1 markScientists measure ATP levels in muscle cells before and after exercise. They observe that ATP is continuously used and replenished.
Which statement best explains why cells require a constant supply of ATP?
ATP is needed for transport of water through aquaporins.
ATP is an energy-storing molecule that powers metabolic processes.
ATP is a waste product of respiration.
ATP is not required in anaerobic conditions.
Did this page help you?
1 markA scientist observes yeast cells placed in two sealed test tubes, one containing oxygen and the other without oxygen. In the oxygen-deprived tube, ethanol and carbon dioxide accumulate.
Which metabolic process gives the most accurate description of what is occurring in the yeast cells without oxygen?
Oxidative phosphorylation
Anaerobic respiration
Alcohol fermentation
Lactic acid fermentation
Did this page help you?
1 markA student conducts an experiment where they measure oxygen consumption in germinating seeds. They find that oxygen use increases as cellular respiration increases.
Why is oxygen required for cellular respiration?
Oxygen acts as the final electron acceptor in the electron transport chain.
Oxygen breaks down glucose in glycolysis.
Oxygen provides energy directly to ATP synthase.
Oxygen donates electrons to NADH.
Did this page help you?
Glycolysis is a biochemical pathway that releases energy in glucose.
Which of the following describe the products formed during glycolysis?
ADP and inorganic phosphate, NADH and pyruvate
ATP, NAD+ and pyruvate
ADP and inorganic phosphate, NAD+ and pyruvate
ATP, NADH and pyruvate
Did this page help you?
1 markIn the Krebs cycle, during cellular respiration, electrons are transferred to coenzymes.
Which of the following shows the correct coenzymes that accept electrons during the Krebs cycle?
NADH and FADH2
NAD+ and FADH2
NADH and FAD+
NADH and FADH
Did this page help you?
1 markGlycolysis is the first stage of cellular respiration. This process occurs in the cytoplasm and can happen in both aerobic and anaerobic conditions. Which of the following statements about glycolysis is correct?
Pyruvate produced during glycolysis remains in the cytoplasm.
NADPH, pyruvate and ATP are products of glycolysis.
Electrons transferred during glycolysis enter the electron transport chain.
Glycolysis can occur in the absence of NAD+.
Did this page help you?
1 markElectron transport chain inhibitors are molecules that disrupt the electron transport chain in cells. Some electron transport chain inhibitors function as uncouplers, breaking the connection between the electron transport chain and ATP synthase. Which of the following is the most likely effect of an uncoupler on oxidative phosphorylation?
Oxygen will still be used up but less ATP will be produced.
Oxygen use and ATP production will both decrease.
Fewer protons will be pumped across the inner mitochondrial membrane.
Less heat is generated.
Did this page help you?
1 markThe Krebs cycle, also known as the citric acid cycle, is a series of reactions that occur in the mitochondrial matrix. It uses acetyl-CoA as a substrate and produces high-energy electron carriers, which are then used in the electron transport chain. Figure 1 shows a representation of the Krebs cycle.
Which of the following descriptions of the Krebs cycle shown in Figure 1 are correct?
Oxidation of coenzymes occurs at stages 3, 4, 6 and 8.
Phosphorylation occurs at stage 5.
Carbon dioxide is a Krebs cycle reactant.
NADH is the only reduced coenzyme produced by the Krebs cycle.
Did this page help you?
1 markA researcher investigated respiration in yeast cells. They set up an airtight container with yeast and a suitable respiratory substrate. The oxygen, carbon dioxide and ethanol concentrations in the container were measured over 10 hours. The results of this experiment are shown in Figure 1 below.
Which of the following claims is best supported by the data in Figure 1?
Yeast cells begin alcohol fermentation when oxygen concentration drops below a certain level.
Yeast cells rely on alcohol fermentation to produce ATP.
Yeast cells switch from aerobic respiration to alcohol fermentation when oxygen concentration drops below a certain level.
Yeast cells can only respire aerobically.
Did this page help you?
1 markThe electron transport chain consists of a series of protein complexes embedded in the inner mitochondrial membrane. Protein complexes I, II, III and IV are illustrated in Figure 1 below, along with some of the events that occur on complexes I and II.
Amobarbital is an example of an oxidative phosphorylation inhibitor. It binds to complex I in the electron transport chain. Which of the following describes a consequence of exposure to amobarbital?
An increased proton concentration inside the intermembrane space.
An increased ratio of NADH to NAD+.
Increased phosphorylation of ADP.
Increased oxygen consumption.
