NCERT Solutions for Class 10 Science Chapter 5 Life Processes

In a single-celled organism, every part is in direct contact with the surroundings, so oxygen simply diffuses in across the whole surface. A human body is not built that way — most cells lie buried deep inside tissues, very far from the air outside.

For those interior cells, diffusion from the body surface would be far too slow to supply the oxygen they need to release energy.

This is why a multicellular organism builds a transport system: lungs collect oxygen at a surface, blood picks it up using haemoglobin, and the heart pushes that oxygen-rich blood to every cell.

The textbook notes that if diffusion alone moved oxygen in our body, it would take about three years for one oxygen molecule to travel from the lungs to the toes (NCERT, p. 90). Diffusion only works over tiny distances; a body needs a pump and carrier to cover large ones.

Visible movement is the everyday test — a running dog, a chewing cow, a shouting person — but it is not reliable. A plant that is not visibly growing is still alive, and some animals breathe without visible movement.

The dependable criterion is molecular movement: the invisible movement of molecules inside the body that repairs and maintains the organised structure of living tissue.

Because the environment constantly breaks down ordered structures, living organisms must keep moving molecules around to repair and rebuild them. Where there is no molecular movement — the chapter cites viruses, which show none until they infect a host — biologists debate whether the thing is truly alive.

So the test is not what we see from the outside, but maintenance through molecular activity. (NCERT, p. 80)

Organisms use outside raw material for two distinct purposes. The first is to provide energy for constant maintenance, even when nothing visible is happening — sitting in class, or being asleep, still requires energy to repair ordered structures. This is supplied through nutrition.

The second purpose is growth: to increase body size, the organism needs carbon-based molecules from outside, since most biological structures are carbon-based.

Energy sources on the outside vary, so the body must break those molecules down and rebuild them into a uniform internal fuel. Oxygen acquired from the environment drives this breakdown through oxidising-reducing reactions — the process we call respiration. So raw materials feed both repair and growth. (NCERT, pp. 80–81)

The four processes this chapter treats as essential are nutrition, respiration, transportation, and excretion. Nutrition transfers a source of energy from the outside (food) into the body. Respiration acquires oxygen from the outside and uses it in the step-by-step breakdown of food for cellular needs.

Transportation carries food and oxygen from the place they are taken in to every cell that needs them.

The fourth process, excretion, removes the harmful waste by-products created when chemical reactions use the carbon source and oxygen. The chapter stresses that these maintenance jobs must go on even when the organism is asleep — so all four are continuous processes, not occasional activities. (NCERT, p. 81)

Autotrophs and heterotrophs differ in where their carbon source comes from, in their dependence on other organisms, and in whether they must use enzymes to break complex food down. Autotrophs build their own food from simple inorganic molecules; heterotrophs consume food that autotrophs have already built. The table below compares them on the three criteria the textbook emphasises.

Both modes ultimately serve the same purpose — supplying carbon-based molecules and energy for maintenance and growth — but the pathway differs fundamentally because one group can build and the other must break down. (NCERT, pp. 81–82)

Plants gather the four named raw materials from four different routes. Carbon dioxide is taken in from the air through tiny pores on the leaf surface called stomata, whose guard cells control their opening and closing. Water is absorbed from the soil by the roots and carried up through the xylem.

Sunlight is captured by chlorophyll, the green pigment inside chloroplasts in the leaf cells — the leaf cross-section above shows these green dots clearly. Chlorophyll itself is built using nitrogen, which the plant takes up from the soil.

Nitrogen is absorbed mainly as inorganic nitrates or nitrites dissolved in soil water; some plants get it through organic compounds prepared by nitrogen-fixing bacteria. So the four raw materials — CO₂, water, sunlight, and chlorophyll — each arrive by a separate path. (NCERT, pp. 81–83)

The gastric glands in the stomach wall release hydrochloric acid alongside a protein-digesting enzyme called pepsin and a protective layer of mucus. HCl plays two roles. First, it creates the acidic medium that pepsin needs to begin protein digestion.

