NCERT Solutions Class 10 Science Chapter 5 Life Processes

The clean way to remember this is the surface-to-volume idea. When an organism gets larger, the number of cells inside (its volume) grows fast, but the outer surface for gases grows much more slowly. So the supply route cannot keep up with demand.

• Diffusion is fast over a few micrometres but extremely slow over centimetres. In an amoeba, oxygen crosses only one cell; in a human, it could never diffuse to a toe cell in time.
• A complex body also has a division of labour, so a working organ needs oxygen on demand, which a passive process cannot deliver.

Answer: Because inner cells are too far from the surface and diffusion over such distances is far too slow, a large body needs an active circulatory system.

Start with the everyday picture the textbook uses. We say a dog is alive because we see it move. But how do we know a plant, or a sleeping animal, is alive when we see no movement? That is the trap here.

• Movement is not always visible. Plants make slow movements and small organisms move in ways we cannot see, so a lack of visible movement does not mean a thing is dead.
• The deeper, surer test is molecular movement, which goes on even at rest and needs energy, which is why the body keeps respiring.

Answer: Something is alive if it shows life processes: some movement (often only molecular), nutrition, respiration, growth, response and reproduction.

Split the use of raw materials into three clear purposes: energy, growth and repair.

• Energy: glucose and oxygen combine in respiration to release the energy that keeps the body in an ordered, living state.
• Growth: raw materials supply the carbon, nitrogen and other blocks needed to make proteins for new cells.
• Repair: cells wear out, and the body constantly replaces them using materials from food.

Because needs differ (a plant takes in carbon dioxide and minerals; an animal takes in complex food), the textbook stresses that the exact raw materials depend on how the organism is built.

Answer: Raw materials are used for three purposes: producing energy by respiration, building new material for growth, and repairing and maintaining the body.

Group the answer around one idea: a body must take in what it needs, use it, move it about and throw out the waste. Each step matches one life process.

• Take in and use: nutrition supplies food and respiration breaks it down for energy.
• Move and remove: transportation carries materials to every cell while excretion clears the harmful by-products.

Some books also count control and coordination and reproduction, but the four named here are the ones this chapter treats as essential for keeping one individual alive day to day.

Answer: Nutrition, respiration, transportation and excretion are the essential life processes; together they supply, use, move and clear materials.

The two words tell you the answer. "Auto" means self, so autotrophs are self-feeders. "Hetero" means other, so heterotrophs feed on food built by others.

• An autotroph like a green plant joins simple molecules (carbon dioxide, water, minerals) into glucose using sunlight trapped by chlorophyll. This is photosynthesis.
• A heterotroph cannot do this, so it takes in complex food already made and breaks it down for energy and materials.

The two are linked: heterotrophs ultimately depend on autotrophs, the original food makers. Compare food source, raw materials, energy source and one example for full marks.

Answer: Autotrophic nutrition makes its own food from simple inorganic materials using sunlight; heterotrophic nutrition depends on ready-made food from other organisms.

Pair every raw material with the exact part of the plant and the place it comes from.

• Carbon dioxide enters from the air through the stomata; oxygen made in photosynthesis diffuses out the same way.
• Water comes from the soil through the roots and root hairs, then travels up the xylem to the leaves.
• Minerals such as nitrogen, magnesium and iron come from the soil through the roots; they make chlorophyll, enzymes and proteins.
• Sunlight provides the energy; chlorophyll absorbs it to convert CO₂ and water into glucose.

Answer: CO₂ from air via stomata; water and minerals from soil via roots; and light energy from the Sun absorbed by chlorophyll.

See stomach acid as the helper that sets up the right conditions for digestion, rather than something that digests food itself.

• Pepsin is inactive unless its surroundings are acidic. HCl turns the contents acidic and switches pepsin on to break proteins.
• Food carries microbes from outside; the strong acid kills most of them, a simple line of defence.
• Cells in the lining secrete a thick mucus that shields the wall; if it breaks down, the acid can cause an ulcer.

