Respiration in Plants - Class 11 Biology - Chapter 19 - Notes, NCERT Solutions & Extra Questions
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Extra Questions - Respiration in Plants | NCERT | Biology | Class 11
$C_{4}$-cycle mechanism is given by -
A. Hill
B. Arnan
C. Hatch & Slack
D. Calvin
The $C_4$ cycle mechanism, often referred to as the Hatch-Slack pathway, was discovered by scientists Hatch and Slack. This special photosynthetic process is primarily found in certain plants which survive in hot and dry environments where the atmospheric CO$_2$ concentration is lower and oxygen concentration can be higher. These conditions could potentially promote high rates of photorespiration.
To understand the $C_4$ cycle, consider the following key points:
The process begins when CO$_2$ is absorbed from the atmosphere and attached to a three-carbon molecule, phosphoenolpyruvate (PEP), through the action of the enzyme PEP carboxylase. This reaction forms a four-carbon molecule (commonly oxaloacetate), which is subsequently transformed into other four-carbon compounds like malate.
These four-carbon acids are then transported to specialized cells known as bundle sheath cells, where they release CO$_2$. The released CO$_2$ is then used in the Calvin cycle to produce sugars.
The key advantage of the $C_4$ pathway is that by concentrating CO$_2$ in bundle sheath cells and minimizing oxygen exposure (due to their oxygen-proof characteristics), the process dramatically reduces unwanted photorespiration, conserving energy, and improving water-use efficiency.
This adaptation allows $C_4$ plants not only to survive but also to thrive under conditions that are less favorable for other plants using the more common $C_3$ pathway. The accurate contribution by Calvin pertained to the $C_3$ cycle, also known as the Calvin cycle. Therefore, the correct answer to which scientist(s) gave the $C_4$ cycle mechanism is C. Hatch & Slack.
Glycolysis takes place in:
A. Mitochondria
B. Cytoplasm
C. Nucleus
D. Chloroplast
Glycolysis, a fundamental pathway in cellular metabolism, occurs in the cytoplasm of cells. During glycolysis, a single glucose molecule is broken down into two molecules of pyruvate (pyruvic acid). This process results in the net generation of two molecules of ATP. Glycolysis is crucial as it provides the energy currency essential for many cellular activities.
Furthermore, glycolysis can lead to other processes like fermentation. If oxygen levels are low, cells can undergo fermentation to continue producing energy. In muscle cells, this results in the production of lactic acid (homolactic fermentation), and in yeast, it leads to the production of ethanol and carbon dioxide (ethanol fermentation).
Given the choices for the location of glycolysis: A. Mitochondria B. Cytoplasm C. Nucleus D. Chloroplast
The correct answer is: B. Cytoplasm
Which of the following helps life to sustain in water?
Option 1: Dissolved Oxygen in water.
Option 2: Plants
Option 3: Water
Option 4: Undissolved Oxygen in water.
The correct option is 1: Dissolved Oxygen in water.
Like all other living organisms, aquatic animals require oxygen to survive and carry out their life processes. The presence of dissolved oxygen in water supports and sustains aquatic life by facilitating vital biological functions.
The correct order of lung capacities is:
$\mathrm{FRC}<\mathrm{EC}<\mathrm{IC}<\mathrm{VC}$
To solve the problem of determining the correct order of lung capacities, let's first understand the abbreviations and their meanings:
Expiratory Capacity ($\text{EC}$): It is the volume of air that can be forcefully expired after a normal expiration. It relates to the expiratory reserve volume (ERV).
Functional Residual Capacity ($\text{FRC}$): This is the amount of air remaining in the lungs after a normal expiration. It is the sum of the expiratory reserve volume and the residual volume (RV).
Inspiratory Capacity ($\text{IC}$): This is the maximum amount of air that can be inhaled after a normal exhalation. It combines the tidal volume (TV) and the inspiratory reserve volume (IRV).
Vital Capacity ($\text{VC}$): This is the maximum amount of air that can be exhaled after the fullest possible inspiration. It includes the tidal volume, expiratory reserve volume, and inspiratory reserve volume.
