12. Respiration in Plants

Class 11 Biology Chapter 12 Respiration in Plants

Chapter 12 : Respiration in Plants

Class 11 Biology Chapter 12 Respiration in Plants Exercise Questions and Answers :

1. Differentiate between

(a) Respiration and Combustion

(b) Glycolysis and Krebs’ cycle

Answer : (a) The differences between respiration and combustion :

Respiration	Combustion
Generate energy for living organisms, primarily ATP	Release energy as heat and light
Living organisms, occurs in cellular structures (e.g., mitochondria)	Non-living, often involves fuels and oxygen in the presence of oxygen
Inside cells of living organisms	Various settings, including engines, industrial processes, and open flames
Carbon dioxide () and water ()	Carbon dioxide () and water (), heat, and light
Highly regulated within the organism, subject to biochemical feedback loops	Less tightly regulated, influenced by fuel type and combustion conditions .

(b) The differentiating glycolysis and the Krebs' cycle :

Glycolysis	Krebs' Cycle (Citric Acid Cycle)
Occurs in the cytoplasm of the cell	Takes place in the mitochondria
Can occur in the presence or absence of oxygen (anaerobic and aerobic)	Requires oxygen (aerobic process)
Generates a small amount of ATP (2 ATP per glucose molecule)	Produces a significant amount of ATP (up to 34 ATP per glucose molecule)
Begins with glucose or other sugars	Starts with acetyl-CoA derived from pyruvate
Produces pyruvate as the end product	Produces carbon dioxide, ATP, NADH, , and precursor molecules for other metabolic pathways
Initiates glucose breakdown and produces pyruvate	Completes the oxidation of pyruvate and other fuel molecules to produce more ATP and NADH for the electron transport chain

Aerobic Respiration	Fermentation
Requires oxygen for the complete breakdown of glucose into carbon dioxide and water.	Does not require oxygen; it occurs in the absence of oxygen.
Takes place in the mitochondria of eukaryotic cells or the cytoplasm of prokaryotic cells.	Occurs in the cytoplasm of the cell.
Produces a significantly higher amount of ATP (usually 36-38 ATP molecules per glucose).	Produces a much smaller amount of ATP (typically 2 ATP molecules per glucose).
Aerobic respiration is highly efficient in terms of energy production per glucose molecule.	Fermentation is less efficient in terms of energy production compared to aerobic respiration.
Produces carbon dioxide, water, and a large amount of ATP.	Produces various end products depending on the type of fermentation, such as ethanol (in alcohol fermentation) or lactic acid (in lactic acid fermentation).
Found in aerobic organisms like mammals, birds, and many microorganisms.	Found in various organisms, including yeast, certain bacteria, and human muscle cells during anaerobic exercise.

2. What are respiratory substrates? Name the most common respiratory substrate.

Answer : Respiratory substrates are molecules that are used by cells as a source of energy through the process of cellular respiration. The most common respiratory substrate in biological systems is glucose. Glucose is a carbohydrate that is readily broken down to produce energy in the form of adenosine triphosphate (ATP) through glycolysis and the subsequent stages of cellular respiration. However, cells can also use other respiratory substrates, such as fatty acids and amino acids, depending on their energy needs and the availability of these molecules.

3. Give the schematic representation of glycolysis .

Answer :

The schematic representation of glycolysis

4. What are the main steps in aerobic respiration? Where does it take place?

Answer : Aerobic respiration consists of several main steps, and it primarily occurs within the mitochondria of eukaryotic cells.

The main steps in aerobic respiration :

(a) Occurs in the cytoplasm and breaks down glucose into pyruvate, generating a small amount of ATP and NADH.

(b) Pyruvate is transported from the cytoplasm into the mitochondria.

(d) In the mitochondrial matrix, acetyl CoA enters the TCA cycle, generating NADH, and a small amount of ATP.

(e) Located on the inner mitochondrial membrane, the ETC passes high-energy electrons from NADH and , ultimately leading to the production of ATP.

(f) ATP is synthesized using the proton gradient established by the ETC, with ATP synthase on the inner mitochondrial membrane.

These steps collectively make up aerobic respiration, where glucose is converted into energy (ATP) through a series of chemical reactions within the cell's mitochondria.

5. Give the schematic representation of an overall view of Krebs’ cycle.

Answer :

The schematic diagram of Krebs’ cycle .

6. Explain ETS.

Answer : The Electron Transport Chain (ETC) is a critical component of cellular respiration, which is the process by which cells generate energy in the form of ATP.