Did this page help you?
1 markScientists conduct an experiment on isolated mitochondria to study ATP production. They introduce a chemical inhibitor that specifically prevents the oxidation of NADH at Complex I of the electron transport chain (ETC). Complex I is the first large protein in the ETC.
After inhibition, they observe the following results:
Experimental Condition | Oxygen Consumption Rate | ATP Production Rate |
|---|---|---|
Normal Mitochondria | High | High |
NADH Oxidation Inhibited | Low | Low |
Observing the data, what is the most likely explanation for the decrease in ATP production?
Glycolysis becomes the dominant ATP-producing pathway, compensating for the loss of oxidative phosphorylation.
The decrease in ATP production is due to the lack of oxygen availability, preventing the mitochondria from using oxidative phosphorylation.
Oxygen is no longer required for cellular respiration, leading to a decrease in ATP production.
Electrons from NADH can no longer enter the electron transport chain, reducing proton gradient formation.
Did this page help you?
Scientists study human populations living at different altitudes to investigate how mitochondrial density and ATP production change with decreasing oxygen availability. They measure mitochondrial density in muscle cells and ATP production per glucose molecule at different altitudes.
The results are shown in the table below.
Altitude (m) | Mitochondrial density (arbitrary units) | ATP production per glucose |
|---|---|---|
Sea Level | 50 | 36 |
2,500 | 65 | 32 |
4,000 | 80 | 28 |
5,500 | 95 | 24 |
Based on the data, what is the most likely explanation for why populations at higher altitudes have increased mitochondrial density?
At higher altitudes, mitochondria produce ATP exclusively through glycolysis, reducing their need for oxygen.
Higher mitochondrial density compensates for lower oxygen availability, maintaining ATP production through oxidative phosphorylation.
Increased mitochondrial density at higher altitudes compensates for the lower oxygen availability by allowing cells to produce more ATP per glucose molecule.
Higher mitochondrial density reduces metabolic rate, decreasing oxygen demand and ATP use.
Did this page help you?
1 markScientists introduce Oxamate, a chemical inhibitor that prevents lactate dehydrogenase (LDH) from converting pyruvate to lactate, into a culture of human muscle cells under anaerobic conditions. After adding Oxamate, they observe a decline in ATP production and an accumulation of pyruvate in the cells.
Which of the following best explains why ATP production decreases in the presence of Oxamate?
Oxamate blocks the breakdown of glucose, preventing glycolysis from generating ATP.
Oxamate prevents the regeneration of NAD⁺, leading to a shortage of NAD⁺ for glycolysis, which reduces ATP production.
Oxamate blocks oxidative phosphorylation, preventing mitochondria from using pyruvate for ATP synthesis.
Oxamate prevents pyruvate from entering the mitochondria, causing a buildup of ATP in the cytoplasm.
Did this page help you?
1 markAn athlete ran 1600m on a treadmill, and the speed intensity was varied throughout to simulate race conditions.
The athlete's blood was sampled every 60 seconds, and the blood lactate concentration was measured as shown.
Which statement provides the most likely explanation for the blood lactate concentration between 3 to 5 minutes?
The athlete increases their running intensity, leading to anaerobic respiration, followed by a slower pace where oxygen is used to break down lactate.
The athlete increases their running intensity, leading to anaerobic respiration, followed by stopping completely, allowing carbon dioxide to break down lactate.
The athlete maintains the same pace but lacks sufficient oxygen to break down lactate, followed by a slower pace that reduces lactate production.
The athlete increases their running intensity, relying on aerobic respiration, followed by a slower pace that reduces lactate production.
Did this page help you?
1 markOxidative phosphorylation occurs in the mitochondria and involves a sequence of processes that lead to ATP production. The following steps describe key events involved in oxidative phosphorylation.
Protons are moved across the cristae to the intermembrane space
Oxygen molecules combine with protons and electrons to form water
NADH and FADH donate electrons to the first transport protein in the chain
Hydrogen ions (protons) are also released from the coenzymes
A high concentration of protons in the intermembrane space creates an electrochemical gradient
Electrons move down the electron transport chain
Protons move down the electrochemical gradient through enzyme ATP synthase during chemiosmosis
Which of the following shows the correct sequence for these steps?
1 → 4 → 6 → 2 → 5 → 7→ 3
3 → 4 → 6 → 1 → 5 → 7→ 2
3 → 6 → 1→ 5 → 7→ 2 → 4
6 → 3 → 5 → 7→ 2→ 4 → 1
Did this page help you?