Based on the information given, let's list the average volumes for each capacity:
Vital Capacity ($\text{VC}$): 4,800 ml
Inspiratory Capacity ($\text{IC}$): 3,800 ml
Functional Residual Capacity ($\text{FRC}$): 2,500 ml
Expiratory Capacity ($\text{EC}$): 1,100 ml
From these volumes, we can deduce the correct order of lung capacities:
$$\text{EC} < \text{FRC} < \text{IC} < \text{VC}$$
Thus, the correct order is:
$$\boxed{\text{FRC} < \text{EC} < \text{IC} < \text{VC}}$$
The movement of air observed in the following diagram is caused by the:
Contraction of external intercostal muscles
Relaxation of external intercostal muscles
Contraction of internal intercostal muscles
Relaxation of the phrenic muscles
The movement of air observed in the diagram is caused by the contraction of external intercostal muscles.
Explanation:
The diagram illustrates the process of inhalation. Here’s a step-by-step breakdown of what happens during this process:
Inhalation:
Air enters the lungs.
The ribs and sternum are raised.
The diaphragm contracts and moves downward, increasing the volume of the thoracic cavity.
As a result of the increased thoracic volume:
The internal intercostal muscles relax.
The external intercostal muscles contract, causing the ribcage to move upward and outward.
Consequences:
The volume of the thoracic cavity increases.
The air pressure inside the thoracic cavity decreases, allowing air to flow into the lungs.
Given this sequence of events, it is clear that the correct cause of the observed air movement in the diagram is the contraction of external intercostal muscles.
Conclusion:
Therefore, the correct answer is:
Contraction of external intercostal muscles
Which of the following happens during expiration?
Increase in the pulmonary volume decreases the intrapulmonary pressure
Increase in the pulmonary volume increases the intrapulmonary pressure
Decrease in the thoracic volume decreases the intrapulmonary pressure
Increases the intrapulmonary pressure
During expiration, the following occurs:
Expiration is the process of breathing out. Here is what happens during expiration:
The diaphragm relaxes.
As the diaphragm relaxes, the thoracic cavity becomes smaller.
Due to the decrease in the thoracic cavity volume, the intrapulmonary pressure increases.
Now, let's evaluate the options given:
Increase in the pulmonary volume decreases the intrapulmonary pressure: This is incorrect because during expiration, the pulmonary volume actually decreases.
Increase in the pulmonary volume increases the intrapulmonary pressure: This is incorrect because the pulmonary volume decreases, not increases.
Decrease in the thoracic volume decreases the intrapulmonary pressure: This is incorrect because a decrease in thoracic volume actually increases the intrapulmonary pressure.
Increases the intrapulmonary pressure: This option correctly identifies the increase in intrapulmonary pressure during expiration due to a decrease in thoracic volume.
Thus, the correct answer is:
$$ \boxed{\text{Increases the intrapulmonary pressure}} $$
So the final answer is:
D. Increases the intrapulmonary pressure.
The volume of thoracic chamber increases in the dorso-ventral axis due to the contraction of:
A. Phrenic muscles
B. External intercostal muscles
C. Abdominal muscles
D. Internal intercostal muscles
To answer the question on how the volume of the thoracic chamber increases in the dorso-ventral axis due to muscle contraction, we need to understand the mechanisms involved in the process of breathing.
When we inhale, the thoracic chamber needs to expand to allow the lungs to fill with air. This expansion occurs in multiple directions, including the dorso-ventral axis (from the back to the front). The key muscles responsible for this increase in volume are:
Diaphragm: This muscle contracts and flattens, moving downward to increase the vertical volume of the thoracic cavity.
External Intercostal Muscles: These muscles, located between the ribs, contract to lift the ribs upward and outward, increasing the anteroposterior and dorso-ventral dimensions of the thoracic chamber.
Thus, the contraction of the external intercostal muscles primarily facilitates the increase in the dorso-ventral axis of the thoracic chamber. Hence, the correct answer is:
B. External intercostal muscles
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Ask Chatterbot AINCERT Solutions - Respiration in Plants | NCERT | Biology | Class 11
Differentiate between
(a) Respiration and Combustion
(b) Glycolysis and Krebs' cycle
(c) Aerobic respiration and Fermentation
(a) Respiration and Combustion
Respiration:
Biological Process: Occurs within living cells.
