1. Carbon Dioxide (CO2): This is the source of carbon atoms used to build sugars. It enters the plant through tiny pores called stomata on the leaves.

2. Water (H2O): Water is used as a source of electrons and hydrogen ions (protons). It's absorbed from the soil through the roots.

3. Light Energy: Sunlight provides the energy needed to drive the chemical reactions of photosynthesis. This light is absorbed by chlorophyll, a green pigment found in chloroplasts.

4. Chlorophyll (and other pigments): Chlorophyll is the main pigment responsible for absorbing light energy. Other pigments like carotenoids can also absorb light energy and pass it to chlorophyll.

5. Enzymes: Various enzymes catalyze (speed up) the chemical reactions involved in photosynthesis.

In addition to these substances, the plant also needs nutrients like nitrogen, phosphorus, and potassium, which are absorbed from the soil. These nutrients are essential for the growth and development of the plant, including the production of chlorophyll and other components necessary for photosynthesis.