Second, it kills many harmful bacteria that enter the stomach with food, reducing the risk of infection — this is the textbook’s implied function when it asks what else the acid serves.

This acidic environment is corrosive enough to harm the stomach lining. The mucus secreted by the same gastric glands forms a barrier that shields that lining from acid damage under normal conditions. When that mucus protection fails, the acid attacks the lining and we experience acidity — the “acidity” the chapter mentions. (NCERT, p. 85)

Digestive enzymes are biological catalysts — they speed up the conversion of complex food molecules into simpler ones small enough to be absorbed through the intestinal wall. Without this breakdown, complex food cannot enter the bloodstream. The chapter categorises their action by food type.

Specifically, the intestinal enzymes finally convert proteins to amino acids, complex carbohydrates to glucose, and fats to fatty acids and glycerol (NCERT, p. 85). Before this final step, the stomach’s pepsin begins protein digestion, the pancreas’s trypsin continues it, and lipase breaks down emulsified fats. Each enzyme is specific to one substrate; digestion is a sequential, compartment-by-compartment process. (NCERT, p. 85)

The small intestine is designed to absorb digested food efficiently because absorption depends on surface area. The inner lining is folded into numerous finger-like projections called villi (NCERT, p. 86). Each villus is itself a finger of tissue, and the millions of villi together vastly increase the area of wall in contact with the digested food.

Each villus is richly supplied with blood vessels. The absorbed food — glucose, amino acids, fatty acids, glycerol — passes into these blood vessels, which carry it to every cell of the body for energy, tissue building, and repair.

The villi are also finger-thin so that molecules have only a short distance to cross from the intestinal cavity into the blood — a structural shortcut that combines with the large surface area to make uptake fast and complete.

Oxygen dissolves poorly in water. An aquatic organism must pump large volumes of water past its gills to scrape out the small amount of dissolved oxygen it needs, so its breathing rate is high. A terrestrial organism breathes air, which is about 21% oxygen — a far richer supply than any water body holds.

Because the surrounding air contains much more oxygen per unit volume, a terrestrial animal extracts the same amount of oxygen with far less breathing effort. Activity 5.6 in the textbook shows this directly: fish open and close their mouths far more often than humans breathe in and out.

In short, land animals get more oxygen, more easily, so they can support higher energy needs. (NCERT p. 89)

In every pathway, glucose is first broken into two three-carbon pyruvate molecules in the cytoplasm. From there, three routes are possible depending on the organism and oxygen availability.

• Aerobic respiration (in mitochondria): pyruvate breaks down using oxygen to give CO₂, water, and a large amount of energy. Most organisms use this route.
• Anaerobic respiration in yeast (in cytoplasm): pyruvate converts to ethanol and CO₂ with a small energy release. This is fermentation.
• Anaerobic respiration in muscle cells (in cytoplasm): when oxygen is in short supply during sudden activity, pyruvate converts to lactic acid, again releasing little energy. The lactic acid build-up causes muscle cramps.

Aerobic releases a lot more energy because glucose is broken down fully; in anaerobic pathways, the products (ethanol, lactic acid) still hold locked-up energy. (NCERT, pp. 87–88)

The two gases travel in the blood by different routes because their solubility in water differs. Oxygen has very low solubility, so it cannot ride dissolved in plasma.

Instead, the respiratory pigment haemoglobin in the red blood corpuscles has a high affinity for oxygen; it binds O₂ in the lungs and releases it in the tissues that are deficient in oxygen (NCERT, p. 90).

Carbon dioxide is more soluble in water than oxygen is, so it is mostly transported dissolved in blood plasma. Some CO₂ is also carried by haemoglobin, but the dominant mode is the dissolved form. So oxygen is carried inside red blood cells by a pigment; carbon dioxide is carried in the fluid medium itself.

Exchange of gases requires a large, thin, moist surface supplied with blood. The lung delivers this by ending its branching tubes in millions of balloon-like alveoli (NCERT, p. 90).

