BharatNotes Why this chapter matters for UPSC: This is Chapter 5 of NCERT's Class X Science (Reprint 2026-27). It explains four maintenance processes, nutrition, respiration, transportation and excretion, each worked out for plants and for human beings. Prelims general science draws on these paired comparisons (photosynthesis and digestion, stomata and lungs, xylem and blood vessels), and the chapter is the physiology behind health questions on tobacco, blood pressure, dialysis and organ donation.
Contemporary hook: The sixth National Family Health Survey (NFHS-6), conducted in 2023-24 with the International Institute for Population Sciences and released by the Ministry of Health and Family Welfare on 29 May 2026, found stunting (low height for age) among children under five down from 35.5 % to 29.3 %. The release reads this as an improvement in long-term nutritional outcomes; nutrition is the first life process in this chapter.
🧠 First Principles — Read This First
Living things are ordered, and order keeps breaking down. The environment constantly wears down the organised structure of a living body, so the body must keep repairing itself, moving molecules around even in sleep. That needs energy and raw materials from outside. Taking them in is nutrition; breaking food down to release energy is respiration; moving materials around the body is transportation; removing harmful by-products is excretion.
Size changes everything. A single-celled organism is in contact with its surroundings over its whole surface, so diffusion is enough. In a large body most cells are far from the surface, and diffusion is far too slow: NCERT estimates that it would take three years to move a molecule of oxygen from the lungs to the toes. Large bodies therefore need specialised organs for intake and removal, and a transport system linking them to every cell. Read the whole chapter as the answer to that one problem.
PART 1 — Quick Reference
Table 1: The four life processes
| Process | What it does | In human beings | In plants |
|---|---|---|---|
| Nutrition | Brings in a source of energy and raw material for growth | Digestion along the alimentary canal; absorption in the small intestine | Photosynthesis; water and minerals taken up from the soil by roots |
| Respiration | Breaks food down, using oxygen in most organisms, and stores the energy as ATP | Lungs and alveoli; haemoglobin carries oxygen | Gas exchange through stomata and across the surface of stems, roots and leaves |
| Transportation | Moves food, oxygen and wastes to where they are needed | Heart, blood vessels, blood and lymph | Xylem (water and minerals) and phloem (food) |
| Excretion | Removes harmful metabolic wastes, especially nitrogenous ones | Kidneys, ureters, urinary bladder, urethra | Vacuoles, falling leaves, resins and gums, release into the soil |
Source: NCERT, Science Class X, ch. 5, Reprint 2026-27, section 5.1 and the chapter summary (pp. 79-81, 98-99).
Table 2: Photosynthesis and its raw materials
| Item | NCERT's account |
|---|---|
| Three events | (i) Absorption of light energy by chlorophyll; (ii) conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen; (iii) reduction of carbon dioxide to carbohydrates |
| Timing | The steps "need not take place one after the other immediately": desert plants take up carbon dioxide at night and prepare an intermediate that is acted upon by the energy absorbed during the day |
| Where | Chloroplasts, the green dots seen in leaf cells, contain chlorophyll |
| Storage | Unused carbohydrate is stored as starch; animals store energy as glycogen |
| Carbon dioxide | Taken in through stomata; guard cells swell when water flows into them, opening the pore, and shrink to close it |
| Water | Taken up from the soil by the roots in terrestrial plants |
| Nitrogen | Taken up as inorganic nitrates or nitrites, or as organic compounds prepared by bacteria from atmospheric nitrogen |
| Other minerals | Phosphorus, iron and magnesium from the soil |
Source: NCERT, Science Class X, ch. 5, Reprint 2026-27, section 5.2.1 (pp. 81-84).
Table 3: Digestion in human beings
| Part | What happens there |
|---|---|
| Mouth | Teeth crush the food; saliva from the salivary glands wets it; salivary amylase breaks starch down into simple sugar; the tongue mixes the food |
| Oesophagus | Carries food to the stomach by peristaltic movements, rhythmic contractions of the muscles that line the canal |
| Stomach | Gastric glands release hydrochloric acid, pepsin (a protein-digesting enzyme) and mucus; the acid helps pepsin act, and mucus protects the lining from the acid |
| Sphincter | Releases food from the stomach into the small intestine in small amounts |
| Small intestine | Site of complete digestion of carbohydrates, proteins and fats; bile from the liver makes the food alkaline and its salts break fat into smaller globules; pancreatic juice has trypsin (proteins) and lipase (emulsified fats); intestinal juice, from glands in the walls of the small intestine, finishes the job: proteins to amino acids, complex carbohydrates to glucose, fats to fatty acids and glycerol |
| Villi | Finger-like projections of the small intestine's lining that increase the surface for absorption; richly supplied with blood vessels |
| Large intestine | Its wall absorbs more water; the rest leaves through the anus, regulated by the anal sphincter |
Source: NCERT, Science Class X, ch. 5, Reprint 2026-27, section 5.2.4 (pp. 84-86).
