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AP®BiologyCollege BoardExam QuestionsUnit 3: Cellular EnergeticsEnergy & Photosynthesis

Energy & Photosynthesis (College Board AP® Biology): Exam Questions

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Energy & Photosynthesis

1
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The laws of thermodynamics are fundamental principles that govern the transfer of energy, including energy within living systems. A scientist is studying energy flow in an aquatic ecosystem.

Which of the following best applies the second law of thermodynamics to this biological system?

  • Living organisms in the ecosystem are always transferring energy to their surroundings, increasing the overall entropy of the universe.

  • Energy within the ecosystem cannot be created or destroyed.

  • The total energy of the ecosystem remains constant, even if converted between forms.

  • Living organisms in the ecosystem need energy to fuel metabolism, meaning that they decrease the entropy of the universe.

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2
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All organisms require a constant input of energy. Cells obtain energy through chemical means, such as feeding or photosynthesis.

Which of the following best explains why organisms need a constant input of energy?

  • To allow transfer of energy to the environment.

  • To create energy during metabolic reactions.

  • To maintain order, and power chemical processes inside cells.

  • To enable cells to decouple energy-requiring processes from energy-releasing processes.

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3
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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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4
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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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5
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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.

Five test tubes labelled 1 to 5, containing chloroplast suspension, DCPIP, water, isolation medium, and ammonium hydroxide, with varying contents.

Which tube in Figure 1 acts as a control that allows the effect of ammonium hydroxide to be clearly determined?

  • Tube 1

  • Tube 2

  • Tube 3

  • Tube 4

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61 mark

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 vs. wavelength for chlorophyll a, chlorophyll b, and carotenoids, with peaks around 450 nm and 670-700 nm.
Figure 1.

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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7
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The evolution of photosynthesis in prokaryotic organisms transformed the Earth's atmosphere and allowed for the development of complex life. Scientists claim that the first early photosynthetic organisms, known as cyanobacteria, evolved around 2.3 billion years ago.

Which of the following graphs provides evidence for this?

  • Graph showing atmospheric oxygen percentage over 4 billion years ago. Oxygen levels remain low until a significant increase near 1 billion years ago.
  • Graph showing atmospheric oxygen percentage over billions of years. Oxygen rises sharply around 2 billion years ago, stabilising thereafter.
  • Graph showing atmospheric oxygen percentage over time, billions of years ago. Oxygen stable at 10% from 4 to 3 billion years ago, then declines.
  • Graph showing atmospheric oxygen percentage over time, with a peak around 2 billion years ago. Oxygen levels rise sharply then fall again towards 1 billion years ago.

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