What is photosynthesis?

Photosynthesis is fundamentally the process by which green plants, algae, and certain bacteria convert light energy from the sun into chemical energy stored in glucose. This process occurs primarily in the chloroplasts of plant cells, using chlorophyll to capture sunlight. The overall equation for photosynthesis can be simplified to show that carbon dioxide and water, in the presence of sunlight, are transformed into glucose and oxygen.

The significance of photosynthesis lies in its role in the ecosystem. It is the primary source of organic matter for nearly all living organisms. Plants produce glucose, which serves as food for themselves and other organisms that consume them, thus forming the base of the food chain. Oxygen produced as a byproduct is essential for the survival of aerobic organisms, including humans.

The other choices pertain to different biological processes. Cellular respiration is the method that organisms use to extract energy from food, and fermentation is a type of anaerobic respiration that occurs in the absence of oxygen. A technique for extracting energy from food could refer broadly to metabolism, which encompasses many processes, including cellular respiration and fermentation. In contrast, photosynthesis specifically refers to the conversion of light energy into chemical energy, making option B the correct choice.