Life Processes in Living Organisms Part 1 — Maharashtra (SSC) Class 10 Science Solutions (Free)

Nutrition is the process of obtaining food and nutrients for energy and growth. Autotrophs make their own food: plants photosynthesize using sunlight, water, CO2 to produce glucose and O2. Chemosynthetic bacteria use chemical reactions. Heterotrophs depend on external food: herbivores eat plants, carnivores eat animals, omnivores eat both. Decomposers (bacteria, fungi) break down dead matter. All organisms require C, H, O, N, P, S and minerals.

Light reactions (thylakoid): chlorophyll absorbs photons, electrons excited, water split (photolysis) releasing O2, electron transport chain pumps H+ creating ATP and NADPH. Equation: 2H2O + light → 4H+ + O2 + 4e-. Dark reactions/Calvin cycle (stroma): CO2 fixed by RuBisCO into 3-PGA, reduced to G3P using ATP and NADPH from light reactions, regenerates RuBP. Overall: 6CO2 + 6H2O + light → C6H12O6 + 6O2. Location: chloroplasts.

Respiration is oxidation of glucose to release energy (ATP). Aerobic respiration (in mitochondria): C6H12O6 + 6O2 → 6CO2 + 6H2O + 2880 kJ/mol. Three stages: glycolysis (cytoplasm, net 2 ATP), Krebs cycle (matrix, produces NADH, FADH2), electron transport (cristae, generates ~32 ATP). Anaerobic respiration (no O2): fermentation produces ethanol + CO2 (yeast) or lactate (muscle), yields only 2 ATP. Anaerobic is less efficient.

Glycolysis (cytoplasm): glucose → 2 pyruvate, net 2 ATP, produces 2 NADH. Krebs/TCA cycle (mitochondrial matrix): acetyl-CoA enters, 8 enzyme steps oxidize it completely, produces 3 NADH, 1 FADH2, 1 ATP per acetyl-CoA. Electron transport chain (cristae): NADH and FADH2 oxidized, electrons pass through cytochrome complexes (I, III, IV), proton pumping creates gradient, ATP synthase uses gradient to generate ~32 ATP. O2 is final electron acceptor forming H2O.

Mitochondria is the powerhouse: site of aerobic respiration. Structure: outer membrane (permeable), inner membrane (impermeable, folds into cristae), matrix. Krebs cycle and electron transport chain occur here. Inner membrane cristae house electron transport complexes and ATP synthase. Proton gradient across membrane drives ATP synthesis. Each glucose yields ~30-32 ATP in mitochondria (vs. 2 ATP in cytoplasm from glycolysis). Energy currency ATP is produced here.