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Every NCERT book that matters for UPSC — open a book, then a chapter. Learn each chapter's concepts, then how UPSC tests them — with diagrams, flowcharts and the past questions to attempt.
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← Exploration — all chaptersTissues in Action
Start here: why this chapter matters
In simple wordsA single brick can't be a house, and a pile of bricks isn't one either; bricks have to be laid together into walls, floors and a roof, each doing a different job. Cells are the bricks (Chapter 2); tissues are the walls and floors — groups of similar cells doing one job together. This chapter shows how plants and animals build very different houses from the same kind of bricks.
This is Chapter 3 of Exploration, NCERT's new Class 9 science textbook for NCF-2023 (book pages 28–47; the contents page gives the same title, and Chapter 4, Describing Motion Around Us, starts on page 48). It asks why plant and animal tissues differ (3.1), then covers tissues for plant growth and permanent plant tissues (3.2), the four animal tissues (3.3), the musculoskeletal system (3.4), joints (3.5) and the skeleton (3.6). It has 25 figures, 7 tables, 5 activities, a ‘Meet a Scientist’ and a ‘Meet the Scientists’ box, two ‘Ready to Go Beyond’, two ‘Bridging Science and Society’, one ‘Think as a Scientist’, five ‘Pause and Ponder’ questions and 15 end exercises. This page has nine concept sections.
- Neighbouring chapters on this site: Cell: The Building Block of Life (Class 9, Ch 2) for cell walls, vacuoles, mitosis, Haberlandt's totipotency and crown gall — read it first; Life Processes (Class 10) for transport in xylem and phloem, transpiration and blood; Control and Coordination (Class 10) for neurons and reflexes; How do Organisms Reproduce (Class 10) and Biotechnology and its Applications (Class 12) for tissue culture and micropropagation; Biotechnology: Principles and Processes (Class 12) for Agrobacterium; Human Health and Disease (Class 12) for blood cancers. The Class 11 NCERT chapters Anatomy of Flowering Plants, Structural Organisation in Animals and Locomotion and Movement take this chapter further.
- UPSC relevance: Prelims science has asked plant tissue–function matches, haemoglobin, blood composition, bones and stem cells (1985 to 2012, linked below). GS3 Science and Technology: stem cell therapy for leukaemia and thalassaemia (Mains 2017, linked), tissue culture and haploid breeding, Agrobacterium-based genetic engineering. GS3 agriculture and environment: micropropagation, tree rings as climate records, grassland regrowth. GS2 health: bone health, yoga and lifestyle diseases.
| Word | What it means here |
|---|---|
| Tissue | a group of cells, similar in structure, working together to perform a specific function |
| Division of labour | different tissues doing different jobs, which makes a multicellular body efficient |
| Meristem | plant tissue of actively dividing cells, responsible for growth |
| Differentiation | cells losing the ability to divide and becoming specialised for one job |
| Permanent tissue | plant tissue of cells that have stopped dividing; simple (one cell type) or complex (several) |
| Xylem / phloem | complex tissues that carry water and minerals / food |
| Epithelium | animal tissue that covers the body and lines organs; cells tightly packed |
| Connective tissue | connects and supports: blood, bone, cartilage, tendons, ligaments |
| Matrix | the material between connective-tissue cells — watery in blood, hard in bone |
| Totipotency | the ability of a single plant cell to regenerate a whole plant |
Reading NCERT's chapter opening and ‘Think It Over’ (page 28)An illustration in two halves: a girl skipping with a rope, her body cut away to show brain, lungs, heart, gut and bones, with arrows to icons of nerve, skin, heart, stomach, bone and knee; and a scientist at a laminar-flow cabinet working with flasks of tiny plantlets beside a potted seedling. A QR code labelled 0906CH03 sits by the title. ‘Think It Over’ asks how studying cells and tissues helps human welfare, why plant and animal tissues differ, and how division of labour links structure to function. The point: the same idea — tissues — explains both a body in motion and a plant grown in a flask.
Common confusions
- A tissue is a group of cells; an organ is made of more than one tissue type.
- Unicellular organisms such as Amoeba have no tissues: one cell does every job.
- ‘Similar cells’ fits simple tissues; complex tissues like xylem have several cell types working together (exercise 11).
At a glance — the six ideas to carry away
- Tissue = similar cells, one job → division of labour (cell → tissue → organ → organ system → organism). Plants (fixed, walled cells, photosynthesis, lifelong growth) and animals (mobile, flexible cells) need different tissues.
- Meristems (small, thin-walled, dense cytoplasm, big nucleus, no vacuoles): apical (tips: length — Activity 3.1, cut root tips stop growing), lateral (ring: girth; annual rings give age), intercalary (nodes: grass regrows).
- Permanent tissues form by differentiation. Epidermis: one layer, cuticle, root hairs, stomata. Simple: parenchyma (living, stores), collenchyma (living, pectin corners, flexible), sclerenchyma (dead, lignin, hard: coconut husk).
- Complex: xylem (tracheids, vessels, fibres — dead; xylem parenchyma the only living part) carries water up; phloem (sieve tubes, companion cells, parenchyma, fibres — mostly living) carries food. Three tissue systems: dermal, ground, vascular.
- Animal tissues: epithelium (Table 3.2: exchange, protection, secretion, sensory, absorption) · connective (blood 55% plasma / 45% cells; bone, cartilage, tendon muscle→bone, ligament bone→bone) · muscle (skeletal, smooth, cardiac) · nervous (dendrites, cell body, axon).
- Musculoskeletal system: skeleton ≈ 12–15% of body weight; joints — ball and socket (shoulder), hinge (elbow, knee), pivot (neck), fixed (skull); 12 pairs of ribs. Steward (1958): carrot phloem cells regenerate whole plants — totipotency, tissue culture.
1. Why plant and animal tissues differ
In simple wordsA banyan tree and a cricketer face different problems. The tree can't run from a storm, so it builds stiff walls and grows thicker every year. The cricketer must sprint, bend and dive, so his body uses soft, stretchy tissues and a jointed skeleton. Different lifestyles, different building materials.
Most plants are fixed in one place and must stay firm and upright; their cells have cell walls for rigidity. Most animals move (sponges are an exception); without walls, their cells change shape easily, which suits locomotion. Nutrition differs too: animals have tissues to digest food from many sources, plants have tissues to capture sunlight for photosynthesis. Both need distinct tissues to transport food and water, and their growth differs: plants keep growing in particular zones all their lives, while animals grow throughout the body until adulthood (Beyond NCERT wording). Each tissue's structure fits its function.
| Feature | Plants | Animals |
|---|---|---|
| Movement | mostly fixed in one place | mostly move (sponges are immobile) |
| Cell wall | present — rigid support | absent — flexible cells |
| Food | made by photosynthetic tissues | digested by tissues of the gut |
| Growth | in meristems, throughout life | throughout the body, limited (Beyond NCERT wording) |
| Main tissue grouping | meristematic and permanent | epithelial, connective, muscular, nervous |
| Much of the tissue | dead and supportive (wood, sclerenchyma) | living (Beyond NCERT wording) |
Common confusions
- Plant and animal tissues are not classified the same way: plants by ability to divide (and function), animals by structure and function into four kinds.
- ‘Plants don't move’ is about place to place; plant parts still move (tendrils coil, leaves turn to light).
- Dead cells can be useful tissue: xylem vessels and sclerenchyma work dead.
2. Meristems: how plants grow in length, girth and after cutting
In simple wordsA road under construction grows only at its ends, where workers keep laying new stretches; widen it, and workers along the sides add lanes. Plants grow the same way: dividing cells at the root and shoot tips make them longer, a ring of dividing cells in the stem makes it thicker, and dividing zones low on grass stems let a mown lawn grow back.