Table 4: Pathways for breaking down glucose
| Step or pathway | Where | Products |
|---|---|---|
| First step, in all cases | Cytoplasm | Glucose (six carbons) → pyruvate (three carbons) |
| Fermentation in yeast (anaerobic) | Cytoplasm | Pyruvate → ethanol + carbon dioxide + energy |
| Lack of oxygen in muscle cells | Muscle cells | Pyruvate → lactic acid (three carbons) + energy |
| Aerobic respiration | Mitochondria | Pyruvate → carbon dioxide + water + energy; "a lot greater" release of energy than the anaerobic process |
Source: NCERT, Science Class X, ch. 5, Reprint 2026-27, section 5.3, Figure 5.8 and the ATP box (pp. 87-88).
Table 5: The heart and the blood vessels
| Item | NCERT's account |
|---|---|
| Heart | A muscular organ "as big as our fist", with chambers that keep oxygen-rich blood from mixing with blood carrying carbon dioxide |
| Left side | Oxygen-rich blood from the lungs enters the left atrium, passes to the left ventricle, and is pumped to the body |
| Right side | De-oxygenated blood from the body enters the right atrium, passes to the right ventricle, and is pumped to the lungs |
| Walls and valves | Ventricles have thicker muscular walls than atria; valves stop blood flowing backwards |
| Four chambers | Birds and mammals, which have high energy needs and constantly use energy to maintain body temperature |
| Three chambers | Amphibians and many reptiles; they tolerate some mixing of oxygenated and de-oxygenated blood |
| Two chambers | Fishes; blood goes through the heart only once in each cycle through the body |
| Arteries | Carry blood away from the heart; thick, elastic walls because the blood is under high pressure |
| Veins | Bring blood back to the heart; thinner walls, with valves for one-way flow |
| Capillaries | The smallest vessels, with walls one cell thick; exchange with the surrounding cells happens here |
| Blood pressure | Normal systolic about 120 mm of Hg and diastolic 80 mm of Hg; measured with a sphygmomanometer |
Source: NCERT, Science Class X, ch. 5, Reprint 2026-27, section 5.4.1 (pp. 91-94).
Table 6: Xylem and phloem
| Xylem | Phloem | |
|---|---|---|
| Carries | Water and minerals from the soil | Products of photosynthesis, plus amino acids and other substances |
| Direction | Upwards, from roots to leaves | Both upwards and downwards, to storage and growing organs |
| Structure | Vessels and tracheids, interconnected from roots to leaves | Sieve tubes, with adjacent companion cells |
| Driving force | Largely simple physical forces: root pressure (more important at night) and transpiration pull (the major force by day) | Energy from ATP loads material such as sucrose, which raises osmotic pressure and draws water in |
Source: NCERT, Science Class X, ch. 5, Reprint 2026-27, section 5.4.2 (pp. 94-96).
Table 7: The kidney and the artificial kidney
| Kidney (nephron) | Artificial kidney (hemodialysis) | |
|---|---|---|
| Filter | A cluster of very thin-walled capillaries with the cup-shaped Bowman's capsule | Tubes with a semi-permeable lining in a tank of dialysing fluid |
| How waste leaves | Filtration into the tubule | Diffusion into a fluid with the same osmotic pressure as blood but no nitrogenous wastes |
| Re-absorption | Glucose, amino acids, salts and a major amount of water are selectively re-absorbed | None |
| Volumes | Initial filtrate about 180 L a day; only "a litre or two" excreted |
Source: NCERT, Science Class X, ch. 5, Reprint 2026-27, section 5.5.1 and the hemodialysis box (pp. 96-97).
