1. From Cells to Tissues — Division of Labour
A multicellular organism contains many cells. Instead of every cell performing every task, groups of specialised cells work together. These groups are called tissues.
A tissue is a group of cells that are similar in structure and work together to perform a particular function. The organisation of multicellular life can be viewed as:
Why are plant and animal tissues different?
| Feature | Plants | Animals |
|---|---|---|
| Movement | Most plants remain fixed in one place and need strong supporting tissues. | Animals generally move, so their tissues must support movement and flexible body shapes. |
| Nutrition | Plants manufacture food using photosynthesis. | Animals obtain and digest food from external sources. |
| Transport | Specialised tissues transport water, minerals and food. | Specialised tissues transport substances throughout the body. |
| Growth | Growth is concentrated in specialised meristematic regions. | Growth and tissue replacement occur throughout many parts of the body. |
2. Plant Tissues
Plant tissues can be broadly understood as meristematic tissues, which actively divide, and permanent tissues, whose cells have become specialised.
Plant tissues also work together as protecting, supporting and conducting systems.
3. Meristematic Tissues — Growth Regions
Meristematic cells are actively dividing cells. They generally have dense cytoplasm, a prominent nucleus and little or no large central vacuole. Their divisions produce new cells that may later differentiate into specialised permanent tissues.
| Type | Location | Main role |
|---|---|---|
| Apical meristem | Tips of roots and shoots | Increases length of the plant. |
| Lateral meristem | Along sides of stems and roots, such as cambium regions | Increases thickness or girth. |
| Intercalary meristem | Near nodes or bases of leaves/internodes in some plants | Supports growth and regrowth of particular regions, especially in grasses. |
4. Permanent Tissues
Permanent tissues develop from meristematic cells after differentiation. Their cells generally lose the ability to divide actively and become specialised for particular functions.
Simple permanent tissues
| Tissue | Key features | Functions |
|---|---|---|
| Parenchyma | Usually living cells with thin walls; often loosely arranged. | Storage and, in some tissues, photosynthesis and repair. |
| Collenchyma | Living cells with unevenly thickened walls, especially at corners. | Flexible support in growing parts such as young stems and leaf stalks. |
| Sclerenchyma | Usually dead at maturity with thick, lignified walls. | Strength and rigidity. |
Protecting tissues
The epidermis forms an outer protective covering of young plant parts. In older stems, cork can provide protection. The waxy cuticle on many aerial parts reduces water loss.
5. Conducting Tissues — Xylem and Phloem
Plants need transport systems to move water, minerals and food. Xylem and phloem form the main conducting tissues.
| Feature | Xylem | Phloem |
|---|---|---|
| Material transported | Water and dissolved minerals. | Food, mainly sugars produced by photosynthesis. |
| Direction | In a growing plant, movement of water/minerals is mainly from roots towards aerial parts. | Food can be transported from sources such as leaves to other parts that need or store it; movement can occur in different directions depending on source and sink. |
| Main components | Tracheids, vessels, xylem parenchyma and xylem fibres. | Sieve tubes, companion cells, phloem parenchyma and phloem fibres. |
| Living/dead | Most conducting elements are dead at maturity; xylem parenchyma is living. | Most functional conducting elements are living; phloem fibres are dead at maturity. |
6. Animal Tissues
Animal tissues are commonly grouped into four major categories: epithelial, connective, muscular and nervous tissue.
7. Epithelial Tissue
Epithelial tissue forms coverings and linings. Cells are closely packed, leaving little intercellular space. Its structure varies with its function.
| Type / example | Typical function |
|---|---|
| Squamous epithelium | Thin covering; useful where rapid diffusion or exchange is required. |
| Columnar epithelium | Absorption and secretion in regions such as the intestine. |
| Ciliated epithelium | Cilia move materials along surfaces, such as in parts of the respiratory tract. |
| Glandular epithelium | Secretion of substances. |
8. Connective Tissue
Connective tissues support, bind, connect and transport. Unlike epithelial tissue, connective tissue generally contains cells embedded in an extracellular matrix, whose composition varies with function.
| Connective tissue | Function / importance |
|---|---|
| Areolar tissue | Fills spaces, supports tissues and helps in repair. |
| Adipose tissue | Stores fat and provides insulation and cushioning. |
| Tendon | Connects muscle to bone; strong and relatively inelastic. |
| Ligament | Connects bone to bone at joints and provides stability while allowing movement. |
| Cartilage | Provides flexible support and reduces friction at many joints. |
| Bone | Provides rigid support, protects organs and helps form the framework for movement. |
| Blood | Fluid connective tissue that transports gases, nutrients, hormones, wastes and cells. |
9. Muscular Tissue — Movement Through Contraction
Muscle tissue is specialised to contract. Different muscle types have different structures and control mechanisms.
