Tissues in Action – Class 9 Science Chapter 3 Notes & NCERT PDF

Class 9ScienceChapter 3NCERT book: Exploration - Science Class 9

Notes and a simple summary of Chapter 3 of the NCERT Class 9 Science book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 3: Tissues in Action

Think It Over

Why is studying cells and tissues important for understanding life and for human welfare?

How are plant and animal tissues different, and why?

How does division of labour relate structure to function in multicellular organisms?

Introduction

Life begins as a single cell that divides many times; the cells gradually form skin (protection), muscles (movement), bones (support) and nerves (control). Multicellular organisms show a hierarchy of organisation:

Cells → tissues → organs → organ systems → organism.

A tissue is a group of cells, similar in structure, that work together to perform a specific function. Different tissues bring division of labour, making the body efficient. In an amoeba one cell does everything; in plants and animals different groups of cells share the work — muscle tissue for movement, nervous tissue for messages, xylem for water, phloem for food.

Key Concepts

3.1 Why are plant and animal tissues different?

Most plants are fixed; their cells have rigid walls for support. Animals move; their flexible cells suit locomotion.

Nutrition differs: animals have tissues to digest food; plants have tissues for photosynthesis.

Transport and growth patterns differ because the tissues responsible differ.

3.2 Tissues for growth in plants — meristems

Plants grow in length, in girth, and regrow after cutting or grazing, thanks to actively dividing meristematic tissue.

Apical meristem — at root and shoot tips; increases length. (Activity 3.1: onion roots with cut tips stop growing.)

Lateral meristem — a ring of dividing cells in the stem; increases girth. It produces annual growth rings; counting them gives a tree's age and hints at past climate.

Intercalary meristem — at the base of internodes or just above nodes; helps regrowth (bushy hedges after trimming, grass after mowing or grazing).

Meristem cells are small, thin-walled, with a large prominent nucleus, dense cytoplasm, no vacuoles, and are tightly packed — suited to rapid division.

Differentiation: some new cells lose the ability to divide and become specialised permanent tissues.

3.2.4 Permanent tissues (seen in a T.S. of a sunflower stem)

(i) Protective tissue — epidermis

Single layer of tightly packed, flat rectangular cells covering the plant.

Covered by a waxy cuticle (cutin) — thick in dry-habitat plants to reduce water loss; protects against injury and parasites.

Root hairs increase surface area for absorbing water and minerals.

Stomata allow gas exchange and transpiration, which creates a transpiration pull in xylem and helps remove wastes.

(ii) Supporting tissues — simple permanent tissues

Parenchyma — living, thin-walled, loosely packed with intercellular spaces; stores food, photosynthesises in green parts; in aquatic plants forms air spaces for floating.

Collenchyma — living cells with corners unevenly thickened by pectin; gives support with flexibility (stems and tendrils bend without breaking).

Sclerenchyma — thick walls with lignin, hard and strong, mostly dead; in stems, leaf veins, seed coats, coconut husk and walnut shell.

(iii) Conducting tissues — complex permanent tissues

Xylem — carries water and minerals from roots upward and gives strength. Made of tracheids, vessels, xylem parenchyma (the only living part) and xylem fibres.

Phloem — mostly living; carries food from leaves. Made of sieve tubes, companion cells (regulate loading and unloading of sugars), phloem parenchyma (stores food, resin, tannins, latex) and phloem fibres.

Tissue systems: dermal (outer covering), ground (parenchyma, collenchyma, sclerenchyma), and vascular (xylem and phloem).

In older stems, cork cambium forms dead, impermeable cork cells — the bark.

Sipra Guha Mukherjee and S. C. Maheshwari grew complete plants through anther culture.

B. G. L. Swamy — botanist; his Kannada book Hasuru Honnu won the Kendra Sahitya Akademi Award in 1978.

3.3 Animal tissues

Epithelial tissue — covers the body and lines internal organs; closely packed cells prevent germ entry and water loss.

Exchange — single layer of thin, flat cells; lining of blood vessels and lungs.

Protection — many layers, outer cells flat; skin, mouth, oesophagus.

Secretion — cuboidal or columnar gland cells; salivary glands, sweat glands, stomach lining.

Sensory — receptor cells with cilia; nostrils, taste buds, inner ear.

Absorption — single layer of tall pillar-like cells; small intestine.

Connective tissue — connects and supports; differs by its matrix.

Blood — fluid matrix: plasma (55%) and formed elements (45%). RBCs (haemoglobin; live about 4 months), WBCs (fight infection, cause swelling/pus), platelets (clotting).

Bone — rigid matrix of calcium and phosphorus compounds; strength and protection.

Cartilage — soft, flexible matrix; ear, nose, cushions bone ends.

Tendon — connects muscle to bone.

Ligament — connects bone to bone, limits movement, prevents dislocation.

Muscular tissue

Skeletal — voluntary; long, cylindrical, unbranched, multinucleate, striated fibres.

Smooth — involuntary; spindle-shaped, single nucleus, no striations; stomach and intestines.

Cardiac — only in the heart; cylindrical, branched, single nucleus, faint striations; works without fatigue.

Nervous tissue — neurons receive, process and transmit messages. Parts: cell body (nucleus), dendrites (receive signals), axon ending in axon terminals (pass messages on).

3.4 The musculoskeletal system

Bones, muscles, joints, cartilage, tendons and ligaments let us stand, move, keep posture and protect organs, under nervous control. A contracting muscle pulls a tendon, moving a bone at a joint. The skeleton is about 12–15 per cent of adult body weight; muscle is about 40–50 per cent in adult males and 30–40 per cent in adult females.

