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Bioenergetics

Rate of photosynthesis

  • 3 things to know
  • Biology Paper 1

Overview

How light intensity, carbon dioxide, temperature and chlorophyll affect the rate, calculating and graphing a rate from bubble counts, limiting factors on graphs, the inverse square law, greenhouse costs, the pondweed investigation with its controls, gas syringe and hazards, writing and testing a hypothesis, and rates from tangents.

What you need to know

Answer each one before you reveal it.

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Key term

Define a limiting factor, and say what limits photosynthesis in a bright warm field, at low light intensity, and at 20 °C versus 30 °C.

Key term

Describe the effect of increasing light intensity on the rate of photosynthesis.

Key term

Explain why raising the carbon dioxide concentration around a plant can increase its rate of photosynthesis.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Describe the effect of increasing light intensity on the rate of photosynthesis.

    Model answer

    The rate increases as light intensity increases, then levels off at high intensities.

  2. 2

    Explain why raising the carbon dioxide concentration around a plant can increase its rate of photosynthesis.

    Model answer

    Carbon dioxide is a raw material for photosynthesis, so supplying more of it lets the reaction go faster.

  3. 3

    Explain why the rate of photosynthesis first rises and then falls as temperature is increased.

    Model answer

    It rises because the reacting molecules and enzymes have more energy, but above the optimum the enzymes are denatured so the rate falls.

  4. 4

    How does the amount of chlorophyll in a leaf affect the rate of photosynthesis?

    Model answer

    Less chlorophyll means less light is absorbed, so the rate of photosynthesis is lower.

  5. 5

    How is the rate of photosynthesis of a piece of pondweed calculated from a count of gas bubbles?

    Model answer

    Divide the number of bubbles produced by the time taken, giving a rate in bubbles per minute.

  6. 6

    A piece of pondweed releases 90 bubbles in 3 minutes. Calculate the rate of photosynthesis in bubbles per minute.

    Model answer

    30 bubbles per minute.

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