Plants grow in length (stem height, root depth), in girth (stem thickness) and by regrowth after cutting or grazing — all through actively dividing cells forming meristematic tissue. In Activity 3.1, two onion bulbs root in jars of water; on day 3 the root tips in Jar B are cut by about 1 cm; Jar A's roots keep lengthening while Jar B's stop. Roots grow only from their tips, which hold continuously dividing cells (the mitosis seen in onion root tips in Chapter 2); shoot tips are similar. These growth zones are apical meristems. Dicot stems also thicken: a ring of dividing cells, the lateral meristem, adds new cells inward and outward concentrically. The wood of a cut trunk shows annual growth rings — wide in favourable years, narrow in poor ones — so counting them estimates a tree's age and the climate it grew in. If a young stem's tip is cut, it stops lengthening but new branches arise from the nodes; hedges turn bushy after trimming and grass grows back after mowing or grazing. NCERT links this regrowth to the intercalary meristem, at the base of the internode or just above the node (a node is where leaves or branches arise; an internode is the stretch between two nodes).
Meristematic cells are small, with thin walls, a large, prominent nucleus and dense cytoplasm rich in organelles; vacuoles are generally absent and cells are tightly packed with little or no intercellular space — all suited to continuous, rapid division. Some new cells stay meristematic; others lose the ability to divide, change in structure and function and become permanent tissues, specialised for support, transport or storage. This specialisation is differentiation.
⤵ Activity 3.1: do roots grow from their tips?
Set up two jarsan onion bulb on each, base in water (Jar A and Jar B)
Measureroot length from the base of the bulb on days 1, 2 and 3
Cuton day 3, cut about 1 cm off the root tips in Jar B only
Keep measuringdays 4 to 7 in both jars; fill Table 3.1
ConcludeA keeps growing, B stops: growth happens only at the tips (apical meristem)
| Meristem | Where | Adds | Example |
|---|---|---|---|
| Apical | tips of roots and shoots | length (height, root depth) | onion root tips (Activity 3.1) |
| Lateral | a ring along the circumference of the stem | girth; annual rings | tree trunks (dicots) |
| Intercalary | base of internodes, just above nodes | regrowth after cutting; branching | grass after mowing or grazing |
Reading NCERT's Activity 3.1, Fig. 3.1, Table 3.1 and Fig. 3.2 (pages 29–30)Fig. 3.1 photographs two red onions on narrow glass jars of water, Jar A and Jar B. Table 3.1 is a blank grid for root length on days 1–7. Fig. 3.2 is a line graph of root length (0–6 cm) against days: Jar A's line climbs steadily to near 6 cm by day 7; Jar B's climbs with it, drops by about 1 cm when cut, then stays flat. The point: no tip, no lengthening. Note: the text says the cut is on day 3, but the graph draws the drop at day 4.
Reading NCERT's Figs. 3.3 and 3.4 — apical meristems and annual rings (page 30)Fig. 3.3 shows a young sapling with arrows to the shoot apical meristem at its tip and the root apical meristem at the root tip in soil. Fig. 3.4 photographs the pale cut face of a tree trunk with many concentric rings. The point: length comes from the tips; girth leaves a yearly record in the wood.
Reading NCERT's Figs. 3.5 and 3.6 — new branches and lawn mowing (page 31)Fig. 3.5 shows a potted rose-like stem cut across the top with two new branches growing from the nodes below the cut. Fig. 3.6 is a photograph of a man pushing a lawn mower over grass. The point: cut plants regrow from dividing zones low on the stem.
Reading NCERT's ‘Meet a Scientist’ — B. G. L. Swamy (page 29)With a portrait of an elderly smiling man. B. G. L. Swamy, an Indian botanist known for plant morphology and anatomy, wrote the popular Kannada book Hasuru Honnu, a blend of science, satire and culture describing botanical excursions in the Western Ghats — plant descriptions, uses, conservation practices, folklore and myths; it won the Kendra Sahitya Akademi Award in 1978. The point: plant anatomy and Indian-language science writing go together.
Common confusions
- Apical = length, lateral = girth, intercalary = regrowth at nodes — don't swap them.
- Meristem cells have no large vacuoles and thin walls; thick walls belong to permanent tissues (exercise 1).
- Meristems are not only at tips (exercise 13): lateral and intercalary meristems exist too.
- NCERT credits new branches on a cut stem and bushy hedges to the intercalary meristem; standard botany credits them to axillary buds at the nodes, released when the tip is removed (Beyond NCERT). In exams, intercalary meristem's classic example is grass regrowing after grazing.
- Only dicot stems (and gymnosperms) thicken this way; most monocots such as grasses do not form annual rings (Beyond NCERT).
Beyond NCERT
- The lateral meristem that makes wood is the vascular cambium; the one that makes bark is the cork cambium (see section 4).
- Dating events and climates from tree rings is dendrochronology; a ring is one year's light early wood plus dark late wood.
- Removing a shoot tip to make a plant bushy works because the tip suppresses side buds — apical dominance; gardeners and tea growers use it when pruning.
3. Permanent tissues I: epidermis and the simple tissues
In simple wordsA school building needs plaster on the outside (to keep rain out), ordinary rooms (for storage and work), flexible joints that sway in an earthquake, and steel bars that never bend. A plant has all four: the epidermis is the plaster, parenchyma the rooms, collenchyma the flexible joints, sclerenchyma the steel.
Looking at a transverse section (T.S.) of a sunflower stem shows different groups of cells, each specialised: these are permanent tissues — simple (one cell type) or complex (several). The epidermis is the outermost layer: a tightly packed single layer of flat, rectangular cells that protects against injury, water loss, microbes and extremes. It is covered by a waxy cuticle of cutin, thick in dry-habitat plants to cut water loss through transpiration, and also a guard against injury and parasites. Epidermal cells may bear hairs — in roots, root hairs increase the surface for absorbing water and minerals. Leaf epidermis has pores, stomata, for gas exchange and transpiration (evaporation of water vapour), which creates a transpiration pull in the xylem and helps remove wastes.
The three simple permanent tissues (NCERT groups them as supporting tissues): parenchyma — living, thin-walled, loosely packed with intercellular spaces; mainly stores food, photosynthesises in green parts, and in aquatic plants forms air spaces that help them float. Collenchyma — living cells with corners unevenly thickened by pectin (a rubbery, flexible substance); support with flexibility, so stems and tendrils bend without breaking. Sclerenchyma — cells with thick walls of lignin, hard and strong (the woody structure); mostly dead; found in stems, leaf veins and hard seed and nut coverings such as coconut husk and walnut shell.
| Parenchyma | Collenchyma | Sclerenchyma | |
|---|---|---|---|
| Living? | yes | yes | mostly dead |
| Wall | thin | thickened at corners (pectin) | uniformly thick (lignin) |
| Spaces between cells | present | little | very little |
| Main job | storage; photosynthesis; buoyancy | flexible support | hardness and strength |
| Where (NCERT) | most soft parts; air spaces in water plants | stems, tendrils, leaf stalks | stems, leaf veins, coconut husk, walnut shell, seed coats |
| Fresh twig vs dry twig | — | fresh twig bends | woody, dry twig snaps |
⤵ From a dividing cell to a working tissue
Dividemeristem cells divide continuously
Some stay meristematicto keep the growing zone going
Others stop dividingthey lose the ability to divide
Differentiatewalls, shape and contents change to suit one job
Permanent tissueepidermis, parenchyma, collenchyma, sclerenchyma, xylem or phloem
Reading NCERT's Fig. 3.7 — internal structure of a sunflower stem (page 32)A sunflower plant (Helianthus annuus) with arrows to its stem, the stem cut to show vascular tissue, a round coloured T.S., and an enlarged wedge labelled epidermal hair, cuticle, epidermis, collenchyma, parenchyma, sclerenchyma, phloem, lateral meristem, xylem and ground tissue. The point: one section holds every plant tissue in this chapter. Our schematic T.S. is in section 4.
