Tissues in Action Class 9 Notes, Diagrams and Questions

What Tissues in Action is about

Weightage: This chapter is part of Unit I, World of Living, which carries 27 of the 80 theory marks in the school annual exam, shared with Cell: The Building Block of Life, Reproduction: How Life Continues and Patterns in Life: Diversity and Classification.Source: CBSE Science (086) syllabus, Class IX 2026-27, course structure, Unit I World of Living

Key concepts

Tissues and levels of organisation

NCERT section 3.1 Why are Plant and Animal Tissues Different?

A tissue is a team of cells of similar build that carry out one particular job together.

In every many-celled organism there is a ladder of organisation:

cell → tissue → organ → organ system → organism

For example: a muscle cell → muscle tissue → the heart (an organ, which also has nervous and connective tissue) → the circulatory system → a human being.

In a one-celled organism such as *Amoeba*, one cell does everything: feeding, moving, getting rid of waste and reproducing. In plants and animals, different groups of cells take on different jobs. This sharing of work is called division of labour. It makes the body efficient, just as a school runs better when some staff teach, some keep accounts and some run the library.

Examples of division of labour: muscle tissue moves the body, nervous tissue carries messages, xylem carries water and phloem carries food in plants.

Worked example

Arrange in the correct order, from simplest to most complex: stomach, human being, muscle cell, digestive system, muscle tissue. What is the advantage of this organisation?

Try it first, then show the solutionSolution

1. Smallest unit: muscle cell.
2. Similar cells together: muscle tissue.
3. Several tissues together: stomach (an organ).
4. Several organs together: digestive system; all systems together: human being.
5. Advantage: each tissue specialises in one job (division of labour), so the body works efficiently.

Answer: Muscle cell → muscle tissue → stomach → digestive system → human being; division of labour makes the body efficient.

Why plant and animal tissues differ

NCERT section 3.1 Why are Plant and Animal Tissues Different?

Plant and animal tissues are different because their ways of life are different.

Need	Plants	Animals
Movement	mostly fixed in one place	most move about (sponges are an exception)
Support	rigid cell walls and supporting tissues keep them upright	cells have no wall, so they can change shape; this suits movement
Food	tissues for photosynthesis (make their own food)	tissues to digest food taken in
Growth	growth continues in certain regions (meristems) throughout life	growth is more uniform and stops at a certain size
Transport	xylem (water) and phloem (food)	blood and blood vessels

So plants have more dead, strong supporting tissue, while animals have more living tissue that uses energy for movement.

Worked example

Give two reasons why plants have more dead supporting tissue than animals do.

Try it first, then show the solutionSolution

1. Plants stay fixed and must stand upright against wind and rain, so they need strong, rigid tissue such as sclerenchyma.
2. Plants do not move about, so they need less energy; dead tissue needs no energy to maintain.
3. Animals move, so most of their tissue is living and uses energy.

Answer: Plants are fixed and need rigid support; they use less energy, so dead supporting tissue suits them, while moving animals need living tissue.

Meristematic tissue: apical, lateral and intercalary

NCERT section 3.2 Tissues for Growth in Plants

Plants grow in three ways: in length, in girth (thickness) and by regrowth after cutting or grazing. All three need cells that keep dividing. A tissue of such cells is a meristematic tissue (meristem).

Meristem	Where	What it does
Apical	tips of root and shoot	increases length (height and root depth)
Lateral	a ring along the circumference of the stem (and root)	increases girth; makes annual rings in trees
Intercalary	at the base of internodes or just above nodes (e.g. grasses)	regrowth after mowing or grazing

A node is the point on a stem where a leaf or branch arises; the stretch between two nodes is an internode.

Features of meristematic cells (all suit fast division): small cells; thin cell walls; a large, prominent nucleus; dense cytoplasm with many organelles; no vacuoles (or very small ones); tightly packed with almost no intercellular spaces.

Annual rings: the lateral meristem adds a new layer of wood each year. Wide rings mean good growing years; narrow rings mean poor years. Counting the rings gives the tree's age.

Worked example

In Activity 3.1, the roots of onion A grow from 1.0 cm on day 3 to 5.5 cm on day 7. The root tips of onion B were cut on day 3 and its roots stay at about 2.5 cm. Find the average growth per day of A from day 3 to day 7, and explain B.

