In plants, it occurs in both cellular respiration and extracellular respiration.
Cellular Respiration
- Krebs Cycle (Citric Acid Cycle): The oxidation of pyruvate to CO2, occurring in the mitochondrial matrix.
- Electron Transport Chain: The transfer of electrons to oxygen, producing ATP, occurring in the inner mitochondrial membrane.
Types of Cellular Respiration:
- Aerobic Respiration: Occurs in the presence of oxygen, producing the most ATP.
- Anaerobic Respiration: Occurs in the absence of oxygen, producing less ATP and producing byproducts like ethanol or lactic acid.
Extracellular Respiration
- Root Respiration: Roots absorb oxygen from the soil and release carbon dioxide.
- Lenticels: Small pores on the stems of woody plants that allow for gas exchange.
Factors Affecting Respiration:
- Temperature: Higher temperatures generally increase respiration rates.
- Oxygen Availability: Aerobic respiration requires oxygen.
- Substrate Availability: The presence of organic molecules affects respiration rates.
Significance of Respiration:
- Energy Production: Respiration provides energy for plant growth, development, and other vital processes.
- Carbon Cycle: Respiration releases carbon dioxide into the atmosphere, contributing to the carbon cycle.
Exercise
1. Differentiate between
(a) Respiration and Combustion
(b) Glycolysis and Krebs’ cycle
(c) Aerobic respiration and Fermentation
Ans :
(a) Respiration and Combustion
| Feature | Respiration | Combustion |
| Process | Controlled breakdown of organic molecules to release energy | Rapid, uncontrolled oxidation of a substance |
| Organisms | Occurs in living organisms | Can occur in living or non-living systems |
| Products | Carbon dioxide, water, and energy (ATP) | Carbon dioxide, water, and heat |
| Efficiency | More efficient, releasing energy gradually | Less efficient, releasing energy rapidly |
(b) Glycolysis and Krebs’ cycle
| Feature | Glycolysis | Krebs Cycle |
| Location | Cytoplasm | Mitochondrial matrix |
| Starting Molecule | Glucose | Acetyl-CoA (derived from pyruvate) |
| Products | Pyruvate, ATP, NADH, FADH2 | CO2, ATP, NADH, FADH2 |
| Role | Initial breakdown of glucose | Further oxidation of carbon compounds |
(c) Aerobic respiration and Fermentation
| Feature | Aerobic Respiration | Fermentation |
| Oxygen Requirement | Requires oxygen | Does not require oxygen |
| Energy Yield | High (produces significant ATP) | Low (produces less ATP) |
| End Products | CO2, H2O | Lactate (in animals) or ethanol (in plants and microorganisms) |
| Location | Mitochondria | Cytoplasm |
2. What are respiratory substrates? Name the most common respiratory substrate.
Ans :
Respiratory substrates are the organic molecules that are broken down during respiration to release energy.
Other respiratory substrates include:
- Fatty acids: These are broken down through beta-oxidation to produce acetyl-CoA, which enters the Krebs cycle.
- Amino acids: Amino acids can be deaminated (removed of their amino group) and then converted into pyruvate, acetyl-CoA, or other intermediates of cellular respiration.
3. Give the schematic representation of glycolysis?
Ans :
Here’s a simplified schematic representation:
Glucose (6-carbon) → Glucose-6-phosphate → Fructose-6-phosphate → Fructose-1,6-bisphosphate → Glyceraldehyde-3-phosphate (2 molecules) → 1,3-Bisphosphoglycerate (2 molecules) → 3-Phosphoglycerate (2 molecules) → 2-Phosphoglycerate (2 molecules) → Phosphoenolpyruvate (2 molecules) → Pyruvate (2 molecules)
Net Yield: 2 ATP, 2 NADH, 2 Pyruvate
4. What are the main steps in aerobic respiration? Where does it take place?
Ans :
Aerobic respiration is a complex process that occurs in the presence of oxygen and involves the breakdown of glucose to produce ATP, the energy currency of cells. It takes place in the mitochondria, specifically in the matrix and inner mitochondrial membrane.
Here are the main steps of aerobic respiration:
- Pyruvate Oxidation: Pyruvate is converted into acetyl-CoA, which enters the mitochondria.
- Citric Acid Cycle (Krebs Cycle): Acetyl-CoA is oxidized to CO2, producing ATP, NADH, and FADH2.
- Electron Transport Chain: NADH and FADH2 donate electrons to the electron transport chain, which pumps protons across the inner mitochondrial membrane.
- Oxidative Phosphorylation: The flow of protons back across the membrane drives the synthesis of ATP.
The overall equation for aerobic respiration is:
C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP
Aerobic respiration is a highly efficient process, producing significantly more ATP than anaerobic respiration. It is essential for most organisms to meet their energy needs.
5. Give the schematic representation of an overall view of Krebs’ cycle.
Ans :
1 ATP (per cycle)
3 NADH (per cycle)
1 FADH2 (per cycle)
2 CO2 (per cycle)
6. Explain ETS
Ans :
ETS (Electron Transport System) is a series of protein complexes embedded in the inner mitochondrial membrane that play a crucial role in cellular respiration. It is responsible for generating the majority of ATP, the energy currency of the cell.