Table 8: NCERT lines to read with care
| NCERT says | The record |
|---|---|
| "This build-up of lactic acid in our muscles during sudden activity causes cramps." (Class X, p. 88) | NCERT's Class XI Biology puts it differently: "Repeated activation of the muscles can lead to the accumulation of lactic acid due to anaerobic breakdown of glycogen in them, causing fatigue." Use the Class X line for a Class X question, and know that Class XI ties lactic acid to fatigue. |
| Lymph forms when "some amount of plasma, proteins and blood cells escape into intercellular spaces in the tissues" (Class X, p. 94) | Class XI is more precise: "some water along with many small water soluble substances move out into the spaces between the cells of tissues leaving the larger proteins and most of the formed elements in the blood vessels." Both agree that lymph carries less protein than plasma. |
| Activity 5.7 asks you to find the normal range of haemoglobin, and whether it differs between children, men and women (p. 91) | The Class X chapter gives no figure. Class XI gives one range for "a healthy individual": 12-16 g of haemoglobin per 100 mL of blood. Neither book gives separate figures for men, women or children. |
Source: NCERT, Science Class X, Reprint 2026-27, ch. 5 (pp. 88, 91, 94); NCERT, Biology Class XI, ch. 15 "Body Fluids and Circulation" and ch. 17 "Locomotion and Movement".
PART 2 — Concepts & Narrative
What are life processes? (5.1)
How do we tell living from non-living? Visible movement is not enough, so biologists look for movement at the scale of molecules. "In fact, viruses do not show any molecular movement in them (until they infect some cell), and that is partly why there is a controversy about whether they are truly alive or not."
Life processes: "The processes which together perform this maintenance job are life processes." They run all the time, even when the organism is doing nothing in particular, because the organised structure of a living body keeps breaking down and must be repaired.
Since life on earth depends on carbon-based molecules, most food sources are carbon-based too. Oxidising-reducing reactions, in many organisms using oxygen taken from outside the body, break them down to release energy (respiration); the by-products must be removed (excretion).
Autotrophic nutrition (5.2.1)
Autotrophs, "green plants and some bacteria", use simple inorganic materials, carbon dioxide and water. Heterotrophs, animals and fungi, use complex substances that must first be broken down by enzymes, so they depend directly or indirectly on autotrophs.
Photosynthesis turns carbon dioxide and water into carbohydrates in the presence of sunlight and chlorophyll. Its three events and the desert-plant exception are in Table 2.
Activity 5.1: is chlorophyll essential? A plant with variegated leaves (money plant or crotons) is kept in a dark room for three days so that all its starch is used up, then in sunlight for about six hours. A leaf is traced, dipped in boiling water, heated in alcohol on a water-bath, and tested with dilute iodine. Comparing the stained leaf with the tracing shows that starch has formed only where the leaf was green. Activity 5.2 asks the same about carbon dioxide: two destarched plants under sealed bell-jars, one beside a watch-glass of potassium hydroxide, which absorbs carbon dioxide.
Stomata. Stomata are tiny pores on the surface of leaves through which "massive amounts of gaseous exchange" take place for photosynthesis. Large amounts of water can also be lost through them, so the plant closes them when it does not need carbon dioxide. "The guard cells swell when water flows into them, causing the stomatal pore to open. Similarly the pore closes if the guard cells shrink."
Heterotrophic nutrition (5.2.2-5.2.3)
How an organism feeds depends on its food and how it obtains it. Fungi such as bread moulds, yeast and mushrooms break food down outside the body and then absorb it; other organisms take food in whole. Parasites draw nutrition from plants or animals without killing them: NCERT's examples are cuscuta (amar-bel), ticks, lice, leeches and tape-worms.
In single-celled organisms the whole surface can take in food. Amoeba wraps temporary finger-like extensions of its surface around a food particle, forming a food-vacuole in which the food is broken down; undigested material is thrown out at the surface. Paramoecium has a definite shape and takes in food at a specific spot, to which the cilia covering the cell sweep the food.
Nutrition in human beings (5.2.4)
The alimentary canal is a long tube from the mouth to the anus, with each region specialised (Table 3).
Mouth. In Activity 5.3, 1 mL of 1 % starch solution is left with 1 mL of saliva for 20-30 minutes and compared, using dilute iodine, with a tube without saliva. "The saliva contains an enzyme called salivary amylase that breaks down starch which is a complex molecule to give simple sugar."
Peristalsis: the lining of the alimentary canal "has muscles that contract rhythmically in order to push the food forward". These peristaltic movements occur all along the gut and move food in a regulated way, so each part can process it.