Try it first, then show the solutionSolution

1. Growth of A $=5.5-1.0=4.5$ cm in $7-3=4$ days.
2. Average rate $=\frac{4.5}{4}=1.125$ cm per day, about 1.1 cm per day.
3. B stopped growing because the dividing cells at the root tip (the apical meristem) were removed.

Answer: About 1.1 cm per day for A; B stops because its apical meristem was cut off, showing roots grow only from their tips.

Differentiation and permanent tissue: the epidermis

NCERT section 3.2 Tissues for Growth in Plants

Some new cells made by a meristem stay meristematic. Others lose the power to divide and change their shape and contents to do one job well (support, transport or storage). This change is called differentiation, and the result is a permanent tissue.

• Simple permanent tissue: one type of cell (parenchyma, collenchyma, sclerenchyma).
• Complex permanent tissue: more than one type of cell working as a unit (xylem, phloem).

Protective tissue: the epidermis

• The outermost layer of the plant: a single layer of flat, rectangular, tightly packed cells.
• Covered by a waxy cuticle (made of cutin) that cuts down water loss and keeps out parasites. Desert plants have a thick cuticle.
• Root hairs are outgrowths of root epidermal cells that give a large surface for absorbing water and minerals.
• Leaf epidermis has pores called stomata for gas exchange and transpiration (loss of water vapour). Transpiration creates a pull that draws water up the xylem and also helps remove wastes.

In older trees, a cork cambium forms below the epidermis and makes dead, waterproof cork cells: the bark.

Worked example

A thick cuticle helps a cactus but would harm a water lily's leaves that lie in water. Explain both.

Try it first, then show the solutionSolution

1. The cuticle is waxy and waterproof, so it reduces loss of water vapour.
2. In a desert, water is scarce, so saving water helps the cactus survive.
3. A water-lily has plenty of water; a thick cuticle would make exchange of gases and water through the surface harder, with no benefit.

Answer: It saves scarce water for the cactus, but for a water plant it only blocks exchange of gases and water.

Simple permanent tissues: parenchyma, collenchyma, sclerenchyma

NCERT section 3.2 Tissues for Growth in Plants

	Parenchyma	Collenchyma	Sclerenchyma
Cells	living	living	mostly dead
Wall	thin	thickened at the corners, unevenly (pectin)	thick all round, with lignin
Spaces between cells	many	few	almost none
Main job	storage of food; photosynthesis in green parts; air spaces for floating in water plants	support with flexibility	strength and hardness
Where	soft parts of stem, root, leaf, fruit	leaf stalks, young stems, tendrils	stems, leaf veins, seed coats, coconut husk, walnut shell

• Pectin acts a bit like rubber, so collenchyma lets a part bend without breaking. That is why a fresh twig or a coriander leaf stalk bends.
• Lignin makes walls hard and waterproof, forming the woody part. That is why a dry twig or coconut husk fibre is stiff and snaps or resists.
• Parenchyma in aquatic plants with large air spaces is called aerenchyma; parenchyma with chloroplasts is called chlorenchyma (names used in higher classes).

Worked example

A fresh twig bends but a dry twig breaks. Name the tissues responsible and explain using the structure of their walls.

Try it first, then show the solutionSolution

1. A fresh, young twig has living collenchyma whose walls are thickened only at the corners with pectin, which is flexible.
2. So it bends without breaking.
3. A dry, older twig has more sclerenchyma with thick, lignified walls and its cells have lost water.
4. Lignin is hard and rigid, so the twig snaps instead of bending.

Answer: Collenchyma (pectin, flexible) lets the fresh twig bend; lignified sclerenchyma makes the dry twig rigid, so it breaks.

Complex permanent tissues: xylem, phloem and tissue systems

NCERT section 3.2 Tissues for Growth in Plants

Xylem carries water and minerals upwards from the roots, and also gives strength.

• Made of tracheids, vessels (both tube-like with thick walls), xylem parenchyma and xylem fibres.
• Only xylem parenchyma is living; the rest are dead, thick-walled cells.

Phloem carries food (sugars) from the leaves to other parts, up or down.

