Life Processes

This is the fifth chapter of NCERT's Class 10 Science textbook (pages 79–99 of the 2026-27 reprint; the contents page and the PDF agree). It has five parts — what life processes are (5.1), nutrition (5.2: autotrophic, heterotrophic, how organisms obtain food, nutrition in human beings), respiration (5.3), transportation (5.4: in human beings and in plants) and excretion (5.5: in human beings and in plants) — with 8 activities, Figures 5.1–5.14 plus two unnumbered pictures (a blood-pressure cuff and a dialysis machine), five ‘More to Know!’ boxes, two ‘Do You Know?’ boxes, a ‘Think it over!’ box on organ donation, five in-text ‘Questions’ boxes (21 questions), a summary and 13 exercise questions. Every equation on this page is atom-checked in the source, and every carbon in the respiration diagram is counted.

• Neighbouring chapters: Carbon and its Compounds (Chapter 4) gave the chemistry of carbon compounds and the soap micelle that this chapter compares bile to; Acids, Bases and Salts (Chapter 2) gave the lime-water test and the stomach's hydrochloric acid; Control and Coordination (Chapter 6, next) adds nerves and hormones that run these organs; Our Environment (Chapter 13) uses photosynthesis to start every food chain. In Class 12, Sexual Reproduction in Flowering Plants and Principles of Inheritance and Variation are already live.
• Prelims — science: UPSC has asked about photosynthesis and chlorophyll (1980, 1982, 1986, 1987, 2014), plant gas exchange at night (1979), girdling and the phloem (2011), xylem and phloem (1990), how water reaches tree-tops (1999), saliva and digestive enzymes (1988, 2001, 2007, 2010), bile and the liver (1985, 2006, 2008), protein digestion (2005), aerobic respiration (1998), lactic acid and muscle fatigue (2000), alveoli (1991), oxygen transport (1997), haemoglobin and anaemia (1979, 1990), blood pressure (1990, 1993), the kidney (1987, 1991, 2003), dialysis (1979, 1980), eye donation (2001) and parasites (1984).
• GS2 — health: anaemia, hypertension, kidney failure and dialysis, organ and tissue donation, and tobacco are public-health topics; the chapter gives the biology behind them. GS3 — science and environment: photosynthesis as the planet's carbon sink and oxygen source, stomata and plant water loss, fermentation (ethanol, Chapter 4), dissolved oxygen for aquatic life.

• Life processes = nutrition, respiration, transport, excretion — maintenance that goes on even in sleep. Single cells manage by diffusion across their whole surface; large many-celled bodies need specialised organs and a transport system.
• Autotrophs (green plants, some bacteria) make food: 6CO₂ + 12H₂O —[chlorophyll, sunlight]→ C₆H₁₂O₆ + 6O₂ + 6H₂O. Three events: light absorbed by chlorophyll → light energy to chemical energy, water split → CO₂ reduced to carbohydrate. Extra carbohydrate stored as starch (we store glycogen). CO₂ enters through stomata, opened when guard cells swell with water.
• Heterotrophs (animals, fungi) use ready-made food: digest outside then absorb (bread mould, yeast, mushrooms), take in and digest inside, or parasites (Cuscuta, ticks, lice, leeches, tapeworms). Humans: saliva (amylase: starch → sugar) → stomach (HCl, pepsin, mucus) → small intestine (bile emulsifies fat; pancreatic trypsin and lipase; intestinal juice finishes) → villi absorb → large intestine takes back water.
• Respiration: glucose (6C) → 2 pyruvate (3C) in the cytoplasm; then → ethanol + CO₂ (yeast, no O₂), → lactic acid (muscle short of O₂ — cramps), or → CO₂ + water in mitochondria (most energy). Energy is banked as ATP (30.5 kJ/mol released when its last phosphate bond is broken with water).
• Breathing and blood: nostrils → throat → trachea → bronchi → bronchioles → alveoli (about 80 m²). Haemoglobin in red cells carries O₂; CO₂ travels mostly dissolved (NCERT). Four-chambered heart, double circulation (fish: two chambers, single circulation); arteries thick and elastic, veins with valves, capillaries one cell thick; BP about 120/80 mm Hg; platelets clot; lymph returns fluid and carries fat.
• Plants: xylem carries water and minerals up (root pressure at night, transpiration pull by day); phloem carries sugar and amino acids up and down using ATP (translocation). Excretion: kidneys → ureters → bladder → urethra; nephron = glomerulus in Bowman's capsule + tubule; about 180 L filtrate a day becomes 1–2 L urine. Dialysis filters without re-absorption. Plants shed wastes in leaves, store them in vacuoles, resins and gums, or release them into the soil.

