NIOS Biology Chapter 12 Respiration in Plants Solutions

NIOS Biology Chapter 12 Respiration in Plants Solutions provide clear and simple answers to terminal exercises. The chapter explains aerobic and anaerobic respiration, glycolysis, the Krebs’ cycle, and energy release in plants. Students learn how respiration supports growth and development.

Solved exercises strengthen exam preparation by making revision easy. This chapter is crucial for understanding plant physiology and helps learners gain confidence in NIOS Class 12 Biology with accurate and exam-oriented solutions.

NIOS Biology Chapter 12 Respiration in Plants Solutions

1. Define respiration

Respiration is the process by which fats and protein’s the energy stored in organic molecules, is released by oxidation.

2. What is the role of O₂ in the electron transport chain (ETC)?

The electron transport chain (ETC in respiration initiates oxidative phosphorylation. The hydrogen carriers pass through the inner membrane of the mitochondria. During this passage, the hydrogen ions are oxidised in a series of steps. Some of these steps release a large amount of energy, which is used to make ATP from ADP and inorganic phosphate (Pi). This oxidative phosphorylation is the main source of ATP production, and the oxygen molecule is the final electron acceptor in this series. When oxygen accepts the hydrogen ions, it is reduced to form water or H₂O.

3. How many molecules of ATP are released when a molecule of glucose is oxidised to

(a) CO₂ and H₂O?

(b) Ethyl alcohol and CO₂?

Ans: 2 and 38.

4. Write the equation for aerobic respiration.

C₆H₁₂O₆ → 6CO₂ + 6H₂O+ 6O₂ +38 ATP

5. Name the end products of electron transport chains.

ATP and H₂O

6. Respiration is a continuous process in green plants. Then why is it that they give out O₂ and not CO₂ during the day?

In plants, O₂ released during photosynthesis during the day is made available for respiration. However, the rate of photosynthesis is higher than that of respiration. Thus, plants give out excess O₂ in the daytime. However, these plants release only CO₂ at night as photosynthesis stops in the absence of sunlight. Animals give out CO₂ at all times.

7. What is the site for

(a) Glycolysis,

(b) Krebs Cycle,

(c) ATP generation by oxidative phosphorylation?

Glycolysis- Cytosol
Kreb’s Cycle- Matrix of mitochondria
Oxidative Phosphorylation- Cristae

8. What is the fate of pyruvic acid in the (a) presence, and (b) absence of oxygen?

Write the equations representing the processes that take place in (a) & (b).

Fate of pyruvic acid in the presence of oxygen

In the presence of oxygen, pyruvic acid enters mitochondria. It is first decarboxylated and dehydrogenated to form Acetyl-CoA, which enters the Krebs’ Cycle. There, it will be broken down into CO₂ and H₂O.

2Pyruvic acid + 8NAD + 2FAD + 2ADP → 6CO₂ + 8NADH + 2FADH₂ + 2ATP

Fate of pyruvic acid in the absence of oxygen

In the absence of oxygen, pyruvic acid undergoes fermentation as in yeast or lactic acid as in muscle cells.
In yeast, pyruvic acid is reduced to form ethyl alcohol and releases CO₂.
In muscle cells. Pyruvic acid forms lactic acid and oxidises NADH into NAD⁺.

2 Pyruvic acid → 2 Ethanol + CO₂ + 2 ATP

2 Pyruvic acid → 2 Lactic acid+ NAD⁺

9. What is the significance of the stepwise oxidation of organic molecules instead of a step reaction?

Each step in the oxidation of organic molecules releases chemical energy stored in their bonds. When the bonds are broken, the released energy is used to generate energy molecules such as ATP, NADP, NADPH, etc.

In addition, these steps generate intermediate compounds that can be used for the biosynthesis of other organic molecules such as fats, amino acids, and proteins.

Some of the oxidation steps also regenerate some compounds, such as oxaloacetic acid, which are reused in the next cycle of the same reaction, such as in the Krebs’ Cycle.

10. What is the significance of photorespiration?

The respiration that is initiated in chloroplasts and occurs in the presence of light and high concentrations of O2 (and low CO2) is called photorespiration. Photorespiration occurs in plants during intense light and low levels of carbon dioxide. Although there is no net gain of ATP, it protects the chlorophyll pigments from photo-oxidation when light intensity is very high.

11. List the substrates that enter and the products produced in

(a) Glycolysis

(b) Krebs Cycle

Glycolysis

The substrate is glucose.
Products are 2 molecules of pyruvate and 2 ATP molecules.

Kerb’s Cycle

The substrate is Acetyl-CoA.

End products are 2 molecules of CO₂, 3 NADH, one FADH_2, and 1 ATP.

12. How is yeast useful in industry? Give any three examples.

1. In bakeries for preparing bread, cakes, and biscuits.
2. In breweries for preparing wine and other alcoholic drinks.
3. In producing vinegar and in the tanning and curing of leather.
4. Ethanol is used to make gasohol, a fuel that is used for cars in Brazil.

13. How does the exchange of respiratory gases take place in plants

Plants do not have specific oxygen carriers. In plants, the atmospheric air moves in and out by simple diffusion that takes place through,

(a) the general body surface of the plant (stems, roots, fruits, and seeds);
(b) lenticels (openings in the bark of the tree trunk.
(c) Stomata are present in the leaves and young, green parts of the stems.