Answer: Stomach acid provides the acidic medium pepsin needs to digest proteins and kills germs in food; mucus protects the lining.

Think of each digestive enzyme as a pair of scissors that cuts one kind of food molecule into smaller pieces, very fast.

• Carbohydrates are long sugar chains, proteins are long amino-acid chains, fats are fatty acids and glycerol joined together. None can pass through the gut wall as they are.
• Amylase turns starch into glucose, pepsin and trypsin turn proteins into amino acids, lipase turns fats into fatty acids and glycerol. Each enzyme is specific.

Answer: Digestive enzymes act as biological catalysts that break complex food into simple, soluble forms (sugars, amino acids, fatty acids) that the body can absorb.

The whole design answers one need: to absorb as much digested food as possible. Every feature increases either the surface or the speed of carrying food away.

• Length: the long, coiled tube keeps food in contact with the wall for a long time.
• Surface area: the lining is folded into countless villi, multiplying the absorbing surface far beyond a smooth tube.
• Blood supply: each villus is packed with fine blood vessels, and its thin wall keeps the diffusion distance short.

Answer: Its great length, villi-covered inner wall (huge surface area) and rich blood supply in each villus make the small intestine ideal for absorbing digested food.

The cleanest comparison is the amount of oxygen available, because that decides how easy breathing is.

• Air is rich in oxygen, about one part in five, so a land organism is bathed in oxygen and gets it easily.
• Only a small amount of oxygen dissolves in water, and even less in warm or still water, so an aquatic organism has much less to draw on.

To make up for this, an aquatic organism moves a large volume of water across its gills and breathes faster. The land organism's advantage is simply a richer, more reliable oxygen source.

Answer: A terrestrial organism gets oxygen from air, which is far richer in oxygen than water, so it obtains oxygen more easily and breathes more slowly.

Organise the answer as: one start, three endings.

• The shared start is glucose to pyruvate in the cytoplasm, with no oxygen, in every respiring cell.
• Aerobic: with oxygen, pyruvate breaks completely into CO₂ and water in the mitochondria, releasing a lot of energy.
• Fermentation in yeast: with no oxygen, pyruvate becomes ethanol and CO₂.
• Anaerobic in muscles: in oxygen-starved muscle, pyruvate becomes lactic acid, which makes muscles ache.

Answer: Glucose to pyruvate (cytoplasm) is common; then pyruvate goes to CO₂ + water with oxygen, to ethanol + CO₂ in yeast, or to lactic acid in oxygen-starved muscles.

The interesting point is that the two gases are carried differently, and the reason lies in how well each dissolves in water.

• Oxygen does not dissolve well, so red blood cells are packed with haemoglobin, which binds oxygen tightly in the lungs and unloads it in the tissues.
• Carbon dioxide is much more soluble, so most of it simply dissolves into the plasma and is carried back to the lungs to be breathed out.

Answer: Oxygen is transported by haemoglobin in red blood cells; carbon dioxide, being more soluble, is transported mostly dissolved in the plasma.

Three design features work together for one goal: large surface area, thin walls and a rich blood supply.

• Surface area: the air tubes end in millions of alveoli whose total wall area is enormous.
• Thin walls: each alveolus wall is about one cell thick, so the diffusion distance is tiny.
• Blood supply: each alveolus is wrapped in a dense net of vessels, keeping the concentration difference high.

Answer: Branching air tubes end in millions of thin-walled alveoli that give a huge surface area, and a rich blood supply around them makes the exchange efficient.

Think of the circulatory system as a pump, a fluid and a set of pipes, like a water supply in a building.

• The pump is the heart, made of muscle, which contracts to push blood out and draw it back.
• The fluid is the blood, the actual carrier of oxygen, food, hormones, CO₂ and wastes.
• The pipes are the vessels: thick-walled arteries away from the heart, veins back to it, and thin capillaries where the real exchange happens.