3.5 Types of joints

Ball and socket — shoulder; movement in all directions.

Hinge — elbow and knee (with kneecap); one direction only.

Pivot — skull on backbone; side-to-side turning ("no").

Fixed — skull bones; no movement, protecting the brain.

3.6 Skeletal system

Vertebral column of vertebrae with cartilage discs as cushions.

12 pairs of ribs form the rib cage, attached to the spine and the sternum by flexible cartilage, so the cage expands and contracts during breathing.

Posture, nutrition, exercise and yoga (International Yoga Day, 21 June) keep bones and joints healthy.

Think as a Scientist — Totipotency

F. C. Steward (1958) grew whole carrot plants from single phloem cells in a nutrient medium: cells dedifferentiated, formed a mass, then redifferentiated into roots, shoots and a plant. Crown gall disease (caused by Agrobacterium tumefaciens) produces tumour-like swellings; this bacterium is now used to insert useful genes into plants.

Activities in the Chapter

Activity 3.1 — Onion root growth: Two onions over water; on day 3 cut 1 cm of root tips in Jar B. Jar A roots keep growing; Jar B roots stop — growth comes from tips (apical meristem).

Activity 3.2 — Blood in daily life: A cut clots (platelets); infection turns red and swollen (WBCs); exercise makes breathing faster and the face red (more oxygen and blood flow).

Activity 3.3 — Feel connective tissues: elbow (bone), ear/nose (cartilage), forearm while wiggling fingers (tendon), knee movement limit (ligament).

Activity 3.4 — Body weight share: Estimate bone and muscle mass from your weight using the percentages.

Activity 3.5 — Joint movements: Test rotation and bending at elbow, shoulder, knee, neck, fingers, toes and wrist.

Key Terms

Tissue (ऊतक) — group of similar cells with a common function

Meristematic tissue (विभज्योतक) — actively dividing plant tissue

Differentiation (विभेदन) — specialisation of cells into permanent tissue

Parenchyma (मृदूतक) — living, thin-walled storage tissue

Collenchyma (स्थूलकोण ऊतक) — flexible supporting tissue

Sclerenchyma (दृढ़ ऊतक) — hard, lignified, mostly dead tissue

Xylem (जाइलम / दारु) — conducts water and minerals

Phloem (फ्लोएम / पोषवाह) — conducts food

Epithelium (उपकला) — covering and lining tissue

Connective tissue (संयोजी ऊतक) — connects and supports

Tendon (कंडरा) — muscle to bone

Ligament (स्नायुबंधन) — bone to bone

Neuron (तंत्रिका कोशिका) — nerve cell

Joint (संधि) — junction of two or more bones

Totipotency (पूर्णशक्तता) — a cell's ability to regenerate a whole plant

Real-life Connections

Mowed lawns and trimmed hedges regrow because of intercalary meristems.

Tree rings tell age and past climate.

Coconut husk mats are strong because of sclerenchyma.

Bone marrow stem cell transplants treat leukaemia and thalassaemia.

Yoga and Surya Namaskar improve flexibility and posture.

Common Misconceptions

"Meristems are found only at root and shoot tips." — Lateral and intercalary meristems exist too.

"Tendons connect bone to bone." — Tendons join muscle to bone; ligaments join bone to bone.

"All xylem cells are dead." — Xylem parenchyma is living.

"Epithelium for gas exchange is thick." — It is a single layer of thin, flat cells for fast diffusion.

"A tissue always has only one cell type." — Complex tissues like xylem and phloem have several.

Exercise Hints

Meristem cells divide because of thin walls, dense cytoplasm and a large nucleus.

Food transport failure → phloem; water transport → xylem.

Flexible sapling stems → collenchyma; replacing it with sclerenchyma would make stems break.

Sugarcane cuttings sprout only if they include a node (intercalary meristem).

For the teak table, diameter grows with age and one ring forms each year — lateral meristem is responsible.

💡 Key Learning Points

✓A tissue is a group of similar cells working together; tissues create division of labour in multicellular organisms
✓Apical, lateral and intercalary meristems make plants grow in length, girth and regrow after cutting
✓Permanent plant tissues include protective epidermis, simple tissues (parenchyma, collenchyma, sclerenchyma) and complex tissues (xylem, phloem)
✓Animal tissues are epithelial, connective, muscular and nervous, each structured for its function
✓Bones, muscles, joints, tendons and ligaments form the musculoskeletal system under nervous control

👨‍🏫 Teaching Tips

→Start Activity 3.1 a week early so students can graph root growth in cut and uncut onions
→Bring a tree-trunk slice or photo and let students count annual rings to estimate age
→Contrast a fresh twig (bends — collenchyma) with a dry twig and coconut husk (breaks/hard — sclerenchyma)
→Use Activity 3.3 so students feel bone, cartilage, tendon and ligament on their own bodies
→Map joint types onto classical and folk dance poses from the chapter's Pause and Ponder
→Make a matching game of epithelial types, structures and body locations
→Tell the F. C. Steward carrot story and discuss why animal cells cannot do the same easily

📋 Assessment Questions

Can the student name the three meristems, where they are and what growth they cause?
Can the student distinguish parenchyma, collenchyma and sclerenchyma by cell features and function?
Can the student name the components of xylem and phloem and what each transports?
Can the student compare skeletal, smooth and cardiac muscle?
Can the student match joint types to body parts and allowed movements?

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