Stomach. Gastric glands in its wall release hydrochloric acid, which creates the acidic medium pepsin needs, along with pepsin and mucus. "The mucus protects the inner lining of the stomach from the action of the acid under normal conditions."
Small intestine. It is the longest part of the canal, packed in by extensive coiling, and its length varies with diet: herbivores eating grass need a longer one to digest cellulose, while meat is easier to digest, "hence carnivores like tigers have a shorter small intestine". Food arrives acidic and is made alkaline by bile juice from the liver, so that the pancreatic enzymes can act.
Emulsification. Fats sit in the intestine as large globules that enzymes struggle to act on. Bile salts break them into smaller globules, "increasing the efficiency of enzyme action", much as soap acts on dirt (Chapter 4). Lipase then digests the emulsified fat, and intestinal juice finally converts fats into fatty acids and glycerol.
Dental caries. Bacteria acting on sugars produce acids that soften or demineralise the enamel. Bacteria and food particles stick to the teeth as dental plaque, which keeps saliva from reaching the tooth surface to neutralise the acid; brushing after eating removes plaque before the bacteria produce acids.
Respiration (5.3)
In Activities 5.4 and 5.5, exhaled air turns lime water milky faster than ordinary air pumped through with a syringe or pichkari, because it carries more carbon dioxide; the gas from yeast fermenting fruit juice or sugar solution turns lime water milky too.
Every pathway begins in the cytoplasm, where glucose (six carbons) is broken down into pyruvate (three carbons) (Table 4). In yeast, without oxygen, pyruvate becomes ethanol and carbon dioxide: anaerobic respiration. In the mitochondria, with oxygen, it becomes carbon dioxide and water: aerobic respiration, which releases far more energy. Muscle cells short of oxygen make lactic acid instead (Table 8 compares how Class X and Class XI describe the effect).
ATP: "the energy currency for most cellular processes". Energy from respiration makes ATP from ADP and inorganic phosphate. Breaking ATP's terminal phosphate linkage with water releases energy "equivalent to 30.5 kJ/mol", which drives endothermic reactions in the cell. NCERT's analogy is a battery: like one battery that can power many devices, ATP powers muscle contraction, protein synthesis and the conduction of nervous impulses.
Gas exchange in plants. Plants exchange gases through stomata, and large inter-cellular spaces keep every cell in contact with air. "At night, when there is no photosynthesis occurring, CO2 elimination is the major exchange activity going on." By day, carbon dioxide from respiration is used in photosynthesis, so oxygen release is the major event.
Breathing in water and on land. "Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms." Fishes force water past the gills, where blood takes up the dissolved oxygen. On land, the breathing surface is large, fine and delicate, so it is placed inside the body, with passages to bring air to it and a mechanism to move air in and out.
The human respiratory system. Air enters through the nostrils, where fine hairs and mucus filter it; rings of cartilage in the throat stop the air-passage from collapsing. In the lungs the passage divides into ever smaller tubes ending in alveoli, whose walls carry an extensive network of blood vessels. Breathing in, we lift the ribs and flatten the diaphragm, enlarging the chest cavity. "During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released."
Why we need haemoglobin. In large animals diffusion alone cannot deliver oxygen everywhere, so a respiratory pigment takes up oxygen in the lungs and releases it in tissues short of oxygen. In human beings it is haemoglobin, "which has a very high affinity for oxygen", carried in the red blood corpuscles. Carbon dioxide "is more soluble in water than oxygen is and hence is mostly transported in the dissolved form in our blood". Spread out, the alveolar surface "would cover about 80 m2".
Tobacco and smoking. NCERT's boxes warn that tobacco in any form harms the tongue, lungs, heart and liver, and that "There is a high incidence of oral cancer in India due to the chewing of tobacco in the form of gutkha." Smoking destroys the cilia of the upper respiratory tract that normally remove germs, dust and other harmful particles, so these reach the lungs and cause infection, cough and even lung cancer.
Transportation in human beings (5.4.1)
Blood is a fluid connective tissue. Its plasma carries food, carbon dioxide and nitrogenous wastes in dissolved form; the red blood corpuscles carry oxygen. The body needs a pump, a network of tubes, and a way to repair leaks.
The pump. Thin-walled atria collect blood; each muscular ventricle pumps it out, the left one to the body and the right one to the lungs (Table 5).
Double circulation: blood "goes through the heart twice during each cycle" in vertebrates other than fishes, once through the right side on the way to the lungs and once through the left side on the way to the body. In fishes, with a two-chambered heart, blood is pumped to the gills, oxygenated there, and passes directly to the rest of the body, going "only once through the heart" in each cycle.
