Plants and cyanobacteria are autotrophic organisms that prepare their own food by the process of photosynthesis. Conversely, animals are heterotrophic, meaning they depend on plants and other animals for their nutritional requirements. All the food taken up needs to be broken down so that energy can be liberated. Here is a collection of important questions related to cellular respiration and the process of synthesis of ATP.

1. Which of the following is the site for cellular respiration in plants?

(a) Golgi apparatus

(b) Cytoplasm and mitochondria

(c) Chloroplast

(d) Nucleus

Answer: (b)

Explanation: There are two kinds of respiration –

• Aerobic Respiration: It is the complete oxidation of CO₂ and H₂O in the presence of oxygen. It happens in both cytoplasm and mitochondria.
• Anaerobic Respiration: It is the incomplete breakdown of organic molecules to release energy in the absence of oxygen. It happens in cytoplasm only.

2. Which of the following substances liberates the maximum energy?

(a) Carbohydrates

(b) Fats

(c) Proteins

(d) Organic acids

Answer: (b)

Explanation: Fats and lipids provide more energy as compared to carbohydrates and proteins. Carbohydrate is still preferred as a substrate because it can easily enter the respiratory pathway and can be metabolised quickly. Proteins are rarely used as respiratory substrates because they are used at the time of starvation.

3. Which of the following statements correctly describes respiratory substrates?

(a) Substances which do not produce energy.

(b) Substances that are released after respiration.

(c) Substances which are excreted out of the body.

(d) Substances which are broken down during respiration.

Answer: (d)

Explanation: The organic substances that are broken down during respiration and release energy are termed as respiratory substrates. The common respiratory substrates are fats, carbohydrates, proteins and organic acids.

4. What are the products of aerobic respiration?

(a) CO₂, H₂O, energy

(b) CO₂, ethanol, energy

(c) Lactic acid, energy

(d) Lactic acid, H₂O

Answer: (a)

Explanation: Aerobic respiration is the process of oxidation of glucose (or any other respiratory substrate) in the presence of oxygen to liberate energy along with carbon dioxide and water. On the other hand, in anaerobic respiration, either ethanol, CO₂ and energy or lactic acid and energy are produced as a result of incomplete oxidation in the absence of oxygen.

5. Which is the hexose molecule that is acted upon by aldolase and broken down into two triose molecules during glycolysis?

(a) Glucose

(b) Fructose

(c) Glucose-6-phosphate

(d) Fructose-1,6-bisphosphate

Answer: (d)

Explanation: The aldolase enzyme acts on fructose 1,6 bisphosphate (hexose) to produce two triose sugars namely, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate that are also isomers of each other.

6. Net gain of ATP molecule during glycolysis is

(a) 2

(b) 4

(c) 24

(d) 38

Answer: (a)

Explanation: 2 molecules of ATP are used up in the preparatory phase of glycolysis. 4 ATP molecules are produced in the later stages. Therefore, net gain of ATP molecules during glycolysis is 2.

7. Conversion of pyruvic acid into ethyl alcohol is mediated by

(a) phosphatase

(b) dehydrogenase

(c) decarboxylase and dehydrogenase

(d) catalase

Answer: (c)

Explanation: During alcoholic fermentation pyruvate obtained from the glycolytic pathway is converted into acetaldehyde in the presence of pyruvate decarboxylase, and the acetaldehyde is converted into ethanol by alcohol dehydrogenase. Alcoholic fermentation is a type of anaerobic respiration.

8. The common phase between aerobic and anaerobic respiration is

(a) Glycolysis

(b) Krebs cycle

(c) TCA cycle

(d) Photorespiration

Answer: (a)

Explanation: Cellular respiration begins with the process of glycolysis which can occur either in the presence or absence of oxygen. In the next step, pyruvate (the end product of glycolysis) undergoes aerobic respiration which includes Krebs cycle and electron transport chain if oxygen is present. Otherwise it will undergo anaerobic respiration where fermentation takes place in the absence of oxygen.

9. Which one of the following mammalian cells are not capable of metabolising glucose aerobically?

(a) WBCs

(b) mature RBCs

(c) unstriated muscle cells

(d) liver cells

Answer: (b)

Explanation: Young RBCs have membrane-bound organelles such as mitochondria and nucleus; but during maturation, they attain a biconcave shape and lose all their organelles. Hence, mature RBCs are not able to respire aerobically because they do not have mitochondria to undergo Krebs cycle or electron transport chain.

10. Pyruvate dehydrogenase complex is used in converting

(a) pyruvate to glucose

(b) glucose to pyruvate

(c) pyruvic acid to lactic acid

(d) pyruvate to acetyl CoA

Answer: (d)

Explanation: Pyruvate undergoes oxidative decarboxylation inside the mitochondria to produce CO₂ and NADH₂. The product combines with sulphur-containing coenzyme A to form acetyl CoA or activated acetate. This reaction occurs in the presence of an enzyme complex called pyruvate dehydrogenase.