• Made of sieve tubes (long cells joined end to end through perforated walls called sieve plates), companion cells, phloem parenchyma and phloem fibres.
• Mostly living; only phloem fibres are dead. Companion cells control the sieve tubes and the loading and unloading of sugar; phloem parenchyma stores food, resin, tannins and latex.

Tissue systems: tissues are grouped into three systems:
1. Dermal: outer covering (epidermis, later bark).
2. Ground: the main body between skin and pipes (parenchyma, collenchyma, sclerenchyma).
3. Vascular: the conducting tissues (xylem and phloem).

Totipotency (Think as a Scientist): in 1958 F. C. Steward grew a whole carrot plant from single phloem cells in a nutrient medium. The cells first lost their specialisation (dedifferentiated), divided, then redifferentiated into root and shoot. This is the basis of plant tissue culture.

Worked example

A ring of bark (which includes the phloem) is removed from a tree trunk, leaving the wood (xylem) intact. Predict what happens (i) to the leaves in the next few days (ii) to the roots over months.

Try it first, then show the solutionSolution

1. Xylem is intact, so water still reaches the leaves: they stay green for now.
2. Phloem is removed, so sugars made in the leaves cannot travel down past the ring.
3. The roots get no food, slowly use up their stores and die.
4. Once the roots die, water uptake stops and the whole tree dies.

Answer: (i) Leaves stay fresh at first (xylem works). (ii) Roots starve because phloem is cut, and eventually the tree dies.

Epithelial tissue

NCERT section 3.3 Animal Tissues

Epithelial tissue covers the body (skin) and lines internal organs such as the mouth, lungs, blood vessels and intestine. Its cells are packed closely with very little space between them, so it keeps out germs, cuts down water loss and controls what is absorbed or released.

Job	Structure	Where
Exchange (fast diffusion)	one layer of thin, flat cells	lining of blood vessels and air sacs of lungs
Protection from wear and germs	many layers; outer cells flat and tight	skin, mouth, oesophagus
Secretion (mucus, enzymes, hormones, sweat, saliva)	cube-shaped or tall gland cells	salivary and sweat glands, stomach lining
Sensing (smell, taste, hearing, balance)	receptor cells with hair-like cilia	nose, taste buds, inner ear
Absorption	one layer of tall, pillar-like cells, often with tiny hair-like projections	lining of small intestine

The rule: thin where things must pass, thick where wear and tear is high.

Worked example

Why is the lining of the lung air sacs a single layer of flat cells while the lining of the oesophagus has many layers?

Try it first, then show the solutionSolution

1. In the lungs, oxygen and carbon dioxide must diffuse quickly between air and blood; a thin, single layer gives the shortest path.
2. In the oesophagus, food rubs against the lining; many layers protect it, and worn outer cells can be replaced from below.

Answer: Thin single layer for fast gas exchange in the lungs; many layers for protection against friction in the oesophagus.

Connective tissue: blood, bone, cartilage, tendon, ligament

NCERT section 3.3 Animal Tissues

A connective tissue joins and supports other tissues. Its cells lie in a matrix (the material between cells). The matrix decides how the tissue behaves.

Blood has a fluid matrix, plasma (about 55% of blood volume). The formed elements (about 45%) are:

• Red blood cells (RBCs): contain haemoglobin, an iron-rich protein that carries oxygen; live about 4 months (120 days).
• White blood cells (WBCs): fight infection; they gather at an infected spot, causing redness, swelling and pus.
• Platelets: help blood clot at a cut.

Tissue	Matrix	Job
Bone	hard, with calcium and phosphorus compounds	strength, support, protection
Cartilage	soft, jelly-like but firm	flexibility; cushions bone ends (ear, nose tip, joints)
Tendon	tough, strong fibres	joins muscle to bone; passes the muscle's pull to the bone
Ligament	tough, slightly stretchy fibres	joins bone to bone; keeps joints stable and limits movement

Worked example

A girl's blood volume is about 4.5 litres. Using the NCERT proportions, estimate the volume of plasma and of formed elements. Which formed element helps when she cuts her finger?

Try it first, then show the solutionSolution

1. Plasma $=55\%$ of $4.5$ L $=0.55\times 4.5=2.475$ L, about 2.5 L.
2. Formed elements $=45\%$ of $4.5$ L $=0.45\times 4.5=2.025$ L, about 2.0 L.
3. Check: $2.475+2.025=4.5$ L.
4. Platelets help blood clot at the cut.