Controlled by Enzymes: Series of enzyme-controlled reactions.
Substrate: Primarily glucose but also includes fats and proteins.
Products: Carbon dioxide, water, and ATP (energy).
Energy Release: Gradual release of energy.
Temperature: Takes place at normal body temperature.
Pathway: Multi-step, involving glycolysis, Krebs' cycle, and Electron Transport System (ETS).
Combustion:
Chemical Process: Occurs outside living systems.
Not Enzyme-Controlled: Uncontrolled and happens spontaneously.
Substrate: Organic matter such as wood, fossil fuels.
Products: Carbon dioxide, water, and energy (as heat and light).
Energy Release: Rapid release of energy.
Temperature: Takes place at high temperatures.
Pathway: Single-step and rapid.
(b) Glycolysis and Krebs' Cycle
Glycolysis:
Location: Occurs in the cytoplasm of the cell.
Anaerobic Condition: Can occur with or without oxygen.
Initial Substrate: Glucose.
End Products: Two molecules of pyruvate, two ATP, and two NADH.
Pathway Type: Linear pathway involving 10 steps.
Purpose: Breaks down glucose into pyruvate, yielding a small amount of ATP.
Krebs' Cycle (Tricarboxylic Acid Cycle):
Location: Occurs in the mitochondrial matrix.
Aerobic Condition: Requires oxygen.
Initial Substrate: Acetyl CoA (derived from pyruvate).
End Products: Three NADH, one FADH2, one GTP (converted to ATP), and two CO₂ per acetyl CoA.
Pathway Type: Cyclic pathway.
Purpose: Completes the oxidation of carbohydrates, fats, and proteins, generating high-energy electron carriers (NADH, FADH2) for ATP synthesis.
(c) Aerobic Respiration and Fermentation
Aerobic Respiration:
Oxygen Requirement: Requires oxygen.
Location: Takes place in the mitochondria.
End Products: Carbon dioxide, water, and a large amount of ATP.
Efficiency: Highly efficient (around 38 ATP per glucose molecule).
Pathway Involvement: Involves glycolysis, Krebs' cycle, and Electron Transport Chain (ETS).
Fermentation:
Oxygen Requirement: Occurs in the absence of oxygen.
Location: Takes place in the cytoplasm.
End Products: Ethanol and carbon dioxide (alcoholic fermentation) or lactic acid (lactic acid fermentation).
Efficiency: Less efficient (2 ATP per glucose molecule).
Pathway Involvement: Involves only glycolysis, followed by either alcohol or lactic acid fermentation.
What are respiratory substrates? Name the most common respiratory substrate.
Respiratory substrates are compounds that are oxidized during the process of respiration to release energy.
The most common respiratory substrate is glucose.
Give the schematic representation of glycolysis?
Here's a schematic representation of glycolysis outlining the ten steps involved in the breakdown of glucose to pyruvate:
Key Points:
Glucose is phosphorylated to glucose-6-phosphate.
Glucose-6-phosphate is isomerised to fructose-6-phosphate.
Fructose-6-phosphate is converted to fructose-1,6-bisphosphate.
Fructose-1,6-bisphosphate splits into dihydroxyacetone phosphate and 3-phosphoglyceraldehyde (PGAL).
PGAL is oxidised to 1,3-bisphosphoglycerate (BPGA).
BPGA is converted to 3-phosphoglyceric acid (PGA).
PGA is converted to phosphoenolpyruvate (PEP).
PEP is converted to pyruvate.
ATP and NADH Production:
ATP is utilised at two steps: the conversion of glucose to glucose-6-phosphate, and fructose-6-phosphate to fructose-1,6-bisphosphate.
NADH is formed when PGAL is converted to BPGA.
ATP is synthesised during the conversion of BPGA to PGA and PEP to pyruvate.
End Product:
The key end product of glycolysis is pyruvate.
