Life Processes Class 10 Science — Revision Notes

TL;DR: This chapter covers the fundamental processes that maintain life in organisms including nutrition, respiration, and circulation. Students learn how or…

This chapter covers the fundamental processes that maintain life in organisms including nutrition, respiration, and circulation. Students learn how organis

Nutrition

• Autotrophic nutrition: organisms synthesize own food (plants use photosynthesis)
• Heterotrophic nutrition: organisms consume other organisms for food
• Photosynthesis: 6CO2 + 6H2O + light = C6H12O6 + 6O2
• Chlorophyll in chloroplasts absorbs light energy in leaves

Respiration

• Aerobic respiration: C6H12O6 + 6O2 = 6CO2 + 6H2O + energy (38 ATP)
• Occurs in mitochondria releasing large amounts of energy
• Anaerobic respiration: occurs without oxygen in muscles during exercise
• Lactic acid fermentation produces lactate causing muscle fatigue

Circulation

• Heart pumps blood through arteries to body and veins back to heart
• Pulmonary circulation: heart to lungs and back
• Systemic circulation: heart to body and back
• Blood pressure varies: systolic during heart contraction, diastolic during relaxation

Excretion

• Kidneys filter blood to remove nitrogenous wastes forming urine
• Urine stored in bladder and eliminated through urethra
• Lungs excrete carbon dioxide during respiration
• Skin excretes sweat containing water and salts

Key Terms

• Photosynthesis: Process where plants convert light energy into chemical energy in glucose
• ATP: Adenosine triphosphate - energy currency of cells
• Mitochondria: Powerhouse of cell where aerobic respiration occurs

What counts as a life process, and why there are four

The processes that together perform maintenance of the body are called life processes. The chapter takes four of them: nutrition, respiration, transportation and excretion. Each answers one question about keeping a body running — where the raw material comes from, how energy is released from it, how it is moved to where it is needed, and how the waste is removed.

The order is not arbitrary. Food taken in during nutrition is broken down in respiration to release energy; both the food and the oxygen have to be carried to every cell by transportation; and the by-products of those reactions must be removed by excretion. Losing that thread is why the chapter feels like a list of diagrams to memorise when it is really one continuous argument.

A point worth noticing early: multicellular organisms need transport systems precisely because they are large. In a single-celled organism the whole body surface is in contact with the environment, so diffusion is enough. Once the body is many cells thick, the cells in the interior cannot exchange material with the outside directly, and specialised tissues become necessary.

Why the human heart has four chambers

The heart is a muscular organ divided into four chambers: the right atrium, right ventricle, left atrium and left ventricle. Oxygenated blood arrives from the lungs at the left atrium, passes to the left ventricle and is pumped out to the body. Deoxygenated blood returns to the right atrium, passes to the right ventricle and is pumped to the lungs.

The point of the division is to keep the two streams separate. Mixing oxygenated and deoxygenated blood would lower the efficiency of oxygen supply, and birds and mammals need a high and steady supply because they use energy to maintain their body temperature. Animals that do not maintain a constant body temperature can tolerate some mixing.

Two structural details follow from function, and both are examined. The ventricles have thicker muscular walls than the atria because they must pump blood out of the heart rather than merely receive it, and the left ventricle is the thickest of all because it pumps blood to the entire body while the right ventricle sends it only as far as the lungs. Valves between the chambers, and at the exits, ensure the blood flows in one direction only.

Because blood passes through the heart twice in one complete cycle of the body — once on the way to the lungs and once on the way to the rest of the body — this arrangement is called double circulation.

Nutrition — autotrophic and heterotrophic

Photosynthesis is the process by which autotrophs take in substances from outside and convert them into stored forms of energy.

