1. Explain the process of glycolysis and its role in plant respiration.
Answer:
Glycolysis is the first step in cellular respiration, occurring in the cytoplasm of plant cells. It involves the breakdown of one glucose molecule into two molecules of pyruvate. This process is anaerobic and does not require oxygen. The key stages include:
- Glucose Activation: Glucose is phosphorylated to form fructose-1,6-bisphosphate using ATP.
- Cleavage: Fructose-1,6-bisphosphate is split into two 3-carbon molecules, glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP).
- Energy Harvesting: G3P is converted into pyruvate, producing 2 ATP molecules and 2 NADH molecules.
Glycolysis provides substrates for further aerobic respiration and generates energy in the form of ATP.
2. Describe the Krebs cycle and its importance in plant respiration.
Answer:
The Krebs cycle, also called the citric acid cycle, occurs in the mitochondrial matrix. It processes acetyl-CoA, derived from pyruvate, to produce energy. Key steps include:
- Acetyl-CoA and Oxaloacetate Formation: Acetyl-CoA combines with oxaloacetate to form citrate.
- Oxidation Reactions: Citrate undergoes a series of enzymatic reactions, releasing two molecules of CO2 and regenerating oxaloacetate.
- Energy Production: Each cycle produces 3 NADH, 1 FADH2, and 1 ATP (via GTP).
The cycle is critical as it supplies electrons to the electron transport chain for ATP synthesis and intermediates for biosynthesis.
3. How does the electron transport chain function in plant respiration?
Answer:
The electron transport chain (ETC) is located in the inner mitochondrial membrane. Electrons from NADH and FADH2, generated in previous steps, pass through a series of protein complexes:
- Electron Transfer: Electrons move through complexes I-IV, releasing energy.
- Proton Pumping: The energy is used to pump protons from the matrix into the intermembrane space, creating a proton gradient.
- ATP Synthesis: Protons flow back into the matrix via ATP synthase, driving the conversion of ADP to ATP.
The ETC generates the majority of ATP in aerobic respiration and consumes oxygen as the final electron acceptor, forming water.
4. Compare aerobic and anaerobic respiration in plants.
Answer:
| Aspect | Aerobic Respiration | Anaerobic Respiration |
|---|---|---|
| Oxygen Requirement | Requires oxygen | Does not require oxygen |
| Energy Yield | High (32-38 ATP) | Low (2 ATP) |
| End Products | CO2 and H2O | Ethanol and CO2 (or lactate) |
| Pathways Involved | Glycolysis, Krebs cycle, ETC | Glycolysis only |
5. What are the key differences between respiration and photosynthesis?
Answer:
| Feature | Respiration | Photosynthesis |
|---|---|---|
| Purpose | Energy release | Energy storage |
| Location | Mitochondria | Chloroplast |
| Reactants | Glucose and O2 | CO2 and H2O |
| Products | CO2, H2O, and ATP | Glucose and O2 |
| Energy | Exergonic (releases energy) | Endergonic (requires energy) |
6. What is the significance of the respiratory quotient (RQ) in plants?
Answer:
Respiratory quotient (RQ) is the ratio of CO2 produced to O2 consumed during respiration.
RQ=CO2 producedO2 consumed\text{RQ} = \frac{\text{CO2 produced}}{\text{O2 consumed}}RQ=O2 consumedCO2 produced
- Carbohydrates: RQ = 1 (e.g., glucose respiration).
- Proteins: RQ < 1 due to partial oxidation.
- Fats: RQ < 1 as more oxygen is consumed.
It helps in understanding the type of substrate utilized during respiration and the metabolic activity in plants.
7. Explain the role of ATP in plant metabolism.
Answer:
ATP (adenosine triphosphate) serves as the primary energy currency in plants. Its functions include:
- Energy Transfer: Provides energy for biochemical reactions, such as protein synthesis and active transport.
- Cellular Processes: Powers cytoplasmic streaming, stomatal movement, and photosynthetic reactions.
- Biosynthesis: Supplies energy for synthesizing macromolecules like carbohydrates, proteins, and lipids.
8. Describe the importance of alternative respiratory pathways in plants.
Answer:
Alternative pathways, like the C4 pathway and CAM, ensure efficient respiration under stress conditions:
- Energy Diversification: Maintain ATP production during low oxygen.
- Heat Production: Alternative oxidase generates heat in plants like thermogenic flowers.
- Stress Adaptation: Prevent ROS formation during fluctuating oxygen levels.
9. How does temperature affect plant respiration?
Answer:
- Low Temperatures: Slow enzymatic activities, reducing respiration rates.
- Optimal Temperatures: Maximize enzymatic efficiency and ATP production.
- High Temperatures: Enzyme denaturation can inhibit respiration, causing oxidative stress.
10. What is photorespiration, and why is it significant?
Answer:
Photorespiration occurs when Rubisco enzyme fixes O2 instead of CO2, producing glycolate instead of 3-PGA.
- Significance:
- Protects the plant from photodamage under high oxygen/low CO2 conditions.
- Leads to energy wastage and reduced photosynthetic efficiency.
11. Discuss the role of mitochondria in plant respiration.
Answer:
Mitochondria are the site of aerobic respiration in plants, performing:
- ATP Production: Host the Krebs cycle and ETC.
- Metabolic Intermediates: Supply intermediates for biosynthetic pathways.
- Regulation: Balance cellular energy requirements.
12. How is fermentation different from aerobic respiration in plants?
Answer:
Fermentation occurs in the absence of oxygen and results in ethanol and CO2 in plants. It generates only 2 ATP per glucose molecule, compared to 32-38 ATP in aerobic respiration.
13. What are the main substrates for plant respiration?
Answer:
- Carbohydrates (glucose): Primary substrate.
- Fats: Used during seed germination.
- Proteins: Metabolized under starvation or stress.
14. What is oxidative phosphorylation, and where does it occur?
Answer:
Oxidative phosphorylation is the production of ATP using energy derived from the electron transport chain. It occurs in the inner mitochondrial membrane.
15. Describe the role of NADH and FADH2 in plant respiration.
Answer:
NADH and FADH2 are electron carriers that donate electrons to the ETC, facilitating ATP production.
16. How does waterlogging affect plant respiration?
Answer:
Waterlogging limits oxygen availability, forcing plants into anaerobic respiration, leading to energy deficits and ethanol toxicity.
17. Why do plants need respiration at night?
Answer:
At night, photosynthesis ceases, and respiration provides energy for growth, repair, and maintenance processes.
18. Explain the role of pentose phosphate pathway in plant respiration.
Answer:
The pentose phosphate pathway produces NADPH and ribose-5-phosphate for biosynthetic reactions and nucleotide synthesis.
19. What are the products of anaerobic respiration in plants?
Answer:
Ethanol, CO2, and 2 ATP molecules are the primary products.
20. What is the significance of respiration in plant development?
Answer:
Respiration provides ATP and intermediates for growth, cell division, stress adaptation, and biosynthesis of essential molecules.