Answer: About 2.5 L plasma and 2.0 L formed elements; platelets help clotting.

Muscular and nervous tissue

NCERT section 3.3 Animal Tissues

Muscle tissue contracts and relaxes to cause movement.

	Skeletal (striated)	Smooth	Cardiac
Control	voluntary	involuntary	involuntary
Shape	long, cylindrical, unbranched fibres	spindle-shaped (pointed ends)	cylindrical and branched
Nuclei	many per fibre	one	one
Stripes (striations)	clear light and dark bands	none	faint
Where	attached to bones (arms, legs)	stomach, intestine, blood vessels	heart only
Work	quick, strong, tires	slow, steady (moves food)	rhythmic, never tires

Nervous tissue is made of neurons (nerve cells) that receive, process and pass on messages.

• Cell body: contains the nucleus and controls the cell.
• Dendrites: short branches that receive signals.
• Axon: one long fibre that carries the message away, ending in axon terminals that pass it to the next cell.

The brain is the control centre. Muscles do not act on their own; nerves tell them when to contract. During exercise, the brain signals the heart to beat faster.

Worked example

A slide shows long, unbranched cylindrical fibres with many nuclei and clear stripes. Another shows branched fibres with one nucleus each and faint stripes. Identify both and give one place where each is found.

Try it first, then show the solutionSolution

1. Long, unbranched, multinucleate, clearly striped: skeletal muscle.
2. Branched, one nucleus, faint stripes: cardiac muscle.
3. Skeletal muscle: biceps of the arm; cardiac muscle: wall of the heart.

Answer: First: skeletal muscle (e.g. arm); second: cardiac muscle (heart).

The musculoskeletal system, joints and skeleton

NCERT section 3.4 The Musculoskeletal System

The musculoskeletal system is bones, muscles, joints, cartilage, tendons and ligaments working together under the nervous system. It lets us stand, move, keep posture and protects soft organs. The skeleton is about 12 to 15% of an adult's body weight.

Muscles can only pull. When a muscle contracts, its tendon pulls on a bone and the bone moves at a joint (a place where two or more bones meet).

Joint	Movement	Example
Ball and socket	in all directions, including circles	shoulder, hip
Hinge	back and forth in one plane, like a door	elbow, knee (protected by the kneecap)
Pivot	turning side to side	skull on the backbone (shaking the head 'no')
Fixed	no movement	bones of the skull

Skeletal system:

• Backbone (vertebral column): a chain of small bones (vertebrae) with cartilage discs between them that cushion and allow bending; it protects the spinal cord.
• Rib cage: 12 pairs of ribs, joined to the backbone behind and to the breastbone (sternum) in front through flexible cartilage. It guards the heart and lungs and can rise and fall for breathing.
• Skull: flat bones fused by fixed joints to protect the brain, eyes and ears.

Bone marrow contains stem cells that make new blood cells; bone marrow transplants treat leukaemia and thalassaemia.

Worked example

Using the NCERT figure that bone is about 12 to 15% of body weight, estimate the mass of the skeleton of a 60 kg adult.

Try it first, then show the solutionSolution

1. Lower estimate $=0.12\times 60=7.2$ kg.
2. Upper estimate $=0.15\times 60=9$ kg.

Answer: Between about 7.2 kg and 9 kg.

Caring for bones, muscles and joints

NCERT section 3.6 Skeletal System

The CBSE syllabus asks for an elementary idea of injuries and how to look after this system.

Common injuries

• Fracture: a crack or break in a bone. Keep the part still (a splint), and get an X-ray.
• Sprain: a ligament stretched or torn, often at the ankle or wrist when it twists.
• Strain: a muscle or tendon over-stretched, for example a 'pulled' thigh muscle.
• Dislocation: a bone pushed out of its joint, often the shoulder.
• Cartilage tear: damage to the cushioning cartilage, often in the knee.

First aid for sprains and strains: rest the part, apply a cold pack, support it with a bandage and keep it raised; see a doctor if it is badly swollen or cannot bear weight.