Each reaction is catalysed by specific enzymes and involves a series of precise and regulated steps.
What are the main steps in aerobic respiration? Where does it take place?
Aerobic respiration involves several key steps and processes which primarily take place in the mitochondria of eukaryotic cells. The main steps include:
Glycolysis: This occurs in the cytoplasm where a glucose molecule is broken down into two molecules of pyruvate, producing a net gain of 2 ATP and 2 NADH.
Pyruvate Oxidation: The pyruvate is transported into the mitochondria where it undergoes oxidative decarboxylation to form Acetyl CoA, releasing 1 NADH and 1 CO₂ per pyruvate.
Krebs' Cycle (Citric Acid Cycle): This series of reactions also takes place in the mitochondrial matrix. Acetyl CoA is fully oxidized to CO₂, generating 3 NADH, 1 FADH₂, and 1 GTP (converted to ATP) per Acetyl CoA.
Electron Transport System (ETS) and Oxidative Phosphorylation: This is located on the inner mitochondrial membrane. Electrons from NADH and FADH₂ are transferred through a series of carriers, ultimately to molecular oxygen (O₂), generating water (H₂O). The energy released during electron transfer is used to synthesize ATP from ADP and inorganic phosphate (Pi) via ATP synthase.
To summarize:
Glycolysis: Cytoplasm
Pyruvate Oxidation & Krebs' Cycle: Mitochondrial matrix
Electron Transport System and Oxidative Phosphorylation: Inner mitochondrial membrane
These processes ensure the complete oxidation of glucose into CO₂ and H₂O, while generating a large amount of ATP.
Give the schematic representation of an overall view of Krebs' cycle.
Below is the schematic representation of the Krebs' Cycle (also known as the Citric Acid Cycle or TCA Cycle):
Schematic Representation of Krebs' Cycle:
Acetyl CoA (from pyruvate) combines with Oxaloacetic Acid (OAA) to form Citrate, catalyzed by Citrate Synthase.
Citrate is isomerized to Isocitrate by Aconitase.
Isocitrate is converted to α-Ketoglutarate by Isocitrate Dehydrogenase, producing NADH and releasing CO₂.
α-Ketoglutarate is converted to Succinyl-CoA by α-Ketoglutarate Dehydrogenase, again producing NADH and releasing CO₂.
Succinyl-CoA is converted to Succinate by Succinyl-CoA Synthetase, producing GTP (which can be converted to ATP).
Succinate is converted to Fumarate by Succinate Dehydrogenase, producing FADH₂.
Fumarate is converted to Malate by Fumarase.
Malate is converted to Oxaloacetic Acid (OAA) by Malate Dehydrogenase, producing NADH.
Key Outputs per cycle:
3 NADH
1 FADH₂
1 GTP (which can be converted to ATP)
2 CO₂
Figure 12.3 The Citric Acid Cycle
By understanding this cycle, you can appreciate the central role it plays in cellular respiration and energy production.
Explain ETS.
Electron Transport System (ETS) and Oxidative Phosphorylation
The Electron Transport System (ETS) is a series of protein complexes located in the inner mitochondrial membrane. It plays a crucial role in cellular respiration by managing the transfer of electrons from NADH and FADH₂ to oxygen, resulting in the formation of water. Here's a step-by-step explanation:
Electron Donation:
NADH and FADH₂ produced during the Krebs cycle donate electrons to the ETS. NADH transfers electrons to Complex I (NADH dehydrogenase), while FADH₂ transfers electrons to Complex II.
Electron Transport:
Complex I: Electrons from NADH are transferred to ubiquinone (also known as coenzyme Q), passing through Complex I.
Complex II: Electrons from FADH₂ enter the ETS via this complex but do not pump protons.
Ubiquinone: Acts as a mobile electron carrier, transporting electrons from Complex I and Complex II to Complex III.
Complex III: Transfers electrons from ubiquinone to cytochrome c.
Cytochrome c: Another mobile electron carrier that transfers electrons from Complex III to Complex IV.
Complex IV: Contains cytochromes a and a₃, which transfer electrons to oxygen, the final electron acceptor. Oxygen combines with electrons and protons to form water.
