1. Sunlight: Sunlight provides the energy that drives the process of photosynthesis. It is absorbed by chlorophyll, a green pigment found in chloroplasts within plant cells.

2. Carbon dioxide (CO2): This gas is taken in from the atmosphere through tiny openings on leaves called stomata. CO2 serves as the source of carbon atoms that are used to build sugars during photosynthesis.

3. Water (H2O): Water is absorbed from the soil through roots and transported to the leaves. It provides the hydrogen atoms needed to make the sugars and is also used in the process of splitting water molecules to release oxygen.