Postural care: sit with the back straight and supported; keep screens at eye level; carry a school bag on both shoulders; bend the knees, not the back, to lift something heavy; avoid sitting still for hours.

Nutrition: calcium and phosphorus (milk, curd, paneer, ragi, green leafy vegetables) and vitamin D (sunlight) for bones; protein (pulses, eggs, nuts) for muscles.

Exercise: running, skipping, games, yoga and Surya Namaskar keep bones strong, muscles fit and joints flexible. International Yoga Day is on 21 June.

Worked example

During a kabaddi match, Arjun twists his ankle; it swells but he can move his toes and there is no bent shape. Which tissue is most likely injured, what is the injury called, and what first aid should be given?

Try it first, then show the solutionSolution

1. A twisted joint usually over-stretches the ligament that joins bone to bone at the ankle.
2. This is a sprain (no bent shape suggests no fracture, but an X-ray confirms).
3. First aid: rest, a cold pack, a supporting bandage and keeping the foot raised; see a doctor if pain or swelling is severe.

Answer: A ligament: a sprain. Rest, cold pack, bandage support and raise the foot; get it checked.

Science in real life: Tissues in Action

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Topics in this chapter

• Animal Tissues and the Musculoskeletal System
• Plant Tissues: Meristematic and Permanent

Tissues in Action: formulas and key facts

Levels of organisation

1. 1.Cell
2. 2.tissue
3. 3.organ
4. 4.organ system
5. 5.organism.

Meristems

Apical (tips): length. Lateral (ring in stem): girth. Intercalary (base of internode or above node): regrowth after cutting.

Meristematic cell

Small, thin wall, big nucleus, dense cytoplasm, no vacuole, no intercellular spaces.

Simple permanent tissues

Parenchyma: living, thin wall, storage. Collenchyma: living, corners thickened with pectin, flexible support. Sclerenchyma: dead, lignin, strength.

Xylem

Tracheids, vessels, xylem parenchyma (only living part), xylem fibres; water and minerals upwards.

Phloem

Sieve tubes, companion cells, phloem parenchyma, phloem fibres (only dead part); food from leaves to all parts.

Blood

Plasma about 55%, formed elements about 45% (RBCs, WBCs, platelets). RBC life about 4 months.

Tendon and ligament

Tendon: muscle to bone. Ligament: bone to bone.

Muscles

Skeletal: voluntary, striated, multinucleate, unbranched. Smooth: involuntary, spindle, one nucleus, no stripes. Cardiac: involuntary, branched, one nucleus, faint stripes.

Joints

Ball and socket: shoulder, hip. Hinge: elbow, knee. Pivot: skull on backbone. Fixed: skull bones.

Body numbers

$Skeletonabout12to15$

Tissues in Action: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Tissues in Action

The question patterns to expect, and the method that works for each.

Tricks to remember Tissues in Action

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Tip, ring, node

  Apical at the Apex (tip) for length; Lateral round the Line of the circumference for girth; Intercalary In between (at nodes) for regrowth.

  Use it when: Matching meristems to growth.

• P-C-S: soft, bendy, hard

  Parenchyma = Packing and storage; Collenchyma = Corners and bending; Sclerenchyma = Stiff and dead (S for sclerosis, hardening).

  Use it when: Telling simple permanent tissues apart.

• Xylem up, phloem food

  XYlem carries water up the sky; PHloem carries PHood (food) everywhere.

  Use it when: Conducting tissues.

• TMB, LBB

  Tendon: Muscle to Bone. Ligament: Bone to Bone.

  Use it when: Connective tissue MCQs and assertion-reason.

• Skeletal = Stripes, Several nuclei, Self-controlled

  Skeletal muscle has three S's; smooth has none of them; cardiac is the branched one that never rests.

  Use it when: Comparing the three muscle types.

Tissues in Action: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section E style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 4-mark question split into 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Tissues in Action

The slips examiners see most often, and what to write instead.

• ✗Mistake: Swapping tendon and ligament

  Both are tough connective tissues near joints.

  Wrong working

  Ligaments join muscles to bones.

  Right working

  Tendons join muscle to bone; ligaments join bone to bone.

  ✓Do this: TMB, LBB.

  Usually costs: 1 mark, and the whole assertion-reason answer.