The explanation of the ETC :

(i) The ETC is located on the inner mitochondrial membrane in eukaryotic cells.

(ii) Its main purpose is to extract energy from high-energy electrons carried by molecules like NADH and , generated during previous stages of cellular respiration.

(iii) The ETC is a series of protein complexes (cytochromes) embedded in the inner mitochondrial membrane. Electrons from NADH and are passed along this chain of proteins.

(iv) As electrons move through the protein complexes, they release energy. This energy is used to actively pump protons ( ions) across the inner mitochondrial membrane, creating a proton gradient.

(v) The pumping of protons creates a concentration gradient, with more protons on one side of the membrane compared to the other.

(vi) The proton gradient stores potential energy, similar to a charged battery. This potential energy is used to drive ATP synthesis through ATP synthase, an enzyme also embedded in the inner mitochondrial membrane.

(vii) ATP synthase uses the flow of protons back into the mitochondrial matrix to produce ATP from adenosine diphosphate (ADP) and inorganic phosphate (Pi).

(viii) Oxygen () serves as the final electron acceptor at the end of the ETC. It combines with electrons and protons to form water ().

(ix) The ETC is responsible for the majority of ATP production in cellular respiration.

7. Distinguish between the following:

(a) Aerobic respiration and Anaerobic respiration

(b) Glycolysis and Fermentation

Answer : (a) Difference between Aerobic respiration and Anaerobic respiration :

Aerobic Respiration	Anaerobic Respiration
Requires oxygen ()	Does not require oxygen
Takes place in mitochondria	Occurs in the cytoplasm
Highly efficient, yielding more ATP	Less efficient, yielding less ATP
Oxygen () is the final electron acceptor	In the absence of oxygen, various other molecules (like pyruvate or nitrate) may serve as the final electron acceptor
Carbon dioxide () and water () are produced	Varies depending on the type of anaerobic respiration. Common products include lactic acid or ethanol, (as well as ) and water in some cases
Used during prolonged, low-intensity exercise	Used during short bursts of high-intensity exercise, causing muscle fatigue
Some microorganisms, like bacteria and yeast, can undergo fermentation	Many microorganisms perform anaerobic respiration in the absence of oxygen .

(b) The difference between Glycolysis and Fermentation :

Glycolysis	Fermentation
Can occur in the presence or absence of oxygen (anaerobic and aerobic)	Occurs in the absence of oxygen (anaerobic)
Generates a small amount of ATP (2 ATP per glucose molecule)	Does not produce additional ATP; instead, it regenerates to keep glycolysis going
Produces pyruvate as the end product	End products vary depending on the type of fermentation, but commonly includes lactic acid or ethanol
Serves as the initial step in glucose metabolism, breaking down glucose into pyruvate	Regenerates to sustain glycolysis in the absence of oxygen and to dispose of excess pyruvate

Glycolysis	Citric Acid Cycle (Krebs Cycle)
Occurs in the cytoplasm of cells	Takes place in the mitochondria
Can occur in the presence or absence of oxygen (anaerobic and aerobic)	Requires oxygen (aerobic process)
Generates a small amount of ATP (2 ATP per glucose molecule)	Produces a significant amount of ATP (up to 34 ATP per glucose molecule)
Begins with glucose or other sugars	Starts with acetyl-CoA derived from pyruvate
Produces pyruvate as the end product	Produces carbon dioxide, ATP, NADH, , and precursor molecules for other metabolic pathways
Initiates glucose breakdown and produces pyruvate	Completes the oxidation of pyruvate and other fuel molecules to produce more ATP and NADH for the electron transport chain

8. What are the assumptions made during the calculation of net gain of ATP ?

Answer : The assumptions made during the calculation of the net gain of ATP for glucose oxidation, although theoretical, include :

(i) The assumption of a sequential, orderly pathway, where one substrate leads to the next, with glycolysis, the TCA cycle, and the electron transport system occurring in a specific order.

(ii) The assumption that NADH produced in glycolysis is transferred into the mitochondria and participates in oxidative phosphorylation.

(iii) Assuming that none of the intermediates in the pathway are used to synthesize other compounds; all energy produced is directed towards ATP production.

(iv) The assumption that only glucose is respired, with no alternative substrates entering the pathway at intermediary stages.

