IB Biology HL C1.3 Photosynthesis Questions

Practise IB Biology HL C1.3 by linking pigments and limiting factors to photosystems, photophosphorylation and carbon fixation evidence.

Exam points

Explain how Photosystem II photolyses water to replace electrons and release oxygen and hydrogen ions; identify oxygen as a product of oxygenic photosynthesis.
Separate photosynthetic pigments by chromatography and describe the procedure or calculate and interpret Rf values to identify pigments.
Compare absorption and action spectra, interpret wavelength evidence and relate peaks to photosynthetic rate.
Interpret limiting-factor curves and evaluate controlled photosynthesis experiments, including temperature, CO₂ enrichment and FACE evidence.
Identify photosystems and pigment arrays in thylakoid membranes, then trace light-excited electron movement from Photosystem II to Photosystem I.
Explain electron transfer, proton pumping and proton flow through ATP synthase as chemiosmosis and photophosphorylation.
Explain how Photosystem I reduces NADP and how light-dependent ATP and reduced NADP support the Calvin cycle.
Trace Calvin-cycle carbon from Rubisco fixation of CO₂ to RuBP into glycerate 3-phosphate, then its ATP- and reduced-NADP-dependent reduction to triose phosphate.
Explain RuBP regeneration and use Calvin-cycle stoichiometry to relate triose phosphate, glucose formation and the regenerated acceptor.

Covered syllabus points

C1.3.1—Light energy → chemical energy C1.3.2—CO₂ → glucose C1.3.3—Oxygen as by-product C1.3.4—Photosynthetic pigment separation C1.3.5—Absorption of specific wavelengths C1.3.6—Absorption vs. action spectra C1.3.7—Limiting factors investigation C1.3.8—CO₂ enrichment experiments C1.3.9 (HL)—Photosystems C1.3.10 (HL)—Advantages of pigment arrays C1.3.11 (HL)—Photolysis of water C1.3.12 (HL)—ATP production in thylakoids C1.3.13 (HL)—NADP reduction C1.3.14 (HL)—Thylakoids as light-dependent systems C1.3.15 (HL)—Carbon fixation by Rubisco C1.3.16 (HL)—Triose phosphate synthesis C1.3.17 (HL)—RuBP regeneration C1.3.18 (HL)—Synthesis of other compounds C1.3.19 (HL)—Interdependence of light and light-independent reactions

[Maximum number: 8]

In ecosystems, energy is used to convert inorganic compounds into organic matter. Energy enters ecosystems through producers.

Explain the processes by which light energy is converted into chemical energy.

[Maximum number: 9]

In water, shorter wavelengths of light such as blue and green penetrate deepest, and longer wavelengths of light penetrate less far. Red light does not reach depths of more than 50 m . Marine algae live at various water depths. Certain species of algae contain the pigments that enable them to adapt to life at different depths.

The graphs show the absorption and action spectra for two species of algae: Ulva taeniata, which is green, and Porphyra nereocystis, which is red.

Absorption / %

(a)

In each species, identify the colour of light that is used mainly for photosynthesis.

Ulva taeniata:

Porphyra nereocystis:

[ 2 ]

(b)

Deduce, with a reason, which algae lives at a greater depth.

[ 1 ]

(c)

Describe how the rate of photosynthesis could be measured in a marine alga, to produce an action spectrum.

[ 3 ]

(d)

Outline the structure and location of photosystems.

[ 2 ]

(e)

State the method used to separate photosynthetic pigments in a leaf extract.

[ 1 ]

[Maximum number: 10]

(a)

Distinguish between the absorption of red light, blue light and green light by plants.

[ 4 ]

(b)

Outline how light intensity and concentration of carbon dioxide affect photosynthesis.

[ 6 ]

[Maximum number: 1]

Absorption / %

State the method used to separate photosynthetic pigments in a leaf extract.

[Maximum number: 4]

Distinguish between the absorption of red light, blue light and green light by plants.

[Maximum number: 2]

Boreal forests stretch across Canada, Russia and Scandinavia. This northern ecosystem accounts for 29 % of the world's forest areas. The long, cold winters favour tall evergreen trees with either needles or scale-like leaves. These trees are wind-pollinated and their seeds are not enclosed in a fruit. The photograph shows a typical boreal forest in winter.

Boreal forest in winter, with a dense stand of tall pointed trees covered in snow beside an open snow-covered foreground.