Reading NCERT's Fig. 3.8 — simple permanent tissues (page 32)Three micrographs: (a) parenchyma, pale rounded thin-walled cells with spaces; (b) collenchyma, white cells set in pink-stained thickenings at their corners; (c) sclerenchyma, small cells with very thick reddish lignified walls. The point: wall thickness tells the three apart.
Reading NCERT's ‘Pause and Ponder’ 1 (page 33)Why are coconut husk fibres hard and brittle while coriander leaf stalks are soft and flexible? The point: sclerenchyma vs collenchyma (outline in the intext section).
Common confusions
- Collenchyma ≠ sclerenchyma: collenchyma is living, thickened at corners with pectin, flexible; sclerenchyma is dead, thickened all over with lignin, rigid.
- Cuticle (waxy cutin layer) sits on top of the epidermis (cells); they are not the same thing.
- Root hairs are outgrowths of single epidermal cells, not separate roots.
- Transpiration is evaporation through stomata, not water being pumped out.
- NCERT calls parenchyma a ‘supporting’ tissue with the other two, though its main job is storage.
Beyond NCERT
- Each stoma is bordered by two guard cells that open and close it.
- Parenchyma with chloroplasts is called chlorenchyma; parenchyma with large air spaces, aerenchyma (as in water hyacinth and lotus).
- Sclerenchyma comes as long fibres (jute, coir) and short sclereids (the grit in a pear, nut shells). Jute and coir industries depend on sclerenchyma fibres.
4. Permanent tissues II: xylem, phloem, tissue systems and bark
In simple wordsA city has water pipes running up from the reservoir and delivery vans carrying cooked food from kitchens to homes. A plant has both: xylem is the water-pipe network — made of dead, hollow tubes — and phloem is the living delivery service carrying sugar from the leaves (kitchens) to roots, fruits and growing tips.
Xylem and phloem are complex permanent tissues — several cell types working together. Xylem carries water and minerals from the roots to other parts and also gives strength; it consists of tracheids, vessels (tubular, thick-walled), xylem parenchyma (the only living component) and xylem fibres; tracheids, vessels and fibres are mainly sclerenchymatous. Phloem is mostly living: sieve tubes (long tubular cells joined end to end by perforated walls) carry food from leaves to other parts; companion cells, specialised parenchyma, regulate sieve-tube cells and monitor loading and unloading of sugars; phloem parenchyma stores food, resin, tannins and latex; phloem fibres give strength.
Tissues work together in three tissue systems: the dermal system (outer covering; protects, cuts water loss), the ground system (the main body between dermal and conducting tissues: parenchyma, collenchyma, sclerenchyma) and the vascular system (xylem and phloem). As plants age, some cells below the stem epidermis regain the ability to divide, act as lateral meristem and form the cork cambium; it makes cork cells — dead, compact, impermeable to water and gases — which form the bark.
| Xylem | Phloem | |
|---|---|---|
| Carries | water and minerals | food (sugars) |
| Direction (NCERT) | from roots upward to other parts | from leaves to other parts |
| Cell types | tracheids, vessels, xylem parenchyma, xylem fibres | sieve tubes, companion cells, phloem parenchyma, phloem fibres |
| Living or dead | mostly dead; only xylem parenchyma lives | mostly living; phloem fibres are not |
| Driving force | transpiration pull from the leaves | loading and unloading of sugar by companion cells |
| Extra job | strength (wood) | storage of food, resin, tannins, latex |
⤵ Water's route up a plant
Root hairs absorbwater and minerals enter from the soil
Into the xylemthrough the root to dead, hollow vessels and tracheids
Up the stema continuous column of water in the xylem
Out of the leafwater evaporates through stomata (transpiration)
Pull from the topthe loss pulls the water column up — transpiration pull
Reading NCERT's Fig. 3.9 — xylem and phloem (page 33)Two 3-D blocks: (a) brown xylem, cut to show a wide vessel, tracheids, xylem parenchyma and xylem fibres; (b) blue phloem showing sieve tubes with sieve pores, companion cells (one highlighted red) and phloem parenchyma. The point: complex tissues are bundles of different cells. Our schematic is above.
Reading NCERT's Fig. 3.10 — tissue systems in plants (page 33)A plant from leaf to root, with arrows to three cross-sections: a leaf (xylem above phloem in the midrib, epidermal tissue), a stem (a ring of bundles with xylem and phloem in ground tissue inside epidermal tissue) and a root (xylem in a star-like centre with phloem between its arms). The point: all three organs use the same three systems, arranged differently.
Reading NCERT's ‘Ready to Go Beyond’ — cork and bark, and ‘Pause and Ponder’ 2–4 (page 34)The box: young plants have a single-layered epidermis; older stems form a cork cambium whose dead, compact, waterproof cork cells make the bark. Pause and Ponder asks why a thick cuticle helps a desert plant but not an underwater one, how ‘dead’ xylem works with living leaf cells to lift water, and what would happen without stomata. The point: protection and transport must be balanced (outlines in the intext section).
Common confusions
- Xylem = water, phloem = food (UPSC 1990; exercise 2).
- The only living part of xylem is xylem parenchyma; phloem is mostly living.
- Companion cells belong to phloem, not xylem.
- Xylem carries water only upward; phloem moves food wherever it is needed — up or down (Beyond NCERT's ‘from leaves to other parts’).
- Bark is not the epidermis: it is cork formed later by the cork cambium (with, in common usage, the phloem inside it — exercise 8).
Beyond NCERT
- Cork cells are waterproof because their walls contain suberin; bottle corks come from the bark of the cork oak.
- Girdling — removing a full ring of bark — cuts the phloem, starves the roots and can kill a tree; this is why debarking by elephants (exercise 8) matters.
- Gymnosperms such as pines have tracheids but generally no vessels; vessels are typical of flowering plants.
5. Totipotency and tissue culture: one cell to a whole plant
In simple wordsTake one brick from a finished wall and ask it to grow into a whole house — impossible for a brick. But a single mature cell from a carrot, given food, hormones and care, can grow into an entire new carrot plant. Plant cells keep the full instruction book and can ‘go back to school’ to become any kind of cell.
In 1958 F. C. Steward showed that single cells from the phloem of carrot could regenerate whole plants. His team cultured small fragments (about 2 mg) of carrot root in a liquid nutrient medium with simple sugars and hormones; stirring sheared off single cells, which divided into a mass of cells, then into an embryo-like plant, a plantlet on agar, and finally an adult plant in soil. The phloem cells first dedifferentiated (regained the ability to divide), formed an undifferentiated mass, and then redifferentiated into root, shoot and the whole plant — totipotency, like a zygote's ability to form a whole organism (Haberlandt proposed it in 1902 — Cell: The Building Block of Life). In India, Sipra Guha Mukherjee with S. C. Maheshwari regenerated complete plants by anther culture on an artificial nutrient medium, a breakthrough for crop improvement. Crown gall shows the other side: the bacterium Agrobacterium tumefaciens causes tumour-like swellings by uncontrolled cell division, and studying how it transfers its genes into plant cells turned it into a tool for genetic engineering.
| Steward's conditions (Table 3.6) | Medium | Change in fresh weight |
|---|---|---|
| light, no air | solid medium + nutrients | reduced |
| light, air | liquid medium + nutrients | 20% increase |
| no light, air | liquid medium + nutrients | reduced |
⤵ Steward's carrot: from one cell to a plant (Fig. 3.19)
Take tissuesmall (about 2 mg) fragments of carrot root phloem
Culturein a liquid nutrient medium with sugars and hormones; stirring frees single cells
Dedifferentiatesingle cells start dividing into an unspecialised mass
Redifferentiatean embryo-like plant forms, with root and shoot
Grow onplantlet on agar, then planted in soil: an adult carrot
Reading NCERT's ‘Think as a Scientist’, Fig. 3.19 and Table 3.6 (page 42)With a portrait of a moustached man in a suit. Fig. 3.19 is a cartoon sequence: a carrot root and its cross-section, 2-mg fragments in a flask of medium, single cells dividing, an embryonic plant, a plantlet in a tube on agar, and an adult carrot plant with flowers. Table 3.6 lists three combinations of light, air and medium with the change in cell weight. Questions (a)–(d) follow. The point: a mature plant cell can be reprogrammed, and conditions decide whether cultured cells thrive (answers in the intext section).
