CAPF AC 2020 Q29: Science & Technology – Biology
Which one of the following statements is correct?
- (a) Glucose breaks down to CO₂, H₂O and energy in all organisms
- (b) Glucose breaks down into ethanol, CO₂ and energy in our muscle cells
- (c) Glucose breaks down into CO₂, H₂O and energy in all aerobic tissues
- (d) Glucose breaks down into lactate and energy in yeast
Answer: (c) Glucose breaks down into CO₂, H₂O and energy in all aerobic tissues
Explanation
Breakdown of glucose
How to think: the end product depends on whether oxygen is present and on which cell it is.
Match each option with the right row.
| Condition | Where | Products |
|---|---|---|
| With oxygen (aerobic) | Mitochondria of aerobic cells | Carbon dioxide, water and a lot of energy |
| Without oxygen | Yeast | Ethanol, carbon dioxide and a little energy |
| Lack of oxygen | Muscle cells | Lactic acid and a little energy |
The options checked:
| Option | Verdict |
|---|---|
| (a) To CO₂, H₂O and energy in all organisms | Incorrect; yeast and some bacteria do not do this |
| (b) Into ethanol, CO₂ and energy in our muscle cells | Incorrect; muscles make lactic acid |
| (c) Into CO₂, H₂O and energy in all aerobic tissues | Correct |
| (d) Into lactate and energy in yeast | Incorrect; yeast makes ethanol |
Answer: (c) Glucose breaks down into CO₂, H₂O and energy in all aerobic tissues.
Why each option is right or wrong
- (a) Incorrect. Not in all organisms; anaerobic organisms such as yeast give other products.
- (b) Incorrect. Muscle cells short of oxygen form lactic acid, not ethanol.
- (c) CORRECT. In aerobic tissues glucose is fully broken down to carbon dioxide and water.
- (d) Incorrect. Yeast forms ethanol and carbon dioxide, not lactate.
Key point
Aerobic: glucose to carbon dioxide + water + much energy. Yeast: ethanol + carbon dioxide. Muscle without oxygen: lactic acid.
Remember
Yeast = ethanol; muscle = lactic acid; with oxygen = carbon dioxide and water.
Common mistakes
- Swapping the two anaerobic paths: ethanol belongs to yeast, lactic acid to muscle.
- Accepting the word all in option (a) without checking for exceptions.
- Thinking anaerobic respiration gives more energy; it gives far less.
Exam tip
Watch the word all. Option (a) says all organisms, option (c) says all aerobic tissues; only the second is safe.
Sources
- NCERT Class X Science — Life Processes (respiration)
- NCERT Class XI Biology — Respiration in Plants