UPSC Prelims 2014 Q65: Science & Technology – Biology
Which one of the following is the process involved in photosynthesis?
- (a) Potential energy is released to form free energy
- (b) Free energy is converted into potential energy and stored
- (c) Food is oxidized to release carbon dioxide and water
- (d) Oxygen is taken in, and carbon dioxide and water vapour are given out
Answer: (b) Free energy is converted into potential energy and stored
Explanation
Process involved in photosynthesis
In photosynthesis, green plants use sunlight to make glucose from carbon dioxide and water.
Light energy (free energy) is changed into chemical energy and stored as potential energy in food.
| Option | Describes | Verdict |
|---|---|---|
| (a) Potential energy is released to form free energy | Respiration | Incorrect |
| (b) Free energy is converted into potential energy and stored | Photosynthesis | Correct |
| (c) Food is oxidized to release carbon dioxide and water | Respiration | Incorrect |
| (d) Oxygen is taken in, and carbon dioxide and water vapour are given out | Respiration | Incorrect |
The two processes compared:
| Feature | Photosynthesis | Respiration |
|---|---|---|
| Energy | Stored | Released |
| Takes in | Carbon dioxide, water | Oxygen, glucose |
| Gives out | Oxygen, glucose | Carbon dioxide, water |
| Where | Chloroplast | Mitochondria |
Answer: (b) Free energy is converted into potential energy and stored.
Why each option is right or wrong
- (a) Incorrect. Releasing potential energy describes respiration.
- (b) CORRECT. Photosynthesis converts free energy of light into stored potential energy.
- (c) Incorrect. Oxidizing food to carbon dioxide and water is respiration.
- (d) Incorrect. Taking in oxygen and giving out carbon dioxide is respiration.
Key point
Photosynthesis stores light energy as chemical (potential) energy in glucose; respiration releases it. They are opposite processes.
Remember
Photosynthesis stores energy; respiration releases it.
Common mistakes
- Mixing up photosynthesis and respiration.
- Thinking plants only give out oxygen; they also respire.
- Forgetting that photosynthesis happens in the chloroplast.
Exam tip
Three of the four options describe respiration. The odd one out is photosynthesis.
Sources
- NCERT Class XI — Biology (Photosynthesis in Higher Plants)
- NCERT Class X — Science, Ch 5 (Life Processes)