11. How many NADH + H⁺ are formed per turn of the Krebs cycle?

(a) 2

(b) 3

(c) 4

(d) 5

Answer: (b)

Explanation: 3 NADH + H⁺ are produced per turn of the Krebs cycle. Since one glucose molecule undergoes two Krebs cycles, we can say that a glucose molecule produces 6 NADH + H⁺.

12. In the Krebs cycle, FAD participates as electron acceptor during the conversion of

(a) succinyl CoA to succinic acid

(b) ɑ-ketoglutarate to succinyl CoA

(c) succinic acid to fumaric acid

(d) fumaric acid to malic acid

Answer: (c)

Explanation: In the sixth step of Krebs cycle, oxidation of succinate occurs. Succinate is converted into fumaric acid by the removal of hydrogen (dehydrogenation) in the presence of a membrane base enzyme called succinate dehydrogenase. FADH₂ is also produced in this step.

13. Acetyl CoA undergoes condensation with _____ in the Krebs cycle.

(a) malic acid

(b) fumaric acid

(c) ɑ-ketoglutaric acid

(d) oxaloacetic acid

Answer: (d)

Explanation: The acetyl CoA undergoes condensation with oxaloacetic acid as a very first step of Krebs cycle to form citric acid.

14. During conversion of succinyl CoA to succinic acid, a molecule of GTP is formed in a reaction known as

(a) oxidative phosphorylation

(b) substrate-level phosphorylation

(c) phosphorylation

(d) terminal oxidation

Answer: (b)

Explanation: The direct synthesis of ATP or GTP from metabolites is known as substrate-level phosphorylation (SLP).

15. Electron transport chain is present in ______________ .

(a) the outer membrane of mitochondria

(b) the intermembrane space of mitochondria

(c) the inner membrane of mitochondria

(d) the matrix of mitochondria

Answer: (c)

Explanation: The electron transport chain (ETC) is a series of complexes made up of proteins and organic molecules in the inner membrane of mitochondria. The electrons are transported from NADH + H⁺ and FADH₂ to molecular oxygen through the complexes of the ETC.

16. ______ is the terminal cytochrome that donates electrons to oxygen during the electron transport chain.

(a) Cytochrome a

(b) Cytochrome a₃

(c) Cytochrome b

(d) Cytochrome c

Answer: (b)

Explanation: The electrons released by the oxidation of NADH + H⁺ move to complex I, and then get transferred to ubiquinone located within the inner membrane. Ubiquinone also receives the electrons released by the oxidation of FADH₂ through complex II. The electrons from ubiquinone are passed on to cytochrome b and cytochrome c1 of complex III.

The electrons are then further transported to cytochrome c which is a mobile carrier that transfers electrons between complex III and IV. In complex IV, the electrons pass through cytochrome a and then to cytochrome a₃. From complex IV, the electrons are passed on to the final acceptor, i.e., oxygen and are converted into water.

17. Cytochrome c is a mobile carrier of electrons between __________.

(a) complex I and complex II

(b) complex II and complex III

(c) complex III and complex IV

(d) complex I and complex IV

Answer: (c)

Explanation: Cytochrome c is a mobile carrier of electrons attached on the outer side of the inner mitochondrial membrane. It transfers the electrons between complex III and complex IV.

18. The chemiosmotic theory is based on ______________.

(a) accumulation of Na⁺ ions

(b) accumulation of K⁺ ions

(c) proton gradient

(d) membrane potential

Answer: (c)

Explanation: The chemiosmotic theory is based on the proton gradient. It explains the process of ATP synthesis. The energy available in the electrons is used to pump the protons from the matrix of mitochondria to the intermembrane space. These protons accumulate in the intermembrane space. This increases the concentration of protons in the intermembrane space and creates a driving force. The concentration difference is called the proton gradient. The protons move back into the matrix of mitochondria through complex V.

19. How does temperature affect the rate of respiration?

(a) Increase in optimum temperature decreases the rate of respiration

(b) Increase in temperature up to a limit increases the rate of respiration

(c) Decrease in optimum temperature increases the rate of respiration

(d) Temperature has no effect on the rate of respiration

Answer: (b)

Explanation: Increase in temperature up to a limit will increase the rate of respiration.

20. Respiratory quotient of carbohydrates is

(a) 1

(b) less than 1

(c) greater than 1

(d) 0

Answer: (a)

Explanation: Respiratory quotient (RQ) is the ratio of volume of carbon dioxide evolved to volume of oxygen consumed. RQ of carbohydrates is 1.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

RQ = = 1

Stay tuned to BYJU’S for more important updates related to NEET.

Recommended Video:

Also Check:

• Human Excretory System
• Systole and Diastole
• MCQ on Parenchyma Cells