During photolysis in photosynthesis, what is primarily cleaved by an activated electron?

In the process of photolysis during photosynthesis, water molecules are primarily cleaved. Photolysis occurs in the thylakoid membranes of chloroplasts when light energy is absorbed by chlorophyll pigments. This energy excites electrons, which become activated and are transferred through a series of proteins known as the electron transport chain.

When water molecules are split, they yield oxygen, protons, and electrons. The reaction can be summarized as ( 2H_2O \rightarrow 4H^+ + 4e^- + O_2 ). The cleaved electrons from the water molecule enter the electron transport chain, replacing electrons lost by chlorophyll. This process is crucial because it not only provides electrons needed for the continuation of photosynthesis but also generates oxygen as a byproduct.

The other options do not accurately represent what is cleaved during photolysis. Glucose is produced later in the photo-synthetic pathway through the fixation of carbon dioxide, while carbon dioxide is utilized during the Calvin cycle and is not a product of photolysis. Chlorophyll itself is not cleaved but rather serves as the molecule that absorbs light energy to initiate the process.