Answer: Heart (muscular pump), blood (fluid carrier) and blood vessels (arteries, veins, capillaries) circulate oxygen, food, carbon dioxide and wastes through the body.

Connect the heart design to the warm-blooded way of life.

• Birds and mammals stay warm and active, so their cells respire fast and need a constant, generous oxygen supply.
• If oxygenated and deoxygenated blood mixed, the body would get only partly oxygenated blood and could not keep up its energy or temperature.

So their hearts have a complete partition: oxygenated blood goes to the body, deoxygenated blood goes to the lungs, and the two never mix.

Answer: Because warm-blooded mammals and birds need a high, steady oxygen supply, keeping oxygenated and deoxygenated blood separate ensures fully oxygen-rich blood always reaches the body.

A complex plant runs two separate pipelines, so name each pipeline and the cargo it carries.

• The xylem is made of hollow tube-like cells from roots to leaves, drawing up water and dissolved minerals, mainly upward.
• The phloem carries the sugar made in the leaves to growing tips, storage organs and roots, and can move in more than one direction.

Answer: The transport system of highly organised plants is the vascular tissue made of xylem (water and minerals) and phloem (food).

Picture a push from the roots combined with a pull from the leaves, both acting on the water in the xylem.

• Root cells actively take in ions, so water flows in by osmosis, building up root pressure that pushes water up, best at night.
• By day, water evaporating from the leaves tugs on the water column (because water molecules stick together), pulling a continuous thread of water up even to the top of a tall tree.

Answer: Roots absorb water and minerals, which rise through the xylem; root pressure pushes water up at night, and transpiration pull draws it up during the day, the main force in tall plants.

Food transport differs from water transport in one big way: it needs energy, so make the active nature clear.

• The plant uses ATP to load sugar into the phloem, which makes the sugar concentration high.
• Water then moves in by osmosis, raising the pressure, which pushes the sugary fluid from high pressure (near leaves) to low pressure (where food is used or stored).

Because the system is driven by energy and pressure, food can travel up to a shoot or down to the roots.

Answer: Food is transported in the phloem by translocation: sugar is loaded using ATP, water enters and raises the pressure, and this pressure drives the food in any direction.

Learn the nephron as a three-stage machine: filter, recover, drain.

• Filtration: blood at high pressure in the glomerulus pushes small molecules (water, glucose, amino acids, salts, urea) into Bowman's capsule; cells and proteins are too big and stay in the blood.
• Selective reabsorption: along the tubule, nearly all glucose, most water, amino acids and useful salts are taken back into the blood.
• Urine formation: what remains (mainly urea, excess salts and water) is urine, draining to the ureter and bladder.

For full marks, draw a labelled nephron and describe these three stages.

Answer: Each nephron filters blood in the glomerulus, recovers useful substances along the tubule by selective reabsorption, and drains the leftover urea, salts and water as urine.

A plant has no single excretory organ, so the answer is a short list with a one-line reason for each method.

• Gases: carbon dioxide and oxygen diffuse out through stomata and root surfaces.
• Storage: many wastes are locked away in the large vacuoles of plant cells.
• Gums and resins: some wastes are deposited in old xylem, like the resin of pine trees.
• Shedding: a plant loses waste when it drops old leaves and bark.
• Into soil: some wastes are released from the roots.

Answer: Plants remove wastes by diffusing out gases, storing wastes in vacuoles or as gum and resin, shedding leaves and bark, and releasing some wastes into the soil.

The kidney does not just remove waste; it manages the body's water, and the urine volume is the result.

• Two factors set the volume: how much water the body has, and how much dissolved waste (mainly urea) must leave dissolved in water.
• Control happens in the tubule: reabsorbing a lot of water gives a small amount of concentrated urine; reabsorbing little water gives a large amount of dilute urine.

This is why you pass less, darker urine on a hot day, when the body holds on to water.

