Chapter 3: Tissues in Action
Complete Study Notes Plant & Animal Tissues Exam-Ready Format
1. Introduction — The Idea of a Tissue
A tissue is a group of cells that are similar in structure and work together to perform a specific function. The formation of tissues creates division of labour in the body, which increases efficiency and allows complex life processes to occur.
In unicellular organisms (e.g., Amoeba), a single cell performs all life functions. In multicellular organisms (plants and animals), different groups of specialised cells carry out different functions — this is why tissues exist.
Why Are Plant and Animal Tissues Different?
| Basis | Plants | Animals |
|---|---|---|
| Movement | Fixed in one place; need support to stay upright | Generally capable of movement (except a few like sponges) |
| Cell wall | Present — gives rigidity and strength | Absent — allows change of shape, aiding locomotion |
| Mode of nutrition | Autotrophic — tissues help utilise solar energy via photosynthesis | Heterotrophic — tissues help digest food from external sources |
| Growth pattern | Localised growth (only at meristems) — growth continues throughout life | Generalised growth — occurs throughout the body, but growth stops after a point |
2. Tissues for Growth in Plants
Plants grow in three distinct ways:
- Increase in length — height of stem and depth of roots
- Increase in girth — thickness of the stem
- Regrowth — after cutting of branches or grazing by animals
All three types of growth depend on actively dividing cells, collectively called meristematic tissue. There are three types, based on location and function.
2.1 Apical Meristem — Growth in Length
Two onion bulbs are placed in water-filled jars (Jar A and Jar B). Root growth is measured daily. On Day 3, the root tips of Jar B are cut by about 1 cm.
Observation: Roots in Jar A continue growing in length steadily. Roots in Jar B stop growing after their tips are removed.
Conclusion: Roots grow only from their tips, which contain cells that divide continuously (confirmed earlier by observing mitosis in onion root tips).
This growth zone at the tips of roots and shoots is called the apical meristem. It is responsible for increase in length of the plant.
2.2 Lateral Meristem — Growth in Girth
Located along the circumference of the stem (in a ring), this meristem produces new cells inside and outside in a concentric manner, increasing the stem’s diameter. This is called the lateral meristem (also linked to formation of annual growth rings seen in a cut tree trunk).
2.3 Intercalary Meristem — Regrowth After Cutting
Located at the base of the internode, or just above a node (the point where branches/leaves arise). When the tip of a stem is cut, growth in length stops, but new branches sprout from the nodes — this is why hedges become bushier after trimming and grass regrows after mowing/grazing.
Characteristics of Meristematic Cells
- Small in size, with thin cell walls
- Large, prominent nucleus and dense cytoplasm rich in organelles
- Vacuoles generally absent
- Tightly packed with little/no intercellular space
These features allow rapid and continuous cell division.
3. Permanent Tissues in Plants
Permanent tissues are classified as:
- Simple — composed of only one type of cell (parenchyma, collenchyma, sclerenchyma)
- Complex — composed of more than one type of cell working together (xylem, phloem)
3.1 Protective Tissue — Epidermis
The epidermis is the outermost layer of the plant body — a single, tightly packed layer of flat, rectangular cells. It is covered by a waxy layer called the cuticle, which reduces water loss. In roots, epidermal projections form root hairs that increase surface area for water/mineral absorption. In leaves, the epidermis contains pores called stomata, which allow gaseous exchange and transpiration (evaporation of water vapour), creating a transpiration pull that helps move water up through the xylem.
3.2 Supporting Tissues (Simple Permanent Tissues)
| Feature | Parenchyma | Collenchyma | Sclerenchyma |
|---|---|---|---|
| Cell nature | Living, thin-walled | Living, unevenly thickened corners (pectin) | Mostly dead, thick walls (lignin) |
| Packing | Loosely packed, intercellular spaces present | Fairly compact | Compact, no intercellular space |
| Function | Food storage; photosynthesis in green parts; aquatic forms have air spaces for floating | Provides flexibility — allows stems/tendrils to bend without breaking | Provides strength & rigidity (woody structure) |
| Location example | Cortex, pith | Petioles, young stems | Stems, leaf veins, seed/nut coverings (coconut husk, walnut shell) |
3.3 Conducting Tissues (Complex Permanent Tissues)
Xylem
- Transports water and minerals from roots upward
- Also gives mechanical strength
- Components: tracheids, vessels, xylem parenchyma, xylem fibres
- Only xylem parenchyma is living; tracheids, vessels, fibres are sclerenchymatous (dead, thick-walled)
Phloem
- Transports food (organic nutrients) from leaves to rest of plant
- Mostly made of living cells
- Components: sieve tubes, companion cells, phloem parenchyma, phloem fibres
- Companion cells regulate loading/unloading of sugars in sieve tubes
3.4 Plant Tissue Systems
All plant tissues are organised into three larger tissue systems:
- Dermal tissue system — outer covering; protects and reduces water loss (epidermis)
- Ground tissue system — main body between dermal and vascular tissue; includes parenchyma, collenchyma, sclerenchyma
- Vascular tissue system — conducting tissues: xylem and phloem
4. Animal Tissues
Animal tissues are broadly of four types: Epithelial, Connective, Muscular, and Nervous.
