Chapter 12: Respiration in Plants

Key Concepts

• Breathing vs. Respiration: Breathing is essential for life to facilitate energy production through the breakdown of food molecules.
• Photosynthesis and Respiration: Photosynthesis captures energy, while respiration releases it.
• ATP: Acts as the energy currency of the cell.

12.1 Do Plants Breathe?

• Plants require oxygen (O2) for respiration and release carbon dioxide (CO2).
• Gaseous Exchange: Plants use stomata and lenticels for gas exchange, unlike animals.
• Photosynthesis: While photosynthesizing, oxygen is released within the cells making O2 availability not an issue.
• Diffusion: Gases diffuse short distances even in large plants due to thin layers of living cells.

12.2 Glycolysis

• Definition: Breakdown of glucose to pyruvic acid.
• Location: Occurs in the cytoplasm.
• Process: Glucose to glucose-6-phosphate, fructose-6-phosphate to pyruvic acid.
• Energy Yield: Direct ATP synthesis and NADH production.

12.3 Fermentation

• Types: Lactic acid fermentation and alcoholic fermentation.
• Conditions: Occurs under anaerobic conditions.
• Energy Yield: Much less energy than aerobic respiration.

12.4 Aerobic Respiration

• Location: Occurs in mitochondria.
• Pyruvate Oxidation: Produces acetyl CoA, enters TCA cycle.
• TCA Cycle: Complete oxidation of acetyl CoA into CO2.
• ETS & Oxidative Phosphorylation: Electron transfer leading to ATP production.

12.4.1 Tricarboxylic Acid Cycle

• Steps: Conversion of acetyl CoA to citric acid, oxidation through the cycle.
• Products: NADH, FADH2, and GTP/ATP.

12.4.2 Electron Transport System

• Location: Inner mitochondrial membrane.
• Process: Electrons from NADH and FADH2 pass through complexes leading to ATP synthesis.
• Role of Oxygen: Final electron acceptor, forming water.

12.5 Respiratory Balance Sheet

• Theoretical ATP Yield: 38 ATP per glucose molecule in aerobic respiration.
• Comparison: Fermentation yields less ATP than aerobic respiration.

12.6 Amphibolic Pathway

• Definition: Respiration pathway involves both breakdown (catabolism) and synthesis (anabolism).

12.7 Respiratory Quotient (RQ)

• Formula: RQ = CO2 evolved / O2 consumed.
• Values: RQ differs depending on the substrate (e.g., carbohydrates, fats).

Summary Points

• Gaseous Exchange in Plants: No specialized systems, diffusion through stomata and lenticels.
• Cellular Respiration: Oxidation of glucose leading to energy release.
• Pathways: Anaerobic (Fermentation) vs. Aerobic (TCA, ETS).
• ETS and ATP Synthesis: Oxygen's role as the final electron acceptor.

Exercises

1. Differentiate respiration and combustion, glycolysis and Krebs cycle, aerobic respiration and fermentation.
2. Define respiratory substrates; most common is glucose.
3. Schematic representation of glycolysis.
4. Main steps in aerobic respiration and its location.
5. Overall view of Krebs cycle.
6. Explain ETS.
7. Distinctions between aerobic/anaerobic respiration, glycolysis/fermentation, glycolysis/citric acid cycle.
8. Assumptions in net ATP gain calculation.
9. Discuss amphibolic nature of the respiratory pathway.
10. Define RQ and its value for fats.
11. Define oxidative phosphorylation.
12. Significance of step-wise energy release in respiration.