Each alveolus has thin walls and is wrapped in an extensive network of blood vessels, so air inside the sac sits separated from blood by only a very thin barrier that gases diffuse across easily.

The collective surface area of all alveoli, if spread out, is about 80 square metres — a huge exchange surface packed into the chest cavity. The design also keeps a residual volume of air in the lungs between breaths, so gas exchange continues even during exhalation; fresh incoming air mixes with this residual air rather than meeting an empty lung. (NCERT, p. 90)

The human transport system has three components, and each has a distinct job.

• Heart: a muscular pumping organ that pushes blood around the body — the left side pumps oxygenated blood to the body, the right side pumps deoxygenated blood to the lungs.
• Blood: a fluid connective tissue that actually carries materials — red blood corpuscles carry oxygen using haemoglobin, plasma transports food, CO₂, and nitrogenous wastes in dissolved form, white blood cells defend against infection, and platelets help blood clot at injury points.
• Blood vessels: the network of tubes that reaches every tissue — arteries carry blood away from the heart and have thick elastic walls to withstand high pressure; veins collect blood back to the heart and have valves to prevent backflow; capillaries are one-cell thick and are where actual exchange of food, oxygen, and waste between blood and cells occurs.

Together they do one job: move food, oxygen, and waste to and from every cell. (NCERT, pp. 91–93)

Mammals and birds are warm-blooded: they use energy continuously to maintain a constant body temperature regardless of the environment. That constant energy demand requires a high and steady supply of oxygen to their cells.

If oxygenated and deoxygenated blood were allowed to mix, the blood reaching the body would be a diluted mixture with less oxygen per unit blood — far too little to support the energy output warm-blooded animals need.

Keeping the two blood streams fully separated ensures the body always receives pure oxygen-rich blood pumped at full pressure. This is why birds and mammals have a four-chambered heart. By contrast, amphibians and many reptiles — which do not maintain a constant body temperature and tolerate some mixing — can survive with three-chambered hearts because their energy needs are lower. (NCERT, p. 92)

Highly organised plants have conducting tubes composed of two vascular tissues: xylem and phloem. These two pathways run as independently organised conducting tubes throughout the plant body — xylem moves water and minerals, and phloem moves the products of photosynthesis.

Xylem vessels and tracheids in the roots, stem, and leaves interconnect to form a continuous water-conducting channel reaching all parts of the plant. Phloem’s sieve tubes, with adjacent companion cells, translocate sucrose and other substances from the leaves where they are made to the rest of the plant. Both tissues are part of the vascular tissue system. (NCERT, p. 94)

Water does not climb a tree by magic. Soil-rooted plants use two forces together to move water and dissolved minerals up the xylem.

First, root pressure: root cells in contact with the soil actively take up ions, creating a concentration difference that draws water into the root xylem. This steadily pushes a column of water upward.

Second, transpiration pull: water evaporates from the stomata in the leaf surfaces, and this loss creates a suction (negative pressure) that pulls more water up the xylem from the roots — the narrow xylem tubes hold a continuous water column that is pulled up like water through a straw.

The textbook says transpiration pull is the major driving force during the day when stomata are open, while root pressure dominates at night. (NCERT, pp. 94–95)

Food transport in plants is called translocation, and it happens in the phloem. Unlike xylem, phloem moves material both upward and downward based on the plant’s needs — to storage organs (roots, fruits, seeds) or to growing buds.

The mechanism uses energy from ATP. Sucrose is loaded into the phloem tissue using ATP; this raises the solute concentration (osmotic pressure) of the phloem, so water from the surrounding xylem moves into it by osmosis.

That incoming water raises the pressure inside the phloem at the source, pushing the sap toward a sink — a region of lower pressure such as a growing root, fruit, or bud. At the sink, sucrose is unloaded and used or stored, water leaves the phloem, pressure drops, and the cycle continues.