• The events of photosynthesis are: absorption of light energy by chlorophyll; conversion of light energy into chemical energy together with the splitting of water molecules into hydrogen and oxygen; and the reduction of carbon dioxide to carbohydrates.
• These steps need not take place one immediately after the other, and in some plants the carbon dioxide is taken up at night and used during the day.
• Carbon dioxide enters through stomata, which also lose large amounts of water as vapour. The pore is bounded by two guard cells: when water flows into them they swell, the curved shape opens the pore, and when they shrink the pore closes.
• Heterotrophic nutrition takes three named forms. Saprophytic organisms such as bread mould, yeast and mushrooms break down food outside the body and then absorb it. Parasites such as cuscuta, ticks, lice, leeches and tapeworms derive nutrition from a living host without killing it immediately.
• Holozoic nutrition, seen in Amoeba and in humans, involves taking in whole material and then breaking it down inside the body. Amoeba engulfs food using temporary finger-like extensions called pseudopodia, forming a food vacuole; Paramoecium uses cilia to sweep food to a fixed spot.

The human digestive system, gland by gland

Follow the food along the alimentary canal and pair each region with the secretion that acts there — that pairing is what the marks are for.

• In the mouth, saliva from the salivary glands contains the enzyme salivary amylase, which breaks down starch into sugar. The teeth crush the food and the tongue helps mix it.
• The food is pushed along the oesophagus by rhythmic contractions of the muscular lining called peristaltic movements, which occur throughout the canal.
• In the stomach, gastric glands secrete hydrochloric acid, a protein-digesting enzyme called pepsin, and mucus. The acid creates the acidic medium in which pepsin works and also kills many germs, while the mucus protects the stomach's own lining from that acid. A sphincter muscle regulates the exit of food into the small intestine.
• The small intestine is the longest part of the alimentary canal and is the site of the complete digestion of carbohydrates, proteins and fats.
• It receives bile from the liver, which makes the acidic food alkaline so that pancreatic enzymes can act, and which emulsifies fats — breaking large globules into smaller ones to increase the surface area for enzyme action.
• Pancreatic juice contains trypsin for digesting proteins and lipase for breaking down emulsified fats. The intestinal juice finally converts proteins to amino acids, complex carbohydrates to glucose and fats to fatty acids and glycerol.
• The inner lining of the small intestine has numerous finger-like projections called villi, which greatly increase the surface area for absorption and are richly supplied with blood vessels.
• The unabsorbed food passes into the large intestine, where villi absorb water, and the remaining material is removed through the anus, regulated by the anal sphincter.

Respiration — three pathways from one starting point

All three routes begin identically, which is the fact that makes the comparison table easy to reconstruct rather than memorise.

• Glucose, a six-carbon molecule, is first broken down in the cytoplasm into a three-carbon molecule called pyruvate. This step is common to all organisms.
• In the absence of oxygen, in yeast, pyruvate is converted into ethanol and carbon dioxide with the release of energy. This is fermentation, and it is the basis of brewing and baking.
• In our muscle cells, when oxygen supply is insufficient during sudden vigorous activity, pyruvate is converted into lactic acid. The accumulation of lactic acid causes muscle cramps.
• In the presence of oxygen, in the mitochondria, pyruvate is broken down into carbon dioxide and water, releasing much more energy than either anaerobic route.
• The energy released is used to make ATP, which is the energy currency of the cell; the energy is made available when ATP is broken down.
• Aquatic organisms must breathe faster than terrestrial ones because the amount of dissolved oxygen in water is low compared with the oxygen available in air.
• In humans, air passes through the nostrils, nasal passage, pharynx, larynx and trachea, which is supported by rings of cartilage preventing it from collapsing, then into the bronchi, bronchioles and finally the alveoli.
• The alveoli are balloon-like structures providing a very large surface for gas exchange, and their walls contain an extensive network of blood vessels.
• Oxygen is carried by the respiratory pigment haemoglobin present in red blood cells, while carbon dioxide, being more soluble in water, is mostly transported in the dissolved form in the plasma.

Transportation and excretion

Both systems exist because a large body cannot rely on diffusion alone.

