Why is photosynthesis considered an endergonic reaction?

• A. Because it decreases the overall free energy of the system.
• B. Because it requires an input of energy from sunlight to convert carbon dioxide and water into glucose.
• C. Because it occurs only in the absence of light.
• D. Because it releases energy by breaking down glucose into carbon dioxide and water.

Answer: (B)

Verified step by step guidance

1. Understand the concept of an endergonic reaction: An endergonic reaction is a chemical process that requires an input of energy to proceed. It is characterized by an increase in the free energy of the system (ΔG > 0).
2. Recognize the role of sunlight in photosynthesis: Photosynthesis is a process where plants, algae, and some bacteria use sunlight as an energy source to drive the conversion of carbon dioxide (CO₂) and water (H₂O) into glucose (C₆H₁₂O₆) and oxygen (O₂).
3. Analyze the energy requirements of photosynthesis: The reaction requires energy input because the products (glucose and oxygen) have higher energy than the reactants (carbon dioxide and water). This energy is provided by sunlight, making the process endergonic.
4. Compare photosynthesis to exergonic reactions: Unlike exergonic reactions, which release energy (e.g., cellular respiration), photosynthesis stores energy in the chemical bonds of glucose, further confirming its endergonic nature.
5. Conclude why photosynthesis is endergonic: Photosynthesis is considered an endergonic reaction because it requires an input of energy from sunlight to synthesize glucose from carbon dioxide and water, increasing the system's free energy.