Because it depends on the plant’s growth and storage needs, translocation is bidirectional. (NCERT, p. 95)

A nephron works like a two-step filter. First it dumps everything small enough through the capillary wall into Bowman’s capsule; then it reclaims the useful molecules as the filtrate flows along the tubule, leaving only the waste behind as urine.

Structure: each nephron begins with a cup-shaped Bowman’s capsule that wraps around a cluster of very thin-walled capillaries (the glomerulus). A long, coiled tubule runs from the capsule, eventually joining a collecting duct that drains into the ureter. (NCERT, p. 96) Functioning:

• Filtration: blood pressure forces water and small dissolved molecules out of the capillary cluster into Bowman’s capsule — this creates a large initial filtrate.
• Selective reabsorption: as the filtrate passes along the tubule, the useful substances — glucose, amino acids, salts, and most of the water — are reabsorbed into the blood vessels around the tubule.
• Remaining waste: the fluid that is left is urine, which passes through the collecting duct into the ureter, then to the urinary bladder for storage and release.

So a kidney “filters” in two stages — dump everything small, then reclaim what is useful. (NCERT, p. 96)

Plants do not have a dedicated excretory organ, so they get rid of waste in four different low-energy ways. Because a lot of plant tissue is dead anyway, they can simply store waste where it will cause no harm, or shed it.

• Many plant waste products are stored in cellular vacuoles, isolating them from the cytoplasm.
• Some waste products are stored as resins and gums, especially in old xylem tissue that is no longer living and active.
• Some waste is moved into leaves that are about to fall off — the shedding of leaves carries the waste out of the plant.
• Some waste substances are excreted into the surrounding soil directly through the roots.

Oxygen produced during photosynthesis can itself be thought of as a waste product the plant gets rid of through its stomata. Excess water leaves as vapour through transpiration. (NCERT, p. 98)

The amount of urine the body produces is regulated at the second step of nephron function — selective reabsorption of water. After filtration, how much water the tubule reabsorbs depends on two things the body senses at that moment: how much excess water is in the body, and how much dissolved waste has to be got rid of.

The tubule adjusts water reabsorption accordingly.

This is why we produce a small volume of concentrated urine on a hot day when we have little excess water (the body reabsorbs more), and a large volume of dilute urine after drinking plenty of water (the body reabsorbs less).

The chapter quantifies the scale: of about 180 L of initial filtrate produced daily in a healthy adult kidney, only 1–2 L are actually excreted — the rest is reabsorbed. The regulation happens at the reabsorption step, not at filtration. (NCERT, p. 96)

Correct answer: (c) excretion. Kidneys filter nitrogenous waste products such as urea and uric acid out of the blood and excrete them as urine — that is an excretory function.

Why each distractor fails:

• (a) Nutrition refers to the intake and use of food by an organism; kidneys do not take in or digest food.
• (b) Respiration is about acquiring oxygen and breaking down food for energy, which happens in the lungs and mitochondria — not the kidneys.
• (d) Transportation itself moves food, oxygen, and waste around the body via the heart and blood vessels — kidneys filter waste, but they are not a transport organ.

So the choice that matches the kidney’s job is excretion — option (c). The common slip: students say kidneys are part of the excretory system but forget that the nephron performs selective reabsorption, not just filtration, which is what makes it a true excretory unit rather than a one-way filter.

Correct answer: (a) transport of water. Xylem vessels and tracheids form a continuous water-conducting channel that moves water and dissolved minerals from the roots up to the leaves.

Why each distractor fails:

• (b) transport of food is the job of phloem, which translocates sucrose and other photosynthetic products from leaves to the rest of the plant.
• (c) transport of amino acids also happens in phloem — translocation moves both sugars and amino acids, not xylem.
• (d) transport of oxygen in plants happens by simple diffusion through stomata and intercellular spaces; plants do not have a dedicated vascular tissue for gases.

So xylem = water + minerals = option (a).