• Arteries carry blood away from the heart, have thick elastic walls because the blood emerges under high pressure, and have no valves. Veins carry blood back to the heart, have thinner walls and possess valves that ensure blood flows only in one direction.
• Capillaries have walls only one cell thick, which is what allows the exchange of materials between the blood and the surrounding cells.
• Platelets circulate in the blood and plug leaks by helping the blood to clot. Lymph is a colourless fluid that carries digested and absorbed fat from the intestine and drains excess fluid from the tissues back into the blood.
• In plants, xylem carries water and minerals from the roots to the leaves. Transpiration — the loss of water vapour from the stomata — creates a suction called transpiration pull, which draws water upward during the day; at night root pressure is the main force.
• Phloem carries the products of photosynthesis from the leaves to other parts, a process called translocation. Unlike transport in xylem, translocation uses energy from ATP, and material can move in either direction as required.
• The human excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. The basic filtration unit in the kidney is the nephron.
• Each nephron has a cluster of very thin-walled blood capillaries called the glomerulus, associated with a cup-shaped end called Bowman's capsule. Filtration occurs here, and as the filtrate flows along the tubule, useful substances such as glucose, amino acids, salts and a major amount of water are selectively reabsorbed.
• When the kidneys fail, the blood can be cleaned artificially by dialysis using an artificial kidney.
• Plants use quite different strategies: oxygen is a waste product of photosynthesis, excess water is removed by transpiration, and other wastes are stored in cellular vacuoles, in leaves that fall off, as resins and gums in old xylem, or are excreted into the surrounding soil.

Worked Examples

• Muscle cramp after running hard — Sudden vigorous activity outruns the oxygen supply to the muscles, so pyruvate is converted to lactic acid instead of being fully oxidised. The accumulated lactic acid causes cramps.
• Bile contains no enzyme yet is essential for fat digestion — Bile makes the acidic food from the stomach alkaline so pancreatic enzymes can act, and it emulsifies fats into small globules, increasing the surface area on which lipase can work.
• Villi increase surface area for absorption — The finger-like projections lining the small intestine multiply the absorptive surface many times over and are richly supplied with blood vessels that carry the absorbed food away.
• The left ventricle has the thickest wall — It pumps blood to the whole body, while the right ventricle sends it only to the lungs. Wall thickness follows directly from the distance the blood must be driven.

Common Mistakes Students Make

• Writing that digestion is completed in the stomach. Only protein digestion begins there; carbohydrates, proteins and fats are all completely digested in the small intestine.
• Saying bile is an enzyme or that it digests fat. Bile contains no digestive enzyme — it neutralises the acid and emulsifies fat so that lipase can act.
• Claiming anaerobic respiration in humans produces alcohol. Yeast produces ethanol and carbon dioxide; human muscle produces lactic acid.
• Forgetting that all three respiratory pathways share the first step. Glucose is broken to pyruvate in the cytoplasm in every case; only what happens to pyruvate differs.
• Stating that arteries always carry oxygenated blood. The pulmonary artery carries deoxygenated blood to the lungs, and the pulmonary vein carries oxygenated blood back — the definition depends on direction relative to the heart, not on oxygen content.
• Saying veins have thick walls to withstand pressure. It is arteries that have thick elastic walls; veins have thinner walls and valves, because blood in them is no longer under high pressure.
• Confusing xylem and phloem. Xylem carries water and minerals upward and does not require energy in the same way; phloem translocates food in either direction using energy from ATP.
• Describing the nephron as merely a filter. Filtration at the glomerulus is followed by selective reabsorption of glucose, amino acids, salts and much of the water as the filtrate moves along the tubule.

Where This Shows Up in Real Life

Dialysis when the kidneys fail

The nephron works by filtering the blood at the glomerulus and then selectively reabsorbing what the body needs. When kidneys stop performing this, nitrogenous wastes accumulate in the blood and become poisonous. An artificial kidney carries out haemodialysis, passing the patient's blood through tubes surrounded by a dialysing fluid that has the same osmotic composition as blood except that it contains no nitrogenous waste, so the waste diffuses out while useful substances are retained. The device is a direct engineering copy of the two-stage principle the nephron uses.