The maintenance must go on even when we are asleep, and it needs energy from outside — that is food, brought in by nutrition. Growth needs extra raw material too. Because life is built on carbon-based molecules, food is mostly carbon-based, and organisms with access to simpler or more complex carbon sources use different kinds of nutrition. Food from outside varies, so the body must break it down or build it up into a uniform energy source, through chemical reactions — oxidising–reducing reactions are the commonest, and many organisms use oxygen from outside for them: respiration. Single-celled organisms need no special organs, as their whole surface touches the environment. In many-celled organisms not every cell touches the outside, so simple diffusion is not enough: specialised tissues take in food and oxygen, a transport system carries them, and a specialised tissue removes harmful by-products — excretion.

Autotrophs meet their carbon and energy needs by photosynthesis: they take in carbon dioxide and water and, in the presence of sunlight and chlorophyll, convert them into carbohydrates — stored chemical energy. NCERT writes it as 6CO₂ + 12H₂O —[chlorophyll, sunlight]→ C₆H₁₂O₆ + 6O₂ + 6H₂O (glucose). Carbohydrate not used at once is stored as starch, the plant's internal energy reserve; we store some of our food energy as glycogen. Three events happen: (i) chlorophyll absorbs light energy; (ii) light energy is converted to chemical energy and water molecules are split into hydrogen and oxygen; (iii) carbon dioxide is reduced to carbohydrate. These steps need not follow one another at once — desert plants take in CO₂ at night, make an intermediate, and finish the job in the day with light energy absorbed by chlorophyll.

Carbon dioxide enters mainly through stomata (Figure 5.3), tiny pores in the leaf surface, though gases are also exchanged across the surface of stems, roots and leaves. Open stomata also lose large amounts of water, so the plant closes them when it does not need CO₂. The guard cells control the pore: when water flows into them they swell and the pore opens; when they shrink it closes. Other raw materials: water comes from the soil through the roots (in land plants), and so do nitrogen, phosphorus, iron and magnesium. Nitrogen, needed for proteins and other compounds, is taken up as inorganic nitrates or nitrites, or as organic compounds made by bacteria from atmospheric nitrogen.

Each organism is adapted to its food: whether the food stays put (grass) or runs (a deer) shapes the feeding apparatus of a cow and a lion. Three strategies: break food down outside the body and absorb it (fungi such as bread moulds, yeast and mushrooms); take in whole material and break it down inside; or take nutrition from a living plant or animal without killing it — parasites such as Cuscuta (amar-bel), ticks, lice, leeches and tapeworms. Heterotrophs depend directly or indirectly on autotrophs, and use enzymes to break complex food into simple substances.

How unicellular organisms feed (5.2.3): the whole surface may take in food. Amoeba pushes out temporary finger-like extensions of the cell (pseudopodia) that fuse round a food particle to form a food vacuole; inside it complex substances are broken down and diffuse into the cytoplasm; the undigested remainder moves to the surface and is thrown out. Paramoecium has a definite shape and takes in food at one specific spot; the cilia covering the whole cell sweep food to it.

The alimentary canal is a long tube from mouth to anus with specialised regions. Mouth: teeth crush food into small, even particles; saliva from the salivary glands wets it and contains salivary amylase, which breaks starch into simple sugar; the muscular tongue mixes it. The canal's muscles contract rhythmically — peristalsis — all along the gut. Oesophagus (food-pipe) → stomach, which expands and churns food with gastric juice from gastric glands: hydrochloric acid (makes the medium acidic so pepsin can work), the protein-digesting enzyme pepsin, and mucus, which protects the stomach lining from the acid. A sphincter releases food into the small intestine a little at a time.