Reading NCERT's ‘Meet the Scientists’ — Sipra Guha Mukherjee and S. C. Maheshwari (page 34)With portraits of a woman in a sari and a man in a jacket and tie. Their research produced complete plants through anther culture on an artificial nutrient medium under controlled conditions — pioneering work for crop improvement and modern agriculture. The point: Indian scientists opened a major route in plant tissue culture.
Reading NCERT's ‘Bridging Science and Society’ — crown gall, and Fig. 3.20 (page 43)Fig. 3.20 photographs a tree trunk with large, lumpy dark swellings. The box: crown gall tumours come from rapid, uncontrolled cell division caused by Agrobacterium tumefaciens; scientists studied how it transfers genetic material into plant cells and now use it to introduce useful genes for phytochemicals, improved crops and disease resistance. The point: studying a disease created a biotechnology tool — see Biotechnology: Principles and Processes (Class 12).
Common confusions
- Haberlandt (1902) proposed totipotency; Steward (1958) demonstrated it with carrot phloem cells.
- Dedifferentiation (back to dividing) comes before redifferentiation (into new specialised cells).
- Table 3.6: only light + air + liquid medium increased weight; the table cannot rank the two ‘reduced’ rows against each other.
- Agrobacterium is a bacterium that causes crown gall; it is also the vector used to put genes into plants.
- UPSC 1985 asked ‘what is tissue culture?’ with an odd stored key (‘preparation of fragments of cells for biochemical examination’, which describes cell fractionation); the key is disputed. Tissue culture means growing cells, tissues or organs on a nutrient medium in sterile conditions.
- Totipotency is shown for plant cells; mature animal cells generally cannot regrow a whole animal on their own (‘The Quest Continues’).
Beyond NCERT
- Guha (later Guha-Mukherjee) and Maheshwari reported haploid plants from anther culture of Datura at the University of Delhi in 1964; haploids speed up breeding of pure lines.
- The undifferentiated cell mass in culture is a callus. Commercial micropropagation (banana, orchids, sugarcane) clones disease-free plants in large numbers; India certifies tissue-culture plants under the Department of Biotechnology's National Certification System for Tissue Culture Raised Plants.
6. Epithelial tissue: coverings and linings
In simple wordsThink of floor tiles: in a lab where liquids pass through, you'd use thin, single tiles; on a busy road, thick layered paving; in a kitchen, tiles with built-in drains. Epithelium is the body's tiling, and each area gets the type of tile its job needs.
Animal cells, too, group into specialised tissues. Blink, clench a fist, breathe deeply, touch something warm: muscle moves you, nerves sense, the lining of the lungs lets oxygen into the blood, and connective tissue holds the body together. Epithelial tissue forms the outer covering of the body (skin) and lines internal organs — mouth, lungs, blood vessels, intestine. Its cells are closely packed with very little space between them, which keeps germs out, reduces water loss and helps absorb, secrete and move substances. Each kind is shaped for its job (Table 3.2).
| Function (Table 3.2) | Structure | Where |
|---|---|---|
| Exchange: rapid diffusion of liquids and gases | single layer of thin, flat cells | lining of blood vessels and lungs |
| Protection: against injury, friction, microbes | many layers; outer cells flat, tightly packed | skin, mouth, oesophagus |
| Secretion: mucus, enzymes, hormones, sweat, saliva | cells specialised to make and release; cuboidal or columnar | salivary and sweat glands, stomach lining |
| Sensory: smell, taste, sound, balance | receptor cells with hair-like cilia | nostrils, taste buds, inner ear |
| Absorption: uptake of nutrients and water | single layer of tall, pillar-like cells, often with hair-like structures | lining of small intestine |
Reading NCERT's Table 3.2 and Fig. 3.11 — epithelial tissues (page 35)Fig. 3.11 shows a man's torso cut away to the lungs and gut, with arrows to five 3-D blocks of pink cells: (a) a flat single sheet, (b) many stacked layers, (c) tall cells in a row, (d) cells topped with hair-like cilia, (e) tall cells with a fringe. Table 3.2 pairs each with function and location. The point: thin where things must pass, thick where things must be kept out.
Common confusions
- Linings for exchange are one cell thick so that diffusion is quick (exercise 3; exercise 6A's ‘multiple layers of tall cells’ is false).
- Skin epithelium is many-layered for protection; lung and blood-vessel linings are single-layered.
- Glands are made of epithelial cells; ‘secretion’ is an epithelial job.
- Epithelium has almost no space between cells; connective tissue has lots of matrix between them.
Beyond NCERT
- Standard names: squamous (flat), cuboidal, columnar, ciliated; one layer = simple, many = stratified. The fringe on intestinal cells is microvilli, the ‘brush border’.
- Most cancers in adults arise from epithelia (carcinomas) — linking to Human Health and Disease (Class 12).
7. Connective tissue: blood, bone, cartilage, tendons and ligaments
In simple wordsConnective tissues are like the materials that hold a tent together: the poles (bone), the springy rubber caps on pole ends (cartilage), the ropes tying canvas to poles (tendons), the clips joining pole to pole (ligaments) — plus a delivery truck driving around inside (blood). Different jobs, same family: cells sitting in a matrix.
A tissue that connects and supports other tissues is connective tissue. Blood and bone are both connective tissues, but blood is fluid and bone is hard because of their matrix — watery and jelly-like in blood, hard and rigid in bone. Blood is about 55% plasma and 45% formed elements. Its red colour comes from haemoglobin, an iron-rich protein in red blood cells (RBCs), which live about 4 months; platelets help clotting; during exercise breathing and blood flow increase; white blood cells (WBCs) gather at infections, causing redness, swelling and pus. Bone has a rigid matrix of calcium and phosphorus compounds; cartilage has a soft, jelly-like matrix that gives flexibility and cushions bone ends; tendons connect muscle to bone; ligaments connect bone to bone, giving stability and preventing excessive movement and dislocation.
| Action (Table 3.4) | What you feel | Connective tissue | Job |
|---|---|---|---|
| touch your elbow | hard, rigid | bone | strength, support, protection |
| fold your ear, press your nose | soft, flexible, springs back | cartilage | flexibility; cushions bone ends |
| feel the forearm while wiggling fingers | movement far from the fingers | tendon | joins muscle to bone, transmits pull |
| raise your leg as far as the knee allows | the joint stops at a limit | ligament | joins bone to bone; stability; limits movement |
Reading NCERT's Activity 3.2 and Table 3.3 — blood in daily life (page 36)Recall a small cut (blood oozes, then clots), a skin infection (redness, swelling, maybe fever) and exercise (faster breathing, a red face); the book then explains haemoglobin, platelets, increased blood flow and WBCs. The point: everyday experiences are blood's components at work.
