Optometry Admission Test (OAT) Practice

What occurs during the light reactions of photosynthesis?

1. Water is split to release oxygen

2. Carbon dioxide is fixed into glucose

3. Light energy is captured to produce ATP

4. Chlorophyll captures light energy to generate high-energy molecules

The correct answer is: Chlorophyll captures light energy to generate high-energy molecules

During the light reactions of photosynthesis, chlorophyll plays a crucial role by capturing light energy from the sun. When chlorophyll absorbs light, it becomes excited and initiates a series of reactions that convert this radiant energy into chemical energy. This energy is used to generate high-energy molecules, specifically ATP and NADPH, which are essential for the subsequent phase of photosynthesis, known as the Calvin cycle. The process begins in the thylakoid membranes of the chloroplasts, where absorbed light energy drives the movement of electrons through the electron transport chain. This movement helps pump protons into the thylakoid lumen, creating a proton gradient. As protons flow back into the stroma through ATP synthase, ATP is produced. Additionally, the electrons are used to reduce NADP+ to NADPH. By focusing on the role of chlorophyll and the generation of high-energy molecules, it underscores the primary function of the light reactions, which is to convert light energy into a form that can be utilized in the next stages of photosynthesis. Other options describe processes related to photosynthesis but do not accurately reflect the main outcome of the light reactions. For instance, while water splitting and oxygen release occur in these reactions, the primary focus is