Proton Pumping and ATP Synthesis:
The transfer of electrons through Complexes I, III, and IV is coupled with the pumping of protons (H⁺) from the mitochondrial matrix into the intermembrane space, creating a proton gradient (proton-motive force).
The ATP Synthase Complex (Complex V): Utilizes the energy stored in the proton gradient to synthesize ATP from ADP and inorganic phosphate as protons flow back into the mitochondrial matrix through the ATP synthase channel.
Oxidative Phosphorylation:
The entire process of ATP synthesis driven by the electron transport chain and proton gradient is called oxidative phosphorylation.
Oxygen is vital as it serves as the terminal electron acceptor, capturing electrons and forming water, thus maintaining the flow of electrons through the ETS.
Diagrammatic Representation:
Key Points:
The ETS is responsible for the production of ATP through oxidative phosphorylation.
Oxygen acts as the final acceptor of electrons, essential for driving the entire process.
NADH oxidation yields 3 ATP molecules, while FADH₂ oxidation yields 2 ATP molecules.
This process efficiently captures energy from substrates through a series of controlled steps, maximally exploiting the potential energy in glucose.
Distinguish between the following:
(a) Aerobic respiration and Anaerobic respiration
(b) Glycolysis and Fermentation
(c) Glycolysis and Citric acid Cycle
(a) Aerobic Respiration and Anaerobic Respiration
Aerobic Respiration:
Occurs in the presence of oxygen.
Complete oxidation of glucose to CO₂ and H₂O.
Produces a large amount of energy: 38 ATP molecules per glucose molecule.
Occurs in the mitochondria.
Typical in higher organisms.
Anaerobic Respiration:
Occurs in the absence of oxygen.
Incomplete oxidation of glucose.
Produces less energy: 2 ATP molecules per glucose molecule.
Occurs in the cytoplasm.
Typical in some bacteria, yeast, and muscle cells under oxygen-deficit conditions.
(b) Glycolysis and Fermentation
Glycolysis:
Occurs in the cytoplasm of all living cells.
Initial pathway in both aerobic and anaerobic respiration.
Converts glucose to two molecules of pyruvic acid.
Produces a net gain of 2 ATP and 2 NADH molecules.
Does not require oxygen.
Fermentation:
Follows glycolysis under anaerobic conditions.
Converts pyruvic acid into either ethanol and CO₂ (alcoholic fermentation) or lactic acid (lactic acid fermentation).
Produces no additional ATP beyond glycolysis.
Regenerates NAD⁺ for glycolysis to continue.
(c) Glycolysis and Citric Acid Cycle
Glycolysis:
Occurs in the cytoplasm.
Breaks down glucose into two molecules of pyruvic acid.
Produces a net gain of 2 ATP and 2 NADH molecules.
Involves 10 steps controlled by different enzymes.
Occurs regardless of oxygen presence (aerobic or anaerobic).
Citric Acid Cycle (Krebs Cycle):
Occurs in the mitochondrial matrix.
Processes acetyl-CoA derived from pyruvate.
Completely oxidizes acetyl-CoA to CO₂.
Produces 3 NADH, 1 FADH₂, and 1 ATP (or GTP) per acetyl-CoA molecule.
Part of aerobic respiration and depends on oxygen indirectly by requiring it for oxidative phosphorylation.
What are the assumptions made during the calculation of net gain of ATP?
During the calculation of the net gain of ATP, the following assumptions are made:
Sequential, orderly pathway functioning: One substrate forms the next, with glycolysis, TCA cycle, and ETS pathway following one after another.
NADH transfer: The NADH synthesized in glycolysis is transferred into the mitochondria and undergoes oxidative phosphorylation.
No intermediate utilization: None of the intermediates in the pathway are utilized to synthesize any other compounds.
Only glucose as the substrate: Only glucose is being respired, with no other alternative substrates entering the pathway at any intermediary stages.
Discuss "The respiratory pathway is an amphibolic pathway."
