Question 29

Water supplies electrons in the light reactions of photosynthesis.

In the process of photosynthesis, water plays a crucial role by providing electrons that are essential for the light reactions. This supply of electrons is necessary for the conversion of light energy into chemical energy.

A) Combines with carbon dioxide

While water does participate in the overall process of photosynthesis, it does not directly combine with carbon dioxide. Instead, carbon dioxide is fixed in the Calvin cycle, which occurs after the light reactions where water is primarily involved.

B) Absorbs light energy

Water itself does not absorb light energy; rather, it is the chlorophyll and other pigments in the chloroplasts that capture light energy during photosynthesis. Water's primary role is to provide electrons, rather than to absorb light.

C) Supplies electrons in the light reactions

Water is vital in the light reactions of photosynthesis as it donates electrons during the photolysis process, ultimately leading to the formation of NADPH and ATP. This function is essential for the energy conversion that occurs in these light-dependent reactions.

D) Transports hydrogen ions in the dark reactions

Water does not transport hydrogen ions in the dark reactions, also known as the Calvin cycle. Instead, it is the products of the light reactions, such as NADPH and ATP, that drive the reactions in the Calvin cycle.

Conclusion

Water's primary function in photosynthesis is to supply electrons during the light reactions, making option C the correct answer. The other options either misinterpret the role of water or attribute functions that are performed by other components of the photosynthetic process. Thus, understanding the specific contributions of water helps clarify its essential role in photosynthesis.