1. Tissues

a. Definition of tissue [1 mark]

b. Types of tissues in the human body [2 marks]

1. Epithelial tissue
2. Connective tissue
3. Muscular tissue
4. Nervous tissue

c. Different types of tissues in detail [8 marks]

1. Epithelial tissue

• Cells are closely arranged with very little intercellular material.
• It has a free surface and rests on a basement membrane.
• It does not contain blood vessels. It receives nutrition by diffusion from underlying connective tissue.
• It has a high capacity for regeneration.

• Simple epithelium: One layer of cells.
• Stratified epithelium: Many layers of cells.
• Pseudostratified epithelium: Appears multilayered, but all cells rest on the basement membrane.

• Squamous: Flat cells.
• Cuboidal: Cube-shaped cells.
• Columnar: Tall, pillar-like cells.

• Protection, for example skin epithelium
• Absorption, for example intestine
• Secretion, for example glands
• Excretion, for example kidney tubules
• Filtration and diffusion, for example alveoli of lungs
• Sensory reception, for example taste buds

2. Connective tissue

• Cells: Fibroblasts, macrophages, mast cells, adipocytes, and blood cells
• Fibres: Collagen, elastic, and reticular fibres
• Ground substance or matrix: Material between cells and fibres

1. Loose connective tissue
   • Found beneath the skin and mucous membranes.
   • Fills spaces between organs.
   • Supports blood vessels and nerves.
2. Dense connective tissue
   • Contains many collagen fibres.
   • Gives strength.
   • Examples: Tendons and ligaments.
3. Adipose tissue
   • Contains fat cells.
   • Found under the skin and around organs.
   • Functions: Stores fat, provides insulation, and protects organs.
4. Cartilage
   • Firm but flexible connective tissue.
   • Found in nose, ear, trachea, and joints.
   • Functions: Support and shock absorption.
5. Bone
   • Hard connective tissue containing calcium salts.
   • Forms the skeleton.
   • Functions: Support, protection, movement, mineral storage, and formation of blood cells in bone marrow.
6. Blood
   • A fluid connective tissue.
   • Consists of plasma, red blood cells, white blood cells, and platelets.
   • Functions: Transport, defence, and clotting.

• Binding and supporting body parts
• Protection of organs
• Storage of fat and minerals
• Transport of gases, nutrients, and wastes through blood
• Defence against infection
• Repair of damaged tissues

3. Muscular tissue

a. Skeletal muscle

• Attached to bones by tendons.
• Striated or striped in appearance.
• Long, cylindrical, multinucleated cells.
• Voluntary in action.

• Movement of body parts
• Maintenance of posture
• Production of heat

b. Cardiac muscle

• Found only in the wall of the heart.
• Striated, branched cells with one central nucleus.
• Cells are joined by intercalated discs.
• Involuntary in action.

• Rhythmic contraction to pump blood throughout the body.

c. Smooth muscle

• Found in walls of hollow internal organs.
• Non-striated, spindle-shaped cells with a single nucleus.
• Involuntary in action.

• Movement of food through intestine
• Contraction of urinary bladder
• Control of diameter of blood vessels and airways
• Contraction of uterus during childbirth

4. Nervous tissue

a. Neurons

• Cell body: Contains nucleus
• Dendrites: Receive impulses toward the cell body
• Axon: Carries impulses away from the cell body

b. Neuroglial cells or supporting cells

• Brain
• Spinal cord
• Peripheral nerves
• Ganglia

• Receives sensations such as pain, touch, temperature, sight, and sound
• Conducts nerve impulses
• Coordinates body activities
• Controls muscle contraction and glandular secretion
• Helps maintain balance and body responses to the environment

2. Functions of the cell [4 marks]

1. Nutrition and absorption
   The cell takes in nutrients, water, oxygen, and other substances needed for life.
2. Metabolism and energy production
   Cells break down nutrients and produce energy, mainly in mitochondria, for their activities.
3. Synthesis and secretion
   Cells manufacture proteins, enzymes, hormones, and other substances. Some cells release these products outside the cell.
4. Respiration
   Cells use oxygen to release energy from food and produce carbon dioxide.
5. Excretion
   Waste products formed during metabolism are removed from the cell.
6. Growth and repair
   Cells grow, divide, and replace damaged or worn-out cells.
7. Response to stimuli
   Cells respond to changes in their internal or external environment, such as heat, chemicals, light, or nerve impulses.
8. Movement and contraction
   Some cells can move or change shape. Muscle cells contract to produce movement.
9. Reproduction
   Cells divide to form new cells, helping in growth, tissue repair, and reproduction.