Light Reactions

The light reaction is the first stage of photosynthesis. This takes place in the organelles of the plant cell known as the chloroplasts.

If one looks inside the chloroplasts, one can find flattened sacs of membranes called thylakoids.

These membranes contain a special pigment called chlorophyll, which absorbs the sunlight.

Using the energy from sunlight, the water absorbed from the roots is broken down into hydrogen ions, electrons, and oxygen gas.

The electrons then move through a series of steps inside the thylakoid membranes, known as the electron transport chain.

This process generates two energy-rich molecules: adenosine triphosphate, or ATP, and nicotinamide adenine dinucleotide phosphate, or NADPH.

These molecules are like rechargeable batteries, ready to power the next stage of photosynthesis, the dark reaction.

During light reactions, sunlight is the critical component that drives the use of water and the release of oxygen. As these reactions occur only during the day, they are called light reactions.