CAPF AC 2020 Q27: Science & Technology – Biology
In which part of the cell, the glucose is converted into pyruvate?
- (a) Mitochondria
- (b) Nucleus
- (c) Cytoplasm
- (d) Endoplasmic reticulum
Answer: (c) Cytoplasm
Explanation
Where glucose becomes pyruvate
How to think: the first step of respiration is the same in every cell, even in bacteria that have no mitochondria.
So it must happen in the cytoplasm.
This first step is called glycolysis.
One glucose (6 carbons) is split into two pyruvate (3 carbons each).
| Step | Place | Oxygen needed? | Product |
|---|---|---|---|
| Glucose to pyruvate | Cytoplasm | No | Pyruvate and a little energy |
| Pyruvate with oxygen | Mitochondria | Yes | Carbon dioxide, water and much energy |
| Pyruvate in yeast | Cytoplasm | No | Ethanol and carbon dioxide |
| Pyruvate in tired muscle | Cytoplasm | No | Lactic acid |
Answer: (c) Cytoplasm.
Why each option is right or wrong
- (a) Incorrect. The mitochondria break down pyruvate further; they do not make it from glucose.
- (b) Incorrect. The nucleus holds the genetic material and does not carry out respiration.
- (c) CORRECT. Glucose is split into pyruvate in the cytoplasm; this is glycolysis.
- (d) Incorrect. The endoplasmic reticulum makes and transports proteins and lipids.
Key point
Glycolysis: glucose (6 carbons) to pyruvate (3 carbons), in the cytoplasm, without oxygen. Pyruvate then goes to the mitochondria if oxygen is present.
Remember
Glucose to pyruvate = glycolysis = cytoplasm.
Common mistakes
- Choosing mitochondria because it is called the powerhouse of the cell.
- Thinking glycolysis needs oxygen; it does not.
- Forgetting that pyruvate has three carbon atoms.
Exam tip
First step in the cytoplasm, later steps in the mitochondria. The question asks about the first step.
Sources
- NCERT Class X Science — Life Processes (respiration)
- NCERT Class XI Biology — Respiration in Plants (glycolysis)