Class 11 Biology Chapter 12 Respiration In plants

Key Concept: Basic Concept

c) Stomata

[Solution Description] Stomata are small openings on plant leaves and stems that allow for the exchange of gases, such as oxygen and carbon dioxide, with the environment. Lenticels perform similar functions in woody stems.

Key Concept: Basic Concept

b) Respiration

[Solution Description] The process that involves the breakdown of carbon-carbon (C-C) bonds to release energy is called respiration. During respiration, complex molecules are broken down, and this process results in the production of ATP, which is the energy currency of the cell.

Key Concept: Simple Assumptions

b) Only glucose is respired

[Solution Description] While calculating the ATP yield from aerobic respiration, several assumptions are made to simplify the calculations:

– Pathways function sequentially without interference.

– All substrates enter the pathway at once.

– There is no utilization of intermediates for other biosynthetic pathways.

– Only glucose is respired.

Based on these assumptions, the correct answer is that only glucose is assumed to be respired during these calculations.

Key Concept: Proton Motive Force, Comparative Analysis

b) Proton motive force weakens, leading to halted ATP synthesis.

[Solution Description]

Uncouplers like DNP dissipate the proton gradient across the mitochondrial membrane by allowing protons to re-enter the matrix without passing through ATP synthase. This collapse of the proton motive force prevents ATP synthesis despite continued electron transport because the energy from the electron transport chain is released as heat instead of being used to phosphorylate ADP to ATP. Thus, while electron transport continues normally, ATP production declines drastically.

Key Concept: Energy Release Mechanism, Respiratory Quotient

b) 0.8 – 0.9

[Solution Description] Proteins have an RQ value that generally ranges between 0.8 to 0.9. The breakdown of proteins results in the formation of amino acids, which are then converted into intermediates for cellular respiration. As proteins contain both carbon and nitrogen, complete oxidation requires more oxygen relative to carbon dioxide produced.

Key Concept: Comparative Analysis

d) Only alcoholic fermentation releases CO$_2$ as a byproduct.

[Solution Description] Lactic acid fermentation converts pyruvic acid into lactic acid directly using lactate dehydrogenase, without releasing CO$_2$. In contrast, alcoholic fermentation involves two steps: pyruvic acid is first converted to acetaldehyde and CO$_2$ by pyruvic acid decarboxylase, then acetaldehyde is reduced to ethanol by alcohol dehydrogenase.

Key Concept: Basic Definition

c) Both catabolic and anabolic

[Solution Description] Amphibolic pathways serve a dual role in metabolism. They are involved in both catabolic and anabolic processes, meaning they help break down molecules for energy and also synthesize complex molecules.

Key Concept: Substrate Identification

c) Fats

[Solution Description] Fats generally have an RQ value of less than 1 because they require more oxygen for their oxidation compared to the amount of carbon dioxide they release. Specifically, tripalmitin, a type of fat, has an RQ value of 0.7.

Key Concept: NADH Contribution

c) 3

[Solution Description] In the electron transport chain, each NADH molecule is theoretically capable of producing 3 ATP molecules due to its role in transferring electrons and creating a proton gradient.

Key Concept: Comparison with Aerobic Respiration

b) Lower

[Solution Description] In fermentation, glucose is partially oxidized, resulting in the production of only 2 ATP molecules per molecule of glucose. In contrast, aerobic respiration fully oxidizes glucose, producing approximately 36-38 ATP molecules per glucose. Hence, fermentation has a lower energy yield compared to aerobic respiration.

Key Concept: Pathway Integration, Real-world Application

d) Acetyl CoA

[Solution Description] During glycolysis, glucose is converted into pyruvate. Under aerobic conditions, pyruvate is transported into the mitochondria where it is converted to Acetyl CoA. This conversion is catalyzed by the enzyme pyruvate dehydrogenase complex. Acetyl CoA then enters the citric acid cycle (Krebs cycle), thereby linking glycolysis to the Krebs cycle.

Key Concept: Substrate Conversion

b) Amino acids

[Solution Description] Proteins are degraded into amino acids, which can enter as pyruvate, acetyl CoA, or directly within the Krebs’ cycle.

Key Concept: Proton Motive Force, Oxidative Phosphorylation

c) Assertion is true, but Reason is false.

[Solution Description]

The assertion correctly states that the proton gradient, also known as the proton motive force, is essential for ATP synthesis within mitochondria. This gradient provides the necessary potential energy for ATP synthase (Complex V) to phosphorylate ADP into ATP by allowing protons to flow down their gradient through the enzyme.