Separating the two sides "allows a highly efficient supply of oxygen to the body", which birds and mammals need because they constantly use energy to maintain body temperature. Amphibians and many reptiles, whose body temperature depends on the environment, manage with three chambers and some mixing.
Blood pressure. "The force that blood exerts against the wall of a vessel is called blood pressure." It is much greater in arteries than in veins. Systolic pressure is the pressure in an artery during ventricular contraction; diastolic pressure is the pressure during ventricular relaxation. Hypertension (high blood pressure) "is caused by the constriction of arterioles, which results in increased resistance to blood flow. It can lead to the rupture of an artery and internal bleeding."
The tubes. Arteries branch into ever smaller vessels down to the capillaries, whose walls are one cell thick; materials are exchanged across those walls, and capillaries join again to form veins. Repairs: a leak would lose blood and pressure, so platelets plug it by helping blood clot at the point of injury.
Lymph (tissue fluid): fluid that escapes through pores in the capillary walls into the spaces between cells. It is "similar to the plasma of blood but colourless and contains less protein". It drains into lymphatic capillaries, which join into large lymph vessels opening into larger veins. "Lymph carries digested and absorbed fat from intestine and drains excess fluid from extra cellular space back into the blood."
Transportation in plants (5.4.2)
In tall plants, diffusion cannot move raw materials between the roots and the leaves, so a transport system is needed. Plants, though, have low energy needs: they do not move, and many of their tissues are made of dead cells. So relatively slow transport systems are enough, even in tall trees.
Water. The xylem's vessels and tracheids form a continuous system of channels through roots, stems and leaves. Root cells in contact with the soil actively take up ions, which creates a difference in ion concentration between root and soil; water moves into the root to remove it, steadily pushing a column of water up the xylem. That push alone is unlikely to lift water to the tops of tall plants.
Transpiration: "The loss of water in the form of vapour from the aerial parts of the plant". Evaporation from leaf cells "creates a suction which pulls water from the xylem cells of roots". It helps absorb and lift water and dissolved minerals, and helps regulate temperature. In Activity 5.8, a plastic sheet over a potted plant in bright sunlight collects water droplets, unlike a sheet over a stick of the same height.
"The effect of root pressure in transport of water is more important at night. During the day when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem."
Food. Translocation, the transport of soluble products of photosynthesis, takes place in the sieve tubes of the phloem with the help of adjacent companion cells, upwards and downwards, and carries amino acids and other substances too (Table 6).
Why phloem needs energy. Xylem transport "can be largely explained by simple physical forces", but translocation in phloem uses energy. Sucrose is moved into phloem tissue using energy from ATP, which raises the osmotic pressure; water moves in, and the pressure pushes material to tissues with less pressure. So the plant can send food where it is needed: in spring, sugar stored in root or stem tissue moves to the buds, which need energy to grow.
Excretion (5.5)
Metabolism produces nitrogenous wastes that must be removed. Many unicellular organisms lose them by simple diffusion into the surrounding water; complex multi-cellular organisms use specialised organs.
Excretion in human beings (5.5.1). The system has a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. As carbon dioxide leaves the blood in the lungs, nitrogenous wastes such as urea or uric acid leave it in the kidneys, and the filtering unit is again a cluster of very thin-walled capillaries.
Nephron: the filtration unit of the kidney. Each capillary cluster is associated with the cup-shaped end of a coiled tube, Bowman's capsule, which collects the filtrate. Each kidney has large numbers of nephrons packed close together. As the filtrate flows along the tube, glucose, amino acids, salts and a major amount of water are selectively re-absorbed.
How much water is re-absorbed depends on the body's excess water and on how much dissolved waste must be excreted. Urine collects in the muscular bladder, which is under nervous control.
Artificial kidney (hemodialysis). When infection, injury or restricted blood flow reduces kidney function, poisonous wastes accumulate, which can be fatal. In an artificial kidney, blood passes through tubes with a semi-permeable lining in a tank of dialysing fluid that has "the same osmotic pressure as blood, except that it is devoid of nitrogenous wastes"; wastes diffuse out and the purified blood is pumped back. Unlike the kidney, "there is no re-absorption involved"; a healthy kidney re-absorbs most of about 180 L of filtrate a day.
