Life Processes

A leaf can make sugar, a lung can exchange gases and a kidney can filter fluid. None works as an isolated machine. The interesting question is how materials reach the cells that need them—and how useful materials avoid being lost with waste.

These Class 10 Science notes follow NCERT's Life Processes, Chapter 5 in the 2026–27 reprint, and the current CBSE scope: nutrition, respiration, transport and excretion in plants and animals. The investigations are original paper or virtual activities. They are not past-paper questions or practical instructions involving chemicals, breath-holding, blood or urine.

What are Life Processes?

Living structures require continuing maintenance. Cells obtain materials, transform substances, transfer energy and regulate their internal conditions. These processes continue even when an organism appears still: a sleeping person and a seedling without visible movement can both be alive. Visible movement alone is a poor test; a moving car is not an organism.

Nutrition supplies materials and chemical energy sources. Respiration transfers energy through cellular reactions. Transport connects places where materials enter, are made, are used and are removed. Excretion removes metabolic wastes. Reproduction maintains a lineage, but an individual need not reproduce to remain alive.

Small organisms can exchange many substances across their surface. In a large multicellular body, many cells lie far from that surface. Diffusion remains essential across short distances, but it is too slow to serve every cell over long distances by itself. Bulk transport and specialised exchange surfaces work together; a circulatory system does not abolish diffusion.

• Follow one material: oxygen enters through an exchange surface, travels in blood and reaches cells; carbon dioxide can travel back to the lungs. Food follows another entry route. These routes meet functionally in cells, not by sending food through the lungs.

Nutrition

An autotroph builds organic substances from inorganic carbon, commonly carbon dioxide. Green plants capture light energy for this work. A heterotroph obtains organic nutrients from other organisms or their products. The distinction concerns the source of organic material, not whether an organism “needs food”: plants also require substances for growth and respiration.

Heterotrophic strategies differ. Fungi can release digestive enzymes outside their bodies and absorb soluble products: saprotrophic nutrition. An animal can take food inside and digest it: holozoic nutrition. A parasite obtains resources from a living host, usually harming it; “never kills the host” is not part of the definition.

In Amoeba, temporary extensions called pseudopodia surround food, enclosing it in a food vacuole. Digestion releases soluble nutrients, which enter the cytoplasm; undigested material is expelled. Paramecium uses cilia to direct food towards a specialised feeding region. Neither needs a human-style stomach to perform digestion.

Surprise: must every food-producing ecosystem begin with sunlight?

No. Some microbes use energy from chemical reactions to build organic matter. Such chemosynthetic producers support food webs at deep-sea vents and seeps. NOAA's comparison of photosynthesis and chemosynthesis makes the distinction visible. This is enrichment: it challenges “all autotrophs use sunlight” without changing the plant photosynthesis model below.

Photosynthesis: building with carbon, water and light

In green plant cells, chlorophyll in chloroplasts helps capture light energy. Carbon dioxide provides carbon for carbohydrates; water supplies hydrogen and is the source of the oxygen gas released during oxygenic photosynthesis. Light supplies energy, not carbon atoms. Water and mineral ions enter principally through roots, while carbon dioxide reaches leaf interiors through gas-exchange openings.

The familiar net accounting equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, with light and chlorophyll-dependent machinery understood. NCERT also writes the fuller water accounting as 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O. Cancelling six water molecules gives the net equation. Neither is a single collision that instantly makes glucose: photosynthesis involves many linked reactions.

The chapter groups the process into light absorption, conversion of light energy into chemical forms with water splitting, and reduction of carbon dioxide to carbohydrates. Plants can use sugars, transport them or store carbohydrate as starch. Nitrogen for proteins and other molecules must also be acquired, commonly as nitrate or ammonium ions from the soil; sunlight cannot supply that nitrogen.

Stomata are pores associated with guard cells. Changes in guard-cell water content and turgor alter the opening. This regulates gas exchange and water loss. Avoid an absolute day/night rule: conditions and plant adaptations matter. Some plants adapted to dry conditions take in carbon dioxide at night and store it for use in photosynthesis during the day.