• ✗Mistake: Saying xylem carries food or that it is all living

  The two conducting tissues are learnt together.

  Wrong working

  Xylem is made of living sieve tubes and carries food.

  Right working

  Xylem carries water and minerals; only xylem parenchyma is living. Sieve tubes belong to phloem, which carries food.

  ✓Do this: Learn the four elements of each in two separate lists.

  Usually costs: 1 to 2 marks.

• ✗Mistake: Writing that meristematic cells have large vacuoles

  Mature plant cells have large vacuoles, so students assume all do.

  Wrong working

  Meristem cells store food in big vacuoles for division.

  Right working

  Meristematic cells have no (or tiny) vacuoles and dense cytoplasm, leaving room and material for fast division.

  ✓Do this: Remember 'busy cells, no store rooms'.

  Usually costs: 1 mark.

• ✗Mistake: Drawing muscle fibres wrongly

  The diagrams are memorised loosely.

  Wrong working

  Skeletal muscle drawn as spindle cells with one nucleus; smooth muscle drawn with stripes.

  Right working

  Skeletal: long cylinders, many nuclei, clear stripes. Smooth: spindle, one nucleus, no stripes. Cardiac: branched, one nucleus, faint stripes.

  ✓Do this: Practise all three side by side.

  Usually costs: Half the diagram marks.

• ✗Mistake: Calling the knee a ball and socket joint

  The knee feels like it moves a lot.

  Wrong working

  Knee: ball and socket, as it allows free movement.

  Right working

  The knee and elbow are hinge joints (one plane); the shoulder and hip are ball and socket.

  ✓Do this: Try the movement: can it make a full circle? Only ball and socket can.

  Usually costs: 1 mark.

NCERT exercise guide: Tissues in Action

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Practice questions on Tissues in Action

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   Growth in length of a plant is due to
   (a) lateral meristem
   (b) intercalary meristem
   (c) apical meristem
   (d) cork

   Hint

   Where are the tips?

   Answer

   (c) apical meristem

2. Q2 · 1 mark · MCQExam level

   Which joint lets the head turn from side to side?
   (a) Hinge
   (b) Pivot
   (c) Ball and socket
   (d) Fixed

   Hint

   Shaking your head 'no'.

   Answer

   (b) Pivot

3. Q3 · 1 mark · Assertion-reasonExam level

   Assertion (A): A torn ligament makes a joint unstable.
   Reason (R): Ligaments join muscles to bones.
   (a) A and R are both true, and R explains A correctly.
   (b) A and R are both true, but R does not explain A.
   (c) A is true, R is false.
   (d) A is false, R is true.

   Hint

   TMB, LBB.

   Answer

   (c). A is true: ligaments hold the bones of a joint together, so a tear lets the joint wobble. R is false: ligaments join bone to bone; tendons join muscle to bone.

4. Q4 · 2 marks · Very short answerExam level

   Name the four components of blood and give one function of each of the three formed elements.

   Hint

   One fluid, three kinds of cells or pieces.

   Answer

   Plasma, RBCs, WBCs and platelets. RBCs carry oxygen (haemoglobin); WBCs fight infection; platelets help clotting.

5. Q5 · 2 marks · Very short answerHarder exam level

   Why do meristematic cells lack vacuoles? Give two other features that suit them for division.

   Hint

   Busy cells, no store rooms.

   Answer

   Vacuoles store water and wastes in mature cells; dividing cells need the space filled with dense cytoplasm and organelles to make new cells quickly. Other features: large nucleus, thin walls (also tight packing with no intercellular spaces).

6. Q6 · 3 marks · Short answerHarder exam level

   Jute fibres from the stem are made into strong gunny bags. Which plant tissue are these fibres? Give two features of its cells that explain the strength, and one reason the tissue cannot store food.

   Hint

   Lignin.

   Answer

   Sclerenchyma. Its cells have thick lignified walls and are packed closely with almost no spaces, so the fibres are hard and strong. The cells are dead with only a narrow empty lumen, so they have no living contents to store food.

7. Q7 · 3 marks · Short answerHarder exam level

   Bamboo shoots grow quickly in height, a mango trunk gets thicker every year, and grazed grass grows back. Name the meristem responsible in each case and give its position.