Excretion in plants (5.5.2). Plants use completely different strategies. "Oxygen itself can be thought of as a waste product generated during photosynthesis!" Excess water leaves by transpiration. Other wastes are stored in cellular vacuoles, in leaves that fall off, or as resins and gums, especially in old xylem; some are excreted into the soil.
Organ donation. NCERT's "Think it over!" box calls it "a generous act of donating an organ to a person who suffers from non-function of organ(s)", made with the consent of the donor and the family and open to anyone regardless of age or gender. Most donations happen just after death or when a doctor declares a person brain dead, but a kidney, part of a liver, lung and some tissues can be donated by a living donor.
Did the 2020-21 edition differ?
No. In the 2020-21 edition this was Chapter 6 (pp. 93-113); in Reprint 2026-27 it is Chapter 5 (pp. 79-99). Its sections, boxes, activities and exercises read the same; only the chapter's place in the book has changed.
Source: NCERT, Science Class X, 2020-21 edition (whole-book zip, Wayback Machine capture of 9 October 2021), compared with Reprint 2026-27.
Beyond the textbook: what Class XI biology adds
NCERT's Class XI Biology adds the numbers that Class X leaves out.
Blood. Red blood cells are "the most abundant of all the cells in blood": "A healthy adult man has, on an average, 5 millions to 5.5 millions of RBCs mm–3 of blood." They are formed in the red bone marrow in adults, are "devoid of nucleus in most of the mammals" and are biconcave. "A healthy individual has 12-16 gms of haemoglobin in every 100 ml of blood." RBCs live about 120 days and are then destroyed in the spleen, the "graveyard of RBCs". Lymph carries lymphocytes, which are responsible for immune responses, and "Fats are absorbed through lymph in the lacteals present in the intestinal villi."
Energy. Class XI works out a "net gain of 38 ATP molecules during aerobic respiration of one molecule of glucose", but calls the calculation a theoretical exercise, because its assumptions "are not really valid in a living system". Fermentation gives "a net gain of only two molecules of ATP" per glucose. The gap is the number behind Class X's line that aerobic respiration releases far more energy.
Kidneys. "Nearly 99 per cent reabsorption of the filtrate takes place through different parts of the nephrons." The distal tubule and collecting duct "concentrate the filtrate about four times, i.e., from 300 mOsmolL–1 to 1200 mOsmolL–1, an excellent mechanism of conservation of water". This is Class X's 180 L of filtrate and a litre or two of urine, explained.
Source: NCERT, Biology, Class XI, ch. 12 "Respiration in Plants", ch. 15 "Body Fluids and Circulation" (sections on blood and lymph), ch. 16 "Excretory Products and their Elimination".
PART 3 — UPSC Integration
Cross-paper relevance
- Prelims (general science) — photosynthesis and stomata, digestive enzymes, anaerobic pathways, ATP, alveoli, haemoglobin, heart chambers and double circulation, blood pressure, lymph, xylem and phloem, the nephron and dialysis.
- GS3 (Science and technology) — fermentation by yeast, the biological basis of ethanol as a fuel (Chapter 4's "Alcohol as a fuel"); the artificial kidney as a device that copies filtration but not re-absorption.
- GS2 (Health) — undernutrition and stunting (NFHS-6); haemoglobin and oxygen delivery; tobacco and oral cancer; hypertension; dialysis; organ donation and consent.
Past questions on these themes: Mains 2023 GS3 asked candidates to "Discuss the role of micro-organisms in addressing current fuel shortages"; yeast fermentation, which turns sugar into ethanol and carbon dioxide, is the starting point in this chapter.
Frames for Mains Answers
1. Why large bodies need organs. Start from the diffusion limit (three years from lungs to toes), then the design answer: large, delicate exchange surfaces inside the body (alveoli, villi, nephrons), a pump and tubes to every cell, and a system for wastes.
2. Energy needs shape the heart. Four chambers and double circulation in birds and mammals; three chambers and some mixing in amphibians and many reptiles; a single circuit in fishes. Plants, with low energy needs, manage with slow transport.
3. The kidney as a re-absorption machine. About 180 L of filtrate a day, a litre or two of urine. Dialysis filters but does not re-absorb. Close with NCERT's case for organ donation.
4. Micro-organisms and fuel. Without oxygen, yeast turns sugar into ethanol and carbon dioxide; Chapter 4 adds that ethanol from sugarcane molasses gives only carbon dioxide and water on burning in sufficient air. Date and source any blending figure you add.