Reading NCERT's Fig. 3.12 — types of connective tissue (page 36)(a) A test tube of blood: a pale upper layer labelled plasma, 55% of volume, a red lower layer labelled formed elements, 45%, with pictures of a WBC, platelets and RBCs. (b) A human skeleton overlaid on muscles with insets of a collar bone, a long bone and a kneecap. (c) A knee showing a tendon, cartilage and a ligament. The point: one family, very different matrices.
Reading NCERT's Activity 3.3 and Table 3.4 — feel your connective tissues (page 37)Touch the elbow, fold the ear, wiggle fingers while holding the forearm, and raise the leg to the knee's limit; match each experience to bone, cartilage, tendon or ligament. The point: you can identify connective tissues with your own hands.
Common confusions
- Tendon: muscle → bone. Ligament: bone → bone (exercise 6C's assertion is false).
- Blood is a connective tissue, even though it is liquid.
- RBC life: ‘about 4 months’ here and ‘about 120 days’ in Chapter 2 — the same figure (asserted).
- Blood cells are 45% of blood volume, not 70% (UPSC 2002 used this).
- Haemoglobin does not give immunity; WBCs fight infection (UPSC 1990).
- UPSC 1990's bone question is flawed: every option includes the false statement that bone's solid matter is mainly cartilage. What is right: hardness comes from calcium and phosphate salts in the matrix.
Beyond NCERT
- Platelets outnumber WBCs in normal blood (roughly 1.5–4 lakh platelets vs 4,000–11,000 WBCs per microlitre).
- Bone's mineral is mostly calcium phosphate (hydroxyapatite) laid on a protein (collagen) framework; with age, mineral loss can make bones porous and brittle (osteoporosis).
- Adipose (fat-storing) tissue is another connective tissue (UPSC 1983 asked where fat is stored).
8. Muscular and nervous tissue: movement and messages
In simple wordsYour body has three kinds of engines: ones you drive yourself (arm and leg muscles), ones on autopilot that work slowly all day (gut muscles), and one that never stops for a lifetime (the heart). Wires — nerves — carry the instructions to all of them, and the brain is the control room.
Movements under conscious control — running, writing, lifting — are voluntary and done by skeletal muscles attached to the skeleton: bundles of long, cylindrical muscle fibres, unbranched, multinucleate and striated (light and dark bands). Involuntary movements — food moving in the intestine, the heartbeat — use other muscles. Smooth muscle (stomach, intestines): spindle-shaped cells, one nucleus, no striations; slow, continuous movements like digestion. Cardiac muscle, only in the heart: cylindrical, branched fibres, one nucleus, faint striations; works rhythmically for life without fatigue. Muscles cannot act alone: nervous tissue forms the control and coordination network, with the brain as control centre (it signals the heart to beat faster during exercise). Its cells, neurons, receive, process and transmit messages: the cell body holds the nucleus; dendrites receive signals; the axon, a long fibre, carries messages to axon terminals, which pass them on.
| Skeletal | Smooth | Cardiac | |
|---|---|---|---|
| Control | voluntary | involuntary | involuntary |
| Cell shape | long cylinders, unbranched | spindle-shaped | cylindrical, branched |
| Nuclei per cell | many | one | one |
| Striations | yes | no | faint |
| Where | attached to bones | stomach, intestines (organ walls) | heart only |
| Works | quick, tires | slow, continuous | rhythmic, without fatigue |
⤵ Pulling your hand from a hot pan
Sensereceptors in the skin detect heat
Signal inneurons carry the message: dendrites → cell body → axon
Processthe nervous system decides to withdraw
Signal outaxon terminals pass the message to skeletal muscle
Movethe muscle contracts; its tendon pulls the bone; the joint bends
Reading NCERT's Figs. 3.13 and 3.14 — muscles and a neuron (page 38)Fig. 3.13 pairs drawings of skeletal muscle (striped fibres, with an arm), smooth muscle (spindle cells, with stomach and intestine) and cardiac muscle (branched fibres, with a heart). Fig. 3.14 draws a neuron with a branching cell body, nucleus, dendrites, a long green-segmented axon and branched axon terminals. The point: shape tells you the job.
Common confusions
- Skeletal = many nuclei, striated, voluntary. Smooth = one nucleus, no striations, involuntary. Cardiac = one nucleus, branched, faintly striated, involuntary.
- Cardiac muscle is involuntary but striated — the odd one out.
- Messages travel dendrite → cell body → axon → terminals, not the other way.
- Exercise 6B: both statements are true and the reason (many mitochondria, rich blood supply) explains the assertion — option (i).
Beyond NCERT
- The green segments in NCERT's neuron are the myelin sheath, an insulating cover that speeds up signals.
- Muscle contraction needs calcium ions (and sodium for nerve signals) — UPSC 2013 asked which minerals are needed.
- Cardiac muscle cells are joined by intercalated discs that let the heart contract as one unit.
9. The musculoskeletal system, joints and the skeleton
In simple wordsA crane has a steel frame, cables, motors and pivots. Your body's version: bones are the frame, muscles the motors, tendons the cables, and joints the pivots — some swivel all round (shoulder), some open and shut like a door (elbow), some turn like a knob (neck), and some are welded shut (skull).
The musculoskeletal system — bones, muscles, joints, cartilage, tendons and ligaments — lets us stand, move, keep posture and protect organs, under the control of the nervous system. Muscles pull on bones through tendons; when a muscle contracts, the tendon passes the force to the bone and it moves at a joint (a junction of two or more bones; joints allow movement but cannot move bones themselves). The adult skeleton makes up about 12–15 per cent of body weight; NCERT's Activity 3.4 adds average muscle of about 40–50 per cent in adult males and 30–40 per cent in females (for a 50 kg person: about 6–7.5 kg of bone — asserted). Joints: ball and socket — the rounded top of the upper arm bone sits in a shallow hollow of the shoulder bone; with the collarbone it forms the shoulder girdle; moves forward, back, sideways and in circles. Hinge — the elbow bends and straightens in one direction like a door hinge; the knee is similar, protected by the kneecap. Pivot — lets the head turn side to side (‘no’) like a doorknob. Fixed — the flat skull bones are locked together to protect the brain, eyes and ears.
The skeletal system is a framework of bones giving strength and protection: the skull, the vertebral column (backbone, spine) of small bones called vertebrae with a cartilage disc between them as a cushion that allows bending and twisting without injuring the spinal cord, and the rib cage of 12 pairs of ribs protecting heart and lungs. The ribs attach to the spine behind and the breast bone (sternum) in front, joined by flexible cartilage, so the cage expands and contracts in breathing; injured ribs make breathing painful. Bone marrow holds stem cells that divide to make new cells; in a bone marrow transplant, a healthy donor's stem cells are given to patients with blood cancers such as leukaemia or disorders such as thalassaemia. Posture, nutrition, exercise and yoga keep bones strong, muscles fit and joints flexible; 21 June is observed every year as International Yoga Day.
| Body part (Table 3.5) | Complete rotation | Partial rotation | Bending | Joint (NCERT) |
|---|---|---|---|---|
| Elbow | no | no | yes | hinge |
| Shoulder | yes | yes | yes | ball and socket |
| Knee | no | no | yes | hinge |
| Neck | no | yes (side to side) | yes (nodding) | pivot |
| Fingers | no | no | yes | hinge (Beyond NCERT) |
| Toes | no | no | yes | hinge (Beyond NCERT) |
| Wrist | no | yes (with the forearm) | yes | several small joints (Beyond NCERT) |
⤵ How a muscle moves a bone
Nerve signalthe nervous system instructs a skeletal muscle
Contractionthe muscle shortens and pulls
Tendontransmits the pull to the bone it is attached to
Jointthe bone moves at the joint, as far as its type and ligaments allow
Returnanother muscle pulls the other way (muscles can only pull) — Beyond NCERT
Reading NCERT's Fig. 3.15, Activities 3.4–3.5 and Table 3.5 (pages 38–39)Fig. 3.15 is a human figure half skeleton, half muscle, labelled cartilage, bones, joint, muscles, tendon and ligament. Activity 3.4: weigh yourself and estimate bone and muscle mass from average percentages; compare with classmates. Activity 3.5 and Table 3.5: test which body parts rotate fully, partly or only bend (the elbow row is filled: no, no, yes). The point: joints decide how a part can move; our filled table is above.