Correct answer: (d) all of the above. Autotrophic nutrition is photosynthesis — the process by which green plants and some bacteria build their own food. Photosynthesis needs all three inputs the chapter lists in its equation: CO₂ (from air), water (from soil), sunlight (the external energy source), and chlorophyll (the pigment that captures light).

Why each distractor fails:

• (a) CO2 and water alone are not enough — without sunlight to supply energy and chlorophyll to trap it, the reaction cannot proceed.
• (b) Chlorophyll alone is not enough — without the reactants (CO₂ and water) and energy (sunlight), there is nothing to capture or to build with.
• (c) Sunlight alone is not enough — without CO₂, water, and chlorophyll, the light has nothing to drive.

Only (d) all of the above covers the full set, which is exactly what the photosynthesis equation requires.

Correct answer: (b) mitochondria. When oxygen is available, pyruvate (the three-carbon molecule formed from glucose in the cytoplasm) enters the mitochondria and is broken down completely to CO₂, water, and a large amount of energy. This is aerobic respiration.

Why each distractor fails:

• (a) cytoplasm is where glucose first splits into two pyruvate molecules, and also where the two anaerobic pathways take place — but not the aerobic breakdown of pyruvate itself. The cytoplasm finishes a step before the question’s step.
• (c) chloroplast is the site of photosynthesis in plants, not respiration — the two processes run in opposite directions and in different organelles.
• (d) nucleus controls the cell but is not a site of respiration; no energy-releasing breakdown happens here.

So pyruvate → CO₂ + water + energy takes place in mitochondria — option (b).

Fats do not dissolve in water, so enzymes cannot reach inside a fat globule. Bile salts first emulsify the globule into tiny droplets — like soap breaking up grease — vastly increasing the surface area for lipase to attack. Lipase then breaks the fats down into fatty acids and glycerol. The process is two-stage: emulsification first, enzyme action second.

Both stages happen in the small intestine. Bile juice from the liver emulsifies the large fat globules (and also makes the food alkaline so pancreatic enzymes can work). The pancreas secretes lipase, which breaks the emulsified fats into fatty acids and glycerol. The small intestine walls then absorb these small molecules through villi.

So the whole fat-digestion sequence — emulsification followed by lipase action — takes place in the small intestine. (NCERT, p. 85)

Saliva, secreted by the salivary glands, does two jobs at once. First, it contains the enzyme salivary amylase, which begins the breakdown of starch — a complex carbohydrate — into simple sugar while food is still in the mouth. This is the first enzymatic digestion in the alimentary canal.

Second, saliva moistens the food and makes it soft enough to pass smoothly along the digestive tube.

The muscular tongue mixes food with saliva, and peristaltic movements push the softened bolus down the oesophagus. Activity 5.3 in the textbook tests this directly: saliva added to a starch solution stops the iodine turning blue-black, showing the starch has been broken down. So saliva has both a mechanical role (lubrication and softening) and a chemical role (initial starch digestion).

(NCERT, p. 85)

Autotrophic nutrition is photosynthesis, and it requires four conditions from the photosynthesis equation on page 81: carbon dioxide (taken from the air through stomata), water (absorbed by roots from soil), sunlight (the external energy source), and chlorophyll (the pigment in leaf chloroplasts that captures light energy).

Soil nitrogen is also needed, absorbed as nitrates or nitrites, to build the chlorophyll molecule itself.

The by-products — meaning what the reaction produces alongside glucose — are oxygen and water (six molecules of each for every one glucose molecule formed). The oxygen is released into the air through stomata; indeed, the chapter notes that oxygen release is the major daytime event in plants.

So autotrophic nutrition needs CO₂, water, sunlight, and chlorophyll; and it yields glucose (food), oxygen, and water. (NCERT, p. 81)

Aerobic and anaerobic respiration differ on the four dimensions the chapter names — where in the cell each happens, whether oxygen is needed, what the end-products are, and how much energy is released. The table below compares them. All of them start from the same molecule — glucose is first split into pyruvate in the cytoplasm in both cases.

