Name the cell organelle responsible for photosynthesis.

The cell organelle responsible for photosynthesis is the chloroplast.

Chloroplasts are found in green plant cells and algae. They contain a green pigment called chlorophyll, which captures sunlight energy. This energy is then used to convert carbon dioxide and water into glucose (food) and oxygen through photosynthesis. 

The main parts of a chloroplast include the thylakoid membranes (where light reactions occur) and the stroma (where dark reactions occur). Without chloroplasts, plants cannot make their own food or release oxygen needed by other living beings.