How ETS works:
- Electron Donors: NADH and FADH2, produced during glycolysis and the Krebs cycle, donate electrons to the ETS.
- Electron Carriers: These electrons are passed along a series of electron carriers, such as ubiquinone, cytochrome c, and cytochrome oxidase.
- Proton Pumping: As electrons move through the ETS, energy is used to pump protons from the mitochondrial matrix into the intermembrane space, creating a proton gradient.
- Chemiosmosis: The proton gradient drives the flow of protons back into the matrix through ATP synthase, a protein complex that converts the potential energy of the gradient into ATP.
Significance of ETS:
- ATP Production: The ETS is responsible for producing the majority of ATP in cellular respiration, providing the cell with energy for various functions.
- Oxygen Consumption: ETS is the final step in aerobic respiration, where oxygen acts as the final electron acceptor.
- Regulation of Cellular Metabolism: The ETS plays a role in regulating cellular metabolism by controlling the production of ATP.
7. Distinguish between the following:
(a) Aerobic respiration and Anaerobic respiration
(b) Glycolysis and Fermentation
(c) Glycolysis and Citric acid Cycle
Ans :
(a) Aerobic respiration and Anaerobic respiration
| Feature | Aerobic Respiration | Anaerobic Respiration |
| Oxygen Requirement | Requires oxygen | Does not require oxygen |
| Energy Yield | High (produces significant ATP) | Low (produces less ATP) |
| End Products | CO2, H2O | Lactate (in animals) or ethanol (in plants and microorganisms) |
| Location | Mitochondria | Cytoplasm |
(b) Glycolysis and Fermentation
| Feature | Glycolysis | Krebs Cycle |
| Location | Cytoplasm | Mitochondrial matrix |
| Starting Molecule | Glucose | Acetyl-CoA (derived from pyruvate) |
| Products | Pyruvate, ATP, NADH, FADH2 | CO2, ATP, NADH, FADH2 |
| Role | Initial breakdown of glucose | Further oxidation of carbon compounds |
(c) Glycolysis and Citric acid Cycle
| Feature | Glycolysis | Citric Acid Cycle |
| Location | Cytoplasm | Mitochondrial matrix |
| Starting Molecule | Glucose | Acetyl-CoA (derived from pyruvate) |
| Products | Pyruvate, ATP, NADH, FADH2 | CO2, ATP, NADH, FADH2 |
| Role | Initial breakdown of glucose | Further oxidation of carbon compounds |
8. What are the assumptions made during the calculation of net gain of ATP?
Ans :
When calculating the net ATP gain from cellular respiration, several assumptions are made:
- Complete Oxidation of Glucose: It is assumed that glucose is completely oxidized to CO2 in the Krebs cycle. However, in reality, some intermediates may be diverted for other metabolic processes, reducing the net ATP yield.
- Efficient Electron Transport Chain: It is assumed that the electron transport chain operates at maximum efficiency, with all electrons being transferred to oxygen and producing ATP. However, factors such as inhibitors or mutations can reduce the efficiency of the electron transport chain.
- Proton Motive Force: It is assumed that the proton gradient established across the inner mitochondrial membrane is fully utilized for ATP synthesis. However, factors such as uncoupling proteins can dissipate the proton gradient, reducing ATP production.
- No Energy Loss: It is assumed that there is no energy loss during the transfer of electrons and protons in the electron transport chain. However, some energy may be lost as heat during these processes.
9. Discuss “The respiratory pathway is an amphibolic pathway.”
Ans : Amphibolic pathways are metabolic pathways that can function both in anabolism (the synthesis of complex molecules) and catabolism (the breakdown of complex molecules). The respiratory pathway, specifically the Krebs cycle, is an excellent example of an amphibolic pathway.
10. Define RQ. What is its value for fats?
Ans :
RQ (Respiratory Quotient) is the ratio of the volume of carbon dioxide (CO2) produced to the volume of oxygen (O2) consumed during respiration. It is a measure of the type of substrate being respired.
For fats, the RQ is typically around 0.7. This is because fats require more oxygen for complete oxidation compared to carbohydrates, which have a higher ratio of carbon atoms to oxygen atoms.
11. What is oxidative phosphorylation?
Ans : Oxidative phosphorylation is the process by which ATP, the energy currency of the cell, is produced from the energy stored in a proton gradient across the inner mitochondrial membrane. It is the final stage of cellular respiration, occurring in the mitochondria.
12. What is the significance of step-wise release of energy in respiration?
Ans :
Efficient Energy Capture: By breaking down organic molecules gradually, respiration can capture and store energy in small, manageable units (ATP). This allows for efficient utilization of energy by the cell.
Regulation and Control: The step-wise nature of respiration provides numerous opportunities for regulation and control. Enzymes at each step can be activated or inhibited to adjust the rate of energy production based on the cell’s needs.
Metabolic Flexibility: The modular structure of respiration allows for flexibility in utilizing different substrates (e.g., carbohydrates, fats, proteins) as fuel sources.
Coupling with Other Processes: The energy produced in respiration can be coupled with other cellular processes, such as biosynthesis and active transport, to drive essential functions.
Prevention of Energy Waste: By releasing energy gradually, respiration minimizes the loss of energy as heat, ensuring that a significant portion of the energy is captured in ATP.