| Muscle type | Structure | Control | Location / role |
|---|---|---|---|
| Skeletal / striated | Long cylindrical, striated fibres; generally multinucleate. | Usually voluntary. | Attached to bones; body movement. |
| Smooth | Spindle-shaped, non-striated cells; usually one nucleus. | Involuntary. | Walls of organs such as stomach and intestine. |
| Cardiac | Branched, striated muscle cells with specialised connections. | Involuntary. | Heart; rhythmic contraction. |
10. Nervous Tissue — Control and Coordination
Nervous tissue forms the communication network of the body. Its major functional cells are neurons, which receive and transmit electrical and chemical signals.
| Neuron part | Main role |
|---|---|
| Cell body | Contains nucleus and supports the neuron's metabolic activities. |
| Dendrites | Usually receive signals from other cells or receptors. |
| Axon | Carries nerve impulses away from the cell body toward target cells. |
11. Musculoskeletal System and Joints
Movement in animals depends on cooperation among muscles, bones, connective tissues and the nervous system. Muscles generally pull rather than push, so movements around joints are coordinated by groups of muscles.
| Joint type | Example | Movement |
|---|---|---|
| Ball-and-socket | Shoulder, hip | Movement in several directions, including rotation. |
| Hinge | Elbow, knee | Movement mainly in one plane. |
| Pivot | Neck region | Rotation around an axis. |
| Fixed / immovable | Many skull joints | Little or no movement. |
Why are joints important?
- They connect bones while allowing appropriate movement.
- Cartilage and other structures can reduce friction and absorb forces.
- Ligaments help stabilise joints.
- Tendons connect muscles to bones and transmit muscular force.
12. Tissue Culture and Totipotency
Plant tissues can be cultured under suitable laboratory conditions. A remarkable property of many plant cells is totipotency — the ability of a cell to give rise to a complete plant when provided with appropriate conditions.
Plant tissue culture has applications in rapid multiplication of plants, conservation, disease-free planting material and crop improvement.
13. Meet the Scientists — Contributions to Tissue Science
14. Quick Revision Capsule
Most important comparisons
| Pair | Remember |
|---|---|
| Apical vs lateral meristem | Apical increases length; lateral increases girth. |
| Parenchyma vs collenchyma vs sclerenchyma | Storage/basic living tissue; flexible support; rigid strength respectively. |
| Xylem vs phloem | Water/minerals vs food/sugars. |
| Tendon vs ligament | Muscle-bone vs bone-bone. |
| Skeletal vs smooth vs cardiac | Voluntary movement; involuntary organ movement; involuntary rhythmic heart movement. |
15. Practice Questions
Short Answer
- What is a tissue?
- Explain division of labour in multicellular organisms.
- Why are plant and animal tissues different?
- Differentiate between meristematic and permanent tissues.
- Compare apical, lateral and intercalary meristems.
- Write the functions of parenchyma, collenchyma and sclerenchyma.
- Differentiate between xylem and phloem.
- Name the four major types of animal tissue.
- What are the main functions of epithelial tissue?
- Differentiate between tendon and ligament.
- Compare skeletal, smooth and cardiac muscles.
- Describe the basic structure and role of a neuron.
- What are ball-and-socket and hinge joints? Give examples.
- What is plant tissue culture?
- Explain totipotency in plants.
Answer Hints
2. Specialised tissues share different tasks, increasing efficiency.
3. Plants are mostly fixed and photosynthetic; animals generally move and obtain food externally, so their support, transport, nutrition and growth tissues differ.
4. Meristematic cells actively divide; permanent cells are differentiated and specialised.
5. Apical—length; lateral—girth; intercalary—growth/regrowth of specific regions.
6. Parenchyma—storage; collenchyma—flexible support; sclerenchyma—strength.
7. Xylem transports water/minerals; phloem transports food/sugars.
8. Epithelial, connective, muscular and nervous.
9. Protection, lining, absorption, secretion and exchange depending on type.
10. Tendon connects muscle to bone; ligament connects bone to bone.
11. Skeletal is generally voluntary and striated; smooth is involuntary and non-striated; cardiac is involuntary, striated and specialised for rhythmic heart contraction.
12. A neuron has a cell body, dendrites and axon and transmits signals.
13. Ball-and-socket allows movement in several directions; hinge mainly allows bending/straightening.
14. Growing plant cells/tissues under controlled laboratory conditions.
15. The capacity of a suitable plant cell to regenerate a whole plant under appropriate conditions.
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