The table shows the direction and function of substances in a chemical reaction that takes place in the chloroplasts of plant cells. The table is missing information at W, X, and Y.

Without any additional context, it is not possible to determine what substance W is.

Substance W in the chloroplasts of plant cells is sunlight.

To determine the substance W in the given table, we need to understand the components involved in photosynthesis, which is a chemical reaction that takes place in the chloroplasts of plant cells.

Photosynthesis is the process through which plants convert sunlight, water, and carbon dioxide into glucose (sugar) and oxygen. The glucose produced is often stored as starch within the plant.

Considering this information, we can conclude that substance W is starch (option b). Starch is the stored form of glucose produced during photosynthesis.