Life processes are the basic functions performed by all living organisms to maintain life. These include nutrition, respiration, transportation, and excretion. Even though an organism may appear inactive, these processes occur continuously. Any organism that stops performing these processes is considered dead. Energy is required for all life processes, which is why nutrition and respiration are the most fundamental ones.

Nutrition is the process of taking in and using food for energy, growth, and repair. Autotrophic nutrition: organisms make their own food using sunlight (photosynthesis). Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (requires sunlight + chlorophyll). Chloroplasts are the site of photosynthesis; chlorophyll absorbs light. Heterotrophic nutrition: organisms depend on others for food. Types — Holozoic (animals), Saprotrophic (fungi, bacteria on dead matter), Parasitic (leeches, tapeworms). Stomata regulate CO₂ entry and O₂/water exit in leaves.

Digestion breaks complex food into simpler absorbable molecules. Mouth: teeth chew food; salivary amylase begins starch digestion; tongue forms bolus. Oesophagus: peristalsis moves food to stomach. Stomach: HCl kills bacteria and creates acidic medium; pepsin digests proteins; mucus protects stomach lining. Small intestine (longest part): liver secretes bile (emulsifies fats, makes medium alkaline); pancreas secretes pancreatic juice (amylase, lipase, trypsin); intestinal juice completes digestion. Absorption occurs through villi (finger-like projections) which increase surface area. Large intestine: absorbs water; remaining waste forms faeces.

Respiration is the biochemical process of breaking down food (glucose) to release energy (ATP). It occurs in every living cell. Aerobic respiration (with oxygen): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP. Occurs in mitochondria. Anaerobic respiration (without oxygen): In yeast: glucose → ethanol + CO₂ + 2 ATP (used in brewing, bread-making). In human muscles during intense exercise: glucose → lactic acid + 2 ATP (causes cramps and fatigue — oxygen debt). Breathing (pulmonary ventilation) ≠ respiration. Breathing: diaphragm contracts → thoracic cavity expands → air enters lungs. Exchange of gases occurs at alveoli (thin walls, rich blood supply, moist surface, large surface area).

The circulatory system transports nutrients, oxygen, waste, and hormones. Heart: 4 chambers (right atrium, right ventricle, left atrium, left ventricle). Right side carries deoxygenated blood; left side carries oxygenated blood. Double circulation: pulmonary circulation (heart ↔ lungs) + systemic circulation (heart ↔ body). Blood components: RBC (carry O₂ via haemoglobin), WBC (immune defence), platelets (clotting), plasma (liquid medium). Arteries carry blood away from heart (thick walls, no valves). Veins carry blood to heart (thin walls, have valves). Capillaries: exchange materials with tissues. Blood pressure: 120/80 mmHg (systolic/diastolic). Lymphatic system drains excess tissue fluid back to blood. Plants use xylem (water+minerals upward) and phloem (food bidirectionally) for transport.

Excretion is the removal of metabolic waste products from the body. In humans: kidneys are the primary excretory organs. Each kidney contains ~1 million nephrons (functional unit). Filtration occurs in Bowman's capsule (glomerular filtration). Selective reabsorption occurs in tubules (glucose, amino acids, water reabsorbed). Final urine: urea, uric acid, excess salts, water. Urine flows: kidney → ureter → urinary bladder → urethra. Dialysis (kidney machine) mimics nephron function for kidney failure patients. Skin excretes salts via sweat. Lungs excrete CO₂ and water vapour. In plants: CO₂ and O₂ excreted through stomata; excess water by transpiration; some plants store wastes in vacuoles or leaves that fall off.

Plants lack a circulatory system but have specialised tissues. Xylem transports water and dissolved minerals from roots to leaves — driven by transpiration pull (cohesion-tension mechanism) and root pressure. Phloem transports food (sucrose) from leaves to all parts — a process called translocation, driven by osmotic pressure. Water enters roots by osmosis through root hair cells. Loss of water through leaves as water vapour is transpiration — creates suction pull. Guard cells control stomatal opening/closing based on water content.

