Tissues in Action
Complete Visual Notes • Plant Tissues • Animal Tissues • Muscles • Neuron • Joints • Skeletal System • Totipotency • Question Answers
What is a Tissue?
In unicellular organisms, one cell must perform all essential life processes. In multicellular organisms, specialised cells divide the work among themselves.
Examples in Animals
- Muscular tissue produces movement.
- Nervous tissue carries information.
- Bone provides support.
- Blood transports materials.
- Epithelium protects and lines body surfaces.
Examples in Plants
- Meristematic tissues cause growth.
- Epidermis protects the plant.
- Parenchyma commonly stores food.
- Xylem transports water and minerals.
- Phloem transports prepared food.
Levels of Organisation
Why are Plant and Animal Tissues Different?
Plant and animal bodies have very different requirements. Most plants remain fixed in one place, whereas most animals move from place to place.
Plant cells also have rigid cell walls, while animal cells lack such a rigid wall and can therefore change shape more easily.
| Feature | Plants | Animals |
|---|---|---|
| Locomotion | Most remain fixed in one place. | Most show active locomotion. |
| Cell wall | Rigid cell wall gives mechanical support. | No rigid cell wall. |
| Nutrition | Photosynthetic tissues help manufacture food. | Tissues participate in obtaining and digesting food. |
| Transport | Xylem and phloem conduct substances. | Blood transports substances. |
| Growth | Growth is concentrated in specialised meristematic regions. | Growth pattern differs from plants. |
Meristematic Tissues
Plants may increase in length, increase in girth and regenerate after cutting or grazing. These processes require actively dividing cells.
Characteristics of Meristematic Cells
Types of Meristems
Apical Meristem
Location: Root and shoot tips.
Function: Increases length.
Lateral Meristem
Location: Along the circumference of the stem.
Function: Increases girth or diameter.
Intercalary Meristem
Location: Base of internode or near nodes in plants such as grasses.
Function: Regrowth and elongation after cutting.
Activity: Onion Root Tip Experiment
Observation
- Roots in Jar A continue to increase in length.
- Root elongation in Jar B stops or becomes greatly reduced after the tips are removed.
Inference: The root tip contains actively dividing apical meristematic cells.
Lateral Meristem and Annual Growth Rings
Activity of lateral meristem increases stem diameter. The cut surface of a woody trunk may show annual rings. Ring width may vary according to favourable or unfavourable conditions during growth.
Node and Internode
Node
A point on the plant stem from which leaves or branches arise.
Internode
The portion of stem between two successive nodes.
Differentiation
Permanent Tissues
Permanent tissues consist of specialised cells that perform particular functions such as protection, support, storage and transport.
Simple Permanent Tissue
Primarily made of one type of cell.
Examples: Parenchyma, collenchyma and sclerenchyma.
Complex Permanent Tissue
Made of more than one type of cell working together.
Examples: Xylem and phloem.
Internal Organisation of a Stem
4.1 Protective Tissue – Epidermis
The epidermis forms the outermost layer of the plant body. Its closely packed cells protect the tissues beneath.
- Protection against mechanical injury.
- Reduction of excessive water loss.
- Protection from invading microorganisms and parasites.
- Formation of root hairs in roots.
- Presence of stomata in leaves.
Cuticle
Epidermal cells may be covered by a waxy layer of cutin called the cuticle. A thick cuticle helps plants living in dry environments reduce water loss.
Root Hairs
Root hairs are extensions of epidermal cells. They increase the surface area available for absorption of water and minerals.
Stomata
Stomata are pores in the epidermis of leaves. They participate in gaseous exchange and transpiration.
4.2 Supporting Tissues – Parenchyma, Collenchyma and Sclerenchyma
Parenchyma
Cells: Living.
Walls: Thin.
Arrangement: Loosely packed with intercellular spaces.
- Mainly stores food.
- May carry out photosynthesis in green parts.
- Specialised parenchyma containing air spaces helps aquatic plants float.
Collenchyma
Cells: Living.
Walls: Unevenly thickened at the corners because of pectin deposition.
- Provides mechanical support.
- Provides flexibility.
- Allows stems and tendrils to bend without breaking.
Sclerenchyma
Cells: Most are dead at maturity.
Walls: Thick and lignified.
- Provides hardness and strength.
- Occurs in stems and leaf veins.
- Forms strong coverings and fibres.
Examples include coconut husk and hard coverings of nuts.
| Feature | Parenchyma | Collenchyma | Sclerenchyma |
|---|---|---|---|
| Cells | Living | Living | Mostly dead |
| Wall | Thin | Unevenly thickened | Very thick and lignified |
| Main role | Storage and other metabolic functions | Flexible support | Strength and rigidity |
4.3 Conducting Tissues – Xylem and Phloem
Xylem
Xylem transports water and minerals from the roots to other parts of the plant and also contributes to mechanical strength.