Exam Strategy
Prelims fact-traps:
- Autotrophs: green plants and some bacteria. Heterotrophs: animals and fungi. Plants store starch; animals store glycogen.
- Desert plants take in carbon dioxide at night.
- Guard cells swell to open the stomata and shrink to close them.
- Bile is not an enzyme: it makes food alkaline and emulsifies fats. Trypsin digests proteins; lipase digests fats.
- Glucose → pyruvate in the cytoplasm; aerobic breakdown in the mitochondria. Yeast makes ethanol + CO₂; oxygen-starved muscle makes lactic acid.
- Oxygen travels on haemoglobin; carbon dioxide travels mostly dissolved in blood.
- Aquatic animals breathe faster because dissolved oxygen is low.
- Four chambers: birds and mammals. Three: amphibians and many reptiles. Two: fishes (single circulation).
- Normal blood pressure about 120/80 mm of Hg; hypertension from constricted arterioles.
- Lymph is colourless, has less protein than plasma, and carries absorbed fat.
- Root pressure matters more at night, transpiration pull by day; phloem uses ATP.
- About 180 L of filtrate a day, a litre or two of urine; dialysis has no re-absorption.
Mains: Use the chapter's design logic (surface area, a pump, a transport network, re-absorption) as the explanation layer for health questions. Add dated figures only from a named source.
Practice Questions
Questions 1-4 are the NCERT exercise MCQs. Practice (UPSC-pattern, not past papers): questions 5-10.
1. The kidneys in human beings are a part of the system for
(a) nutrition.
(b) respiration.
(c) excretion.
(d) transportation.
Answer: (c) (NCERT Answers, p. 218).
2. The xylem in plants are responsible for
(a) transport of water.
(b) transport of food.
(c) transport of amino acids.
(d) transport of oxygen.
Answer: (a). Food and amino acids move in the phloem (NCERT Answers, p. 218).
3. The autotrophic mode of nutrition requires
(a) carbon dioxide and water.
(b) chlorophyll.
(c) sunlight.
(d) all of the above.
Answer: (d) (NCERT Answers, p. 218).
4. The breakdown of pyruvate to give carbon dioxide, water and energy takes place in
(a) cytoplasm.
(b) mitochondria.
(c) chloroplast.
(d) nucleus.
Answer: (b). Glucose is broken to pyruvate in the cytoplasm; the aerobic breakdown of pyruvate is in the mitochondria (NCERT Answers, p. 218).
5. Consider the following statements:
1. In yeast, pyruvate is converted into ethanol and carbon dioxide in the absence of oxygen.
2. In human muscle cells short of oxygen, pyruvate is converted into lactic acid.
3. The first step of glucose breakdown, to pyruvate, takes place in the mitochondria.
Which of the statements given above are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (a). Glucose is broken down to pyruvate in the cytoplasm.
6. Which of the following animals have a three-chambered heart, according to NCERT?
1. Fishes
2. Amphibians
3. Many reptiles
4. Birds
Select the correct answer using the code given below.
(a) 1 and 2 only
(b) 2 and 3 only
(c) 3 and 4 only
(d) 1, 3 and 4
Answer: (b). Fishes have two chambers; birds and mammals have four.
7. Consider the following statements about transport in plants:
1. Translocation of food takes place in the sieve tubes of the phloem, both upwards and downwards.
2. Loading sucrose into the phloem uses energy from ATP.
3. Root pressure is the major force moving water in the xylem during the day.
Which of the statements given above are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (a). By day, with the stomata open, transpiration pull is the major force; root pressure matters more at night.
8. In human beings, carbon dioxide is mostly transported in the blood
(a) bound to haemoglobin in the red blood corpuscles.
(b) in the dissolved form.
(c) bound to platelets.
(d) in the lymph.
Answer: (b). It is more soluble in water than oxygen is.
9. Consider the following statements about hemodialysis:
1. The dialysing fluid has the same osmotic pressure as blood but no nitrogenous wastes.
2. Waste products pass from the blood into the dialysing fluid by diffusion.
3. Like the nephron, the artificial kidney re-absorbs glucose and water.
Which of the statements given above are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (a). There is no re-absorption in dialysis.