Organisms that use the anaerobic mode include yeast (fungi, which ferment sugar to ethanol and CO₂) and our own muscle cells during sudden activity when oxygen runs short (producing lactic acid). Some bacteria are also obligate anaerobes. (NCERT, p. 87)

Gas exchange by diffusion depends on surface area and on the thinness of the barrier between air and blood. The lung maximises both by ending its branching air passages in millions of balloon-like alveoli.

Each alveolus has thin walls and is wrapped in a dense network of blood vessels, so oxygen in the air and CO₂ in the blood cross only a very thin barrier.

If the alveolar surface were spread out flat, it would cover about 80 square metres — a huge area packed into the chest (NCERT, p. 90). Each alveolus sits at the end of a tiny tube, and the whole network is supplied with blood constantly.

The lungs also retain a residual volume of air between breaths, so the exchange surface never dries out or runs out of air — incoming fresh air always mixes with this residual air, keeping the oxygen concentration at the surface stable.

Together, these three design features — thin walls, extensive blood supply, and enormous surface area held in a protected space — make alveolar exchange highly efficient.

Haemoglobin is the respiratory pigment in red blood corpuscles, and it has a very high affinity for oxygen. It carries oxygen from the lungs to every tissue where energy is released. If haemoglobin is deficient, the amount of oxygen delivered to tissues drops sharply — so the cells cannot release enough energy to meet the body’s needs.

The chapter notes that if diffusion alone moved oxygen in our body, a molecule would take about three years to reach our toes from the lungs (NCERT, p. 90) — haemoglobin is what prevents that. The clinical consequences are the ones common in anaemia: fatigue, tiredness, pale skin, shortness of breath, and reduced capacity for physical activity.

The body tries to compensate by increasing the breathing and heart rate, but the underlying oxygen starvation remains. So haemoglobin deficiency means the body cannot transport enough oxygen — even though the lungs are breathing in plenty — because there is not enough pigment to carry it.

In human beings, blood passes through the heart twice during one complete cycle of passage through the body — once on its way to the lungs and once on its way to the rest of the body. This is double circulation, and it has two sequential loops.

• Pulmonary loop: deoxygenated blood from the body enters the right atrium, flows into the right ventricle, and is pumped to the lungs. In the lungs it picks up oxygen and drops off CO₂. Oxygen-rich blood returns from the lungs to the left atrium.
• Systemic loop: oxygenated blood from the left atrium enters the thick muscular left ventricle, which pumps it out to the rest of the body. Cells take up the oxygen and release CO₂, and the deoxygenated blood returns to the right atrium to begin the cycle again.

This separation is necessary in warm-blooded mammals and birds because they maintain a constant body temperature. Energy must be supplied at a continuous and high rate, which requires blood to reach the body fully oxygenated and at full pressure.

If oxygenated and deoxygenated blood mixed — as they do in amphibians and reptiles, which tolerate the mixing because they do not keep a constant body temperature — the oxygen delivered to cells would be insufficient for mammals’ high energy needs. (NCERT, p. 92)

Xylem and phloem are the two conducting tissues of plants, but they transport different things in different ways. Xylem moves water and minerals upward by physical forces; phloem moves food in both directions using energy from ATP. The table below compares the two on the four dimensions that matter.

So xylem is a one-way upward water channel driven by physical forces; phloem is a two-way food channel driven by energy. (NCERT, pp. 94–95)

Both alveoli and nephrons are tiny, highly-branching functional units that exchange materials between blood and the outside world across a thin, blood-rich surface. But they work quite differently: alveoli exchange gases by diffusion, while nephrons filter blood and then selectively reabsorb useful molecules before waste leaves as urine. The table below compares them on structure and function.

So alveoli specialise in gas exchange by diffusion, while nephrons specialise in waste removal by filtration plus selective reabsorption. Both are small, thin-walled and richly supplied with blood vessels — that shared design maximises exchange — but the mechanisms they use are very different. (NCERT, pp. 90–96)