Answer: The kidney regulates urine volume by adjusting how much water it reabsorbs from the filtrate, based on the body's excess water and dissolved waste.

Test each option against what the kidney actually does.

• Nutrition is food intake and digestion, not the kidney, so (a) is out.
• Respiration is the job of lungs and mitochondria, so (b) is out.
• Transportation is the job of the heart, blood and vessels, so (d) is out.

That leaves excretion: the kidney filters blood and removes urea as urine, which is the definition of excretion.

Answer: (c) excretion, because the kidneys remove the nitrogenous waste urea from the blood as urine.

This MCQ tests whether you can sort the plant's two pipelines by what they carry.

• The xylem is the water pipeline: it moves water and dissolved minerals upward, pointing to option (a).
• Transport of food and amino acids (b and c) is the work of the phloem, not the xylem.
• Transport of oxygen (d) does not apply, because plants have no oxygen-carrying tissue.

Remember the rule: xylem equals water and minerals, phloem equals food.

Answer: (a) transport of water, since the xylem carries water and minerals upward while food is carried by the phloem.

Recall the photosynthesis recipe and test each option against it. The word equation is: carbon dioxide plus water, with chlorophyll and sunlight, gives glucose and oxygen.

• Option (a) gives the raw materials, needed but not the whole story.
• Option (b) gives chlorophyll, needed but not enough alone.
• Option (c) gives sunlight, the energy source, again needed but not by itself.

Since each of the first three is required and none is complete alone, the only fully correct choice is all of the above.

Answer: (d) all of the above, because photosynthesis needs carbon dioxide, water, chlorophyll and sunlight together.

Respiration happens in two locations, so place each step where it belongs and read the question carefully.

• Glucose to pyruvate happens in the cytoplasm without oxygen, which makes (a) a tempting distractor, but it is not the step asked about.
• The breakdown of pyruvate to CO₂ and water with energy needs oxygen and happens in the mitochondria, matching (b).
• Chloroplasts (c) make food, and the nucleus (d) does not respire.

Answer: (b) mitochondria, where pyruvate is completely broken down with oxygen into carbon dioxide and water, releasing energy.

Fats need special treatment because they do not dissolve in water.

• In the small intestine, the food contains large fat globules. A big globule has a small surface, so an enzyme alone would work slowly.
• Bile (made by the liver, stored in the gall bladder) is not an enzyme; it emulsifies the globules into tiny droplets, greatly increasing the surface area.
• Lipase then breaks the emulsified fat into fatty acids and glycerol, small enough to be absorbed.

The sequence is: bile emulsifies, then lipase digests, all in the small intestine.

Answer: Bile from the liver emulsifies fats into tiny droplets and lipase then digests them into fatty acids and glycerol, in the small intestine.

Many students think digestion begins in the stomach, but chemical digestion of carbohydrates starts right in the mouth, thanks to saliva.

• The physical role: saliva wets and softens dry food and helps roll it into a soft ball that slides down easily.
• The chemical role: salivary amylase (ptyalin) acts on starch and breaks it into the simpler sugar maltose, finishing part of carbohydrate digestion before the food leaves the mouth.

This is why bread or rice begins to taste sweet if you chew it for a long time.

Answer: Saliva moistens and softens food for easy swallowing and, through salivary amylase, begins digesting starch into sugar in the mouth.

The question has two halves, conditions and by-products, so split the answer cleanly.

• Conditions: the raw materials carbon dioxide (from air) and water (from soil); chlorophyll, which captures light; and sunlight, the energy. If any one is missing, the plant cannot make food.
• By-products: the chief one is oxygen, released through the stomata as water is split; water is also formed in the later reactions.

The useful product made is carbohydrate (glucose), which stores chemical energy.

Answer: Conditions: carbon dioxide, water, chlorophyll and sunlight. By-products: oxygen (released into the air) and water; the food formed is carbohydrate.