However, the reason provided is incorrect. The electron transport chain does not directly use energy from electron transfers to convert ADP to ATP. Instead, the energy released by these transfers is used to pump protons across the inner mitochondrial membrane, creating a gradient. It is this gradient that indirectly facilitates ATP synthesis when protons flow back into the mitochondrial matrix through ATP synthase. Therefore, while both statements may seem related, they do not logically connect in terms of causality.

Key Concept: Pathway Integration, Enzyme Regulation

d) Low concentrations of ATP and high concentrations of AMP

[Solution Description] Phosphofructokinase is a key regulatory enzyme in glycolysis that is inhibited by high levels of ATP through feedback inhibition. Therefore, if ATP levels are low, inhibition decreases, allowing glycolysis to increase.

Key Concept: Reaction Details

d) NAD\textsuperscript{+} and Coenzyme A

[Solution Description] The oxidative decarboxylation of pyruvate is catalyzed by the enzyme complex called pyruvate dehydrogenase, and it requires NAD\textsuperscript{+} and Coenzyme A as essential coenzymes. Pyruvate loses one carbon atom as CO\textsubscript{2}, and the remaining two-carbon fragment binds with Coenzyme A, forming acetyl CoA.

Key Concept: Gas Exchange in Stems

c) They allow gaseous exchange by diffusion.

[Solution Description] Lenticels are small openings found on the bark of woody stems. They function similarly to stomata but are specifically adapted for the exchange of gases between the internal tissues of plants and the external environment, facilitating diffusion of oxygen, carbon dioxide, and water vapor.

Key Concept: Product Formation

d) GTP

[Solution Description] The conversion of succinyl-CoA to succinic acid is coupled with substrate-level phosphorylation, resulting in the production of GTP.

Key Concept: Cytochrome c Role, Non-Straightforward Path

b) Electron flow through complex IV

[Solution Description]

Cytochrome c acts as an electron carrier between complexes III and IV in the electron transport chain. Over-reduction implies that it cannot accept more electrons, halting electron transfer from complex III to complex IV. This interruption affects the entire electron flow towards oxygen, leading to potential accumulation of reduced components upstream and decreased efficiency in ATP synthesis.

Key Concept: NADH Formation

d) Conversion of PGAL to 1,3-bisphosphoglycerate

[Solution Description]

NADH + H\textsuperscript{+} is formed when 3-phosphoglyceraldehyde is oxidized to 1,3-bisphosphoglycerate ($PGAL \rightarrow BPGA$). This process involves the reduction of NAD\textsuperscript{+} to NADH.

Key Concept: ATP Calculation

b) 6

[Solution Description]

To solve this question, we need to know the net gain of ATP per molecule of glucose during lactic acid fermentation. According to the syllabus, each glucose molecule produces a net gain of 2 ATP molecules. Therefore, for 3 molecules of glucose:

$\text{Net ATP} = 3 \times 2 = 6$

So, the net ATP produced is 6.

Key Concept: Energy Yield

a) Less than 7%

[Solution Description] Fermentation releases less than seven percent of the energy in glucose.

Key Concept: Proton Channel

d) F0

[Solution Description] The ATP synthase enzyme is composed of two main parts: F1 and F0. The F0 component is responsible for forming a channel through which protons can pass from the intermembrane space into the matrix of mitochondria, facilitating ATP synthesis.

Key Concept: Glycolysis Products

b) Pyruvic acid and ATP

[Solution Description] Glycolysis results in the conversion of one molecule of glucose into two molecules of pyruvic acid. Additionally, a net gain of two ATP molecules is achieved through substrate-level phosphorylation.

Key Concept: Basic Comparison

b) Aerobic respiration

[Solution Description] In aerobic respiration, glucose undergoes complete oxidation to carbon dioxide (CO$_2$) and water (H$_2$O). This is a key feature distinguishing it from fermentation, where such complete oxidation does not occur.

Key Concept: Basic Calculation

b) 2

[Solution Description] During glycolysis, a total of 4 ATP molecules are produced through substrate-level phosphorylation. However, 2 ATP molecules are consumed in the initial steps of glycolysis. Thus, the net gain is $$4 – 2 = 2$$ ATP molecules.

Key Concept: Anaerobic Conditions

b) Ethanol

[Solution Description] In yeast cells, under anaerobic conditions, glycolysis leads to alcohol fermentation. During this process, pyruvic acid is converted into ethanol.

Key Concept: Pathway Regulation, Real-world Application, Process Integration

a) Inhibition of citrate synthase, preventing acetyl CoA and oxaloacetate binding.

