Question
A group of students studied how increasing substrate concentration affects the rate of an enzyme-catalyzed reaction when two inhibitory substances are present. The results are presented in the graph.
What can be deduced from these results?
A. At all substrate concentrations, both inhibitors compete for the enzyme’s active site.
B. Both inhibitors are specific for this enzyme – catalyzed reaction.
C. At very low substrate concentrations, inhibitor 2 shows a higher inhibitory effect.
D. Inhibitor 1 and substrate have similar shapes
▶️Answer/Explanation
Answer: C. At very low substrate concentrations, inhibitor 2 shows a higher inhibitory effect.
Explanation:
First, what does this graph tell us?
X-axis: Substrate concentration
Y-axis: Rate of reaction
Lines:
- No inhibitor (top curve): Normal enzyme activity.
- Inhibitor 1 (dashed): Rate increases with substrate conc. but not as high as normal.
- Inhibitor 2 (dotted): Much lower rate, even as substrate increases. Basically, flattens early.
What does this mean?
Let’s break down each option:
Option A: Incorrect.
If they were both competitive inhibitors (i.e., compete for active site), then increasing substrate concentration would eventually outcompete them.
But inhibitor 2 flattens out even at high substrate concentrations → suggests non-competitive inhibition.
Option B: Incorrect
The graph gives no info about specificity. We’d need molecular data or multiple enzymes tested. Can’t be assumed.
Option C: Correct
At low substrate concentration (left side of graph), the dotted line (inhibitor 2) gives the lowest reaction rate → this means strong inhibition.
As substrate concentration increases, it doesn’t help much → that’s typical of non-competitive inhibitors.
Option D: Incorrect
Yes, inhibitor 1 could be competitive, so it might resemble the substrate and bind the active site.
But the graph alone doesn’t prove shape similarity. It only suggests that the inhibition can be overcome by more substrate (which is characteristic of competitive inhibition), not that they have similar shapes.
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
Which is a reduction reaction?
A. ATP changing to ADP
B. Maltose changing to glucose
C. FAD changing to FADH2
D. NADPH changing to NADP
▶️Answer/Explanation
Answer: C. FAD changing to FADH2
Explanation:
What is reduction in biology?
Reduction means gaining electrons or hydrogen atoms. In biological systems, this often happens when molecules like NAD+ or FAD gain hydrogen and become NADH or FADH₂.
A. Incorrect – ATP converting to ADP involves losing a phosphate group and releasing energy it’s not a reduction.
B. Incorrect – Maltose breaking down into glucose is a hydrolysis reaction, not a redox reaction.
C. Correct – FAD gains two hydrogen atoms (and electrons) to become FADH₂ this is a reduction.
D. Incorrect – NADPH converting to NADP⁺ means it’s losing electrons this is oxidation.
Question
The image shows a portion of a cell containing a mitochondrion.
Where do glycolysis and electron transport occur?
▶️Answer/Explanation
Answer: D
Explanation:
Understanding the Processes:
Glycolysis
- Where it occurs: In the cytoplasm of the cell.
- Explanation: This is the first step of cellular respiration. It does not require mitochondria. Glucose is broken down into pyruvate in the cytoplasm, producing a small amount of ATP.
Electron Transport Chain (ETC)
- Where it occurs: On the inner mitochondrial membrane, specifically the cristae.
- Explanation: This is the final step of aerobic respiration. It uses electrons from NADH and FADH₂ to generate a proton gradient, which drives ATP synthesis.
Analyzing the Image Labels:
- P = Cristae (folds of the inner membrane)
- Q = Inner membrane
- R = Mitochondrial matrix
- S = Cytoplasm (outside the mitochondrion)
Matching Structures to Processes:
Glycolysis → S
Because glycolysis occurs in the cytoplasm, and S is outside the mitochondrion, this is correct.
Electron Transport → Q
Q is labeled at the inner membrane, where the electron transport chain is embedded. This is also correct.
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.