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Question 35

A class measures the rate of photosynthesis of pondweed by watching bubbles rise from the cut stem. What are those bubbles, and what do they show?

  1. Bubbles of carbon dioxide, showing how much gas the plant takes in
  2. Bubbles of water vapour, showing how fast water is being used
  3. Bubbles of oxygen, showing how fast the plant is photosynthesisingCorrect answer
  4. Bubbles of air pushed out of the stem as the plant grows

Explanation

The gas the reaction gives off comes out of the cut stem as bubbles, so counting them over a fixed time tracks how fast the reaction is running. The common error names the gas the plant absorbs instead, but that one is taken in from the water around the shoot and would never appear as bubbles leaving it.

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Question 35: A class measures the rate of photosynthesis of pondweed by… · Plants and Photosynthesis · Questena