Which of the following compounds is essential for light-dependent reactions to occur?

Chlorophyll is essential for the light-dependent reactions of photosynthesis because it plays a crucial role in capturing light energy from the sun. This green pigment, found in the chloroplasts of plant cells, absorbs light primarily in the blue and red wavelengths, facilitating the conversion of light energy into chemical energy. During the light-dependent reactions, chlorophyll absorbs photons, which energize electrons. These high-energy electrons move through a series of proteins in the thylakoid membrane, leading to the production of ATP and NADPH, two important energy carriers used in the subsequent light-independent reactions (Calvin cycle) of photosynthesis.

In contrast, while glucose and carbohydrates are products of the overall process and oxygen is a byproduct, they do not play a direct role in the initiation of the light-dependent reactions. Therefore, chlorophyll is the key compound required for these reactions to take place effectively.