Quiz: Metabolism and Energy Balance — 24 questions

1. What does metabolism encompass in a living organism?

A. Exchange processes that move substances across membranes without energy changes

B. Physical movements that transport materials without changing their composition

C. Cellular structures that store genetic information and control reproduction

D. Chemical reactions that transform matter while producing or using energy

Answer: (D)

Explanation

Metabolism comprises the chemical reactions by which cells transform matter while producing and/or using energy. Membrane exchange and genetic control are cellular processes, but they do not define metabolism as a whole.

2. What role does an enzyme play in a cellular chemical reaction?

A. It stores the energy released when the substrate is degraded

B. It facilitates the reaction without being presented as a reactant

C. It supplies the reaction with all of its required chemical matter

D. It is transformed into the main product during the reaction

Answer: (B)

Explanation

An enzyme acts as a catalyst, facilitating a cellular reaction without being presented as a reactant. The substrate, rather than the enzyme, is the substance transformed by the reaction.

3. Which statement correctly distinguishes anabolism from catabolism?

A. Anabolism transports molecules, whereas catabolism stores them

B. Anabolism builds molecules, whereas catabolism breaks molecules down

C. Anabolism regulates signals, whereas catabolism forms cellular compartments

D. Anabolism breaks molecules down, whereas catabolism builds molecules

Answer: (B)

Explanation

Anabolism consists of synthesis pathways that build molecules, while catabolism consists of degradation pathways that break molecules down. Transport, storage, and regulation describe other cellular functions rather than this distinction.

4. Which structure is characteristic of a eukaryotic cell?

A. A tissue layer containing many cells with shared specialized functions

B. A plasma membrane lacking internal membrane-bound compartments

C. A single chemical molecule composed of bonded atoms

D. A nucleus together with cytoplasm and membrane-bound organelles

Answer: (D)

Explanation

Eukaryotic cells contain a nucleus, cytoplasm, and membrane-bound organelles such as mitochondria. A tissue is an organization of cells, while a molecule is a chemical structure rather than a cell.

5. What is the main principle of cellular compartmentalization?

A. Chemical reactions are separated according to the age of each cell

B. All cellular activities occur in one undivided internal region

C. Cells exchange materials without controlling where those materials act

D. Specialized tasks are assigned to specialized cellular locations

Answer: (D)

Explanation

Cellular compartmentalization assigns specialized tasks to specialized locations, allowing different cellular regions or cell types to perform distinct functions. An undivided cell interior would not provide this functional organization.

6. A changing environment triggers cellular responses that keep internal conditions relatively stable. Which process describes this function?

A. Metabolic regulation responding to internal and external signals

B. Molecular synthesis assembling nutrients into larger compounds

C. Passive diffusion moving substances down concentration gradients

D. Cellular degradation breaking reserves into smaller substances

Answer: (A)

Explanation

Metabolic regulation maintains relatively constant living conditions by responding to internal and external signals as the environment changes. Synthesis, degradation, and diffusion may occur in cells but do not describe this regulatory function.

7. What is the defining function of the plasma membrane?

A. It produces all cellular energy through nutrient oxidation

B. It delimits the cell and regulates exchanges with its environment

C. It synthesizes macromolecules from simple metabolic intermediates

D. It organizes cells into tissues with shared structural functions

Answer: (B)

Explanation

The plasma membrane forms the cell boundary and permits regulated exchanges with the environment. Energy production, tissue organization, and macromolecule synthesis are performed by other structures or processes.

8. Why does anabolism require an energy supply?

A. It converts ATP directly into membrane-bound cellular compartments

B. It releases energy by oxidizing food-derived nutrients and reserves

C. It uses energy to synthesize larger molecules from simpler materials

D. It degrades macromolecules into products that require less structure

Answer: (C)

Explanation

Anabolism builds small molecules and macromolecules from simple nutrients or metabolic intermediates, so it requires an energy supply. Oxidative degradation and energy release characterize catabolism instead.

9. Which process produces energy through oxidation and degradation of nutrients and cellular reserves?

A. Catabolism

B. Cellular compartmentalization

C. Metabolic regulation

D. Anabolism

Answer: (A)

Explanation

Catabolism produces energy by oxidizing and degrading food-derived nutrients and cellular reserves. Anabolism builds molecules using energy, while compartmentalization and regulation describe organization and control.

10. What happens to some of the chemical energy produced during catabolism?

A. It is stored in ATP and can support cellular work

B. It is retained in the plasma membrane as a permanent boundary

C. It is converted into nutrients used to build every macromolecule

D. It is transferred into the nucleus to become hereditary information

Answer: (A)

Explanation

Catabolism can produce chemical, electrical, or mechanical energy, and part of its chemical energy is stored as ATP. ATP is an energy-storage and transfer molecule, not a source of nutrients, membranes, or hereditary information.