[Solution Description] The Krebs’ cycle begins with the condensation of acetyl CoA and oxaloacetate to form citric acid. This reaction is catalyzed by citrate synthase. An accumulation of oxaloacetate coupled with low levels of citric acid indicates a possible inhibition or lack of activity of citrate synthase or a shortage of acetyl CoA. Without sufficient acetyl CoA, even excess oxaloacetate cannot proceed to form citric acid, leading to reduced energy production.

Key Concept: Basic Calculation

b) 2

[Solution Description] Each molecule of FADH$$_2$$, when oxidized, yields 2 ATP molecules in the electron transport chain.

Key Concept: Limiting Factors

c) Ethanol concentration above tolerance level

[Solution Description] The limiting factor for alcoholic fermentation in yeast is the concentration of ethanol produced. Yeast can tolerate up to 13\% alcohol; beyond this concentration, the process may be inhibited due to toxicity effects on yeast cells.

Key Concept: Location of Process

c) Inner mitochondrial membrane

[Solution Description] The electron transport chain, where oxygen acts as the final electron acceptor, occurs on the inner mitochondrial membrane.

Key Concept: Advanced Comparison, Real-world Implication

d) Alcoholic fermentation is significant in biofuel production by converting biomass into ethanol.

[Solution Description]

During lactic acid fermentation, glucose is converted into lactic acid without releasing carbon dioxide, while alcoholic fermentation converts glucose to ethanol and carbon dioxide. The efficiency of ATP production in both processes is lesser than that of aerobic respiration due to incomplete oxidation. In terms of industrial usage, alcoholic fermentation is significant for producing biofuels because it converts biomass into ethanol. Lactic acid fermentation is primarily used in the food industry.

Key Concept: Basic Pathway

b) Hexokinase

[Solution Description] The first reaction of glycolysis involves the conversion of glucose to glucose-6-phosphate. This process is catalyzed by the enzyme hexokinase.

Key Concept: Advanced Reaction Analysis, Non-Straightforward Path

b) It regenerates an important TCA cycle intermediate.

[Solution Description] The oxidation of malate to oxaloacetate by malate dehydrogenase involves the reduction of NAD+ to NADH. This step completes the cycle by regenerating oxaloacetate, which can condense with another molecule of acetyl CoA to start the cycle anew. Additionally, the NADH produced provides electrons for the electron transport chain, contributing to ATP synthesis. Thus, it ensures continuity of the cycle and contributes indirectly to energy production.

Key Concept: Diffusion Efficiency, Glycolysis Pathway

d) By facilitating rapid diffusion of metabolites and gases

[Solution Description] The loose packing of parenchyma cells in plants creates an interconnected network of air spaces that help facilitate gas exchange and diffusion. Although glycolysis occurs in the cytoplasm and does not require oxygen, the efficient exchange of gases through these structures ensures that even under anaerobic conditions, glucose can be partially oxidized to pyruvic acid efficiently. This structural adaptation helps maintain metabolic processes when oxygen availability is limited.

Key Concept: Amphibolic Pathway Analysis, Substrate Utilization

c) Assertion is true, but Reason is false.

[Solution Description]

The assertion is true as the respiratory pathway acts as an amphibolic pathway, meaning it has both catabolic characteristics (breaking down molecules to release energy) and anabolic characteristics (providing precursors for biosynthesis). However, the reason provided is false because not only carbohydrates but also proteins and fats can be utilized as substrates in the respiratory pathway under different conditions. Proteins enter through deamination, and fats are broken into glycerol and fatty acids for entry into pathways like glycolysis and the citric acid cycle. Hence, while the assertion is true, the reason is incorrect.

Key Concept: Basic Definition

b) A pathway involved in both breakdown and synthesis

[Solution Description] An amphibolic pathway is one that serves both catabolic and anabolic functions. This means it is involved in breaking down molecules to release energy (catabolism) as well as synthesizing new compounds (anabolism). The respiratory pathway is a classic example of an amphibolic pathway since it manages these dual roles.

Key Concept: Comparative Rates

b) Roots

[Solution Description] The roots of a plant generally have the lowest rate of respiration compared to other parts. This is because they do not carry out photosynthesis; hence, their metabolic needs are relatively less when compared to more active parts like leaves or flowers.

Key Concept: Photosynthesis and Respiration

b) Oxygen is released within the chloroplasts

[Solution Description] During photosynthesis, plants absorb carbon dioxide and release oxygen as a byproduct through the stomata. The oxygen produced internally meets the plant’s immediate needs for respiration, eliminating the necessity for additional absorption from the environment.