   Hint

   Length, girth, regrowth.

   Answer

   Bamboo height: apical meristem at the shoot tip. Mango girth: lateral meristem, a ring along the circumference of the stem. Grass regrowth: intercalary meristem at the base of internodes, near the nodes.

8. Q8 · 3 marks · Short answerHarder exam level

   Compare skeletal and smooth muscle on control, shape, nuclei and striations.

   Hint

   The three S's.

   Answer

   Skeletal: voluntary; long cylindrical unbranched fibres; many nuclei; clear striations. Smooth: involuntary; spindle-shaped; one nucleus; no striations.

9. Q9 · 3 marks · Short answerHarder exam level

   A student weighs 45 kg. Using 12 to 15% for bone and 30 to 40% for muscle, estimate the range of her bone mass and muscle mass. Why might these differ from a classmate of the same weight?

   Hint

   Multiply weight by each percentage.

   Answer

   Bone: $0.12\times 45=5.4$ kg to $0.15\times 45=6.75$ kg. Muscle: $0.30\times 45=13.5$ kg to $0.40\times 45=18$ kg. They differ with age, sex, exercise, diet and body build (more fat or more muscle).

10. Q10 · 5 marks · Long answerHarder exam level

    Draw a labelled diagram of a neuron and explain how a message passes from one neuron to the next.

    Hint

    Dendrites in, axon out.

    Answer

    Diagram: cell body with nucleus, dendrites, long axon, axon terminals. The message is received by dendrites, passes to the cell body, travels along the axon away from the cell body, and the axon terminals pass it on to the dendrites of the next neuron (or to a muscle or gland).

11. Q11 · 3 marks · Short answerHOTS / competency

    A student claims, 'Dead cells are useless to a plant.' Use two plant tissues to argue against this claim.

    Hint

    Think of pipes and strength.

    Answer

    Xylem vessels and tracheids are dead, hollow tubes, so water and minerals flow through them upwards without blocking contents. Sclerenchyma fibres are dead cells with thick lignified walls that give strength to stems, veins and husks. Cork (bark) is also dead and protects the trunk. So dead cells do important jobs.

12. Q12 · 3 marks · Short answerHOTS / competency

    Why does the rib cage need cartilage joints instead of fixed joints like the skull? What would happen to breathing if the ribs were fused?

    Hint

    The cage has to move.

    Answer

    The ribs must move up and out and back during breathing to change the space in the chest. Flexible cartilage allows this. If fused, the chest could not expand, so air could not be drawn in properly and breathing would be shallow and difficult (only the diaphragm could help).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Define a tissue.Show answer

   A group of cells, similar in structure, working together to do a particular job.

2. 2.Which meristem increases the girth of a stem?Show answer

   The lateral meristem.

3. 3.What is differentiation?Show answer

   The process by which cells lose the power to divide and become specialised for a particular job, forming permanent tissue.

4. 4.What is the cuticle made of and what does it do?Show answer

   A waxy substance, cutin; it reduces water loss and protects against injury and parasites.

5. 5.Which substance thickens collenchyma walls, and which thickens sclerenchyma walls?Show answer

   Pectin in collenchyma; lignin in sclerenchyma.

6. 6.Name the only living element of xylem.Show answer

   Xylem parenchyma.

7. 7.What is the job of companion cells?Show answer

   They control the sieve tubes and the loading and unloading of sugar.

8. 8.Which blood component helps clotting?Show answer

   Platelets.

9. 9.Name the three parts of a neuron.Show answer

   Cell body, dendrites and axon (ending in axon terminals).

10. 10.Which joint connects the skull to the backbone?Show answer

    A pivot joint.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you write the five levels of organisation in order?
• ☐Can you name the three meristems, their locations and their jobs?
• ☐Can you list five features of meristematic cells?
• ☐Can you compare parenchyma, collenchyma and sclerenchyma in a table?
• ☐Can you name the four elements each of xylem and phloem?
• ☐Can you match each epithelium to its job and location?
• ☐Can you state what tendons and ligaments join?
• ☐Can you compare the three muscle types on five points?
• ☐Can you draw a neuron and name its parts?
• ☐Can you name four joints with examples and three ways to care for bones?

Tissues in Action: frequently asked questions