Components
- Tracheids
- Vessels
- Xylem parenchyma
- Xylem fibres
Xylem parenchyma is the living component highlighted in the chapter.
Phloem
Phloem transports food manufactured by leaves to other parts of the plant.
Components
- Sieve tubes
- Companion cells
- Phloem parenchyma
- Phloem fibres
Companion cells help regulate loading and unloading of sugars in sieve tubes.
Xylem → Water + minerals
Phloem → Prepared food
4.4 Plant Tissue Systems
Dermal Tissue System
Forms the outer covering and protects internal tissues.
Ground Tissue System
Forms much of the plant body between dermal and conducting tissues.
Vascular Tissue System
Consists of the conducting tissues xylem and phloem.
Cork and Bark
As plants become older, cells beneath the epidermis may develop the ability to divide and form cork cambium. Cork cambium produces compactly arranged cork cells.
Cork cells are dead and form an effective barrier to water and gases. They contribute to the bark of older stems.
Animal Tissues
Animal tissues are specialised according to the functions required by the body.
5.1 Epithelial Tissue
Epithelial tissue forms the outer covering of the body and lines many internal organs such as the mouth, lungs, blood vessels and intestine.
Its cells are closely packed with very little intercellular space.
| Function | Structure | Location |
|---|---|---|
| Exchange | Single layer of thin, flat cells | Lungs and blood vessels |
| Protection | Many layers with flat outer cells | Skin, mouth and oesophagus |
| Secretion | Cells specialised to produce and release substances | Glands and stomach lining |
| Sensory function | Specialised receptor cells | Nostrils, taste buds and inner ear |
| Absorption | Single layer of tall cells with specialised surface structures | Small intestine |
5.2 Connective Tissue
The nature of connective tissue depends greatly on its matrix. The matrix may be fluid, soft, jelly-like or hard.
Blood
Plasma
The fluid matrix of blood in which formed elements are suspended.
Formed Elements
- Red Blood Cells
- White Blood Cells
- Platelets
- RBCs contain haemoglobin, which contributes to the red colour of blood.
- Platelets help in blood clotting.
- WBCs participate in defence against infection.
- Blood transports nutrients, gases, hormones and other substances.
Bone, Cartilage, Tendon and Ligament
Bone
Has a hard, rigid matrix containing calcium and phosphorus compounds.
- Provides strength.
- Provides support.
- Protects organs.
Cartilage
Has a softer, jelly-like matrix.
- Provides flexibility.
- Cushions ends of bones.
- Helps absorb shock.
Tendon
Connects muscle to bone.
It transmits the force of muscle contraction to the skeleton.
Ligament
Connects bone to bone.
It provides stability and restricts excessive movement at a joint.
Ligament = Bone → Bone
Muscular Tissue
Muscles produce movement by contraction. Some movements are under conscious control, whereas others occur automatically.
| Feature | Skeletal | Smooth | Cardiac |
|---|---|---|---|
| Control | Voluntary | Involuntary | Involuntary |
| Shape | Long cylindrical fibres | Spindle-shaped cells | Branched cylindrical fibres |
| Striations | Present | Absent | Faint striations |
| Nucleus | Many nuclei | Single nucleus | Single nucleus as described in the chapter |
| Location | Attached to skeleton | Stomach and intestine | Heart |
Nervous Tissue and the Neuron
Nervous tissue forms the body’s communication and coordination network. Its specialised cells are called neurons.
Dendrites
Receive signals from other neurons or receptors.
Cell Body
Contains the nucleus and controls cellular activities.
Axon
Carries messages away from the cell body and ends in axon terminals.
The Musculoskeletal System
The musculoskeletal system includes bones, muscles, joints, cartilage, tendons and ligaments.
Functions
- Allows movement.
- Helps maintain posture.
- Supports the body.
- Protects delicate organs.
- Works under the control of the nervous system.
Types of Joints
Ball and Socket Joint
The rounded end of one bone fits into a hollow region of another.
Example: Shoulder.
Allows forward, backward, sideways and circular movement.
Hinge Joint
Allows movement mainly in one plane, like a door hinge.
Examples: Elbow and knee.
Pivot Joint
Allows rotational movement such as turning the head from side to side.
Example: Neck region.
Fixed Joint
Bones are joined so firmly that normal movement does not occur.
Example: Skull.
Skeletal System
The skeletal system is a framework of bones that gives the body strength and protects delicate internal organs.
Skull
Protects the brain and contributes to protection of important sensory organs.
Vertebral Column
Formed by a series of vertebrae. Supports the body and protects the spinal cord.
Rib Cage
Twelve pairs of ribs form a protective cage around the heart and lungs.
Cartilage Between Vertebrae
Cartilage discs between neighbouring vertebrae act as cushions and provide flexibility, allowing the backbone to bend and twist.