The small intestine — the longest part, packed in by coiling — is where digestion of carbohydrates, proteins and fats is completed. Its length varies with diet: grass-eaters need a longer one to digest cellulose; meat is easier, so tigers have a shorter one. It receives bile from the liver, which makes the acidic food alkaline for pancreatic enzymes and breaks large fat globules into small ones — emulsification, like soap on dirt (Chapter 4) — and pancreatic juice with trypsin (proteins) and lipase (emulsified fats). Glands in its wall make intestinal juice, whose enzymes finish the job: proteins → amino acids, complex carbohydrates → glucose, fats → fatty acids and glycerol. Numerous villi increase the surface for absorption; richly supplied with blood vessels, they send the food to every cell for energy, new tissue and repair. The large intestine absorbs more water, and the anal sphincter regulates the exit of waste.

Food taken in by nutrition is used in cells to provide energy. In every case the first step is the breakdown of glucose, a six-carbon molecule, into pyruvate, a three-carbon molecule, in the cytoplasm. Then: in yeast, during fermentation, pyruvate becomes ethanol and carbon dioxide — without air, so this is anaerobic respiration. In the mitochondria, using oxygen, pyruvate is broken into three molecules of carbon dioxide, the other product being water — aerobic respiration, which releases a lot more energy. When our muscle cells run short of oxygen (sudden activity), pyruvate becomes lactic acid, also three-carbon; its build-up causes cramps (NCERT).

The energy released is used at once to make ATP (from ADP and inorganic phosphate), which fuels all other activities in the cell; when ATP is broken, it gives a fixed amount of energy that can drive the cell's endothermic reactions. ATP powers muscle contraction, protein synthesis, nerve impulses and much else.

Plants exchange gases through stomata, and large intercellular spaces keep every cell in contact with air; CO₂ and O₂ move by diffusion, in a direction set by conditions and needs. At night, with no photosynthesis, CO₂ release is the main exchange; in the day, CO₂ from respiration is used in photosynthesis and oxygen release dominates. Aquatic animals must use the oxygen dissolved in water, which is much less than in air, so their breathing rate is much faster: fish take water in through the mouth and force it past the gills, where blood takes up the dissolved oxygen. Land animals breathe atmospheric oxygen with organs that have a large, very fine and delicate surface, kept inside the body for protection, with passages to bring air and a mechanism to move it in and out.

Humans (Figure 5.9): air enters through the nostrils, filtered by fine hairs and mucus; passes through the throat to the lungs; rings of cartilage keep the air-passage from collapsing. In the lungs the passage divides into smaller and smaller tubes ending in alveoli, whose walls carry an extensive network of blood vessels. Breathing in, we lift the ribs and flatten the diaphragm; the chest cavity enlarges and air is sucked into the alveoli. Blood brings CO₂ to the alveoli and takes up their oxygen. The lungs always keep a residual volume of air, giving time for the exchange. In large animals diffusion cannot deliver oxygen, so a respiratory pigment — in us, haemoglobin, in the red blood corpuscles, with a very high affinity for oxygen — carries it to oxygen-poor tissues. CO₂, being more soluble in water than oxygen, is carried mostly dissolved in our blood (NCERT's statement — see the trap).

Blood is a fluid connective tissue: a fluid medium, plasma, carries food, carbon dioxide and nitrogenous wastes in dissolved form, plus salts; red blood corpuscles carry oxygen. The heart, a muscular organ about the size of a fist, has separate chambers so that oxygen-rich and carbon dioxide-rich blood do not mix. Step by step (Figure 5.11): oxygen-rich blood from the lungs enters the thin-walled left atrium as it relaxes; the atrium contracts while the left ventricle relaxes and fills; the muscular left ventricle contracts and pumps blood to the body. Deoxygenated blood from the body enters the right atrium; it contracts as the right ventricle dilates; the right ventricle pumps it to the lungs. Ventricles have thicker walls than atria because they pump blood into organs; valves stop backflow.

Keeping the two sides apart gives a highly efficient oxygen supply, useful to animals with high energy needs — birds and mammals, which constantly spend energy keeping their body temperature up. Animals whose body temperature follows the environment — amphibians and many reptiles — have three-chambered hearts and tolerate some mixing. Fishes have two chambers: blood is pumped to the gills, oxygenated there, and goes straight on to the body — it passes the heart once per circuit. Other vertebrates send it through the heart twice per circuit: double circulation.