Why athletes feel sore and why we pant after exertion

During sudden vigorous exercise the muscles demand energy faster than oxygen can be delivered, so respiration in the muscle cells becomes anaerobic and lactic acid accumulates, producing cramps. Rapid breathing afterwards supplies the oxygen needed to deal with that accumulation. This is why gradual warming up and controlled pacing are recommended in physical training — they keep the muscles within the aerobic pathway, which also releases far more energy per glucose molecule.

Fermentation in food and industry

The anaerobic pathway in yeast converts pyruvate into ethanol and carbon dioxide, and both products are useful. The carbon dioxide is what makes bread dough rise, leaving the airy texture of a baked loaf, and the ethanol is the basis of brewing. The same anaerobic principle, using different microorganisms, produces curd from milk. A single step of this chapter therefore underlies a large part of traditional food processing.

Why transpiration is not simply wasted water

A plant loses a very large quantity of water as vapour through its stomata, which looks wasteful. But this loss creates the transpiration pull that draws water and dissolved minerals from the roots all the way up to the leaves, in tall trees against gravity and without any pump. Transpiration also helps in the regulation of temperature in the plant. Understanding this explains why plants wilt in strong sun when soil water is short, and why irrigation timing matters in agriculture.

Board-Style Questions with Model Answers

Describe the process of nutrition in Amoeba. (3 marks)

Amoeba shows holozoic nutrition. It has a flexible cell surface and takes in food using temporary finger-like extensions of the cell surface called pseudopodia, which fuse over the food particle and enclose it in a food vacuole. Inside the food vacuole complex substances are broken down into simpler ones by digestive enzymes, and these diffuse into the cytoplasm where they are used for growth, maintenance and multiplication. The remaining undigested material is moved to the surface of the cell and thrown out.

What is the role of hydrochloric acid, pepsin and mucus in the stomach? (3 marks)

Hydrochloric acid creates an acidic medium in the stomach which is necessary for the action of the enzyme pepsin, and it also kills many of the germs that enter with the food. Pepsin is a protein-digesting enzyme, so it begins the digestion of proteins. Mucus protects the inner lining of the stomach from the action of the hydrochloric acid, because under normal conditions the acid would otherwise damage the stomach wall itself.

Compare aerobic and anaerobic respiration, mentioning the site, the products and the energy released. (5 marks)

Both begin in the same way, with glucose, a six-carbon molecule, being broken down in the cytoplasm into a three-carbon molecule called pyruvate. In aerobic respiration the pyruvate is then broken down in the mitochondria in the presence of oxygen into carbon dioxide and water, and a large amount of energy is released. In anaerobic respiration oxygen is absent: in yeast the pyruvate is converted into ethanol and carbon dioxide, which is the process of fermentation, while in our muscle cells during sudden vigorous activity it is converted into lactic acid, whose accumulation causes cramps. Anaerobic respiration releases much less energy than aerobic respiration from the same amount of glucose. In all cases the energy released is used to make ATP, which serves as the energy currency of the cell.

Why is double circulation necessary in human beings? (3 marks)

In double circulation the blood passes through the heart twice in one complete cycle — once when deoxygenated blood is sent from the right side to the lungs and returns oxygenated, and again when it is pumped from the left side to the rest of the body. This is necessary because the separation of the right and left sides of the heart prevents oxygenated and deoxygenated blood from mixing. Such separation allows a highly efficient supply of oxygen to the body, which is essential for birds and mammals because they constantly use energy to maintain their body temperature. Animals that do not maintain a constant body temperature can tolerate some mixing of the two streams.