Reading NCERT's Fig. 3.16, Fig. 3.17 and ‘Pause and Ponder’ 5 (page 40)Fig. 3.16 is a skeleton with arrows to toy-like models: interlocking puzzle pieces (fixed joint, skull), a ring on a peg (pivot, neck), a ball in a cup (ball and socket, shoulder and hip) and a hinge (knee and elbow). Fig. 3.17 is a row of nine dancers in Indian classical and folk costumes, in varied poses. Pause and Ponder 5 asks which joints each pose uses. The point: dance is applied joint mechanics.
Reading NCERT's ‘Ready to Go Beyond’ — bone marrow stem cells (page 40)Stem cells in bone marrow divide to make new cells; in a bone marrow transplant a healthy person's stem cells go to patients with leukaemia or thalassaemia. The point: tissues can be replaced from stem cells — the theme of UPSC Mains 2017's stem-cell question.
Reading NCERT's ‘Bridging Science and Society’ — yoga, and Fig. 3.18 (page 41)Yoga, described in ancient Indian texts, combines postures, breathing and meditation; research shows it improves flexibility, posture and breathing, reduces stress and helps prevent lifestyle diseases; 21 June is International Yoga Day. Fig. 3.18 shows the 12 numbered poses of Surya Namaskar in a circle. The point: habits keep the musculoskeletal system healthy.
Common confusions
- Knee and elbow are hinge joints; the shoulder (and hip) are ball and socket (exercise 5; the printed key's ‘pivot’ is wrong).
- NCERT says the skull joins the backbone by a pivot joint; strictly, the ‘no’ turn happens at the pivot joint between the first two neck vertebrae (atlas and axis), while nodding ‘yes’ is at the skull–atlas joint (Beyond NCERT).
- Not all 12 pairs of ribs reach the sternum: the last two pairs are ‘floating’ ribs (Beyond NCERT).
- Muscles only pull; joints do not move bones by themselves.
- A hinge joint moves in one plane (exercise 6D's reason, ‘sliding in all directions’, is false).
Beyond NCERT
- The UN General Assembly declared 21 June as the International Day of Yoga in December 2014; it was first observed in 2015.
- The adult human skeleton has about 206 bones; the femur (thigh bone) is the longest. Names in Fig. 3.12b: collar bone = clavicle, kneecap = patella, breast bone = sternum, shoulder blade = scapula (UPSC 2001).
- Thalassaemia is an inherited disorder of haemoglobin production (see Principles of Inheritance and Variation, Class 12); bone marrow transplants use haematopoietic (blood-forming) stem cells.
- The tendon at the back of the ankle (Fig. 3.24) is the Achilles tendon, the body's strongest.
NCERT's activities, in-text questions and ‘Pause and Ponder’ — short answers
The five activities, the five ‘Pause and Ponder’ questions, Steward's four questions and the main in-text questions. Outlines:
Activity 3.1 (pages 29–30): Grow roots on two onions, cut the root tips of one on day 3, and record lengths for seven days. What do you infer?
Jar A's roots keep growing; Jar B's stop after the tips are cut. Roots grow only from their tips, where cells divide continuously — the apical meristem. (NCERT's Fig. 3.2 draws the cut at day 4, the text at day 3.)
Activity 3.2 (page 36): Relate a cut, a skin infection and exercise to blood.
Cut: blood oozes, platelets help it clot. Infection: WBCs gather, causing redness, swelling, maybe pus and fever. Exercise: muscles need more oxygen, so breathing and blood flow increase and the face reddens; the red colour of blood is haemoglobin in RBCs.
Activity 3.3 (page 37): Perform the actions in Table 3.4 and identify the connective tissues.
Elbow — bone (hard, support); ear or nose tip — cartilage (flexible, springs back); forearm moving as fingers wiggle — tendon (muscle to bone); knee stopping at a limit — ligament (bone to bone).
Activity 3.4 (page 39): Estimate the weight of your bones and muscles.
Multiply body weight by the average percentages: for 50 kg, bone 12–15% ≈ 6–7.5 kg; muscle about 20–25 kg (male, 40–50%) or 15–20 kg (female, 30–40%) — asserted. Values differ with age, sex, activity, nutrition and build, which is why class results vary.
Activity 3.5 (page 39): Which body parts rotate fully, partly or only bend?
Shoulder: full rotation (ball and socket). Neck: turns side to side and nods (pivot). Elbow, knee, fingers and toes: bend only (hinge). Wrist: bends and turns partly with the forearm. See the filled Table 3.5 in section 9.
In-text (page 31): Why do meristematic cells lack vacuoles?
Their job is rapid, continuous division; the space is filled with dense cytoplasm and a large nucleus that drive division. Large vacuoles store water and wastes and appear when cells stop dividing and differentiate.
In-text (page 34): Which tissue helps you move, sense heat, take in oxygen, and hold skin to the body?
Move — muscle; sense heat or cold — nervous tissue; oxygen into blood — the thin epithelium of the lungs; holding the body together — connective tissue.
Pause and Ponder 1 (page 33): Why are coconut husk fibres hard and brittle, but coriander leaf stalks soft and flexible?
Coconut fibres are sclerenchyma: dead cells with thick lignified walls — hard but they snap. Coriander stalks are supported by collenchyma: living cells with pectin-thickened corners — flexible.
Pause and Ponder 2 (page 34): Why is a thick cuticle good for a desert plant but bad for a plant living underwater?
In the desert, water is scarce: a thick waxy cuticle cuts water loss. Underwater, there is no shortage of water, and a submerged plant takes in water, minerals and gases through its surface; a thick cuticle would block that exchange.
Pause and Ponder 3 (page 34): How do the ‘dead’ cells of xylem work with living leaf cells to keep water moving up?
Dead vessels and tracheids are empty tubes that hold a continuous column of water. Living leaf cells lose water by transpiration through stomata; this creates a pull that draws the column up the xylem from the roots. Dead pipes give an open path; living leaves give the pull.
Pause and Ponder 4 (page 34): What would happen if there were no stomata in the epidermis?
No gas exchange — little carbon dioxide in for photosynthesis or oxygen out; little transpiration, so weak transpiration pull and slow water and mineral transport; leaves could overheat. Growth would fall sharply.
Pause and Ponder 5 (page 40): Which joints are used in the dance poses of Fig. 3.17, and what movement does each allow?
Raised and swung arms — ball and socket (shoulder): circular, all directions; bent elbows and knees in deep stances — hinge: one plane; turned and tilted head — pivot (neck): side to side; wide leg positions also use the hip's ball and socket; fingers in hand gestures (mudras) bend at hinge-like joints.
Think as a Scientist (page 42), (a)–(b): What do you conclude about carrot phloem cells, and which combination gives the highest and lowest biomass?
(a) Mature carrot phloem cells are totipotent: they can dedifferentiate, divide and redifferentiate into a whole plant. (b) Highest: light + air + liquid medium (20% increase) — cells in liquid are bathed in nutrients and get oxygen. The other two both reduced: without air, cells lack oxygen for respiration and a solid medium limits contact with nutrients; without light, growth fell even with air. The table does not say which of the two fell more.