Both kinds burn the same fuel, glucose, but by different routes, and the differences flow from one fact: whether oxygen is available.

• Oxygen: aerobic runs with oxygen, anaerobic without it.
• Location: aerobic completes the breakdown in the mitochondria; anaerobic stays in the cytoplasm.
• Products: with oxygen, CO₂ and water; without it, ethanol and CO₂ in yeast, or lactic acid in muscles.
• Energy: aerobic releases much more because glucose is fully broken down.

Anaerobic respiration is used by yeast and by certain bacteria that live where there is no oxygen.

Answer: Aerobic: with oxygen, in mitochondria, gives CO₂ + water, much energy. Anaerobic: without oxygen, in cytoplasm, gives ethanol or lactic acid, little energy. Anaerobic organisms include yeast and some bacteria.

Gas exchange across the alveoli happens by diffusion, so the whole design aims to make diffusion as fast as possible. Three features do this.

• Large surface area: millions of tiny sacs together have a huge wall area, far more than a smooth bag of the same size.
• Thin walls: a one-cell-thick wall keeps the diffusion distance tiny.
• Rich blood supply: fresh blood keeps arriving, keeping the concentration difference high so diffusion stays strong.

Answer: Millions of balloon-like alveoli give a large surface area, their one-cell-thick walls keep the diffusion distance short, and their rich blood supply keeps gas exchange fast.

Follow a chain: less haemoglobin leads to less oxygen, which leads to less energy, which leads to the symptoms.

• Haemoglobin is the oxygen carrier of the blood; the oxygen the blood can carry depends directly on how much haemoglobin it has.
• With less of it, the tissues get less oxygen even if breathing and blood flow are normal.
• Cells then release less energy, so the body tires easily and feels breathless, and the skin looks pale.

This condition is anaemia. Since haemoglobin is built using iron, doctors advise iron-rich foods.

Answer: Too little haemoglobin means the blood carries less oxygen, cells release less energy, and the person becomes weak, tired, breathless and pale, the condition called anaemia.

Follow one drop of blood around its full journey and count how many times it passes through the heart.

• Deoxygenated blood from the body enters the right side; the heart pumps it to the lungs. That is the first pass. In the lungs it takes up oxygen.
• This oxygen-rich blood returns to the left side; the heart pumps it to the whole body. That is the second pass.

So in one round the blood goes through the heart twice. Because the heart is fully divided, the two streams never mix, so the body always gets fully oxygenated blood, which warm-blooded humans need to stay warm and active.

Answer: Blood passes through the heart twice each round, once for the lungs and once for the body. This keeps oxygenated and deoxygenated blood from mixing, giving the body the high, efficient oxygen supply that warm-blooded humans need.

The two transport tissues differ in three clear ways, so set the answer out as three contrasts.

• Cargo: the xylem is the water tissue (water and minerals); the phloem is the food tissue (sugar from the leaves).
• Direction: the xylem flows mainly upward, where water evaporates; the phloem can go in any direction, to tips above and roots below.
• Energy: the xylem is driven by physical forces (root pressure, transpiration pull) with little energy; the phloem actively uses ATP to load food.

Answer: Xylem carries water and minerals upward using mostly physical forces and little energy; phloem carries food in any direction and uses ATP energy to do so.

The neat insight is that the body uses the same design idea for two very different tasks.

• Shared design: both are tiny units built in huge numbers, with very thin walls and a rich net of blood vessels, which lets each organ handle a large amount of material efficiently.
• Structures: an alveolus is a thin balloon-like air sac; a nephron is more elaborate, a Bowman's capsule with a glomerulus leading into a long coiled tubule.
• Jobs: the alveolus exchanges gases (respiration); the nephron filters waste, reabsorbs the useful materials and forms urine (excretion).

Answer: Alveoli and nephrons are both many, thin-walled and richly supplied with blood, making exchange efficient; but alveoli exchange gases for respiration while nephrons filter blood for excretion.