The boreal forests are situated close to the north pole and even in summer the intensity of sunlight is lower than at the equator. Sketch a graph showing the effect of light on the rate of photosynthesis, labelling the axes.

Blank graph with horizontal and vertical arrowed axes, provided for sketching and labelling a photosynthesis response.

[Maximum number: 1]

What is an advantage of free-air carbon dioxide enrichment experiments (FACE)?

The carbon dioxide uptake by plants is controlled.

Temperature can be controlled.

Water can be controlled.

Data can more accurately represent future rates of photosynthesis.

[Maximum number: 2]

Absorption / %

Outline the structure and location of photosystems.

[Maximum number: 3]

During photosynthesis plants use water in the conversion of light energy to chemical energy.

Explain how water is used in photosynthesis.

a. water is split/broken «up»/lysed/undergoes photolysis

b. producing/providing electrons

c. replaces electrons lost by Photosystem II / PSII / P680 / chlorophyll a

d. allows electrons «to continue» to pass along the electron transport chain

e. provides protons/ $\mathrm{H}^{+}$ «inside thylakoid» to help generate a «proton» gradient/maintain high concentration inside thylakoid

Marking guidance:
For mpa, reject “water is cut in half”.
For mpa, accept photolysis only if the context shows that water is being split.
For mpc, do not accept just chlorophyll.
For mpe, reject pumping of protons into the thylakoid as photolysis produces them inside the thylakoid.

[Maximum number: 5]

A wide variety of organic compounds are used by living organisms.

Describe how ATP is produced by Photosystem II in the light-dependent stage of photosynthesis.

[Maximum number: 1]

What occurs during photosynthesis?

Water is oxidized by releasing two electrons to NADPH.

Glycerate-3-phosphate (GP) is oxidized by releasing two electrons to photosystem II.

NAD is reduced by accepting two electrons from ATP.

NADP is reduced by accepting two electrons from photosystem I.

[Maximum number: 1]

The diagram shows a section through a thylakoid. Electrons move from X to Y .

Thylakoid section drawn as a curved membrane enclosing a space. X and Y point to two large complexes embedded in its upper membrane, and Z points into the enclosed space.

What do the letters X, Y and Z represent?

photosystem I

photosystem II

thylakoid space

photosystem II

photosystem I

thylakoid space

ATP synthase

photosystem II

stroma

photosystem II

ATP synthase

stroma

[Maximum number: 2]

In some boreal species, Rubisco is down-regulated during the winter months. Describe the role of Rubisco in photosynthesis.

[Maximum number: 1]

What occurs in the light-independent reactions of photosynthesis?

Glycerate 3-phosphate is reduced to triose phosphate.

Ribulose bisphosphate is regenerated using reduced NADP.

Ribulose bisphosphate is oxidized to two molecules of glycerate 3-phosphate.

Both ATP and NADP are used to produce triose phosphate.

[Maximum number: 1]

The Calvin cycle continues throughout the life of a plant. In this cycle, triose phosphate is produced, which is used to form glucose.

In total, how many RuBP molecules are regenerated in the process of creating one glucose molecule?

[Maximum number: 7]

Plants have developed efficient methods for transport and for synthesis of foods.

Explain how the light-independent reactions of photosynthesis rely on the light-dependent reactions.

light-dependent reactions produce ATP/reduced NADP;
ATP generated by chemiosmosis/by photophosphorylation/by ATP synthase;
reduced NADP produced by/using electrons from Photosystem I;
RuBP $+\mathrm{CO}_{2}$ to glycerate 3-phosphate (in light independent reactions);
glycerate 3-phosphate reduced to triose phosphate (in light independent reactions);
ATP/reduced NADP used in the light-independent reactions;
reduced NADP provides electrons/hydrogen / to reduce (glycerate 3-phosphate)
OR
reduced NADP used to convert glycerate 3-phosphate to triose phosphate;
ATP provides energy (for reduction of glycerate 3-phosphate);
ATP needed to regenerate RuBP
ATP/reduced NADP run out in darkness
Calvin cycle only possible with light/in the day/is indirectly dependent on light;

All question bank results loaded

a	carbon fixation/fixes carbon dioxide/carboxylation OR rubisco is used in the Calvin cycle/light independent stage
b	carbon dioxide linked to RuBP/ribulose bisphosphate «by rubisco»
c	glycerate 3-phosphate/glycerate phosphate produced «by rubisco»

Covered syllabus points

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Question (e)

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Question (b)

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