[1]
Suggest two variables that should be controlled.
[1]
Question 19
A lamp is moved from 0.20 m to 0.40 m from a photosynthesizing plant. Using relative light intensity, Irel = 1/d², what happens to the relative light intensity?
A.
It increases fourfold.
B.
It is reduced to one half.
C.
It doubles.
D.
It is reduced to one quarter.
Question 20
During ATP production by chemiosmosis in thylakoids, in which direction do protons move through ATP synthase?
A.
From the cytoplasm into the chloroplast envelope
B.
From photosystem I directly into photosystem II
C.
From the thylakoid space into the stroma
D.
From the stroma into the thylakoid space
Question 21
Where does reduction of NADP occur in relation to the thylakoid membrane?
A.
On the stroma side of the thylakoid membrane
B.
In the nucleus of photosynthetic cells
C.
In the intermembrane space of the chloroplast envelope
D.
Inside the thylakoid space only
Question 22
In regeneration of RuBP in the Calvin cycle, what happens to five molecules of triose phosphate?
A.
They are converted directly into six molecules of carbon dioxide.
B.
They split water to replace electrons in photosystem II.
C.
They reduce NADP on the thylakoid-space side of the membrane.
D.
They are converted into three molecules of RuBP using ATP.
Question 23
The visual shows a paper chromatogram of leaf pigments.
State one measurement needed to calculate the Rf value of pigment X.
[1]
Calculate the Rf value of pigment X if the pigment moved 36 mm and the solvent front moved 90 mm from the origin.
[1]
Question 24
Absorption spectra and action spectra are both used in studies of photosynthesis.
State what is plotted on the y-axis of an action spectrum.
[1]
Distinguish between an absorption spectrum and an action spectrum.
[1]
Question 25
A student uses pondweed in sodium hydrogencarbonate solution to investigate the effect of carbon dioxide concentration on photosynthesis.
Identify the dependent variable.
[1]
Suggest two variables that should be controlled.
[1]
Suggest why using an oxygen probe is more reliable than counting bubbles.
[1]
Question 26
Leaf discs are made to sink by removing air from their internal spaces. In light, some discs later rise to the surface.
State the gas that accumulates in the leaf discs.
[1]
Explain why the discs rise during photosynthesis.
[1]
Question 27
Explain two advantages of a structured array of different pigment molecules in a photosystem. [3]
Question 28
The equation for photolysis in photosystem II can be summarized as:
2H₂O → O₂ + 4H⁺ + 4e⁻
State the role of the electrons produced.
[1]
State the role of the protons produced.
[1]
Explain why oxygen is released.
[1]
Question 29
Outline ATP production by chemiosmosis in thylakoids. [4]
Question 30
State the photosystem that supplies electrons for reduction of NADP.
[1]
Explain how NADP is reduced.
[1]
Question 31
Rubisco is involved in the Calvin cycle.
State the substrates of Rubisco.
[1]
State the immediate product of carbon fixation by Rubisco.
[1]
Outline why high concentrations of Rubisco are found in chloroplast stroma.
[1]
Question 32
The graph shows oxygen production by algal cells exposed to different wavelengths of equal light intensity.
State the wavelength range that gives the highest rate of oxygen production.
[1]
Describe the relationship between wavelength and rate of photosynthesis.
[1]
Explain why rates are lower in the green region of the spectrum.
[1]
Question 33
A sensor measured carbon dioxide concentration in a sealed chamber containing illuminated leaves.
Determine the rate of carbon dioxide uptake during the steepest part of the curve.
[1]
State what happens to the rate later in the experiment.
[1]
Suggest one factor that may have become limiting later in the experiment.
[1]
Question 34
Isolated thylakoids were exposed to light and the pH was measured in the thylakoid space and in the stroma.
State how pH in the thylakoid space changes after illumination.
[1]
Explain the change in pH in the thylakoid space.
[1]
Predict the effect on ATP production if ATP synthase is inhibited.
[1]
Question 35
Carbon dioxide enrichment can be investigated in greenhouses and in free-air carbon dioxide enrichment (FACE) experiments.
Outline why FACE experiments may give more realistic predictions than greenhouse experiments.
[1]
Identify one controlled variable in a FACE experiment and explain why it should be controlled.
[1]
Question 36
The visual shows a thylakoid membrane with photosystem II, photosystem I and ATP synthase.
Identify where photolysis of water occurs.
[1]
Identify where ATP is released.
[1]
Identify where NADP is reduced.
[1]
State why compartmentalization of the thylakoid is essential.