Draw and describe the structure of a nephron and explain how urine is formed. (5 marks)

The nephron is the basic filtration unit of the kidney. Each nephron begins with a cluster of very thin-walled blood capillaries called the glomerulus, which is enclosed within a cup-shaped structure known as Bowman's capsule; this leads into a long coiled tubule that eventually opens into a collecting duct. Blood enters the glomerulus under pressure, and filtration takes place there so that water and small dissolved substances pass into Bowman's capsule while blood cells and large proteins are retained. As the filtrate flows along the tubule, substances useful to the body such as glucose, amino acids, salts and a major amount of water are selectively reabsorbed into the surrounding blood capillaries. The amount of water reabsorbed depends on how much excess water there is in the body and on how much dissolved waste needs to be excreted. The fluid remaining at the end is urine, which is collected by the collecting duct and carried by the ureter to the urinary bladder for storage until it is released through the urethra.

How are the lungs designed in human beings to maximise the area for exchange of gases? (3 marks)

Within the lungs the passage divides into smaller and smaller tubes, the bronchi branching into bronchioles, which finally terminate in balloon-like structures called alveoli. The alveoli provide a very large surface for the exchange of gases, and if the surface of all the alveoli were spread out it would cover a very large area. The walls of the alveoli contain an extensive network of blood vessels, so that oxygen from the air can diffuse into the blood and carbon dioxide can diffuse out over the shortest possible distance. In addition, when we breathe out the lungs retain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for carbon dioxide to be released.

What are the differences between transport in xylem and in phloem? (3 marks)

Xylem conducts water and dissolved minerals from the roots to the leaves and other parts of the plant, and the movement is essentially upward. The force is provided mainly by transpiration pull, created as water evaporates from the stomata during the day, with root pressure acting mainly at night. Phloem carries the products of photosynthesis from the leaves to other parts of the plant, including storage organs such as roots, fruits and seeds, and the process is called translocation. Translocation requires energy in the form of ATP, and material can be moved in either direction according to the needs of the plant, which is not the case for xylem transport.

Assertion–Reason Questions (CBSE Format)

For each question choose: (a) both A and R are true and R is the correct explanation of A; (b) both are true but R is not the correct explanation; (c) A is true but R is false; (d) A is false but R is true.

Quick Self-Check

Key Terms Glossary

Life processes

The processes that together perform maintenance of the body — nutrition, respiration, transportation and excretion.

Autotrophic nutrition

Nutrition in which the organism makes its own food from simple inorganic substances, as in photosynthesis.

Saprophytic nutrition

Nutrition in which the organism breaks down food material outside the body and then absorbs it, as in bread mould and mushrooms.

Holozoic nutrition

Nutrition in which whole material is taken in and then broken down inside the body, as in Amoeba and humans.

Pseudopodia

Temporary finger-like extensions of the cell surface used by Amoeba to engulf food.

Peristaltic movement

Rhythmic contractions of the muscles of the alimentary canal that push food forward.

Emulsification

The breaking of large fat globules into smaller ones by bile, increasing the surface area for enzyme action.

Villi

Finger-like projections lining the small intestine that greatly increase the surface area for absorption.

Alveoli

Balloon-like structures at the ends of the bronchioles that provide a large surface for gas exchange.

Haemoglobin

The respiratory pigment in red blood cells that has a high affinity for oxygen and transports it around the body.

Double circulation

A circulation in which the blood passes through the heart twice in one complete cycle, keeping oxygenated and deoxygenated blood separate.

Lymph

A colourless fluid that carries digested and absorbed fat from the intestine and drains excess fluid from tissues back into the blood.

Translocation

The transport of the products of photosynthesis in the phloem, which requires energy from ATP and can occur in either direction.

Transpiration pull

The suction created by the evaporation of water from the stomata, which draws water upward through the xylem.

Nephron

The basic filtration unit of the kidney, comprising a glomerulus in Bowman's capsule leading to a tubule.