Investigate a leaf without turning an observation into proof of everything

Imagine a teacher supplies these results after a standard starch test on a destarched, variegated leaf exposed to light: green regions become blue-black with iodine; non-green regions do not. The colour indicates starch, not oxygen or chlorophyll itself. The pattern supports a connection between chlorophyll-containing tissue and starch production under the tested conditions.

To investigate light, compare exposed and covered regions while holding other relevant conditions alike. To investigate carbon dioxide, compare otherwise similar plants supplied with and deprived of it. Destarching reduces confusion from starch already present before the trial. These are designs to interpret on paper; the textbook's heated alcohol, iodine and alkali procedures belong in a properly supervised laboratory.

A leaf shows no net carbon dioxide exchange. Has photosynthesis stopped?

Not necessarily. Carbon dioxide consumption by photosynthesis can equal carbon dioxide release by respiration over the measurement interval. A net measurement is a balance of processes. The discovery panel lets you change this balance while keeping track of both rates.

Nutrition in Human Beings

Follow food through the alimentary canal: mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus. The liver and pancreas contribute secretions to the small intestine; food does not travel through those glands. Ingestion takes food in, digestion makes smaller absorbable molecules, absorption moves products across the gut lining, assimilation uses them in the body, and egestion removes material left in the gut.

• Mouth: teeth break food into smaller pieces, increasing the surface available to enzymes. Saliva moistens food. Salivary amylase begins breaking starch into smaller sugars; it does not digest every food component.
• Oesophagus: coordinated muscular waves, called peristalsis, move the swallowed material. The canal is not simply a tube in which gravity does all the work.
• Stomach: muscular mixing combines food with gastric juice. Hydrochloric acid provides an acidic environment for pepsin, which begins protein digestion, and helps limit many swallowed microbes. Mucus helps protect the stomach lining. Acid is not itself the protein-digesting enzyme.
• Small intestine: pancreatic and intestinal enzymes continue digestion. Pancreatic amylase acts on starch, proteases such as trypsin act on proteins, and lipase acts on fats. Digestion produces absorbable sugars, amino acids and smaller lipid components. At this level NCERT summarises fat digestion as fatty acids and glycerol.
• Large intestine: further water absorption helps form faeces. Material is stored in the rectum before elimination through the anus, whose opening is controlled by sphincter muscles.

Tooth decay is different from normal digestion: bacteria using dietary sugars and starches produce acids that can demineralise tooth enamel. The NIDCR explanation of tooth decay connects microbial activity to damage at the tooth surface.

Bile is not a digestive enzyme. The liver makes it, and the gallbladder stores and releases it. Bile helps disperse fat into smaller droplets, increasing the surface available to lipase. Alkaline secretions, including pancreatic bicarbonate and bile, help counter the acidic mixture arriving from the stomach. Emulsification changes droplet size; enzymatic digestion changes molecules.

The small intestine has many finger-like villi, providing a large absorptive surface. Each villus connects absorption to transport. Sugars and amino acids enter blood capillaries; much absorbed fat enters intestinal lymph vessels before reaching the blood. The NIDDK digestive-system account distinguishes the canal, the glands and these transport routes.

Absorbed nutrients have several destinations. Cells may use them for respiration, build their own molecules or store some for later use. Animals can store carbohydrate as glycogen, particularly in liver and muscle; it is incorrect to say that all absorbed food becomes glycogen. Herbivores' digestive systems help process plant material, often with cellulose-digesting microbes. A longer gut can allow more processing time, but length alone cannot supply an enzyme the animal lacks.

Predict what changes if fat is not well emulsified

Large fat droplets offer less surface area than the same amount dispersed into smaller droplets. Lipase therefore has less accessible surface on which to act. The explanation concerns contact between enzyme and substrate; it does not mean that bile normally turns fat directly into glucose.

Respiration

Breathing moves air into and out of lungs. Cellular respiration is a set of chemical processes through which cells transfer energy from nutrients into forms they can use. An organism without lungs can still respire. Digestion and respiration also differ: digestion makes food absorbable; respiration transfers energy through cellular reactions.

