Final answer:
The entire process of photosynthesis takes place within the chloroplast, specifically in the thylakoids that contain chlorophyll. Chloroplasts are enclosed by a double membrane and are located in the mesophyll cells of leaves.
Step-by-step explanation:
The smallest unit in which the entire process of photosynthesis takes place is the chloroplast. In all autotrophic eukaryotes, including plants, photosynthesis occurs inside this organelle. The chloroplasts are located within the mesophyll cells of the leaf.
Chloroplasts contain a double membrane and within them are structures known as thylakoids, which are stacked in some places to form grana. The thylakoids contain chlorophyll, a pigment that absorbs sunlight and initiates the process of photosynthesis.
During photosynthesis, carbon dioxide and water are used along with sunlight to produce glucose and oxygen. The light-absorbing capabilities of chlorophyll allow it to capture the sun's energy, starting the first stage of photosynthesis known as the light reactions. This energy is then used in the Calvin Cycle to synthesize glucose from carbon dioxide and water.
The process also involves the gas exchange of oxygen and carbon dioxide through carefully regulated openings called stomata, located primarily on the underside of the leaf, with each stoma surrounded by guard cells that regulate their opening and closing.