Which one of the following is the process involved in photosynthesis?

The answer is B. In photosynthesis, chlorophyll in chloroplasts captures light energy, which is free energy, and uses it to drive the synthesis of glucose from carbon dioxide and water. The energy is thus stored as chemical potential energy in carbohydrates. The overall reaction is 6CO2 + 6H2O + light energy gives C6H12O6 + 6O2.

• A is wrong. Release of stored potential energy is what happens in respiration, the reverse process.
• C is wrong. Oxidation of food to release CO2 and water is cellular respiration, which occurs in both plants and animals.
• D is wrong. Taking in oxygen and giving out CO2 and water vapour describes respiration. Photosynthesis takes in CO2 and releases oxygen.

The core concept is energy transformation and the flow of energy through ecosystems. For Mains, this links to food chains, primary productivity, the carbon cycle and the role of forests as carbon sinks in climate change discussions.

Trap: Aspirants pick D because the gas exchange looks balanced, but they forget the direction. Photosynthesis consumes CO2 and releases O2, which is the reverse of D.