For the chapter's glucose model, the first stage occurs in the cytoplasm: one six-carbon glucose molecule yields two three-carbon pyruvate molecules. Some ATP is formed. The next route depends on the cell and conditions:

• Aerobic pathway: in cells with mitochondria, further reactions associated with mitochondria use oxygen in the overall process and produce carbon dioxide and water. The complete breakdown of glucose yields substantially more ATP than fermentation. Glycolysis itself still occurs in the cytoplasm.
• Yeast fermentation: without oxygen, yeast can convert the products of glucose breakdown into ethanol and carbon dioxide. The carbon ledger is two two-carbon ethanol molecules plus two one-carbon carbon dioxide molecules per glucose.
• Muscle lactate formation: muscle cells can convert pyruvate into lactate when this route helps sustain glycolysis. Two three-carbon lactate molecules conserve the six carbons of the starting glucose; this route does not release carbon dioxide.

The overall aerobic accounting is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O. For alcoholic fermentation it is C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. Energy transfer accompanies these reactions; energy is not an extra chemical atom to balance. These summaries conceal many enzyme-controlled steps.

NCERT groups the oxygen-free examples under anaerobic respiration. In more detailed biology, fermentation is distinguished from anaerobic respiration that uses an electron transport chain with a different final acceptor. You do not need that machinery here, but it explains why the school umbrella term should not be stretched into “all anaerobic processes make alcohol”.

ATP, adenosine triphosphate, helps couple energy-releasing processes to work such as active transport and muscle contraction. ATP hydrolysis can have a favourable overall energy change, allowing coupled work to proceed. Breaking a chemical bond alone requires energy: the net change depends on all bonds and interactions in the reaction. ATP is continually regenerated, not a permanent battery with an unlimited charge.

A further precision matters: a review of exercise-associated muscle cramps finds that causes can involve multiple factors. Lactate formation is not, by itself, proof of what caused a muscle cramp. Do not use the chapter's simplified lactate story as a medical diagnosis. Lactate can be reused in metabolism; it is not merely a poison that muscles must discard.

Spot the missing carbon in this claim: “glucose becomes one pyruvate”

Glucose has six carbon atoms and pyruvate has three. The first-stage account needs two pyruvates per glucose. Continue the same check: yeast's two ethanols contain four carbons, and its two carbon dioxide molecules account for the remaining two.

Breathing and gas exchange

Human air enters through the nose, where hairs and mucus help trap particles. It passes through the throat, larynx and trachea, then branches into bronchi and smaller bronchioles. Cartilage helps keep larger airways open. At the ends are alveoli: many small air spaces closely associated with capillaries.

During inhalation, the diaphragm contracts and becomes flatter, and the rib cage expands. Chest volume increases, lowering pressure inside the lungs relative to the outside, so air enters. During quiet exhalation, these muscles relax and elastic recoil helps reduce lung volume. Lungs do not empty completely with every breath.

Airway mucus and cilia help trap and clear inhaled material. Smoke can damage the airways and interfere with this protection. This links the textbook’s smoking discussion to respiratory function; it does not make cilia damage the sole explanation for all smoking-related disease.

Alveoli combine a large surface area with a short diffusion distance and a moist exchange surface. Ventilation refreshes alveolar air; circulation brings blood with different gas partial pressures. Oxygen diffuses into blood and carbon dioxide diffuses towards the alveoli. Thin walls are useful only as part of this maintained exchange system.

Most blood oxygen is carried reversibly by haemoglobin in red blood cells; a small amount dissolves in plasma. If haemoglobin is reduced while other conditions remain alike, blood has less capacity to carry oxygen; this is a physiological inference, not a diagnosis from tiredness alone. Most transported carbon dioxide is carried as bicarbonate, with smaller amounts dissolved unchanged or attached to proteins. Thus “carbon dioxide is mainly in plasma” must not imply that it all stays as dissolved CO₂ molecules.

Fish obtain dissolved oxygen using gills. Aquatic oxygen availability differs from that in air, but avoid a universal claim about every animal's breathing rate. Nor do all terrestrial animals have lungs: insects use a tracheal system. Plants exchange gases through surfaces including stomata and respire in living cells by day and by night. In light, photosynthesis may exceed respiration; that does not switch respiration off.

Transportation

Blood provides a moving transport medium. Plasma carries dissolved nutrients, wastes and other substances. Red blood cells contain haemoglobin, white blood cells contribute to defence, and platelets—cell fragments—help initiate clotting. Clot formation limits blood loss and helps preserve the circulating fluid volume.