4.1 Epithelial Tissue
Forms the outer covering of the body (skin) and lines internal organs (mouth, lungs, blood vessels, intestine). Cells are closely packed with minimal intercellular space, preventing entry of germs and reducing water loss.
| Function | Structure | Location |
|---|---|---|
| Exchange (diffusion of gases/liquids) | Single layer of thin, flat cells (squamous) | Lining of blood vessels, lungs |
| Protection | Many layers; outer cells flat and tightly packed (stratified) | Skin, mouth, oesophagus |
| Secretion | Cuboidal/columnar cells specialised for producing & releasing substances | Salivary glands, sweat glands, stomach lining |
| Sensory function | Specialised receptor cells with hair-like cilia | Nostrils, taste buds, inner ear |
| Absorption | Single layer of tall, pillar-like (columnar) cells, often with hair-like structures | Lining of small intestine |
4.2 Connective Tissue
Connects and supports other tissues/organs. Composition varies in the matrix (the substance between cells) — from fluid (blood) to hard (bone).
| Tissue | Matrix / Structure | Function |
|---|---|---|
| Blood | Fluid matrix (plasma ~55%); contains RBCs, WBCs, platelets | Transports nutrients, gases, hormones, wastes |
| Bone | Hard, rigid matrix (calcium and phosphorus compounds) | Gives strength, support, and protection; forms the skeleton |
| Cartilage | Soft, jelly-like matrix | Provides flexibility; cushions bone ends (e.g., nose, ear) |
| Tendon | Tough fibrous connective tissue | Connects muscle to bone; transmits force for movement |
| Ligament | Fibrous connective tissue | Connects bone to bone; provides stability, limits movement, prevents dislocation |
Components of Blood
- Plasma — fluid part (~55% of volume); carries dissolved substances
- RBCs (Red Blood Cells) — contain haemoglobin (iron-rich protein, gives red colour); lifespan ~4 months
- WBCs (White Blood Cells) — fight infection; collect at infected sites causing pus/inflammation
- Platelets — help in blood clotting at injury sites
4.3 Muscular Tissue
| Type | Cell shape | Nuclei | Striations | Control | Location |
|---|---|---|---|---|---|
| Skeletal (striated) | Long, cylindrical, unbranched | Multinucleate | Present (striated) | Voluntary | Attached to skeleton (limbs, etc.) |
| Smooth (unstriated) | Spindle-shaped | Single nucleus | Absent | Involuntary | Stomach, intestines (slow, continuous movement) |
| Cardiac | Cylindrical, branched | Single nucleus | Faint striations | Involuntary | Only in the heart |
4.4 Nervous Tissue
Forms the body’s control and coordination network. Made up of neurons (nerve cells), specialised to receive, process, and transmit messages.
Structure of a Neuron (label carefully for diagram questions)
- Cell body — contains nucleus; controls cell activities
- Dendrites — receive signals from other neurons
- Axon — long fibre carrying messages away from the cell body, ending in axon terminals that transmit signals to other cells
5. The Musculoskeletal System
Made up of bones, muscles, joints, cartilage, tendons, and ligaments. It helps the body stand upright, move, maintain posture, and protect delicate organs — functioning under control of the nervous system. Muscles pull on bones via tendons; muscle contraction → tendon transmits force → movement at a joint.
5.1 Types of Joints
| Joint Type | Movement Allowed | Example Location |
|---|---|---|
| Ball and socket | Free movement — forward, backward, sideways, circular | Shoulder (rounded arm bone fits shoulder bone hollow) |
| Hinge | Movement in one direction only (like a door hinge) | Elbow, knee |
| Pivot | Side-to-side rotation (like a doorknob) | Joint between skull and backbone (neck) |
| Fixed | No movement | Skull bones (protect brain) |
5.2 Skeletal System — Backbone & Rib Cage
- Vertebral column (backbone) — series of small bones called vertebrae; supports the body, allows upright posture. Cartilage discs between vertebrae cushion and allow flexibility while protecting the spinal cord.