10. Why do birds and mammals need to keep oxygenated and de-oxygenated blood apart, while fishes manage with a two-chambered heart? Explain double circulation in your answer. (150 words)
NCERT exercises (where the answers are on this page): 5 the emulsification box and Table 3 (fats are digested in the small intestine); 6 "Mouth" and Table 3; 7 Table 2 and Activity 5.1 (carbon dioxide, water, chlorophyll and sunlight; oxygen is the by-product, NCERT's "waste product generated during photosynthesis"); 8 Table 4 (yeast, and muscle cells short of oxygen); 9 the haemoglobin box and "The human respiratory system"; 10 the haemoglobin box (less haemoglobin means less oxygen carried to the tissues); 11 the double-circulation box; 12 Table 6; 13 Table 7 and the haemoglobin box (both are thin-walled surfaces wrapped in capillaries: alveoli exchange gases, nephrons filter and re-absorb).
📦 Revision Capsule
Hard Facts
- Photosynthesis: light absorbed by chlorophyll; water split into hydrogen and oxygen; carbon dioxide reduced to carbohydrates.
- Glucose (6C) → pyruvate (3C) in the cytoplasm; → ethanol + CO₂ (yeast); → lactic acid (muscle); → CO₂ + water in mitochondria (aerobic).
- ATP → ADP + phosphate releases 30.5 kJ/mol.
- Gastric glands: HCl, pepsin, mucus. Pancreas: trypsin, lipase. Liver: bile.
- Heart: left side oxygen-rich (lungs → left atrium → left ventricle → body); right side de-oxygenated (body → right atrium → right ventricle → lungs).
- Blood pressure about 120/80 mm of Hg.
- Kidney: about 180 L of filtrate a day, a litre or two of urine.
Core Concepts
- Diffusion serves single cells; large bodies need exchange organs and a transport system.
- Exchange surfaces are large, thin and well supplied with blood vessels: villi, alveoli, nephrons.
- Double circulation keeps oxygenated and de-oxygenated blood apart for animals with high energy needs.
- Xylem moves water by physical forces; phloem moves food using ATP and osmotic pressure.
- The nephron filters and then re-absorbs; dialysis only filters.
Confused Pairs
- Autotroph (green plants, some bacteria) vs heterotroph (animals, fungi).
- Starch (plants) vs glycogen (animals).
- Aerobic (mitochondria, more energy) vs anaerobic (ethanol in yeast, lactic acid in muscle).
- Oxygen (on haemoglobin) vs carbon dioxide (mostly dissolved).
- Artery (thick, elastic) vs vein (valves) vs capillary (one cell thick).
- Systolic (ventricle contracting) vs diastolic (ventricle relaxing).
- Plasma vs lymph (colourless, less protein, carries fat).
- Root pressure (night) vs transpiration pull (day).
- Xylem (water, upward) vs phloem (food, both ways).
- Transpiration (water vapour lost) vs translocation (food moved).
Data Points
- Alveolar surface about 80 m²; diffusion alone: about 3 years from lungs to toes.
- Class XI: RBCs 5-5.5 million per mm³ (adult man); haemoglobin 12-16 g per 100 mL; RBC life span 120 days.
- Class XI: about 99 % of the filtrate re-absorbed; urine concentrated about four times (300 to 1200 mOsmol/L); 38 ATP per glucose in theory, 2 in fermentation.
- NFHS-6 (released 29 May 2026): stunting under five 35.5 % → 29.3 %.
PYQ Pattern
- Mains 2023 GS3: the role of micro-organisms in addressing fuel shortages (adjacent: yeast fermentation to ethanol).
Sources
- NCERT, Science, Textbook for Class X, ch. 5 "Life Processes", Reprint 2026-27 — ncert.nic.in PDF.
- NCERT, Science, Class X, Answers, Reprint 2026-27 — ncert.nic.in PDF.
- NCERT, Science, Class X, 2020-21 edition (whole-book zip), as archived on 9 October 2021 — Wayback Machine.
- NCERT, Biology, Textbook for Class XI, ch. 12 "Respiration in Plants" — ncert.nic.in PDF.
- NCERT, Biology, Textbook for Class XI, ch. 15 "Body Fluids and Circulation" — ncert.nic.in PDF.
- NCERT, Biology, Textbook for Class XI, ch. 16 "Excretory Products and their Elimination" — ncert.nic.in PDF.
- NCERT, Biology, Textbook for Class XI, ch. 17 "Locomotion and Movement" — ncert.nic.in PDF.
- PIB (Ministry of Health and Family Welfare), "Union Health Ministry Releases National Family Health Survey – 6", 29 May 2026, Release ID 2266600 — pib.gov.in.