Photosynthesis is the process by which autotrophs make carbohydrates from carbon dioxide and water using sunlight and chlorophyll: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O. It takes place in the chloroplasts of green plant cells. Steps: (1) absorption of light energy by chlorophyll; (2) conversion of light energy into chemical energy and splitting of water into hydrogen and oxygen; (3) reduction of carbon dioxide to carbohydrates. Raw materials: CO₂ (through stomata), water and minerals (from soil through roots), sunlight and chlorophyll. Oxygen is released as a by-product, and the carbohydrates are stored as starch.

Stomata are tiny pores on the surface of leaves surrounded by a pair of guard cells. They allow exchange of gases (CO₂ in, O₂ out) and loss of water vapour in transpiration. When water flows into the guard cells they swell and the pore opens; when the guard cells lose water they shrink and the pore closes. Large amounts of water are lost through stomata, so plants close them when not needed. Roots take in oxygen from air spaces between soil particles; stems and old woody parts exchange gases through lenticels.

Heterotrophs depend on other organisms for food. Holozoic nutrition: ingestion, digestion, absorption, assimilation and egestion of solid food (Amoeba, humans). In Amoeba, food is engulfed with pseudopodia to form a food vacuole in which enzymes digest it; the digested food diffuses into the cytoplasm, and the undigested part is thrown out. Saprotrophic nutrition: organisms break down dead and decaying matter outside the body and absorb the nutrients (fungi such as bread mould, yeast, mushrooms). Parasitic nutrition: the parasite lives on or in a host and draws food from it (Cuscuta or amarbel, tapeworm, lice).

Mouth: salivary amylase breaks down starch into sugar. Stomach: gastric glands release hydrochloric acid (creates acidic medium for pepsin, kills bacteria), pepsin (digests proteins) and mucus (protects the inner lining). Small intestine: bile from the liver is alkaline and emulsifies fats; pancreatic juice contains trypsin (proteins), lipase (fats) and amylase (starch); intestinal juice completes digestion, changing proteins to amino acids, complex carbohydrates to glucose and fats to fatty acids and glycerol. The inner lining has finger-like villi that increase surface area for absorption. The large intestine absorbs water, and the undigested waste leaves via the anus.

Cellular respiration releases energy from glucose in the form of ATP. First, glucose (6C) is broken down in the cytoplasm to pyruvate (3C). Aerobic respiration (mitochondria, with oxygen): pyruvate → CO₂ + water + energy. Anaerobic respiration (without oxygen): in yeast, pyruvate → ethanol + CO₂ + energy; in muscles, pyruvate → lactic acid + energy, and its build-up causes cramps. Human breathing: air passes through nostrils, pharynx, larynx, trachea, bronchi and bronchioles into the alveoli, which are thin-walled, moist sacs with rich blood supply for gas exchange. Haemoglobin in red blood cells carries oxygen.

The heart is a muscular organ with four chambers: two upper atria and two lower ventricles. The right side receives deoxygenated blood and pumps it to the lungs; the left side receives oxygenated blood from the lungs and pumps it to the body. Separation of oxygenated and deoxygenated blood allows a highly efficient supply and high energy needs of humans. Blood goes through the heart twice in one cycle: double circulation (pulmonary and systemic). Arteries have thick elastic walls; veins have thinner walls with valves; capillaries are one cell thick for exchange. Platelets help in clotting. Lymph carries digested fats and drains excess fluid from tissues.

The human excretory system consists of two kidneys, two ureters, a urinary bladder and a urethra. The nephron is the functional unit of the kidney. Urine formation: (1) ultrafiltration in the glomerulus and Bowman's capsule; (2) selective reabsorption of glucose, amino acids, salts and water; (3) tubular secretion of extra wastes. Urine passes through the collecting duct and ureter to the bladder and is expelled via the urethra. In kidney failure, haemodialysis with an artificial kidney cleans the blood. Plants excrete wastes as gums and resins, latex, shed leaves and bark, and release excess water by transpiration.

Life processes: nutrition, respiration, transportation, excretion. Autotrophs make food by photosynthesis; heterotrophs take food. Enzymes: amylase (starch), pepsin (protein), trypsin (protein), lipase (fat). Aerobic respiration yields much more energy than anaerobic. Double circulation; arteries carry blood away from the heart, veins carry blood to the heart. Pulmonary vein carries oxygenated blood; pulmonary artery carries deoxygenated blood. Nephron: filtration, reabsorption, secretion. Xylem carries water; phloem carries food by translocation.