Home >> Science & Nature >> Animals & Science

What Occurs in the Light Reactions Stage of Photosynthesis?

Photosynthesis is the process that converts carbon dioxide into sugars and other organic compounds that provide nutrition for plants. It is a highly complex process through which plants obtain energy. Without photosynthesis, plant cells stop dividing and the plant dies. This process occurs in two phases. Light-dependent reactions occur when the plant is absorbing and converting sunlight, and light-independent reactions occur after the plant has absorbed sufficient sunlight.

Chlorophyll and Light
- Chlorophyll is the green pigment of plants produced in tiny organelles called chloroplasts. In the light reaction stage, each molecule of chlorophyll absorbs one photon of light and loses one electron. This begins the process of the conversion of light into energy for the plant's use.
Electron Transport
- Electron transport chains move electrons from a chemical electron donor to an electron receptor, according to "Biology: Concepts and Connections." In the case of photosynthesis, the enzyme nicotinamide adenine dinucleotide phosphate (NADP) is moved down an electron transport chain and transformed into nicotinamide adenine dinucleotide phosphate-oxidase (NADPH). This enzyme is then used to help the plant produce and metabolize energy.
ATP Synthesis
- "Biology: Life on Earth with Physiology" explains that after an electron transport chain transforms NADP into NADPH, a proton gradient is created that synthesizes adenosine triphosphate, commonly referred to as ATP. ATP powers many of the metabolic reactions within a cell by transporting chemical energy throughout the cell.
Light-Independent Phase
- The light-independent phase begins at the end of the light reaction stage of photosynthesis and cannot occur without light reactions. This process involves the release of sugars that are then converted into starches, a central component of plant bodies.

Animals & Science