One-Minute Revision

• Four life processes: nutrition, respiration, transportation, excretion. Multicellular bodies need transport because diffusion alone cannot reach interior cells.
• Photosynthesis: chlorophyll absorbs light, light energy becomes chemical energy and water splits, carbon dioxide is reduced to carbohydrate.
• Guard cells swell to open the stomatal pore and shrink to close it.
• Heterotrophic types: saprophytic (mushroom), parasitic (cuscuta, tapeworm), holozoic (Amoeba, humans).
• Mouth — salivary amylase on starch. Stomach — HCl, pepsin, mucus. Small intestine — bile, pancreatic juice (trypsin, lipase), intestinal juice.
• Bile has no enzyme: it neutralises acid and emulsifies fat.
• Digestion is COMPLETED in the small intestine; villi then absorb.
• Glucose to pyruvate in the cytoplasm — common to all. Then: yeast → ethanol + CO₂; muscle → lactic acid; mitochondria with oxygen → CO₂ + water, far more energy.
• Trachea has cartilage rings so it does not collapse; alveoli give the surface; haemoglobin carries oxygen, CO₂ travels dissolved in plasma.
• Arteries carry blood AWAY from the heart, thick elastic walls, no valves. Veins carry it TO the heart, thin walls, valves. The pulmonary artery is the oxygen exception.
• Left ventricle is thickest — it pumps to the whole body. Blood crosses the heart twice per cycle: double circulation.
• Xylem carries water up by transpiration pull; phloem translocates food both ways using ATP.
• Nephron: filtration at the glomerulus, then selective reabsorption of glucose, amino acids, salts and water. Dialysis replaces it when kidneys fail.
• Plant excretion: oxygen from photosynthesis, water by transpiration, wastes in vacuoles, in shed leaves, as gums and resins, or into the soil.

Syllabus reference: NCERT Class 10 Science — Life Processes. It is the longest chapter in the Biology section and connects to Control and Coordination and to How do Organisms Reproduce.

Frequently Asked Questions

Why do we need respiration?

Respiration breaks down glucose to release energy in the form of ATP which is used for all life processes including movement, growth, and maintenance.

What is the difference between photosynthesis and respiration?

Photosynthesis uses light energy to make glucose, while respiration breaks down glucose to release energy. Photosynthesis occurs in chloroplasts, respiration in mitochondria.

Do all arteries carry oxygenated blood?

No. An artery is defined by direction — it carries blood away from the heart — not by the oxygen content of that blood. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs, and correspondingly the pulmonary vein carries oxygenated blood from the lungs back to the left atrium. These two vessels are the standard exceptions, and questions are often set on them precisely because the general pattern holds everywhere else.

Why does the stomach not digest itself if it contains hydrochloric acid and a protein-digesting enzyme?

Because the gastric glands secrete mucus alongside the acid and the enzyme. The mucus forms a protective layer over the inner lining of the stomach and prevents the hydrochloric acid from acting on the stomach wall, which is itself made of protein and would otherwise be attacked by pepsin. When this protection fails the wall is damaged, which is what happens in acidity and ulcers, so the mucus is not an incidental secretion but an essential one.

Why is more energy released in aerobic than in anaerobic respiration?

Both pathways begin identically, breaking glucose into pyruvate in the cytoplasm, so the difference lies entirely in what happens next. In anaerobic respiration the pyruvate is converted into ethanol or lactic acid, molecules that still contain a considerable amount of chemical energy that is never extracted. In aerobic respiration the pyruvate is broken down completely in the mitochondria into carbon dioxide and water, so far more of the energy stored in the original glucose molecule is released and made available as ATP.

If transpiration loses so much water, why do plants not simply keep their stomata closed?

Because the same pores serve two purposes. Stomata are the route by which carbon dioxide enters the leaf for photosynthesis, so keeping them shut would stop food production. The plant therefore faces a trade-off and regulates the pores through the guard cells, opening them when carbon dioxide is needed and closing them to limit water loss. The water lost is also not entirely wasted, since transpiration generates the pull that lifts water and minerals from the roots and helps regulate the plant's temperature.

More Class 10 Science Revision Notes

• Chemical Reactions and Equations
• Acids Bases and Salts
• Metals and Non-metals
• Carbon and its Compounds
• Control and Coordination
• How do Organisms Reproduce

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• NCERT Solutions →
• MCQ Practice →
• Previous Year Questions →
• State Board Solutions →
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