Life processes are the processes that together maintain a living organism and ensure its survival. The major life processes are: Nutrition, Respiration, Transportation, and Excretion.
Nutrition
- Autotrophic Nutrition: Organisms make their own food using simple inorganic substances.
- Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2 (in presence of sunlight and chlorophyll)
- Three steps: Light absorption → Water splitting (photolysis) → CO2 fixation (Calvin cycle)
- Stomata: Pores in leaves for gas exchange; controlled by guard cells.
- Heterotrophic Nutrition: Organisms obtain food from other organisms.
- Holozoic (animals), Saprophytic (fungi), Parasitic (tapeworm), Symbiotic
- Human Digestion:
- Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus
- Enzyme actions: Salivary amylase (starch → maltose), Pepsin (protein in stomach), Bile (emulsification of fats), Pancreatic lipase (fat digestion), Intestinal enzymes complete digestion.
- Villi and microvilli in small intestine increase surface area for absorption.
Respiration
- Aerobic Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + 38 ATP (energy)
- Occurs in cytoplasm (glycolysis) and mitochondria (Krebs cycle + oxidative phosphorylation)
- Anaerobic Respiration:
- In yeast: C6H12O6 → 2C2H5OH + 2CO2 + 2 ATP (fermentation)
- In muscles (humans): C6H12O6 → 2 lactic acid + 2 ATP (causes muscle cramps)
Transportation
- In Humans — Blood Circulatory System:
- Heart: 4 chambers (2 atria, 2 ventricles); double circulation (pulmonary + systemic)
- Blood components: RBC (haemoglobin carries O2), WBC (immunity), Platelets (clotting), Plasma
- Arteries carry oxygenated blood (except pulmonary artery); Veins carry deoxygenated blood (except pulmonary vein)
- In Plants:
- Xylem: Carries water and minerals upwards from root to leaves (transpiration pull)
- Phloem: Carries food (glucose/sucrose) in all directions (translocation)
Excretion
- In Humans: Kidneys filter blood and produce urine (urea, water, salts)
- Nephron: Functional unit of kidney; filtration → reabsorption → tubular secretion
- Haemodialysis: Artificial kidney (dialysis machine) filters blood when kidneys fail.
In Plants: CO2 and O2 through stomata; excess water through transpiration; stored wastes in leaves (shed), resins, gums, etc.
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Why do leaves appear green?
- Chlorophyll (green pigment) in chloroplasts absorbs red and blue light and reflects green light.
- Absorbed light energy is used for photosynthesis.
What is the role of HCl in the stomach?
- HCl creates an acidic medium (pH 2) for pepsin enzyme to work.
- It kills bacteria present in food.
- It activates pepsinogen (inactive) into pepsin (active enzyme).
Distinguish between breathing and respiration.
- Breathing: Physical process of inhaling O2 and exhaling CO2.
- Respiration: Chemical process occurring in cells to release energy from glucose. Respiration uses O2 from breathing.
Why do we breathe faster after vigorous exercise?
- During exercise, muscles perform anaerobic respiration → produce lactic acid.
- CO2 levels in blood rise → brain signals diaphragm to contract faster.
- Faster breathing brings more O2 to oxidise lactic acid and repay the "oxygen debt."
How does blood reach from the heart to lungs and back?
- Right ventricle → Pulmonary artery → Lungs (oxygenation) → Pulmonary vein → Left atrium.
- This is pulmonary circulation. It is part of the double circulation of humans.
How do plants transport water to great heights?
- Transpiration pull: Evaporation of water from leaves (stomata) creates a suction force.
- This suction pulls water up through xylem vessels from roots.
- Cohesion (water molecules stick together) and adhesion (water sticks to xylem walls) help maintain the continuous column.
What is the function of the nephron?
- Glomerular filtration: Blood is filtered under pressure in Bowman's capsule; glucose, urea, ions, water pass into filtrate.
- Reabsorption: Useful substances (glucose, water, minerals) are reabsorbed into blood in tubules.
- Secretion: Remaining wastes are concentrated → urine flows to ureter.
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Common mistakes
- Arteries vs. veins: Arteries carry blood AWAY from heart (not always oxygenated — pulmonary artery carries deoxygenated blood).
- Photosynthesis and respiration: Plants do BOTH; photosynthesis during day, respiration continuously.
- Aerobic vs. anaerobic: Aerobic releases more ATP (38 vs. 2). Anaerobic is faster but less efficient.
Summary
Life processes maintain homeostasis. Photosynthesis fixes CO2 into glucose. Human digestion breaks food into absorbable molecules. Aerobic respiration releases maximum energy. Double circulation ensures efficient O2 delivery. Kidneys maintain fluid and waste balance through nephron filtration.