IB DP Biology- C1.2 Cell respiration IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
✅ Answer: (C)
Question
Which molecules are reactants and products during glycolysis?
▶️Answer/Explanation
Answer: C
Explanation:
Glycolysis is the first step of cellular respiration, happening in the cytoplasm, where:
- Glucose (6-carbon sugar) → gets broken down into 2 pyruvate molecules (3-carbon each).
- ATP is used and also made.
- NAD⁺ is reduced to NADH.
So the correct reactants & products of glycolysis are:
- Reactants: Glucose and ATP (ATP is used in early steps).
- Products: Pyruvate, ATP (net gain), and reduced NAD (NADH)
Let’s match this to the options in your table:
| Option | Reactants | Products | Verdict |
|---|---|---|---|
| A | Pyruvate and ATP | Acetyl-CoA, CO₂, NAD | This is link reaction, not glycolysis. |
| B | Glucose and oxygen | Pyruvate, CO₂, ATP | Wrong – glycolysis doesn’t need oxygen. |
| C | Glucose and ATP | Pyruvate, reduced NAD, ATP | Correct |
| D | Pyruvate and oxygen | ATP and reduced NAD | Sounds like aerobic respiration after glycolysis. |
Question
What term is used for ATP synthesis coupled to electron transport and proton movement?
A. Chemiosmosis
B. Oxidation
C. Glycolysis
D. Cell respiration
▶️Answer/Explanation
Answer: A. Chemiosmosis
Explanation:
What is chemiosmosis?
Chemiosmosis is the process where a flow of protons (H⁺ ions) across a membrane drives the formation of ATP. This happens in the mitochondria during oxidative phosphorylation part of aerobic respiration.
A. Correct – This is the definition of chemiosmosis: ATP synthesis driven by a proton gradient.
B. Incorrect – Oxidation is the loss of electrons, not the full process of ATP generation.
C. Incorrect – Glycolysis is the earlier step in respiration, not linked directly to the ETC or ATP synthase.
D. Incorrect – Cell respiration is the entire process, not the specific mechanism.
Question
Where are protons pumped, to allow chemiosmosis in aerobic respiration to occur?
A. From outside the mitochondrion through the double membranes
B. From carrier to carrier in the inner mitochondrial membrane
C. From the matrix of the mitochondrion to the space between the membranes
D. From the space between the membranes to the cytoplasm outside the mitochondrion
▶️Answer/Explanation
Answer: C. From the matrix of the mitochondrion to the space between the membranes
Explanation:
Proton pumping in mitochondria
During electron transport, protons (H⁺) are pumped from the matrix into the intermembrane space of the mitochondrion. This builds up a proton gradient, and the flow of protons back into the matrix through ATP synthase generates ATP.
A. Incorrect – Protons move across the inner membrane, not both membranes, and they stay inside the mitochondrion.
B. Incorrect – Protons are not passed from carrier to carrier; electrons are.
C. Correct – Protons are pumped from the matrix to the space between the membranes (intermembrane space), creating the gradient.
D. Incorrect – Protons do not go to the cytoplasm; they stay within mitochondrial compartments.