From the atmosphere, gases enter the intercellular spaces inside the plants. As O₂ is utilized, more of it diffuses into the plant. Since CO₂ is being continuously formed, its concentration in tissue spaces becomes higher than in the surrounding air. As a result, it diffuses out of the plant, especially when it is not being used for photosynthesis.

14. Define RQ. What is its significance?

RQ stands for Respiratory Quotient, which is the ratio of the volume of CO₂ evolved to the volume of O₂ consumed in aerobic respiration. The kind of substrate being oxidized can be determined by measuring the Respiratory Quotient of the respiratory tissue or oxygen.

15. Mention the significance of the TCA cycle.

The TCA Cycle is the Tricarboxylic Cycle or Krebs’ Cycle.

It is the major pathway to release reduced coenzymes and energy in a controlled manner.
It is the common pathway for the oxidative breakdown of glucose (carbohydrates), fatty acids, and amino acids. The fatty acids undergo β oxidation to produce acetyl-CoA, and amino acids from proteins enter the Krebs’ Cycle after deamination (removal of –NH2 group) of amino acids.
The TCA Cycle provides a series of intermediate compounds needed for the synthesis of other biomolecules like amino acids, nucleotides, chlorophyll, and fats.

16. Why does fermentation yield less energy than aerobic respiration?

Fermentation results only in the partial decomposition of the substrate and occurs when there is insufficient supply of oxygen. Although there is a regeneration of NAD, this does not generate any ATP. This is because there is no electron transport to the oxygen molecule that provides the required energy to form ATP molecules.

17. List any 2 important contributions of PPP in a cell.

The complete oxidation of one glucose molecule through the Pentose Phosphate Pathway or PPP produces 6 molecules of CO₂ and 12 molecules of NADPH₂.
It also generates Ribulose-5-phosphate, which acts as a raw material for RNA synthesis.
The glucose molecule that enters PPP is glucose-6-phosphate, which uses only one ATP molecule as opposed to two ATPs in Glycolysis.

18. What are the three major phases of glycolysis?

The three phases of Glycolysis are,

1. Phosphorylation of glucose to fructose 1,6-diphosphate. This is the activation of glucose, and 2ATPs are used.
2. Splitting of this compound into two 3 3-carbon sugar phosphates, which are interconvertible. Note that this is the origin of the term glycolysis, meaning splitting of glucose.
3. Oxidation by dehydrogenation. Each 3-C sugar phosphate is oxidized by the removal of hydrogen, making a reduced NAD that is NADH and producing 2ATPs.

19. What is the importance of the Krebs’ Cycle?

Significance of the Krebs’ Cycle and Acetyl CoA

1. It is the major pathway to release reduced coenzymes and energy in a controlled manner.
2. It is the common pathway for the oxidative breakdown of glucose (carbohydrates), fatty acids, and amino acids. The fatty acids undergo β oxidation to produce acetyl-CoA, and amino acids from proteins enter the Krebs’ Cycle after deamination (removal of the –NH₂ group) of amino acids.
3. Krebs’ Cycle provides a series of intermediate compounds needed for the synthesis of other biomolecules like amino acids, nucleotides, chlorophyll, and fats.

20. Differentiate between aerobic and anaerobic respiration.

Aerobic respiration	Anaerobic respiration
Takes place in the presence of oxygen.	Takes place in the complete absenceof oxygen.
Leads to the complete oxidation of the organic substrate.	Incomplete oxidation of the organic substrate takes place.
It is most common in higher organisms (both plants and animals).	Takes place in lower organisms such as bacteria, fungi, and in higher animals under limiting conditions of oxygen (e.g., in muscles when oxygen present is insufficient).
C₆H₁₂O₆ → 6CO₂ + 6H₂O + 6O₂ +38 ATP	C₆H₁₂O₆ → 2Ethyl alcohol + 2CO₂ +2 ATP(in yeast) OR C₆H₁₂O₆ → 2 Lactic acid + 2 ATP (in muscles)
Takes place in the cytoplasm and mitochondria in eukaryotes and the plasma membrane in prokaryotes.	Takes place in the cytoplasm.

21. Why is photorespiration a wasteful reaction?

During photorespiration, RUBISCO, the enzyme that carboxylates RuBP, oxygenates RuBP. This is because RUBISCO has the same active site for both CO₂ and O₂.

This oxygenation of RuBP leads to a loss of 25% carbon fixed by plants during the dark reaction. Thus, it is a wasteful reaction.

22. What is the respiratory chain or ETC? What is its significance?

ETC is the Electron Transport Chain, a series of electron carriers that carry hydrogen ions from the mitochondrial matrix to the inner membrane foldings, where the electrons are ultimately accepted by oxygen. ETC is also called the Respiratory Chain.

Hydrogen or electrons at a higher energy level are passed from one carrier to the next, moving downhill in energy terms, until they reach oxygen, the final acceptor of electrons, which, as a result, is reduced to water.

In the ETC, the hydrogen ions undergo a series of oxidation reactions that release energy. Thai energy is used to make ATP molecules by joining ADP with inorganic phosphate.

23. Discuss the site of the Pentose Phosphate Pathway in a cell.

The site of the Pentose Phosphate Pathway is the cytosol of metabolically active tissues of animals. PPP does not require an electron transport chain or mitochondria. This pathway uses PPP, also called the Hexose Monophosphate Shunt pathway (HMP), as glucose-6-phosphate is the main substrate, which will be converted into ribulose-5-phosphate. The ribulose-5-phosphate is used for RNA and DNA synthesis. Moreover, it generates 12 NADPH₂, which can be used to generate ATP molecules.