The respiratory pathway is considered an amphibolic pathway because it is involved in both anabolism and catabolism. Here’s how it fulfills this dual role:
Catabolic Reactions:
Breakdown of Substrates: The respiratory pathway breaks down complex molecules like glucose, fats, and proteins to release energy. This process is predominantly catabolic.
Anabolic Reactions:
Synthesis of Molecules: The intermediates produced in the respiratory pathway are sometimes withdrawn to be used in the synthesis of various cellular components. For example, acetyl CoA, an intermediate, can be used in the synthesis of fatty acids.
Integration of Metabolic Functions:
Entry Points: Various substrates like carbohydrates, fats, and proteins enter the respiratory pathway at different stages, signifying its role in integrating various metabolic processes.
Dual Utilization: These very intermediates can be fed back into the pathway either to release energy (catabolic) or to facilitate biosynthesis (anabolic).
Thus, the respiratory pathway is not limited to breaking down molecules for energy but also provides essential intermediates for building cellular structures, making it a true amphibolic pathway.
Define RQ. What is its value for fats?
RQ (Respiratory Quotient) is the ratio of the volume of CO2 evolved to the volume of O2 consumed during respiration.
$$\mathrm{RQ} = \frac{\text{Volume of } \mathrm{CO}_{2} \text{ evolved}}{\text{Volume of } \mathrm{O}_{2} \text{ consumed}}$$
RQ Value for Fats:
For fats, the RQ value is less than 1. For example, for the fatty acid tripalmitin, the RQ can be calculated as follows:
$$ 2\left(\mathrm{C}_{51} \mathrm{H}_{98} \mathrm{O}_{6}\right) + 145 \mathrm{O}_{2} \longrightarrow 102 \mathrm{CO}_{2} + 98 \mathrm{H}_{2} \mathrm{O} + \text{energy} $$
Thus,
$$ \mathrm{RQ} = \frac{102 \mathrm{CO}_{2}}{145 \mathrm{O}_{2}} = 0.7 $$
So, the RQ value for fats is 0.7.
What is oxidative phosphorylation?
Oxidative phosphorylation is a process in cellular respiration that takes place in the inner mitochondrial membrane. During this process:
NADH and FADH₂, generated in earlier stages of respiration (like glycolysis and Citric Acid Cycle), are oxidized.
Electrons are passed through a series of carriers in the Electron Transport System (ETS).
The energy released during electron transport is used to pump protons (H⁺) across the inner mitochondrial membrane, creating a proton gradient.
The proton gradient drives ATP synthesis by ATP synthase (complex V), by allowing protons to flow back into the mitochondrial matrix through this enzyme complex.
Oxygen acts as the final electron acceptor, combining with protons and electrons to form water.
Overall, the process converts the energy from electrons into the chemical bond energy of ATP, making it a key mechanism for producing ATP in aerobic organisms.
What is the significance of step-wise release of energy in respiration?
The step-wise release of energy in respiration is significant because it allows the energy to be captured efficiently and prevents it from being lost as heat. Here are the key points:
Controlled Release: The energy is released in a series of small, manageable steps, which prevents the cell from overheating and allows for finer control over the energy release.
ATP Synthesis: It enables the energy to be coupled with the synthesis of ATP (adenosine triphosphate), the energy currency of the cell. ATP can then be broken down whenever and wherever energy is needed.
Enzyme Regulation: The step-wise process is regulated by different enzymes, ensuring that the energy is available only when required.
Efficient Utilization: This method ensures most of the energy from the respiratory substrates is trapped and utilized efficiently rather than being dissipated as heat.
Overall, this makes the process of respiration much more efficient and adaptable to the cell's needs.
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Comprehensive Respiration in Plants - Class 11 Notes
Introduction to Respiration in Plants
Respiration is a fundamental process in plants that allows them to fulfil their energy requirements. Unlike animals, plants don’t have specialised organs for gas exchange, but they manage an efficient system to ensure every cell gets the oxygen it needs for respiration.
Do Plants Breathe?
Mechanism of Gas Exchange
Yes, plants breathe. They take in oxygen (O₂) and release carbon dioxide (CO₂), but without specialised respiratory organs. Each part of the plant manages its gas exchange needs through stomata in leaves and lenticels in stems and roots. These small openings facilitate the diffusion of gases between plant tissues and the atmosphere.
