AP®BiologyCollege BoardExam QuestionsUnit 3: Cellular EnergeticsPhotosynthesis

Photosynthesis (College Board AP® Biology)

Exam Questions

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Photosynthesis

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Photosynthesis

1
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Photosynthesis involves two main stages: the light-dependent reactions and the Calvin cycle. During the light-dependent reactions light energy is used to produce ATP and NADPH. Which of the following correctly describes the initial step in the light-dependent reactions?

  • CO₂ is fixed into organic molecules.

  • Light energy excites electrons in chlorophyll molecules within the thylakoid membrane.

  • High-energy electrons are passed from photosystem I to photosystem II.

  • A proton gradient is established across the thylakoid membrane.

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2
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The light-independent reactions of photosynthesis, also known as the Calvin cycle, occur in the stroma of the chloroplast and are responsible for producing complex organic molecules. Which of the following correctly describes an event that occurs during the Calvin Cycle?

  • ATP is synthesised from ADP and inorganic phosphate.

  • NADP+ is reduced to NADPH.

  • Energy from NADH allows the production of glucose.

  • Energy from NADPH allows the production of glucose.

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3
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DCPIP is a chemical compound that is blue when oxidised and colourless when it accepts electrons during the light-independent reaction. Figure 1 shows the experimental set-up of a study that investigates the effect of ammonium hydroxide on the photosynthetic activity of chloroplasts that have been extracted from spinach leaves and suspended in an isolation medium.  All five tubes are placed in a water bath at 20 °C and illuminated from all sides during the investigation.

Diagram of five test tubes with different contents: Tube 1: chloroplast suspension and water, Tube 2: chloroplast suspension, DCPIP, water and a foil covering, Tube 3: isolation medium, DCPIP and water, Tube 4: chloroplast suspension, DCPIP and water, Tube 5: chloroplast suspension, DCPIP and ammonium hydroxide.
Figure 1. The set-up for an investigation into ammonium hydroxide and photosynthesis

Which tube in Figure 1 is most likely to function as a direct experimental control when investigating the independent variable?

  • Tube 1

  • Tube 2

  • Tube 3

  • Tube 4

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4
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Photosynthetic pigments, such as chlorophyll a, chlorophyll b and carotenoids, absorb light energy during photosynthesis. Different pigments absorb light at different wavelengths, as shown in Figure 1.

Graph showing light absorption spectra for chlorophyll a, chlorophyll b, and carotenoids across 400-700 nm wavelengths. Peaks differ for each pigment.
Figure 1. Absorption spectra for different photosynthetic pigments

Which of the following correctly describes the absorption data shown in Figure 1?

  • The highest wavelength at which chlorophyll a has an absorption peak is higher than the equivalent for chlorophyll b.

  • The absorption peak for carotenoids is at 460 nm.

  • Chlorophyll b does not absorb light at a wavelength of 620 nm.

  • The lowest wavelength at which chlorophyll b has an absorption peak is lower than the equivalent for chlorophyll a.

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