11. Which pattern best distinguishes aerobic metabolism from anaerobic metabolism during exercise?

A. Aerobic metabolism occurs without oxygen during sprinting, whereas anaerobic metabolism depends on oxygen during recovery.

B. Aerobic metabolism produces lactate during brief effort, whereas anaerobic metabolism uses oxygen during prolonged activity.

C. Aerobic metabolism stores glucose for later use, whereas anaerobic metabolism converts lipids into long-term reserves.

D. Aerobic metabolism uses oxygen for prolonged effort, whereas anaerobic metabolism supports intense brief effort without oxygen.

Answer: (D)

Explanation

Aerobic metabolism depends on oxygen and is suited to prolonged exercise, while anaerobic metabolism supplies energy without oxygen during intense, brief effort. The distractor involving lactate reverses the defining oxygen requirement and assigns the exercise contexts incorrectly.

12. Which set of products is generated by aerobic oxidation of glucose?

A. Lactate, glycogen, oxygen, and protein

B. Glucose, nitrogen, heat, and phosphocreatine

C. Water, carbon dioxide, heat, and ATP

D. Urea, lipids, carbon monoxide, and ATP

Answer: (C)

Explanation

Aerobic glucose oxidation produces water, carbon dioxide, heat, and ATP as major outputs. Lactate accumulation is associated with anaerobic metabolism rather than being the defining product of aerobic oxidation.

13. What is the immediate metabolic consequence of an arterial occlusion during a myocardial infarction?

A. Increased oxygen delivery causes sustained contraction of the affected myocardium.

B. Reduced oxygen delivery causes ischemia that may progress to tissue necrosis.

C. Reduced glucose storage causes thermogenesis that restores cardiac tissue function.

D. Increased lactate clearance prevents damage despite restricted blood flow.

Answer: (B)

Explanation

An arterial occlusion reduces oxygen delivery, producing ischemia that can lead to necrosis, death, or lasting sequelae. The distractor about increased oxygen delivery contradicts the vascular obstruction that initiates the injury.

14. How does ATP function in cellular energy metabolism?

A. It serves as a long-term nutrient reserve stored mainly in adipose tissue.

B. It serves as an immediate energy intermediary that can be hydrolyzed when energy is needed.

C. It acts as a digestive hormone that directs nutrient storage after meals.

D. It functions as a structural polymer that stores glucose in muscle and liver.

Answer: (B)

Explanation

ATP provides immediately available energy and can be hydrolyzed to meet cellular demands. Glycogen and lipids, rather than ATP, serve as longer-term nutrient reserves.

15. Which distribution of ATP production between the cytosol and mitochondria is most accurate?

A. About 10–15% occurs in the cytosol, while about 85–90% occurs in mitochondria.

B. About 20–30% occurs in the cytosol, while about 70–80% occurs in mitochondria.

C. About 70–80% occurs in the cytosol, while about 20–30% occurs in mitochondria.

D. About 50% occurs in each compartment through identical oxidation pathways.

Answer: (B)

Explanation

Carbohydrate oxidation in the cytosol contributes approximately 20–30% of ATP production, whereas mitochondria generate roughly 70–80% from carbohydrates and lipids. The reversed distribution confuses the smaller cytosolic contribution with the dominant mitochondrial contribution.

16. How does mitochondrial oxidative phosphorylation synthesize ATP?

A. A lipid flow through storage tissue releases ATP directly, with heat forming water.

B. A lactate flow through the cytosol drives ATP synthesis, with carbon dioxide forming oxygen.

C. A proton flow generated by oxidation pathways drives ATP synthesis, with oxygen helping form water.

D. A glucose flow through the nucleus directly joins phosphate groups to produce ATP, with nitrogen forming water.

Answer: (C)

Explanation

Oxidation pathways establish a proton flow across the mitochondrial membrane, and that flow powers ATP synthesis; oxygen participates in water formation. The cytosolic lactate mechanism is incorrect because oxidative phosphorylation is a mitochondrial process dependent on oxidation-generated proton flow.

17. What does resting energy expenditure primarily represent?

A. About 20–25% of total expenditure in sedentary people, reflecting voluntary movement.

B. About 10–15% of total expenditure, reflecting heat production after food intake.

C. About 60–70% of total expenditure, supporting vital functions, muscle tone, and ion transport.

D. About 60–70% of total expenditure in athletes, reflecting exercise performed during training.

Answer: (C)

Explanation

Resting energy expenditure accounts for approximately 60–70% of total energy expenditure and maintains vital functions, resting muscle tone, and active ion transport. The post-prandial thermogenesis range of 10–15% describes a different component of energy expenditure.

