Light reaction in photosynthesis is the initial stage of the process that occurs in the chloroplasts of plants. It is also known as the light-dependent reaction, as it requires light energy to take place. In simple terms, light reaction can be defined as the process where light energy is converted into chemical energy in the form of ATP and NADPH, which are then used in the Calvin cycle to produce glucose.

The key components involved in the light reaction are chlorophyll, water, sunlight, and enzymes. Chlorophyll is a pigment found in the chloroplasts that absorbs light energy. When sunlight hits the chlorophyll molecules, it excites the electrons, leading to the splitting of water molecules into oxygen, protons, and electrons. The electrons are then passed through a series of proteins in the thylakoid membrane, known as the electron transport chain, generating ATP and NADPH.

The overall equation for the light reaction can be summarized as follows:
6H2O + 6CO2 + light energy → C6H12O6 + 6O2
In this equation, water molecules are split into oxygen and hydrogen ions, while carbon dioxide is converted into glucose. The oxygen is released as a byproduct into the atmosphere, which is essential for all aerobic organisms.

To summarize, the light reaction is a crucial step in the process of photosynthesis, where light energy is converted into chemical energy that fuels the production of glucose. Understanding this process is essential for students studying biology in Class 10, as it forms the basis of how plants create their own food using sunlight. By grasping the concept of light reaction, students can appreciate the intricate mechanisms that drive the survival of all living organisms on Earth.