How the Rib Cage Helps Breathing
Totipotency and Plant Tissue Culture
The chapter describes the work of F. C. Steward, who demonstrated that cells from carrot tissue could regenerate an entire plant under suitable culture conditions.
Dedifferentiation
A mature specialised cell may regain the ability to divide and produce a mass of unspecialised cells.
Redifferentiation
The newly dividing cells may later become specialised again and develop into roots, shoots and ultimately a complete plant.
Experimental Conditions
| Light | Air | Medium | Result |
|---|---|---|---|
| Present | Absent | Solid + nutrients | Fresh weight reduced |
| Present | Present | Liquid + nutrients | About 20% increase |
| Absent | Present | Liquid + nutrients | Fresh weight reduced |
Crown Gall Disease and Agrobacterium
The chapter describes crown gall disease as tumour-like swelling caused by rapid uncontrolled cell division after infection by Agrobacterium tumefaciens.
Understanding how this bacterium transfers genetic material into plant cells later contributed to its use as a tool in plant biotechnology.
Scientists Mentioned in the Chapter
B. G. L. Swamy
Indian botanist known for contributions to plant morphology and anatomy.
Sipra Guha Mukherjee & S. C. Maheshwari
Their work in plant tissue culture contributed to development of complete plants through anther culture under laboratory conditions.
F. C. Steward
Demonstrated regeneration of complete carrot plants from cultured cells, providing important evidence for totipotency.
Chapter at a Glance
Textbook Data: Teak Tree Growth
Important CBSE Questions
1. What is a tissue? Why is tissue formation useful?
A tissue is a group of cells working together to perform a specific function.
Tissue formation produces division of labour. Different cell groups become specialised for different functions, increasing the efficiency of a multicellular organism.
2. Why are plant and animal tissues different?
Plants are generally stationary and possess rigid cell walls, whereas animals generally move and their cells lack rigid walls.
Their nutrition, movement, transport and growth requirements also differ. Their tissues are therefore structurally and functionally adapted to different roles.
3. Name the three types of meristematic tissues and give their functions.
- Apical meristem: increases length of roots and shoots.
- Lateral meristem: increases stem girth.
- Intercalary meristem: helps elongation and regeneration after cutting in suitable plants such as grasses.
4. What does the onion root experiment demonstrate?
Roots with intact tips continue to grow, whereas roots whose tips are removed stop or greatly reduce elongation.
This shows that the growing region contains actively dividing apical meristematic cells near the root tip.
5. Why do meristematic cells usually lack large vacuoles?
Meristematic cells divide rapidly and contain dense cytoplasm. Large storage vacuoles would occupy much of the cell volume and are therefore generally absent.
6. Define differentiation.
Differentiation is the process through which cells produced by meristems become structurally and functionally specialised and form permanent tissues.
7. Explain parenchyma.
Parenchyma consists of living, thin-walled cells commonly separated by intercellular spaces.
It mainly stores food. Green parenchyma may carry out photosynthesis, while specialised parenchyma with air spaces helps aquatic plants float.
8. Why does a fresh young stem bend without breaking?
Collenchyma provides flexible mechanical support. Its living cells have uneven wall thickening at the corners, allowing bending without easy breakage.
9. Why are coconut husk fibres hard?
Coconut husk contains sclerenchymatous fibres. Their thick, lignified cell walls provide great mechanical strength and hardness.
10. Explain the importance of epidermis.
Epidermis protects internal tissues from mechanical injury, excessive water loss and invading organisms.
Root epidermis may form root hairs, while leaf epidermis contains stomata involved in gaseous exchange and transpiration.
11. Why is a thick cuticle useful in a desert plant?
A thick waxy cuticle reduces loss of water from the surface. This is advantageous where water is scarce.
12. What would happen if a leaf had no stomata?
Gaseous exchange would be greatly restricted and transpiration would decrease sharply.
This would also reduce the transpiration pull contributing to water movement through xylem.
13. Name the four components of xylem.
- Tracheids
- Vessels
- Xylem parenchyma
- Xylem fibres
14. Name the four components of phloem.
- Sieve tubes
- Companion cells
- Phloem parenchyma
- Phloem fibres
15. Why are xylem and phloem called complex tissues?
They contain more than one type of cell working together for a common function.
16. Why is blood called connective tissue?
Blood connects different parts of the body functionally by transporting gases, nutrients, hormones and other substances. Its cells are suspended in the fluid matrix called plasma.
17. Differentiate between bone and cartilage.
Bone has a hard and rigid matrix and provides strong structural support and protection.
Cartilage has a softer, flexible matrix and provides flexibility and cushioning.
18. Differentiate between tendon and ligament.
Tendon: connects muscle to bone and transmits the pulling force of muscle contraction.
