97. Which of the following is NOT true for microalgae?
1. Microalgae can perform photosynthesis only if the light source is available
2. Respiration by the microalgae continues throughout light and dark period
3. Photosynthesis by microalgae is an oxidation reaction
4. Microalgae can take both 𝐶𝑂2 and bicarbonate as source of carbon

Correct Answer:

3. Photosynthesis by microalgae is an oxidation reaction

Explanation:

Let’s break down each option:

1. Microalgae can perform photosynthesis only if the light source is available

✅ True – Photosynthesis is a light-dependent process. Microalgae, like plants, require light to convert CO₂ and water into glucose and oxygen.

2. Respiration by the microalgae continues throughout light and dark period

✅ True – Respiration occurs continuously to meet the energy needs of the cell, regardless of light conditions. During the dark period, only respiration occurs, while during the light period, both respiration and photosynthesis occur.

3. Photosynthesis by microalgae is an oxidation reaction

❌ False – Photosynthesis is a reduction reaction, not oxidation. In photosynthesis, CO₂ is reduced to form carbohydrates (e.g., glucose), while water is oxidized to release O₂. The overall reaction is driven by light energy, but the key process involves reduction of carbon, not oxidation.

4. Microalgae can take both CO₂ and bicarbonate as source of carbon

✅ True – Microalgae can utilize both CO₂ and bicarbonate (HCO₃⁻) as carbon sources. Some species are adapted to convert bicarbonate into CO₂ enzymatically before fixation in the Calvin cycle.

Conclusion:

The incorrect statement is that photosynthesis by microalgae is an oxidation reaction. Instead, it is primarily a reduction reaction where CO₂ is reduced to organic molecules.

Correct Answer: 3. Photosynthesis by microalgae is an oxidation reaction