Role of Stomata and Lenticels
Stomata, primarily located on leaf surfaces, and lenticels, found on stems and roots, are pivotal for this gas exchange. They ensure an adequate supply of oxygen and expel carbon dioxide produced during respiration.
Glycolysis in Plants
Definition and Importance
Glycolysis is the initial stage of cellular respiration in plants. This process breaks down glucose into pyruvic acid in the cytoplasm, generating a small amount of ATP (energy currency) and NADH (an electron carrier).
Steps of Glycolysis
The glycolytic pathway consists of a series of ten enzymatic reactions that convert glucose into two molecules of pyruvic acid. It begins with the phosphorylation of glucose to glucose-6-phosphate and ends with the formation of pyruvic acid.
Enzymatic Control in Glycolysis
Each step in glycolysis is catalysed by specific enzymes, ensuring the controlled breakdown of glucose and the efficient production of ATP and NADH.
Fermentation in Plants
Lactic Acid Fermentation
Under anaerobic conditions, certain plant cells can convert pyruvic acid into lactic acid. This process is critical during oxygen shortages, such as in waterlogged soils.
Alcoholic Fermentation
Yeast and other microorganisms in plants can convert glucose to ethanol and CO₂ under anaerobic conditions. Though less energy-efficient than aerobic respiration, fermentation is vital when oxygen is unavailable.
Energy Yield of Fermentation
Fermentation yields significantly less energy compared to aerobic respiration. For each glucose molecule, only two ATP molecules are produced, highlighting the efficiency drop under anaerobic conditions.
Aerobic Respiration in Plants
Pyruvate to Acetyl CoA Conversion
Pyruvate produced in glycolysis enters the mitochondria, where it is converted into Acetyl CoA, releasing CO₂ in the process. This step sets the stage for the Tricarboxylic Acid (TCA) cycle.
Tricarboxylic Acid (TCA) Cycle
Also known as the Krebs cycle, this pathway involves a series of reactions that fully oxidise Acetyl CoA to CO₂. During these steps, NADH and FADH₂ are generated, which are crucial for the next phase.
Electron Transport System (ETS)
The ETS, located on the inner mitochondrial membrane, involves electron transfer through complex I-IV and ATP synthase. This process creates a proton gradient across the membrane, driving ATP synthesis.
Oxidative Phosphorylation
Oxidative phosphorylation utilises the energy from NADH and FADH₂ to produce ATP. Oxygen acts as the final electron acceptor, forming water as a by-product.
The Respiratory Balance Sheet
Theoretically, the complete oxidation of one glucose molecule yields up to 38 ATP molecules in plants. However, this is an ideal scenario; actual ATP yield may vary due to multiple regulatory factors in a living cell.
Amphibolic Pathway in Plant Respiration
Dual Role in Anabolism and Catabolism
The respiratory pathway serves both catabolic (breakdown) and anabolic (synthesis) functions, making it amphibolic. Intermediates from respiration are used for synthesising various biomolecules while also generating energy.
Entry Points of Different Substrates
Different substrates like fats and proteins can enter the respiratory pathway at various stages, further underscoring its amphibolic nature.
Respiratory Quotient (RQ)
Definition and Calculation
The respiratory quotient (RQ) is the ratio of CO₂ produced to O₂ consumed during respiration. It varies with the type of substrate used:
graph TD;
A[Carbohydrates] -->|RQ=1| B{Glucose oxidised to CO2 & H2O};
C[Fats] -->|RQ<1| D{Example: Tripalmitin with RQ=0.7};
E[Proteins] -->|RQ~0.9| F{Partial oxidation to intermediates};
Factors Affecting RQ
The RQ provides insights into the metabolic processes in the plant and the type of substrates being oxidised.
Conclusion
Plant respiration is a complex yet highly efficient process, integral to energy production. Through glycolysis, TCA cycle, and the electron transport system, plants convert glucose into ATP, thus meeting their energy needs. The process operates flexibly, adapting to various conditions to sustain life even in challenging environments.
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