Platelets circulate in the blood and plug leaks by helping blood clot at an injury — a leak would lose blood and lower the pressure the pump depends on. Lymph (tissue fluid): some plasma, proteins and blood cells escape through pores in capillary walls into the spaces between cells; this fluid is like plasma but colourless with less protein. It drains into lymphatic capillaries, which join into larger lymph vessels that open into large veins. Lymph carries digested and absorbed fat from the intestine and returns excess fluid to the blood.

Leaves make food; roots, in contact with the soil — the nearest, richest source of nitrogen, phosphorus and other minerals — take up raw materials. Over short distances diffusion would do, but in large plants it cannot carry raw material to the leaves and energy to the roots. Plants do not move and many of their tissues are dead cells, so their energy needs are low and slow transport suffices — though distances in tall trees are huge. Two independent sets of tubes do the work: xylem moves water and minerals from the soil; phloem moves the products of photosynthesis from the leaves to other parts.

Water: in xylem, vessels and tracheids of roots, stems and leaves join into a continuous system of water channels. Root cells in contact with the soil actively take up ions, creating a concentration difference, so water moves in from the soil — a steady push up the root xylem (root pressure). That alone is unlikely to lift water to the heights of trees. Water lost as vapour through stomata is replaced from the leaf xylem: evaporation from leaf cells creates a suction that pulls water up from the roots. This loss of water vapour from aerial parts is transpiration; it helps absorb and lift water and dissolved minerals and also helps regulate temperature. Root pressure matters more at night; by day, with stomata open, the transpiration pull is the main driving force.

Food: transport of soluble products of photosynthesis is translocation, in the phloem. Phloem also carries amino acids and other substances, especially to storage organs (roots, fruits, seeds) and growing organs, in the sieve tubes helped by companion cells, both upward and downward. Unlike xylem (largely physical forces), phloem uses energy: sucrose is loaded using ATP, raising the tissue's osmotic pressure, so water moves in and the pressure pushes material to tissues with less pressure — so the plant moves food according to need, e.g. sugar from root or stem stores to growing buds in spring.

Metabolism makes nitrogenous wastes that must be removed — excretion. Many unicellular organisms simply let them diffuse into the surrounding water. The human excretory system (Figure 5.13) is a pair of kidneys in the abdomen, one on either side of the backbone; a pair of ureters; a urinary bladder; and a urethra. Just as CO₂ leaves the blood in the lungs, urea or uric acid leaves it in the kidneys — and, like the lungs, the kidney's basic filter is a cluster of very thin-walled capillaries (the glomerulus), each sitting in the cup-shaped end of a coiled tube, Bowman's capsule, which collects the filtrate. Each kidney has large numbers of these filtration units, nephrons. As the filtrate flows along the tube, glucose, amino acids, salts and a major amount of water are selectively re-absorbed; how much water is taken back depends on how much excess water the body has and how much dissolved waste must go. Urine from each kidney enters a ureter, is stored in the bladder until its stretching gives the urge to pass it, and leaves through the urethra; the bladder is muscular and under nervous control, so we can usually hold it.

Plants (5.5.2) use quite different strategies. Oxygen from photosynthesis can itself be thought of as a waste, and plants handle O₂ and CO₂ by diffusion; excess water goes by transpiration. For other wastes they use the fact that many tissues are dead cells and that they can shed parts such as leaves: wastes are stored in cell vacuoles, in leaves that fall off, as resins and gums (especially in old xylem), or excreted into the soil around them.

Short outlines in page order for the five ‘Questions’ boxes (21 questions) and the eight activities.

Numbers

One-liners

• Life processes: nutrition, respiration, transport, excretion — maintenance that never stops.
• Photosynthesis: light absorbed → water split, light to chemical energy → CO₂ reduced to carbohydrate.
• Guard cells swell with water → stoma opens; shrink → closes.
• Starch test: de-starch, light, boil in water, alcohol on a water-bath, iodine → blue-black.
• Saliva: amylase (starch); stomach: HCl, pepsin, mucus; bile emulsifies; pancreas: trypsin, lipase.
• Villi increase the small intestine's absorbing surface.
• Glucose → pyruvate in the cytoplasm; aerobic breakdown of pyruvate in mitochondria.
• Yeast: ethanol + CO₂; tired muscle: lactic acid; aerobic: CO₂ + water, most energy.
• ATP is the cell's energy currency.
• Haemoglobin in red cells carries O₂; CO₂ mostly dissolved (NCERT).
• Double circulation: heart → lungs → heart → body → heart.
• Arteries thick and elastic; veins with valves; capillaries one cell thick.
• Xylem: water up (root pressure at night, transpiration pull by day); phloem: food both ways, uses ATP.
• Nephron: glomerulus in Bowman's capsule + tubule; filter then re-absorb.
• Dialysis: diffusion through a semi-permeable lining, no re-absorption.

