Question

The graph shows the relation between light intensity and the giving off and taking up of carbon dioxide by the leaves of a plant. Why is most carbon dioxide given off when the light intensity is zero units?

• A. Because it just the start of the experiment.
• B. Only respiration is taking place at this intensity of light.
• C. Only photosynthesis is taking place at this intensity of light.
• D. The rate of photosynthesis is equivalent to the rate of respiration.
• E. The rate of photosynthesis is more than the rate of respiration.

Answer 1

The correct option is B Only respiration is taking place at this intensity of light.

Photosynthesis and respiration have several limiting factors like light, carbon dioxide concentration, etc. Most carbon dioxide is given off when the light intensity is zero units, because only respiration is taking place. At this intensity of light no photosynthesis occurs, so no consumption of carbon dioxide takes place.

So, the correct answer is 'Only respiration is taking place at this intensity of light.'