Respiration in Plants
Q1. Define respiration. Why is it essential for plants?
Answer: Respiration is a biochemical process in which food molecules are oxidised in a stepwise manner to release energy. It is essential for plants because the energy released is required for growth, maintenance, active transport, biosynthesis, and cell division.
Q2. Why do plants not have specialised respiratory organs like animals?
Answer: Plants do not require specialised respiratory organs because:
- Their metabolic rate is low
- All parts of the plant are in close contact with the atmosphere
- Gaseous exchange occurs by simple diffusion over short distances
Q3. Explain glycolysis. Mention its site and significance.
Answer: Glycolysis is the first step of respiration in which one glucose molecule is converted into two molecules of pyruvic acid through a series of enzyme-controlled reactions. It occurs in the cytoplasm. Glycolysis is significant because it is a universal pathway common to both aerobic and anaerobic respiration and produces ATP and NADH.
Q4. Describe alcoholic fermentation with the help of equations.
Answer: Alcoholic fermentation occurs in yeast and plant cells under anaerobic conditions. Pyruvate is first decarboxylated to acetaldehyde, releasing CO₂, and then reduced to ethanol using NADH. Pyruvate → Acetaldehyde + CO₂ Acetaldehyde + NADH → Ethanol + NAD⁺
Q5. What is lactic acid fermentation? Where does it occur?
Answer: Lactic acid fermentation is an anaerobic process in which pyruvate is reduced to lactic acid. It occurs in muscle cells during strenuous exercise when oxygen supply is insufficient.
Q6. Explain the link reaction in aerobic respiration.
Answer: The link reaction connects glycolysis with the Krebs cycle. In this reaction, pyruvate is oxidatively decarboxylated in the mitochondrial matrix to form acetyl-CoA, releasing CO₂ and reducing NAD⁺ to NADH.
Q7. Describe the Krebs cycle briefly.
Answer: The Krebs cycle occurs in the mitochondrial matrix. Acetyl-CoA combines with oxaloacetate to form citric acid. Through a series of reactions, citric acid is oxidised, releasing CO₂ and producing NADH, FADH₂, and ATP. Oxaloacetate is regenerated at the end of the cycle.
Q8. Why is the Krebs cycle called an amphibolic pathway?
Answer: The Krebs cycle is called amphibolic because it participates in both catabolic and anabolic processes. While it oxidises acetyl-CoA to release energy, its intermediates are also used for synthesis of amino acids, fatty acids, and haem.
Q9. Explain the Electron Transport System and its role in ATP synthesis.
Answer: The Electron Transport System is located on the inner mitochondrial membrane. Electrons from NADH and FADH₂ pass through a series of carriers and finally reduce oxygen to water. The energy released creates a proton gradient, which drives ATP synthesis through ATP synthase. This process is called oxidative phosphorylation.
Q10. What is the respiratory balance sheet? Why is it considered theoretical?
Answer: The respiratory balance sheet summarises the total ATP produced during complete oxidation of glucose. It is considered theoretical because it assumes ideal conditions, no energy loss, and perfect transfer of reducing equivalents, which does not occur in living cells.
Q11. Define Respiratory Quotient (RQ). What is its significance?
Answer: Respiratory Quotient is the ratio of the volume of CO₂ evolved to the volume of O₂ consumed during respiration. It helps in identifying the nature of the respiratory substrate being used by the organism.
Q12. Explain why RQ of fats is less than 1.
Answer: Fats require more oxygen for oxidation compared to the amount of CO₂ released. Hence, the RQ value for fats is less than 1 (approximately 0.7).
Q13. Describe the factors affecting respiration in plants.
Answer: Respiration in plants is affected by temperature, oxygen availability, carbon dioxide concentration, water availability, nature of respiratory substrate, and type of tissue. Young, actively growing tissues respire faster than mature or dormant tissues.
Q14. Why is respiration highest in meristematic tissues?
Answer: Meristematic tissues have high rates of cell division and biosynthesis, which require large amounts of energy, resulting in a higher respiration rate.
Q15. Differentiate between aerobic and anaerobic respiration.
Answer: Aerobic respiration occurs in presence of oxygen and leads to complete oxidation of glucose, producing CO₂, water, and a large amount of ATP. Anaerobic respiration occurs in absence of oxygen, involves partial oxidation of glucose, and produces much less ATP.
Q16. Why is respiration considered a continuous process in plants?
Answer: Respiration is continuous because energy is required at all times for maintenance, growth, and metabolic activities, irrespective of day or night.
Q17. State the importance of respiration in plants.
Answer: Respiration supplies energy for growth, absorption of minerals, translocation of food, synthesis of biomolecules, repair of tissues, and maintenance of cellular structures.