Photosynthesizing cells in algae and plants have structures called chloroplasts. These contain chlorophyll, a specialized compound which facilitates the conversion of light energy to energy stored in carbohydrates in the process photosynthesis. Pigment molecules like chlorophyll in plants and other organisms reflect and absorb light at specific parts of light's electromagnetic spetrum.

Photosynthesis is a chemical pathway that’s integral to producing energy in plants and other primary producers. Energy in the form of molecules of glucose is produced from light, water and carbon dioxide while oxygen is released. This occurs in several complex steps, photosynthesis is a rate limited reaction, depends on several factors including carbon dioxide concentration, ambient temperature and light intensity; the energy is retrieved from photons, I.e. particles of light, and water is used as a reducing agent.

Water supplies the chlorophyll in plant cell with replacement electrons for the ones removed from photosystem II. Additionally, in the light dependent reactions, within chloroplasts of plants, water (H2O) split by light during photolysis into H+ and OH- acts as a source of oxygen along with functioning as a reducing agent; it reduces the molecule NADP to NADPH by providing H+ ions. NADP and NADPH are integral to the Calvin cycle where monosaccharides or sugars like glucose are produced after the modification of several molecules.