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    AP Biology: Photosynthesis

    15 practice questions · 15 flashcards · made from study notes

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    Terms in this set (15)

    What is the primary function of photosynthesis?
    To convert light energy into chemical energy stored in sugar.
    What is the overall equation for photosynthesis?
    6 CO2 + 6 H2O + light → C6H12O6 + 6 O2
    In plants, photosynthesis takes place in organelles called ___.
    chloroplasts
    Define thylakoids.
    Stacks of membrane discs within chloroplasts where light-dependent reactions occur.
    The fluid surrounding the thylakoids within a chloroplast is called the ___.
    stroma
    Where do the light-dependent reactions of photosynthesis occur?
    In the thylakoid membranes.
    What is the role of water (H2O) in the light-dependent reactions?
    Water is split (photolysis) to replace electrons lost from photosystem II, releasing O2 as a by-product and H+ ions.
    The process of using a proton gradient to make ATP during light reactions is called ___.
    photophosphorylation
    What is the primary product of the light-dependent reactions that is then used in the Calvin cycle?
    ATP and NADPH
    Where does the Calvin cycle (light-independent reactions) occur?
    In the stroma.
    The enzyme ___ attaches CO2 to ribulose bisphosphate (RuBP) during carbon fixation in the Calvin cycle.
    rubisco
    What is photorespiration, and when does it occur?
    Photorespiration is a process where rubisco binds O2 instead of CO2, consuming energy and releasing CO2 without producing sugar. It increases in hot, dry conditions when stomata close.
    How do C4 plants reduce photorespiration?
    They separate carbon fixation and the Calvin cycle in space, using PEP carboxylase in mesophyll cells to fix CO2 into a four-carbon acid, which is then transported to bundle-sheath cells where CO2 is released for rubisco.
    Explain how CAM plants reduce photorespiration and conserve water.
    CAM plants separate carbon fixation and the Calvin cycle in time. They open stomata at night to store CO2 as organic acids and close stomata during the day, releasing the stored CO2 for the Calvin cycle.
    List three factors that can limit the rate of photosynthesis.
    Light intensity, CO2 concentration, and temperature.

    Practice questions (15)

    1. 1.What are the primary inputs for the overall process of photosynthesis, which converts light energy into chemical energy?

      • AGlucose, oxygen, and water
      • BCarbon dioxide, water, and light
      • CATP, NADPH, and carbon dioxide
      • DOxygen, water, and light
      Show answer

      Answer: Carbon dioxide, water, and light

      This question checks the student's understanding of the basic requirements for photosynthesis to occur, as shown in the overall equation 6 CO2 + 6 H2O + light → C6H12O6 + 6 O2. Knowing the inputs is fundamental to understanding the entire process.

    2. 2.True or False: The main purpose of photosynthesis is to produce oxygen for animals to breathe.

      • ATrue
      • BFalse
      Show answer

      Answer: False

      This question addresses a common misconception. While photosynthesis does produce oxygen as a by-product, its primary purpose for the plant is to convert light energy into chemical energy stored in sugar (glucose) for its own growth and metabolism.

    3. 3.Based on the overall equation for photosynthesis (6 CO2 + 6 H2O + light → C6H12O6 + 6 O2), what are the two main products of this process?

      Show answer

      Answer: The main products are glucose (C6H12O6) and oxygen (O2).

      This question requires students to identify the outputs from the summary chemical equation of photosynthesis. Recognizing the products is essential for understanding what the process accomplishes.

    4. 4.Which of the following are the primary products of the light-dependent reactions that are used as inputs for the Calvin cycle (the light-independent reactions)?

      • ACO2 and H2O
      • BO2 and Glucose
      • CATP and NADPH
      • DRuBP and G3P
      Show answer

      Answer: ATP and NADPH

      This question directly assesses the student's understanding of the connection between the two main stages of photosynthesis. The light-dependent reactions produce ATP and NADPH, which provide the chemical energy and reducing power needed to drive the Calvin cycle.

    5. 5.True or False: The light-dependent reactions of photosynthesis occur in the stroma of the chloroplast, while the light-independent reactions (the Calvin cycle) take place in the thylakoid membranes.

      • ATrue
      • BFalse
      Show answer

      Answer: False

      This question tests the student's knowledge of the specific locations of the two phases of photosynthesis. It's a common point of confusion, and getting it right is fundamental to understanding how the process is organized within the chloroplast. The locations are reversed in the statement.

    6. 6.What are the three main inputs required for the light-dependent reactions to proceed?

      Show answer

      Answer: The main inputs are light, water (H2O), and NADP+.

      This question requires students to recall the key reactants of the first stage of photosynthesis. It reinforces that while the overall process uses CO2, this specific stage does not. Understanding the inputs is crucial for comparing the two stages.

    7. 7.While both stages of photosynthesis are part of the same overall process, they have distinct roles. Which statement best contrasts the primary function of the light-dependent reactions with the primary function of the light-independent reactions (the Calvin cycle)?

      • AThe light-dependent reactions capture light energy to create chemical energy (ATP and NADPH), while the Calvin cycle uses that chemical energy to synthesize sugars from CO2.
      • BThe light-dependent reactions produce glucose from sunlight, while the Calvin cycle uses CO2 to make ATP and NADPH.
      • CThe light-dependent reactions split water to release CO2, while the Calvin cycle uses oxygen to build sugars.
      • DThe light-dependent reactions fix carbon into organic molecules, while the Calvin cycle generates oxygen as a byproduct.
      Show answer

      Answer: The light-dependent reactions capture light energy to create chemical energy (ATP and NADPH), while the Calvin cycle uses that chemical energy to synthesize sugars from CO2.