These assumptions, while simplifications, do not fully represent the complexity of living systems where pathways work concurrently, substrates enter and exit pathways as needed, and enzymatic rates are controlled by multiple factors. Despite these simplifications, making these calculations helps appreciate the efficiency of energy extraction and storage in biological systems. The net gain of 38 ATP molecules can be theoretically calculated during aerobic respiration of one glucose molecule based on these assumptions

9. Discuss “The respiratory pathway is an amphibolic pathway.”

Answer : The statement that "the respiratory pathway is an amphibolic pathway" reflects the dual nature of the respiratory process in cellular metabolism. An amphibolic pathway is one that has both catabolic (breakdown) and anabolic (biosynthetic) functions. In the case of the respiratory pathway, it plays a significant role in both breaking down complex molecules to release energy and providing precursors for biosynthetic pathways.

(i) The primary catabolic role of the respiratory pathway, including glycolysis, the citric acid cycle, and oxidative phosphorylation, is to break down complex organic molecules (such as glucose and fatty acids) to extract energy in the form of ATP. During this process, these molecules are oxidized, and their chemical energy is released.

(ii) The intermediates and products generated during the catabolic phase of respiration can serve as precursors for the synthesis of other important molecules. For example, the carbon skeletons and reducing equivalents (NADH and ) produced during the citric acid cycle can be used in biosynthetic pathways to create amino acids, nucleotides, and other molecules essential for cell growth and repair.

(iii) The respiratory pathway contributes to gluconeogenesis, the biosynthetic pathway that produces glucose from non-carbohydrate precursors. Some intermediates in the citric acid cycle can be converted into glucose when glucose levels are low in the body.

(iv) Acetyl-CoA, a key intermediate in the citric acid cycle, can also be used to synthesize fatty acids in a process known as lipogenesis.

(v) The respiratory pathway is tightly regulated to meet the dynamic energy and biosynthetic demands of the cell. Depending on the cell's needs, it can shift between catabolic and anabolic functions.

10. Define RQ. What is its value for fats?

Answer : The Respiratory Quotient (RQ) is defined as the ratio of the volume of carbon dioxide () evolved to the volume of oxygen () consumed during aerobic respiration.

The formula for RQ is:

The balanced chemical equation for the complete oxidation of a generic fat molecule (triglyceride) in the presence of oxygen:

In this equation, one molecule of the generic fat reacts with 78 molecules of oxygen () to produce 55 molecules of carbon dioxide () and 52 molecules of water ().

Therefore, the RQ for the complete oxidation of fats is 0.71 .

11. What is oxidative phosphorylation ?

Answer : Oxidative phosphorylation is the final stage of aerobic cellular respiration that takes place in the mitochondria of eukaryotic cells. It is the process by which cells generate the majority of their adenosine triphosphate (ATP), the primary energy currency. During oxidative phosphorylation:

(i) High-energy electrons are transferred through a series of protein complexes in the inner mitochondrial membrane.

(ii) As electrons move through these complexes, they actively pump protons () from the mitochondrial matrix into the intermembrane space, creating a proton gradient.

(iii) The movement of protons establishes a concentration gradient, representing potential energy.

(iv) In the inner mitochondrial membrane, an enzyme called ATP synthase uses the proton gradient to synthesize ATP. Protons flow back into the mitochondrial matrix through ATP synthase, driving the conversion of adenosine diphosphate (ADP) and inorganic phosphate (Pi) into ATP.

(v) Oxygen serves as the terminal electron acceptor at the end of the electron transport chain, combining with electrons and protons to form water ().

Oxidative phosphorylation is highly efficient and plays a central role in producing ATP, ensuring that cells have a reliable and abundant source of energy for their various functions and processes.

12. What is the significance of step-wise release of energy in respiration?

Answer : The step-wise release of energy in respiration is significant for several reasons:

(i) Breaking down complex organic molecules into smaller, manageable steps allows cells to extract energy efficiently. This prevents the wasteful release of energy as heat.

(ii) Each step in respiration produces energy in the form of ATP. This gradual release of energy maximizes ATP production, which is the primary energy currency of cells.

(iii) The step-wise process allows for precise control and regulation of energy production. Cells can fine-tune their energy production to meet their changing energy demands.

(iv) Gradual energy release reduces the risk of cellular stress and damage that can result from sudden, uncontrolled energy release.

(v) The controlled release of energy facilitates the efficient transfer of electrons along the electron transport chain. This is essential for ATP synthesis.

(vi) The step-wise approach minimizes the production of waste products and byproducts, as excess energy and metabolites are harnessed for further energy production or other cellular processes.

(vii) The intermediates and products generated in respiration can be used in other metabolic pathways. This contributes to the synthesis of essential molecules for cell growth and repair.

(viii) Cells can switch between aerobic (oxygen-dependent) and anaerobic (oxygen-independent) respiration based on oxygen availability, ensuring energy production in varying conditions.