Biology XI: 14 Respiration in plants(1 Cellular Respiration)

Cellular Respiration & Glycolysis Cellular Respiration Mechanism of breakdown of food materials within the cell to release energy, and the trapping of this energy for ATP synthesis. Respiratory substrates: Compounds oxidised during respiration; usually carbohydrates; these can also be proteins, fats or organic acids ATP: Energy currency of a cell; broken down whenever energy is needed Plants do not need specialised organs for respiration because: Gaseous exchange occurs in each part of a plant. Gaseous exchange is not a much-needed factor. During photosynthesis, the need for gaseous exchange is met. Each living cell is located close to the surface of a plant. So the distances that the gases must diffuse are not great. Equation for respiration:C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy Glycolysis (Glycos − Sugar, Lysis − Splitting) Breakdown of glucose to pyruvic acid by partial oxidation Scheme given by Embden, Meyerhof and Parnas Common pathway for aerobic and anaerobic cellular respiration Occurs in the cytoplasm of a cell Present in all living organisms In plants, sucrose is converted into glucose. A chain of 10 reactions converts glucose into pyruvate. Hexokinase: Enzyme that phosphorylates glucose to produce glucose − 6 − phosphate 2 ATPs are utilised in two steps: Glucose → Glucose − 6 − phosphate (1 ATP) Fructose − 6 − phosphate → fructose 1, 6 − bisphosphate (1 ATP) Fructose 1, 6 bisphosphate splits into glyceraldehyde − 3 − phosphate and dihydroxy acetone phosphate. Glyceraldehyde − 3 − phosphate converts into two molecules of 1, 3 bisphosphoglycerate (BPGA), with subsequent conversion of NAD+ to NADH + H+. 4 ATPs are yielded in two steps: BPGA → PGA (1 × 2 = 2 ATPs) Phosphoenol pyruvate → Pyruvic acid (1 × 2 =2 ATPs) Net ATPs produced = 4 (produced) − 2 (consumed) = 2 ATPs The pyruvate, so produced, may undergo: Lactic acid fermentation Alcoholic fermentation Aerobic respiration (Krebs cycle)