Key Concept: Basic Definition

a) The ratio of volume of $CO_2$ evolved to the volume of $O_2$ consumed

[Solution Description]

The Respiratory Quotient (RQ) is defined as the ratio of the volume of carbon dioxide ($CO_2$) evolved to the volume of oxygen ($O_2$) consumed during respiration.

Key Concept: Entry Points

b) Fatty acids

[Solution Description] Fatty acids are converted into acetyl CoA before entering the respiratory pathway.

Key Concept: Reaction Environment

b) Muscle cells

[Solution Description] Lactic acid fermentation mainly takes place in muscle cells when there is a lack of oxygen during intense exercise. Under these anaerobic conditions, muscles resort to this process for energy production.

Key Concept: Role of Oxygen

b) Final electron acceptor

[Solution Description]

Oxygen acts as the final electron acceptor in the electron transport chain. It combines with electrons and hydrogen ions to form water, a process that allows for the continuation of electron flow through the chain, facilitating ATP synthesis.

Key Concept: Real-World Application, Role of Oxygen

d) Decrease in ATP synthesis through oxidative phosphorylation

[Solution Description]

Oxygen acts as the final electron acceptor in the electron transport chain. When oxygen levels decline, the chain’s efficiency reduces as the electrons can’t be transferred effectively. This impacts oxidative phosphorylation severely because:

– Without sufficient oxygen, the electron transport slows down, leading to reduced proton pumping by complexes.

– Less proton gradient results in less ATP synthesis via ATP synthase.

Hence, ATP production via oxidative phosphorylation will decrease significantly during low oxygen availability.

Key Concept: Basic Definition

c) To release energy and trap it as ATP

[Solution Description] Cellular respiration primarily serves the purpose of breaking down food materials to release energy, which is then trapped for ATP synthesis.

Key Concept: Real-World Application, Chemiosmotic Hypothesis

c) Decreased proton gradient and reduced ATP synthesis.

[Solution Description]

Oxygen serves as the final electron acceptor in the electron transport chain. In conditions of low oxygen availability, electrons will start accumulating at Complex IV because they cannot be passed onto oxygen to form water. This causes proton pumping to decrease or stop, leading to a diminished proton gradient. The reduction in the proton gradient directly results in decreased ATP synthesis via ATP synthase due to insufficient proton-motive force driving ATP synthesis.

Key Concept: Complex Interactions, Chemiosmotic Hypothesis

d) Decreased ATP synthesis

[Solution Description] Inhibition of Complex III would halt the transfer of electrons from ubiquinol (QH₂) to cytochrome c. As a result, this step prevents protons from being pumped across the mitochondrial membrane by Complex III, disrupting the proton gradient essential for ATP synthesis. Consequently, the chemiosmotic potential decreases, leading to reduced ATP production.

Key Concept: Energy Source

b) Chloroplasts

[Solution Description] Photosynthesis occurs in the chloroplasts of plant cells, where light energy is converted into chemical energy stored in glucose molecules.

Key Concept: Simple Calculation

c) 1.0

[Solution Description] For carbohydrates, when they are completely oxidized, the RQ value is 1. This means that the volume of $CO_2$ evolved equals the volume of $O_2$ consumed.

Key Concept: Energy Yield Comparison

d) It yields significantly less ATP than aerobic respiration.

[Solution Description] Fermentation yields only 2 ATP per glucose molecule because it involves incomplete oxidation of glucose. In contrast, aerobic respiration completely oxidizes glucose to carbon dioxide and water, yielding approximately 36-38 ATP molecules.

Key Concept: Oxidation

d) Oxygen

[Solution Description] In the process of oxidative phosphorylation within the electron transport chain, oxygen acts as the final hydrogen acceptor. This means that after electrons have been transferred through various complexes, they are eventually passed to oxygen. Oxygen then combines with hydrogen ions to form water, completing the electron transport chain.

Key Concept: Real-World Application, Energy Yield

c) Fermentation due to its faster ATP production rate

[Solution Description] Under high energy demand and limited oxygen availability, cells switch to anaerobic pathways such as fermentation. Fermentation regenerates NAD+ from NADH, allowing glycolysis to continue producing ATP at a faster rate compared to waiting for slow ATP generation through the electron transport chain limited by low oxygen. Thus, despite being less efficient in terms of ATP yield, fermentation provides a rapid supply of ATP needed under these conditions.