Traps to avoid

• Respiration (chemical, in cells) ≠ breathing (moving air).
• Guard cells OPEN the pore when they take in water.
• Glycolysis is in the cytoplasm in every pathway; only aerobic pyruvate breakdown is in mitochondria.
• Bile has no enzyme; it is made in the liver and stored in the gall bladder.
• Pulmonary artery carries CO₂-rich blood; pulmonary vein carries O₂-rich blood.
• Fish heart: 2 chambers, single circulation.
• Phloem moves food both ways; xylem only up. Girdling starves the roots.
• Glomerulus is the filter; the nephron is the whole unit. Clean blood leaves by the renal vein.
• Dialysis has no re-absorption.
• NCERT slips: cartilage rings ‘in the throat’ (they are in the trachea); CO₂ ‘mostly dissolved’ (Class 11: mostly bicarbonate); lactic acid as the cause of cramps is a school-level simplification.

Prelims — what UPSC asks

• Photosynthesis and plants: chlorophyll as the green pigment (1980, 1982), the final product (1986), CO₂ assimilation (1986), where it happens (1987), stored energy (2014), sea plants giving oxygen (1979), CO₂ under trees at night (1979), the organelle match (1996), tissue functions (1990), why capillarity cannot lift water (1999) and girdling (2011).
• Digestion: saliva on starch (1988), ptyalin–pepsin–renin–oxytocin (2001), bile from the liver (1985), where bile and pancreatic juice enter (2006), the liver and fat-digesting enzymes (2008), protein digestion (2005), gastrin is not an enzyme (2007), what counts as digestion (2010), parasites (1984).
• Respiration and blood: aerobic respiration (1998), lactic acid (2000), alveoli (1991), the oxygen route (1997), CO₂ in a crowded room (1979), haemoglobin (1990) and anaemia (1979), blood pressure (1990, 1993). Kidney: dialysis (1979, 1980), the glomerulus (1987), urea and kidney damage (1991), kidney function (2003); eye donation (2001).
• Likely next: CAM and C4 plants and water-use efficiency, stomata and rising CO₂, carbon monoxide and haemoglobin, anaemia programmes, hypertension, organ-donation law, dialysis access, ATP and mitochondrial disease.
• Answer-key note (2005, protein digestion): the stored key (a) treats ‘all the proteins in our food are digested in the small intestine only’ as true. NCERT itself says pepsin, a protein-digesting enzyme, acts in the stomach, so the Assertion is false and the Reason (pancreatic protein-digesting enzymes are released into the small intestine) is true: the expected answer is (d). The stored key is likely wrong.
• Answer-key notes that stand: 1987 ‘ultrafiltering units’ — key (b) glomerulus is right even though NCERT calls the nephron the filtration unit; 2000 ‘fatigue’ — key (d) lactic acid matches NCERT, though physiology now treats lactic acid's role in fatigue as disputed; 1990 blood pressure — key (d) ‘all four’ stands, but statement 4 (lower in women) is Beyond NCERT and only true on average.

Mains — where it appears and how to answer

• No GS Mains question in the bank so far is built on this chapter's core content. It supplies the biology for GS2 answers on anaemia, hypertension and non-communicable diseases, kidney failure and dialysis, organ and tissue donation, and tobacco control; and for GS3 answers on photosynthesis as a carbon sink, plant water loss under drought and heat, and fermentation for biofuels.
• Answer frame: the biology in one line (e.g. haemoglobin carries oxygen; nephrons re-absorb about 99% of the filtrate) → the health or environmental consequence → the policy instrument (Anaemia Mukt Bharat, the 1994 transplant law and its 2011 amendment, the 2016 dialysis programme, COTPA 2003) → positions on open questions, each attributed, no verdict.
• A small sketch — the double-circulation figure-of-eight or a nephron with ‘filter → re-absorb’ arrows — fits in a 150-word answer.

Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.

Open any question to attempt it in the Question bank — your attempt is saved to your progress.