The four-chambered human heart has two atria, which receive blood, and two ventricles, which pump it out. Follow the route:

Body → venae cavae → right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta → body.

The right side supplies the lungs; the left supplies the body. The septum separates the sides, and valves favour one-way flow. The left ventricle has a thicker muscular wall because systemic circulation requires greater pumping pressure than the lung circuit. Oxygen-poor blood is not oxygen-free, and ordinary human blood is red even when diagrams colour one route blue.

This is double circulation: a complete route through lung and body circuits passes through the heart twice. Separation supports efficient oxygen delivery. In birds and mammals, this helps meet the high energy demand of maintaining a relatively stable body temperature. Fish have a single main circulation through heart, gills and body, with two principal pumping chambers. Amphibians and many reptiles have three-chambered hearts; crocodilians are a notable four-chambered exception. Do not turn a useful school comparison into an absolute rule for every reptile.

Vessels, pressure and lymph

Arteries carry blood away from the heart; veins carry it towards the heart. These definitions concern direction, not oxygen content. The pulmonary artery and pulmonary veins demonstrate why that matters. Arteries generally have thicker, more elastic muscular walls to withstand higher pressure. Many veins have valves that help prevent backflow, particularly in limbs; venous pressure is lower, not zero.

Arteries branch into arterioles and then capillaries. Capillary walls have a thin endothelial layer, allowing exchange with tissue fluid over short distances. Capillaries lead into venules and veins. Blood pressure is pressure exerted on vessel walls, not simply “the force of the heartbeat”; systolic and diastolic readings describe phases of the cardiac cycle.

Some fluid leaves blood capillaries and enters the spaces around cells. Fluid entering lymph vessels is called lymph. Lymphatic vessels return fluid towards the bloodstream and participate in immune defence. Intestinal lymph vessels also transport much absorbed fat. This does not mean that red blood cells routinely leave intact vessels with all the plasma.

Can a vein carry oxygen-rich blood?

Yes. Pulmonary veins return oxygen-rich blood from lungs to the left atrium. “Towards the heart” makes them veins. An answer based only on red or blue colouring confuses an illustration's convention with the anatomical definition.

Transport in plants

Plants also need long-distance connections. Xylem carries water and mineral nutrients, mainly from roots towards shoots. Root hairs increase the surface available for absorption. Ion uptake can involve active transport, while water moves according to water-potential differences, including by osmosis across cell membranes. Roots do not suck up ready-made carbohydrate as their normal source of food.

Root pressure can push water, especially under some conditions when transpiration is low. For tall plants during active transpiration, a major mechanism is transpiration pull: evaporation from leaf surfaces creates tension transmitted through the continuous water column. Cohesion between water molecules helps maintain that column. Xylem vessels and tracheids form conducting pathways; mature conducting elements are non-living.

Transpiration is loss of water vapour from aerial plant parts, much of it through stomata. It contributes to water movement and evaporative cooling but also creates a risk of water loss exceeding supply. Stomatal regulation balances access to carbon dioxide against water conservation. “More transpiration is always better” ignores that trade-off.

Phloem translocates organic solutes, especially sugars such as sucrose, from sources to sinks through living sieve tubes supported by companion cells. A mature photosynthesising leaf can be a source; a growing root, fruit or bud can be a sink. A storage organ may become a source when its reserves feed new growth. Source and sink are roles, not permanent names for leaves and roots.

In the chapter's pressure-flow model, loading sugar into the transport pathway requires energy. Water enters, producing a pressure difference that drives bulk flow towards an unloading sink. It is not a claim that ATP pushes each sugar molecule along the whole tube. Transport can occur upwards and downwards in different phloem pathways; one stream does not simultaneously flow both ways through the same tube.

A stored root feeds a new shoot. Which tissue moves the sugar, and which organ is the source?

Phloem moves the organic solute. The storage root is now a source and the growing shoot a sink. Choosing “leaf” automatically would miss that source means an exporter in the particular situation.

Excretion

Metabolism produces substances that must be removed or regulated. Excretion concerns metabolic wastes, such as carbon dioxide and nitrogenous wastes. Egestion removes undigested material from the alimentary canal. They are different processes even though both involve material leaving the body.

