What is the energy absorbed by chlorophyll used directly for in plants?

I. To produce ATP 
II. To split water 
III. To fix CO₂

A. I only
B. III only
C. I and II only
D. II and III only

C

This was a multiple completion question. This type of question needs to be constructed carefully and thought about very carefully by candidates. In this case answers B and D could be eliminated because the energy absorbed by chlorophyll is not used to fix CO₂ directly, it must be used to produce to ATP first. The only question was then whether splitting of water is a direct use of energy absorbed by chlorophyll. The expected view was that it is, as water is not split unless excited electrons have been given away by chlorophyll in Photosystem II. An illustration of this is the rapidity with which pondweed stops producing bubbles of oxygen when light intensity is reduced.