[1]
Question 37
A photosynthesizing leaf is suddenly placed in darkness.
State two products of the light-dependent reactions that will no longer be supplied.
[1]
Explain why the Calvin cycle soon stops.
[1]
Question 38
The table compares biomass gain in crop plants grown under ambient and enriched carbon dioxide in a greenhouse and in a FACE experiment.
| Experimental setting | Ambient CO₂ mean ± SD / g plant⁻¹ | Enriched CO₂ mean ± SD / g plant⁻¹ |
|---|---|---|
| Greenhouse | 26.4 ± 2.8 | 39.6 ± 3.5 |
| FACE field plots | 25.8 ± 3.2 | 30.1 ± 3.6 |
State which experimental setting showed the larger response to carbon dioxide enrichment.
[1]
Compare the responses in the two settings.
[1]
Suggest why the greenhouse result may overestimate future field growth.
[1]
Question 39
The concentrations of Calvin cycle intermediates were measured after illuminated leaves were transferred to air without carbon dioxide.
Identify which intermediate accumulates after carbon dioxide is removed.
[1]
Explain why the concentration of GP decreases.
[1]
Explain why photosystem II activity decreases after several minutes without carbon dioxide.
[1]
Question 40
Rubisco activity was measured at different carbon dioxide concentrations using chloroplast extracts containing either low or high Rubisco concentration.
State the effect of increasing carbon dioxide concentration on Rubisco activity.
[1]
Compare the activity of extracts with low and high Rubisco concentration.
[1]
Explain why high concentrations of Rubisco are advantageous in chloroplast stroma.
[1]
Question 41
The diagram summarizes carbon flow through the Calvin cycle after a pulse of labelled carbon dioxide.
| Process | Carbon-flow relationship | Energy input |
|---|---|---|
| Carboxylation | 1 RuBP (5C) + 1 CO2 (1C) -> 2 GP (3C) | None shown |
| Reduction | 1 GP (3C) -> 1 TP (3C) | ATP + NADPH |
| Hexose formation | 2 TP (3C each) leave -> 1 hexose (6C) | None shown |
| RuBP regeneration | 5 TP (3C each) recycle -> 3 RuBP (5C each) | ATP |
Calculate the fraction of triose phosphate that must be recycled to regenerate RuBP if glucose is the named product of photosynthesis.
[1]
Use the diagram to determine how many molecules of carbon dioxide must be fixed to obtain one molecule of glucose as net product.
[1]
Explain why ATP is needed for continued carbon fixation.
[1]
Question 42
Outline how light is absorbed by photosynthetic pigments.
[1]
Explain how absorption spectra and action spectra provide evidence for the role of pigments in photosynthesis.
[1]
Question 43
Outline how light intensity could be varied in an experiment on the rate of photosynthesis.
[1]
Discuss how a valid experiment could be designed to test the effect of one limiting factor on photosynthesis.
[1]
Question 44
Describe one greenhouse method and one FACE method for carbon dioxide enrichment.
[1]
Evaluate the use of carbon dioxide enrichment experiments to predict future plant growth.
[1]
Question 45
State two products or consequences of photosynthesis that are important to ecosystems.
[1]
Explain how photosynthesis supplies energy and matter to most ecosystems.
[1]
Question 46
Chloroplasts were illuminated under two conditions: with available NADP and with NADP supply limited. Rates of ATP production and reduced NADP production were measured.
| Condition | ATP production rate / μmol min⁻¹ mg⁻¹ chlorophyll | Reduced NADP production rate / μmol min⁻¹ mg⁻¹ chlorophyll |
|---|---|---|
| NADP available | 42 | 38 |
| NADP limited | 31 | 4 |
Identify the condition in which cyclic photophosphorylation is more likely.
[1]
Use the data to justify your answer.
[1]
Explain why ATP can still be produced when reduced NADP production is low.
[1]
Question 47
Outline how a proton gradient is generated across the thylakoid membrane.
[1]
Explain how the thylakoid functions as a system for the light-dependent reactions of photosynthesis.
[1]
Question 48
Describe carbon fixation by Rubisco.
[1]
Explain how triose phosphate is produced and used in the Calvin cycle and in synthesis of other carbon compounds.
[1]
Question 49
Outline non-cyclic photophosphorylation.
[1]
Compare and contrast cyclic and non-cyclic photophosphorylation in thylakoids.
[1]
Question 50
Outline the exchange of molecules between the light-dependent reactions and the Calvin cycle.
[1]
Discuss the interdependence of the light-dependent and light-independent reactions under conditions of low light and low carbon dioxide.
[1]
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