Ligament: connects bone to bone and stabilises a joint.
19. What is the function of platelets?
Platelets participate in blood clotting at the site of injury.
20. Why can an infected area become red and swollen?
Infection triggers an inflammatory defence response. White blood cells accumulate in the affected area, which may show redness, swelling and pus formation.
21. Compare skeletal, smooth and cardiac muscles.
Skeletal muscle: voluntary, long cylindrical fibres, striated and multinucleate.
Smooth muscle: involuntary, spindle-shaped, single nucleus and non-striated.
Cardiac muscle: involuntary, branched, cylindrical and rhythmically contracting fibres found only in the heart.
22. Explain the structure of a neuron.
A neuron has dendrites, a cell body and an axon.
- Dendrites receive signals.
- The cell body contains the nucleus.
- The axon carries messages away from the cell body.
- Axon terminals transmit messages to other cells.
23. How do muscles and bones produce movement?
When a skeletal muscle contracts, it pulls on its tendon. The tendon transfers this force to a bone, causing movement at a joint.
24. Why are the joints of the skull fixed?
Fixed joints firmly hold the skull bones together and form a strong protective case around the brain.
25. How does cartilage between vertebrae help?
Cartilage acts as a cushion and allows flexibility between adjacent vertebrae, permitting bending and twisting while protecting the spinal region.
26. What is totipotency?
Totipotency is the ability of certain plant cells to divide, differentiate and regenerate an entire plant under suitable conditions.
Revise, Reflect, Refine – Textbook Solutions
Q1. Which property enables meristematic tissues to divide repeatedly?
Correct answer: Thin walls, dense cytoplasm and a large prominent nucleus.
Q2. A plant cannot transport food from leaves to roots. Which tissue is malfunctioning?
Phloem.
Phloem transports food prepared in leaves to other plant parts.
Q3. Why is epithelium used for exchange usually very thin?
A thin layer provides a short pathway for rapid exchange of substances.
Q4. Why is a normal jump easier than a straight-leg jump?
In a normal jump the knee, ankle and hip joints bend and then extend in a coordinated manner. This enables muscles to generate and transfer force more effectively.
Q5. Which type of joint is involved when the knee bends?
Hinge joint.
Q6A. Assertion: Epithelium is suited for gas exchange in lungs. Reason: It has many layers of tall cells.
Assertion is true but the reason is false.
Exchange surfaces contain a thin layer of cells rather than many thick layers.
Q6B. Cardiac muscle can contract continuously without quickly tiring.
The assertion is true. Cardiac muscle is specialised for rhythmic, continuous activity throughout life.
Q6C. Tendons connect bone to bone.
The assertion is false.
Tendons connect muscle to bone. Ligaments connect bone to bone.
Q6D. A hinge joint moves mainly in one plane.
The assertion is true. A hinge joint primarily permits bending and straightening rather than movement freely in all directions.
Q7. What does the teak tree data show?
Stem diameter increases as the tree becomes older. The number of annual rings also increases with age.
The tissue responsible for increase in girth is the lateral meristem.
Q8. What happens when a tree is severely debarked?
Removal of bark damages the protective covering and exposes the stem to injury and water loss.
If the damage extends inward, conducting tissues may also be affected. Severe phloem damage interferes with food transport, whereas deeper damage may eventually affect xylem.
Q9. Which tissue gives a young mango stem flexibility?
Collenchyma.
Replacing it with sclerenchyma would increase rigidity and decrease flexibility.
Q10. Why can one sugarcane cutting sprout while another cannot?
A successful cutting must contain a suitable node or growing region containing cells capable of producing new growth.
For a fair experiment, light, water, temperature, nutrients, planting conditions and observation time should be kept comparable.
Q11. Is a tissue always composed of identical cells?
Simple tissues are primarily composed of one type of cell. Complex tissues such as xylem and phloem contain several different cell types working together for a common function.
Q12. Why can parenchyma not replace sclerenchyma in coconut husk?
Parenchyma is thin-walled and mainly suited for storage and other metabolic functions. Sclerenchyma has thick lignified walls and therefore provides much greater mechanical strength.
Q13. Are meristematic cells found only at root and shoot tips?
No.
Apical meristems occur at tips, lateral meristem increases girth, and intercalary meristem occurs near nodes or internodes in suitable plants.
Q14. Which normally has the larger vacuole: a mature plant cell or animal cell?
A typical mature plant cell normally has a larger vacuole. The comparison assumes ordinary differentiated cells rather than actively dividing meristematic cells.
Q15. Does every plant tissue perform only one function?
No. A tissue may have a major specialised function but can contribute to more than one process.
- Parenchyma may store food, perform photosynthesis or contain air spaces.
- Epidermis protects, while specialised epidermal structures also assist absorption, gaseous exchange and transpiration.
- Xylem conducts water and minerals and also provides support.
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