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AP Biology 3.4 Photosynthesis

Practise AP Biology 3.4 questions by connecting chloroplast structure and pigments with electron transport, ATP or NADPH production and carbon fixation.

Syllabus
Effective Fall 2025
Course
AP Biology

Exam points

  • locate light reactions in thylakoids and carbon fixation in the stroma
  • trace electron flow, water splitting and NADPH formation in photosystems
  • explain proton gradients, chemiosmosis and ATP synthase in photophosphorylation
  • interpret pigment spectra, DCPIP absorbance and environmental data to predict photosynthetic rate

Covered syllabus points

3.4.A—Describe the photosynthetic processes and structural features of the chloroplast that allow organisms to capture…3.4.B—Explain how cells capture energy from light and transfer it to biological molecules for storage and use

3.4 Photosynthesis question 1

[Maximum number: 4]

A cross section of a chloroplast showing membranes and the spaces between membranes is shown in Figure 1.

Figure 1. A diagram of the cross section of a chloroplast

Figure 1. A diagram of the cross section of a chloroplast

Question (a)

(a)

Describe the major process that takes place in this eukaryotic organelle.

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Question (b)

(b)

Explain the function of the structure labeled with an X in Figure 1.

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Question (c)

(c)

On the template in the space provided for your response, represent the location where carbon fixation takes place by writing " CF " and the location of the electron transport proteins by writing " ETP ".

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Question (d)

(d)

Explain how the shape and stacking of the thylakoids contributes to the rate of carbon fixation by the chloroplast.

TO BEGIN YOUR ANSWER TO QUESTION 5.

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3.4 Photosynthesis question 2

[Maximum number: 4]

Noncyclic electron flow and cyclic electron flow are two major pathways of the light-dependent reactions of photosynthesis. In noncyclic electron flow, electrons pass through photosystem II, then components of a chloroplast electron transport chain, and then photosystem I before finally reducing NADP +{ }^{+}to NADPH. In cyclic electron flow, electrons cycle through photosystem I and some components of the electron transport chain (Figure 1).

Figure 1. The pathways of noncyclic and cyclic (heavy arrows) electron flow. The cytochrome complex is a component of the electron transport chain between the two photosystems.

Figure 1. The pathways of noncyclic and cyclic (heavy arrows) electron flow. The cytochrome complex is a component of the electron transport chain between the two photosystems.

Question (a)

(a)

Describe the role of chlorophyll in the photosystems of plant cells.

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Question (b)

(b)

Based on Figure 1, explain why an increase in the ratio of NADPH to NADP +{ }^{+}will cause an increase in the flow of electrons through the cyclic pathway.

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Question (c)

(c)

Using rice plants, scientists examined the effect of a mutation that results in the loss of the protein CRR6. CRR6 is a part of the photosystem I complex, and its absence reduces the activity of photosystem I. Predict the effect of the mutation on the rate of biomass (dry weight) accumulation.

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Question (d)

(d)

Justify your prediction in part (c).

Write your responses to this question only on the designated pages in the separate Free Response booklet.

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