- Rib cage — 12 pairs of ribs; attached to the spine (back) and sternum/breast bone (front) via flexible cartilage. This flexibility allows the rib cage to expand/contract during breathing.
6. Important Named Concepts & Scientists
Demonstrated that single cells from carrot phloem could regenerate an entire plant. Phloem cells first dedifferentiate (regain ability to divide) forming an unspecialised cell mass, which then divides and redifferentiates into roots, shoot, and a complete plant. This ability of a mature cell to give rise to a whole organism is called totipotency, and such cells are totipotent cells — similar to how a zygote develops into a full organism.
Caused by the bacterium Agrobacterium tumefaciens; produces tumour-like swellings on stems due to uncontrolled cell division. Scientists studied how this bacterium transfers genetic material into plant cells — this knowledge is now used as a tool in plant tissue culture and genetic engineering to introduce useful genes into crops.
Renowned Indian botanist known for contributions to plant morphology and anatomy; authored Hasuru Honnu (Kannada), which won the Kendra Sahitya Akademi Award (1978).
Achieved a breakthrough in plant tissue culture — developed a complete plant through anther culture using an artificial nutrient medium under controlled conditions, contributing significantly to crop improvement.
7. Exam Question Bank
A. Multiple Choice / Assertion-Reason (1 mark each)
- Meristematic tissues can divide repeatedly because their cells have thin walls, dense cytoplasm, and a large prominent nucleus (NOT because they have thick walls or large vacuoles).[1]
- If a plant cannot transport food from leaves to roots, the malfunctioning tissue is Phloem.[1]
- Epithelial tissue lining internal organs is usually one/few cells thick to allow quick exchange of materials by diffusion.[1]
- Bending knees and ankles involves a Hinge joint.[1]
B. Short Answer (2–3 marks)
- Distinguish between xylem and phloem on the basis of function and cell nature (living/dead).[3]
- Why does a fresh green twig bend without breaking, while a dry twig snaps? Name the tissues responsible.[2]
- Differentiate between a tendon and a ligament with one example/function of each.[2]
- Explain why cardiac muscle can work continuously throughout life without fatigue.[2]
- What is meant by differentiation in the context of meristematic tissue?[2]
C. Long Answer / HOTS (4–5 marks)
- An elephant severely debarks a tree to feed on its bark. (a) Which function(s) of the tree are hampered? (b) Which tissue would be further affected if damage continues beneath the bark? (c) What function would be hampered if tissue beneath the bark is severely damaged? — Hint: bark removal damages phloem (just under the bark), disrupting food transport; further damage into the wood affects xylem (water transport) and the lateral meristem (girth growth).[5]
- Explain the totipotency experiment of F. C. Steward using carrot phloem cells. What does this reveal about the potential of mature plant cells?[5]
- With reference to Sohan’s sugarcane cutting experiment (Type A vs Type B), identify the likely difference between the cuttings (presence of a node/bud with meristematic tissue) and explain why only Type B could sprout.[4]
- Explain the three types of meristematic tissues with their location and function. How do they together account for a plant’s overall growth in length, girth, and branching?[5]
- Describe the structure and function of a neuron, and explain how nervous tissue coordinates both voluntary and involuntary muscle activity.[4]
D. Numerical / Graph-Based
- Using the teak tree data (age vs. diameter vs. annual rings), plot the graph and explain the relationship between diameter and number of annual rings formed. Identify the tissue responsible for girth and its location.[5]
At a Glance — Chapter Summary
- Tissue = group of similar cells performing specific functions; enables division of labour.
- Plant tissues: Meristematic (dividing: apical, lateral, intercalary) and Permanent (differentiated: simple & complex).
- Simple permanent tissues: parenchyma (storage), collenchyma (flexibility), sclerenchyma (strength).
- Complex permanent tissues: xylem (water/minerals, mostly dead) and phloem (food, mostly living).
- Animal tissues: Epithelial (covering/lining), Connective (support/connect — blood, bone, cartilage, tendon, ligament), Muscular (movement — skeletal, smooth, cardiac), Nervous (control/coordination — neurons).
- Musculoskeletal system = bones + muscles + joints + cartilage + tendons + ligaments, under nervous system control.
- Joint types: ball & socket (free movement), hinge (one direction), pivot (rotation), fixed (no movement).
- Totipotency: a mature plant cell’s ability to regenerate a whole organism (F. C. Steward, carrot phloem, 1958).