In humans, the liver converts much excess amino nitrogen into urea; research on hepatic urea synthesis distinguishes this production from removal by the kidneys. The kidneys remove urea from blood and help regulate water, salts and acid–base balance. Urine passes from each kidney through a ureter to the urinary bladder, then exits through the urethra. The ureter and urethra are different tubes; the bladder stores urine rather than filtering blood.

The nephron: filter, recover and adjust

A nephron contains a glomerulus, a tuft of capillaries, associated with Bowman's capsule and a tubule. Filtration moves water and many small dissolved substances from blood into the capsule. Blood cells and most large proteins normally remain in the circulation. The blood pathway continues; the entire blood supply does not pour into a urine tube.

Initial filtrate includes useful substances such as glucose, amino acids, salts and water. Tubular reabsorption returns much of this material to blood. Tubular secretion can add selected substances from blood to the tubule, providing another means of adjustment. The final urine differs markedly from the initial filtrate.

Water reabsorption varies with the body's needs and hormonal control. Healthy kidneys normally recover virtually all filtered glucose, but not all filtered water or urea. A model that subtracts reabsorbed amounts from filtered amounts helps explain the principle; it cannot diagnose a person. The discovery panel explicitly leaves secretion out of its small arithmetic example.

If kidney function fails severely, haemodialysis can remove certain wastes and excess fluid. Blood and dialysis fluid move in separate compartments divided by a selectively permeable membrane. This is not blood being mixed with cleaning liquid. Dialysis replaces some kidney functions, not every function, and its composition and operation require clinical control. See NIDDK's haemodialysis explanation for the distinction.

What about plants?

Plants have metabolic wastes too. Gases can diffuse through exchange surfaces; some substances can be stored in vacuoles or in tissues later shed, including leaves. Resins and gums can accumulate in older xylem, and roots may release substances into the surrounding soil. Oxygen produced by photosynthesis can be used in respiration or released. The absence of human-like kidneys does not mean an absence of waste management.

“Glucose enters the nephron, so glucose must leave in urine.” Where does the reasoning fail?

It treats filtration as the final step. Filtered glucose is normally reabsorbed into blood. To predict output, track both entry and recovery, and remember that real tubules also secrete some substances. Finding something in initial filtrate is not enough to predict its amount in final urine.

Why it still matters

A useful biological explanation links structure, process and consequence. Villi increase absorptive surface; absorption connects to transport. Alveoli shorten diffusion distance; breathing and blood flow maintain gas differences. A nephron filters small substances, then selectively recovers useful ones. A leaf admits carbon dioxide while risking water loss. Naming an organ is only the beginning of an explanation.

Explore the California Academy of Sciences' Travel Deep Inside a Leaf animation. It moves from leaf to cell to chloroplast to molecular machinery. Turn on captions; then ask which structures are visible and which materials are omitted. Its colours and slowed motion are modelling choices, not a literal microscope recording. The accompanying transcript identifies deliberate omissions; absence from the picture does not mean absence from photosynthesis.

Make your own investigation: draw three separate routes on paper: a sugar from the intestine towards a body cell, oxygen from an alveolus towards that cell, and urea from the liver towards urine. Mark where a membrane must be crossed and where bulk flow carries material. Use arrows to explain each transfer; do not send food into the trachea or label the first kidney filtrate “finished urine”.

• Revision check: distinguish nutrition from respiration, breathing from gas exchange, artery from oxygen-rich blood, source from leaf, filtration from excretion and egestion from metabolic waste removal. For each pair, give an example that defeats the tempting shortcut.

Sources

• NCERT Science, Chapter 5: Life Processes, 2026–27 reprint—chapter scope, examples and school-level models.
• CBSE Science curriculum 2026–27—Class 10 life-process scope and practical context.
• NIDDK: the digestive system and kidneys and nephrons—organ functions, absorption, filtration and reabsorption.
• NHLBI: heart blood flow and breathing and the lungs—circulation and ventilation.
• OpenStax Biology: metabolism without oxygen, plant transport and gas transport—checks on fermentation terminology, transport models and bicarbonate.
• NOAA Ocean Exploration and California Academy of Sciences—chemical-energy ecosystems and the limits of a leaf animation.