Respiration in Plants

All living organisms need energy for their activities, and this energy is obtained by oxidising food molecules, mainly glucose, in a process called cellular respiration. The energy released is trapped as ATP, the energy currency of the cell. Unlike animals, plants have no specialised organs for gas exchange; their stomata and lenticels allow gases to diffuse in and out. In glycolysis, the EMP pathway in the cytoplasm, one glucose molecule is broken into two molecules of pyruvic acid with a net gain of 2 ATP and 2 NADH. It then explains fermentation, in which yeast forms ethanol and carbon dioxide and muscles form lactic acid, releasing less than 7% of the energy in glucose. You will learn aerobic respiration in mitochondria: the conversion of pyruvate to acetyl CoA, the Krebs or tricarboxylic acid cycle, and the electron transport system with oxidative phosphorylation. The chapter shows how a theoretical net gain of 38 ATP per glucose is calculated, why respiration is an amphibolic pathway, and how the respiratory quotient differs for carbohydrates, fats and proteins.

Detailed Worksheet: Respiration in Plants Section A - Definitions (10 marks) 1. What is glycolysis? Where does it take place? (2 marks) 2. Distinguish between aerobic respiration and fermentation. (2 marks) 3. What is the respiratory quotient? What is its value for carbohydrates? (2 marks) 4. Why is respiration called an amphibolic pathway? (2 marks) 5. What is the role of oxygen in aerobic respiration? (2 marks) Section B - Calculations and Applications (15 marks) 6. Calculate the net ATP produced from one molecule of glucose by glycolysis, link reaction, Krebs cycle and electron transport, taking 3 ATP per NADH and 2 ATP per FADH2. Show the total of 38 ATP. (3 marks) 7. The complete oxidation of tripalmitin follows: 2 C51H98O6 + 145 O2 -> 102 CO2 + 98 H2O + energy. Calculate the respiratory quotient. Explain why RQ is less than 1 for fats. (3 marks) 8. For one turn of the Krebs cycle, calculate the number of NADH, FADH2, ATP (GTP) and CO2 produced. How many turns of the cycle occur per glucose molecule, and what are the totals? (3 marks) 9. Yeast fermentation follows: C6H12O6 -> 2 C2H5OH + 2 CO2. Calculate the mass of ethanol and carbon dioxide formed from 360 g of glucose (C = 12, H = 1, O = 16). (3 marks) 10. Fermentation releases less than 7% of the energy in glucose. If complete oxidation of one mole of glucose releases 2,870 kJ, calculate the maximum energy released by fermentation of one mole. Why is fermentation inefficient? (3 marks) Section C - Diagrams (10 marks) 11. Draw a flowchart of glycolysis showing the main steps, ATP use and ATP formation. (4 marks) 12. Draw a labelled diagram of the Krebs cycle. (3 marks) 13. Draw a labelled diagram of the electron transport system and ATP synthase in the inner mitochondrial membrane. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Explain the electron transport system and oxidative phosphorylation. How does the chemiosmotic mechanism produce ATP? (5 marks) 15. Explain the assumptions made in calculating the net gain of 38 ATP per glucose. Why is the actual yield usually lower? (5 marks) 16. Compare the fate of pyruvic acid under aerobic and anaerobic conditions in plants, yeast and animal muscles. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Draw flowcharts and diagrams neatly with labels. Show equations and calculation steps.