Which organelle is primarily responsible for photosynthesis?

The organelle primarily responsible for photosynthesis is the chloroplast. Chloroplasts contain chlorophyll, the green pigment that captures light energy from the sun. This light energy is then used to convert carbon dioxide and water into glucose and oxygen through a series of biochemical reactions known as the light-dependent and light-independent reactions (or Calvin cycle). This process is fundamental for plants, algae, and some bacteria, as it allows them to produce their own food and release oxygen into the atmosphere, which is essential for life on Earth.

The other organelles listed do not perform photosynthesis. Mitochondria are involved in cellular respiration, which generates energy by breaking down glucose. The Golgi apparatus is responsible for modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles. The nucleus houses the cell's genetic material and coordinates activities such as growth, metabolism, and reproduction, but it does not engage in photosynthesis. Thus, chloroplasts are uniquely equipped to carry out this critical function in photosynthetic organisms.