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In an experiment investigating how light intensity affects the rate of photosynthesis in pondweed (counting gas bubbles as a lamp is moved closer), which gas is released during photosynthesis? A) carbon dioxide B) oxygen C) methane D) nitrogen

A student uses this apparatus to investigate the effect of light intensity on the rate of photosynthesis in pondweed. This is the student’s method. • put a cut piece of pondweed in a beaker of water...
A student uses this apparatus to investigate the effect of light intensity on the rate of photosynthesis in pondweed.

This is the student’s method.

• put a cut piece of pondweed in a beaker of water
• put a lamp 12 cm from the beaker
• count the number of bubbles of gas released from the cut end of the pondweed in one minute
• repeat this count for two more one-minute periods

The student repeats the method, moving the lamp 2 cm nearer the beaker each time.
In an experiment investigating how light intensity affects the rate of photosynthesis in pondweed (c...
Answer

B) Oxygen. During photosynthesis, pondweed produces oxygen gas ($O_2$) as a product, which is released as bubbles from the cut end.

Explanation

What this pondweed bubble experiment is measuring

Counting bubbles from pondweed is a simple way to track a gas made during photosynthesis. The lamp distance changes light intensity, which changes the rate, but the identity of the gas stays the same.

The photosynthesis products

In photosynthesis, plants use carbon dioxide and water to make glucose and oxygen:

$$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$$

The gas that appears as bubbles in pondweed experiments is $O_2$.

Why the other options are wrong

  • A) Carbon dioxide: $CO_2$ is a reactant the plant takes in, not a gas it releases during photosynthesis.
  • C) Methane: not produced by photosynthesis.
  • D) Nitrogen: not produced by photosynthesis; most plants take nitrogen in as nitrates or ammonium, not as a gas product.

Correct option

B) oxygen.

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Skills You Achive
photosynthesis interpreting experiments biology multiple choice

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