18. What role do metabolic intermediates play in metabolism?

A. They provide crossroads where carbohydrate, lipid, and protein pathways interact with energy storage.

B. They serve as contractile proteins that convert chemical energy into muscle force.

C. They act as storage tissues that retain energy reserves without linking nutrient pathways.

D. They function as hormones that trigger nutrient storage after food intake.

Answer: (A)

Explanation

Metabolic intermediates connect carbohydrate, lipid, and protein pathways and link these pathways to energy storage. Storage tissues retain reserves, but they do not constitute the pathway crossroads described by this definition.

19. A biopsy identifies a glucose-storage polymer in skeletal muscle, while imaging shows a lipid reserve in adipose tissue; which identification is correct?

A. The muscle polymer is protein, and the adipose reserve consists of ATP.

B. The muscle polymer is lipid, and the adipose reserve consists of glycogen.

C. The muscle polymer is glycogen, and the adipose reserve consists of lipids.

D. The muscle polymer is ATP, and the adipose reserve consists of glucose.

Answer: (C)

Explanation

Glycogen is the glucose-storage polymer found mainly in muscle and liver, whereas lipids are stored in adipose tissue. The reversed identification incorrectly assigns glycogen to adipose tissue and lipids to muscle.

20. After a carbohydrate-rich meal, which hormonal action most directly promotes storage?

A. Insulin promotes the storage or synthesis of carbohydrates, lipids, and proteins.

B. Insulin stimulates the breakdown of stored nutrients to maintain fasting metabolism.

C. Insulin increases oxygen delivery to muscle while preventing nutrient incorporation into reserves.

D. Insulin blocks protein synthesis while directing glucose toward immediate heat production.

Answer: (A)

Explanation

Insulin acts mainly as a storage hormone after food intake, promoting carbohydrate, lipid, and protein storage or synthesis. The breakdown-focused distractor describes the opposite of insulin’s principal post-meal role.

21. What are the two primary priorities during fasting?

A. Maintaining blood glucose for the brain and red blood cells while preserving muscle protein

B. Maintaining muscle glycogen while converting fatty acids directly into blood glucose

C. Reducing metabolic activity while storing amino acids in adipose tissue

D. Preserving adipose tissue while supplying ketones to the brain and red blood cells

Answer: (A)

Explanation

Fasting initially prioritizes blood-glucose maintenance for the brain and red blood cells, together with preservation of muscle protein mass. Preserving adipose tissue is not identified as the first priority.

22. A person begins fasting and relies on limited liver and muscle glycogen stores for roughly two days; which process is primarily responsible for releasing this glucose?

A. Lipolysis, which converts fatty acids directly into glucose

B. Proteolysis, which converts muscle proteins into ketone bodies

C. Glycogenolysis, which breaks down stored glycogen

D. Gluconeogenesis, which synthesizes glucose from amino acids

Answer: (C)

Explanation

The first fasting phase uses glycogenolysis to release glucose from liver and muscle glycogen and lasts about 48 hours. Gluconeogenesis is a later process that makes new glucose rather than breaking down glycogen.

23. Why does the second fasting phase threaten muscle protein mass?

A. Fatty-acid oxidation prevents amino acids from entering glucose-producing pathways

B. Glycogenolysis converts muscle protein into glucose without an energy cost

C. Ketone-body formation uses amino acids to replenish liver glycogen stores

D. Gluconeogenesis uses amino acids to synthesize glucose and requires energy

Answer: (D)

Explanation

During the second phase, gluconeogenesis synthesizes glucose from amino acids, consumes energy, and can draw on muscle protein over approximately one to three days. Glycogenolysis concerns stored glycogen and does not explain this amino-acid demand.

24. Which statement correctly distinguishes the lipid phase of fasting from glucose-producing pathways?

A. Fatty acids can supply energy through ketone bodies, but lipids do not produce glucose

B. Fatty acids produce glucose directly, whereas ketone bodies provide energy without carbon substrates

C. Lipids replace gluconeogenesis by releasing stored glucose from liver and muscle glycogen

D. Ketone bodies synthesize glucose from lipids, while fatty acids are reserved for muscle protein formation

Answer: (A)

Explanation

In the lipid phase, fatty acids provide energy through ketone bodies, but lipids cannot produce glucose because the relevant metabolic pathway does not exist. The idea that ketone bodies generate glucose from lipids confuses energy production with glucose synthesis.