      This question challenges students to move beyond simple inputs and outputs and analyze the core purpose of each stage. It requires them to synthesize information to see how one stage converts energy and the other uses that energy to build molecules, highlighting their complementary roles.

    8. 8.Explain why the Calvin cycle, also known as the light-independent reactions, cannot proceed for an extended period in the absence of light, despite not using light directly.

      Show answer

      Answer: The Calvin cycle depends on a continuous supply of ATP and NADPH from the light-dependent reactions. Without light, the light-dependent reactions stop, which means ATP and NADPH are no longer produced. Once the existing supply of ATP and NADPH in the stroma is used up, the Calvin cycle halts.

      This question challenges the misconception that 'light-independent' means completely separate from light. It forces students to think critically about the dependency between the two stages, reinforcing that the processes are coupled and the products of the first stage are essential reactants for the second.

    9. 9.What is the primary consequence for a plant when the enzyme rubisco binds to O2 instead of CO2?

      • AThe plant produces excess sugar.
      • BThe plant's chlorophyll production increases.
      • CThe plant releases excess water through its stomata.
      • DThe plant undergoes photorespiration, consuming energy without producing sugar.
      Show answer

      Answer: The plant undergoes photorespiration, consuming energy without producing sugar.

      This question checks the student's understanding of the direct outcome of rubisco's dual activity. It's crucial to know that binding O2 initiates a wasteful process, not a productive or unrelated one.

    10. 10.A plant is in a hot, dry environment, causing its stomata (leaf pores) to close. How does this condition lead to an increase in photorespiration?

      Show answer

      Answer: When stomata close to conserve water, the concentration of CO2 inside the leaf drops. This makes it more likely that the enzyme rubisco will bind with O2 instead of CO2, triggering the wasteful process of photorespiration.

      This question requires students to connect an environmental condition (hot, dry weather) to a physiological response (stomata closing) and then to a specific biochemical outcome (increased photorespiration due to lower internal CO2 levels). It tests their ability to trace a cause-and-effect chain described in the text.

    11. 11.The enzyme rubisco is described as being able to bind to O2 instead of CO2, leading to photorespiration. True or false: Photorespiration is an efficient alternative pathway for producing sugar when CO2 is scarce.

      • ATrue
      • BFalse
      Show answer

      Answer: False

      This question directly challenges a potential misconception. Students must understand that photorespiration is a *wasteful* process that *consumes* energy and does *not* produce sugar, making it an inefficiency, not a helpful alternative.

    12. 12.What is the key difference in how C4 plants (like maize) and CAM plants (like pineapples) separate the initial capture of CO2 from the Calvin cycle to minimize photorespiration?

      Show answer

      Answer: C4 plants separate the two processes in space, moving CO2 from mesophyll cells to bundle-sheath cells. CAM plants separate them in time, capturing CO2 at night and running the Calvin cycle during the day.

      This question requires students to recall and compare the core strategies of C4 and CAM pathways, specifically how they solve the problem of photorespiration differently. It tests their understanding of the spatial vs. temporal separation mentioned in the text.

    13. 13.A key adaptation for both C4 and CAM plants is fixing CO2 into an organic acid before the Calvin cycle. How does this initial step help them outcompete standard C3 plants in hot, dry conditions?

      • AThe organic acid is a better source of electrons than water.
      • BThe organic acid directly powers the production of ATP and NADPH.
      • CIt allows them to keep their stomata (leaf pores) open all day without losing water.
      • DIt allows them to concentrate CO2 around the enzyme rubisco, reducing the wasteful process of photorespiration.
      Show answer

      Answer: It allows them to concentrate CO2 around the enzyme rubisco, reducing the wasteful process of photorespiration.

      This question challenges students to think critically about the 'why' behind the adaptation. The correct answer focuses on the shared advantage of both pathways: overcoming rubisco's inefficiency by creating a high-CO2 environment, which is crucial when stomata are closed in hot, dry weather to conserve water. It forces a deeper analysis of the problem (photorespiration) and the solution (concentrating CO2).

    14. 14.True or False: Both C4 and CAM plants have evolved to use an enzyme other than rubisco for the initial capture of CO2 from the air because that alternative enzyme, PEP carboxylase, does not bind to O2 and is therefore more efficient when CO2 levels are low.

      • ATrue
      • BFalse
      Show answer

      Answer: True

      This question assesses understanding of the specific enzyme adaptation shared by C4 and CAM plants. It confirms that students know why PEP carboxylase is used instead of rubisco for initial fixation—its inability to bind O2 makes it superior in conditions that lead to photorespiration.

    15. 15.If a plant is given plenty of light and water, but the concentration of carbon dioxide (CO2) in the air is very low, which of the following is most likely to be the primary limiting factor for photosynthesis?

      • ALight intensity
      • BWater availability
      • CCO2 concentration
      • DTemperature
      Show answer

      Answer: CO2 concentration

      This question assesses understanding of limiting factors. Even if light and water are abundant, photosynthesis cannot proceed quickly if there isn't enough CO2, which is a key ingredient for the Calvin cycle.

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