Think as a Scientist (page 42), (c)–(d): Would animal cells give the same result? Name two commercial uses.
(c) No — mature animal cells generally cannot regenerate a whole animal in a nutrient medium; whole-animal cloning needs a nucleus put into an egg cell (Beyond NCERT). (d) Micropropagation of disease-free plants in large numbers (banana, sugarcane, orchids); conserving rare plants; producing valuable plant chemicals in culture; haploid plants for faster breeding.
Revise, Reflect, Refine — answer outlines
Reading NCERT's ‘At a Glance’, ‘The Journey Beyond’, ‘The Quest Continues’ and Figs. 3.21–3.25 (pages 43–47)‘At a Glance’ lists fourteen summary points. Fig. 3.21: a girl in a straight-leg standing pose and a deep-squat pose. Fig. 3.22: an elephant stripping bark from a tree trunk. Fig. 3.23: sugarcane cuttings A (a piece without a node) and B (a piece with a node) beside a clump of canes. ‘The Journey Beyond’ suggests asking a doctor about ligament and cartilage rupture and fractures, feeling the tendon above the heel (Fig. 3.24, a hand on an ankle), reflecting on yoga and kabaddi, gardening practices and leaf adaptations, and learning tribal dance steps (Fig. 3.25, a line of dancers with drummers). ‘The Quest Continues’ asks whether a whole animal could be obtained from one animal cell. The Answer Key (page 271) prints 1 (iii), 2 (iii), 3 (ii), 5 (iii), 6 A (iii) B (i) C (iv) D (iii); keys 2, 3 and 5 contradict the chapter and are flagged below.
1. What property lets meristematic cells divide repeatedly: (i) thick walls; (ii) large vacuoles; (iii) thin walls, dense cytoplasm, large prominent nucleus; (iv) functionally differentiated?
(iii) (NCERT key). Thick walls, big vacuoles and differentiation belong to permanent tissues.
2. If a plant cannot transport food from leaves to roots, which tissue is malfunctioning: (i) xylem; (ii) phloem; (iii) epidermis; (iv) sclerenchyma?
(ii) phloem — it carries food (page 33). The printed Answer Key gives (iii) epidermis, which contradicts the chapter; it looks like a misprint. Safe line: phloem.
3. Why are epithelia lining internal organs usually one or a few cells thick: (i) store food; (ii) maximum strength; (iii) quick exchange of materials; (iv) reduce friction?
(iii) — thin linings allow rapid diffusion (Table 3.2). The printed key gives (ii), which contradicts the chapter; keys 2 and 3 appear swapped or misprinted. Safe line: (iii).
4. Compare a straight-leg jump (knees and ankles stiff) with a normal jump (knees and ankles bent). How do ankle, knee and hip positions differ?
Straight-leg: ankles and knees stay locked straight; the push comes mostly from the ankles and the hip moves little; landing is jarring because joints cannot absorb the shock. Normal: ankles, knees and hips bend (hinge joints at knee and ankle, ball and socket at the hip) to store and release force, so the jump is higher and landing softer — cartilage and the bent joints cushion it.
5. Which joint is involved when you bend your knees and ankles: (i) ball and socket; (ii) hinge; (iii) pivot?
(ii) hinge — the knee bends in one plane (page 40). The printed key gives (iii) pivot, which contradicts the chapter. Safe line: hinge.
6. Assertion–reason. A: epithelium suits gas exchange in lungs / R: many layers of tall cells slow diffusion. B: cardiac muscle contracts without fatigue / R: many mitochondria, rich blood supply. C: tendons connect bone to bone / R: tendons transmit force from muscle to bone. D: hinge joint moves in one plane / R: bone ends allow sliding in all directions.
A — (iii): assertion true; the reason is false (lung epithelium is a single thin layer). B — (i): both true, and the reason explains it. C — (iv): assertion false (tendons join muscle to bone), reason true. D — (iii): assertion true, reason false. All four agree with the NCERT key.
7. Plot the teak tree's DBH and number of annual rings against age (Table 3.7). (i) Interpret the diameter over time. (ii) How are diameter and rings related? (iii) Which tissue gives girth, and where is it?
(i) Diameter rises steadily from 4 cm at 5 years to 40 cm at 40 years — about 0.8 cm a year in most periods, but 1.6 cm a year between 10 and 20 years, probably favourable growing years (asserted; see the plot in section 2). (ii) Rings = age: one ring a year; diameter increases as rings are added, but not by the same amount each year — wide rings in good years, narrow in poor. (iii) The lateral meristem, a ring of dividing cells in the stem (between xylem and phloem).
8. An elephant severely debarked a tree. (i) Which functions are hampered? (ii) Which tissue is affected by further damage? (iii) What if tissues beneath the bark were severely damaged? (iv) What assumptions are you making?
(i) Protection against water loss, injury and microbes; and, if the strip includes phloem, food transport from leaves to roots. (ii) The lateral meristem (cambium) and then the xylem. (iii) Water and mineral transport upward and growth in girth would fail; a full ring of damage could kill the tree. (iv) Assumed: bark includes cork and the phloem beneath, and the debarking goes all round. If only outer cork was removed, or only a strip, the tree could heal and survive.
9. A young mango stem bends in monsoon winds without breaking. Which tissue gives this flexibility? What if it were replaced by sclerenchyma?
Collenchyma: living cells with pectin-thickened corners, giving flexible support. Replaced by sclerenchyma (dead, lignified, rigid), the stem would be stiff and snap in strong wind instead of bending.
10. Sugarcane cuttings: type B sprouted, type A did not. (i) Why? (ii) What was different in B? (iii) What was measured? (iv) What must be kept the same?
(i)–(ii) Type B included a node with a bud and the dividing (meristematic) zone just above it; type A was a piece of internode only, with no tissue able to form a new shoot. (iii) Whether, when and how much each cutting sprouted — number of shoots and their length after a few weeks. (iv) Same variety, cutting length and thickness, soil, water, depth and orientation of planting, light and temperature, and several cuttings of each type.
11. Rohan: ‘A tissue is a group of similar cells performing similar functions.’ Rajiv: ‘True for simple tissues, a little different for complex tissues.’ Explain.
Rajiv is right. Simple tissues (parenchyma, collenchyma, sclerenchyma) are made of one type of cell. Complex tissues such as xylem and phloem contain different cell types — vessels, tracheids, fibres and parenchyma; sieve tubes, companion cells, parenchyma and fibres — that do different things but work together for one common function (conduction). A broader definition: a group of cells, similar or different, working together for a common function.
12. Coconut husk fibres make tough mats. Which tissue gives this strength? Why couldn't living parenchyma do the same?
Sclerenchyma: long cells with thick lignified walls, mostly dead, hard and strong. Parenchyma has thin walls and soft living contents with spaces between cells; it would crush, rot and give no lasting strength.
13. Vibha: ‘Meristematic cells are located only at the root and shoot apices.’ Is she right? What could Neha ask?
No. Besides apical meristems there are the lateral meristem (a ring in the stem, giving girth) and intercalary meristems (at nodes). Neha could ask: ‘If growth were only at the tips, how would a tree trunk get thicker every year, or a mown lawn grow back?’
14. A plant cell and an animal cell are the same size. (i) Which has the larger vacuole? (ii) What are you assuming?
(i) The plant cell: a mature plant cell usually has one large central vacuole; animal cells have small vacuoles or none. (ii) Assumed: both are mature, typical cells — a meristematic plant cell has no large vacuole, so the answer would change.
15. A textbook says, ‘Each plant tissue performs only one specific function.’ What questions would you ask, and which tissues would you examine?
Ask: does any tissue do more than one job? Does a tissue's job change with location? Examples: parenchyma stores food, photosynthesises in green parts and gives buoyancy in water plants; xylem conducts water and gives strength; the epidermis protects, exchanges gases (stomata) and absorbs (root hairs); phloem parenchyma stores food, resin, tannins and latex. The statement is too strong.
The Quest Continues (page 47): Could a complete animal be obtained from one animal cell, as with plants? Advantages and challenges?
Not as simply as with plants: mature animal cells are generally not totipotent in culture. Whole animals have been cloned only by transferring a body-cell nucleus into an egg cell whose own nucleus was removed (Dolly the sheep, born in 1996 — Beyond NCERT). Advantages claimed: copying high-yield livestock, saving endangered species, research models, tissues for transplant. Challenges: very low success rates, health problems in clones, loss of genetic diversity, animal welfare, and ethical limits — positions set out in the table below, with no verdict.
| Position on cloning animals (attributed) | What it emphasises |
|---|---|
| NCERT (The Quest Continues, page 47) | asks students to weigh possibility, advantages and challenges; takes no position |
| Supporters (many animal scientists and livestock breeders; some conservation biologists) | multiplying elite dairy and draught animals, rescuing endangered breeds and species, research and medicine |
| Critics (animal-welfare groups, some ethicists, some farmer and religious voices) | suffering and failure rates, narrowing genetic diversity, corporate control of breeds, a slippery slope towards human cloning |
| Regulators and guideline bodies (e.g. India's national guidelines for stem cell research, ICMR and DBT) | permit regulated research but prohibit human reproductive cloning |
The table records positions, not a verdict.
What to remember
Numbers
Chapter pages28–47 (20 pages; Chapter 4 starts on page 48)
Figures / tables / activities25 / 7 / 5
Pause and Ponder / end exercises5 / 15
Types of meristem3: apical, lateral, intercalary
Simple permanent tissues3: parenchyma, collenchyma, sclerenchyma
Cell types in xylem / phloem4 / 4
Plant tissue systems3: dermal, ground, vascular
Main animal tissue types4: epithelial, connective, muscular, nervous
Bloodplasma 55% · formed elements 45%
RBC life spanabout 4 months (≈ 120 days, Ch 2)
Skeleton's share of body weightabout 12–15%
Average muscle share (NCERT)males ~40–50% · females ~30–40%
Ribs12 pairs (24)
Activity 3.1root tips cut by about 1 cm; measured days 1–7
Teak (Table 3.7)40 cm DBH and 40 rings at 40 years; 0.8–1.6 cm a year
Steward's carrot experiment1958 (Haberlandt's idea, 1902)
B. G. L. Swamy's <i>Hasuru Honnu</i>Kendra Sahitya Akademi Award, 1978
International Yoga Day21 June; Surya Namaskar has 12 poses
One-liners
- A tissue is a group of similar cells doing a specific job.
- Tissues give multicellular organisms a division of labour.
- Meristems are tissues of actively dividing cells.
- Apical meristems add length; roots grow only from their tips.
- The lateral meristem adds girth and makes annual rings.
- Intercalary meristems at nodes let grass regrow.
- Meristem cells have thin walls, dense cytoplasm, a big nucleus and no vacuoles.
- Differentiation turns meristem cells into permanent tissue.
- The epidermis is one layer covered by a waxy cuticle.
- Stomata allow gas exchange and transpiration.
- Parenchyma is living, thin-walled and stores food.
- Collenchyma is living with pectin-thickened corners; it bends.
- Sclerenchyma is mostly dead with lignified walls; it is hard.
- Xylem carries water and minerals; only xylem parenchyma is living.
- Phloem carries food; companion cells manage sugar loading.
- Plant tissue systems are dermal, ground and vascular.
- Cork cambium makes cork, which forms bark.
- Epithelial cells are tightly packed with almost no space between them.
- Blood and bone are connective tissues with different matrices.
- Tendons join muscle to bone; ligaments join bone to bone.
- Skeletal muscle is voluntary, striated and multinucleate.
- Cardiac muscle is branched, faintly striated and never tires.
- A neuron has a cell body, dendrites and an axon.
- The shoulder is ball and socket; elbow and knee are hinges.
- Steward showed in 1958 that carrot phloem cells are totipotent.
Traps to avoid
- Apical = length, lateral = girth, intercalary = regrowth.
- Collenchyma is living (pectin); sclerenchyma is dead (lignin).
- Xylem = water up; phloem = food.
- Xylem parenchyma is the only living part of xylem.
- Companion cells are in phloem, not xylem.
- Tendon = muscle to bone; ligament = bone to bone.
- Blood is a connective tissue.
- Cardiac muscle is involuntary but striated.
- Lung and blood-vessel linings are single-layered; skin is many-layered.
- Knee and elbow are hinge joints, not pivot.
- Haberlandt proposed totipotency (1902); Steward demonstrated it (1958).
- NCERT's printed keys to exercises 2, 3 and 5 contradict the chapter.
- Bark is cork from the cork cambium, not the epidermis.
- Annual rings mark years, and their width marks good or poor years.
How to strategise
Prelims — what UPSC asks
- Plant tissues by function: 1990 asked a straight match — sclerenchyma–mechanical strength, xylem–water, phloem–food, meristem–cell division. Learn the section 3–4 tables, including living vs dead and pectin vs lignin; add the Beyond NCERT names (vascular and cork cambium, aerenchyma, sclereids).
- Blood and bone: haemoglobin's iron, oxygen and red colour (not immunity, 1990); blood cells about 45% of volume, platelets outnumbering WBCs (2002); bone hardness from calcium and phosphate salts (1990, a flawed question); bone names — sternum, clavicle, patella, scapula (2001).
- Stem cells and tissue culture: stem cells for drug screening and therapy, and not from mammals only (2012); ‘what is tissue culture’ (1985, disputed key). Know totipotency, Steward and Haberlandt, Guha-Mukherjee and Maheshwari's anther culture, micropropagation and Agrobacterium.
- Likely next: tree rings and climate records, haploid breeding, tissue-culture certification, bone marrow and cord-blood banking, thalassaemia screening, osteoporosis and calcium, International Day of Yoga.
Mains — where it appears and how to answer
- GS3, 2017: ‘Stem cell therapy is gaining popularity … leukaemia, thalassaemia, damaged cornea, burns. Describe what it is and its advantages.’ This chapter's bone marrow box gives the core: stem cells are unspecialised cells that divide and differentiate into needed tissue; bone marrow transplants replace a patient's blood-forming tissue. Frame: definition (sources — bone marrow, cord blood, embryonic; Beyond NCERT) → how it works (division, differentiation) → uses → advantages (repair rather than manage, fewer rejection issues with own cells) → concerns (unproven ‘clinics’, cost, ethics of embryonic cells) → Indian regulation (national guidelines for stem cell research, ICMR and DBT) → conclusion.
- Use the chapter as GS3 science in agriculture answers: micropropagation and anther culture for crop improvement, Agrobacterium for GM crops (attributed positions as in Biotechnology and its Applications), annual rings for climate history, and grazing-tolerant grasses (intercalary meristems) in pasture management.
Self-check
Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.
1. In Activity 3.1 the root tips in Jar B are cut on day 3. Afterwards, Jar B's roots:
2. Grass grows back after grazing mainly because of:
3. Which tissue is living and has walls thickened at the corners by pectin?
4. The only living component of xylem is:
5. Which connective tissue joins a muscle to a bone?
6. Branched fibres with one nucleus and faint striations that work without fatigue are:
7. In blood, plasma makes up about:
8. F. C. Steward's 1958 experiment showed that:
UPSC questions from this chapter
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