Notes on Tissues PDF

**Notes on Tissues** ### 1. Definition of Tissue A tissue is a group of cells that are similar in structure and work together to perform a specific function efficiently. Examples include blood, phloem, and muscle tissues. --- ### 2. Plant Tissues Plant tissues are divided into two main categories...

**Notes on Tissues** ### 1. Definition of Tissue A tissue is a group of cells that are similar in structure and work together to perform a specific function efficiently. Examples include blood, phloem, and muscle tissues. --- ### 2. Plant Tissues Plant tissues are divided into two main categories: #### A. **Meristematic Tissues** - **Definition:** These are actively dividing tissues found in specific regions of the plant. - **Types of Meristematic Tissues:** 1. **Apical Meristem:** Located at the tips of stems and roots; responsible for the lengthwise growth of the plant. 2. **Lateral Meristem (Cambium):** Found in the vascular bundles; increases the girth (thickness) of stems and roots. 3. **Intercalary Meristem:** Present near the nodes; helps in the elongation of internodes. - **Characteristics:** Cells are dense with cytoplasm, thin cellulose walls, prominent nuclei, and lack vacuoles. #### B. **Permanent Tissues** Formed from meristematic tissues after differentiation (loss of division ability). ##### (i) **Simple Permanent Tissues** 1. **Parenchyma:** - **Structure:** Thin-walled, living cells; large intercellular spaces. - **Functions:** Stores food, aids in photosynthesis (chlorenchyma), and provides buoyancy in aquatic plants (aerenchyma). 2. **Collenchyma:** - **Structure:** Living cells with irregularly thickened cell walls; little intercellular space. - **Functions:** Provides flexibility and mechanical support. 3. **Sclerenchyma:** - **Structure:** Dead cells with thick, lignified walls; no internal spaces. - **Functions:** Provides strength and rigidity to plant parts like stems and seeds. ##### (ii) **Complex Permanent Tissues** 1. **Xylem (Conducts Water and Minerals):** - **Components:** - Tracheids and vessels (transport water and minerals). - Xylem parenchyma (stores food). - Xylem fibres (provides support). 2. **Phloem (Transports Food):** - **Components:** - Sieve tubes and sieve cells (conduct food). - Companion cells (support sieve tubes). - Phloem fibres (provide strength). - Phloem parenchyma (stores nutrients). ##### (iii) **Protective Tissue** 1. **Epidermis:** - Single outer layer; secretes a waxy cuticle to prevent water loss. - **Stomata:** Pores for gaseous exchange and transpiration; controlled by guard cells. 2. **Cork:** - Formed from secondary meristem; dead cells with suberin; provides insulation and prevents water loss. --- ### 3. Animal Tissues Animal tissues are categorized into epithelial, connective, muscular, and nervous tissues. #### A. **Epithelial Tissue** - **Function:** Covers and protects body surfaces, lines cavities, and regulates exchange of materials. - **Types:** 1. **Simple Squamous:** Thin and flat; facilitates diffusion (e.g., alveoli, blood vessels). 2. **Stratified Squamous:** Layers of cells; protects against wear and tear (e.g., skin). 3. **Cuboidal:** Cube-shaped; provides mechanical support (e.g., kidney tubules). 4. **Columnar:** Tall, pillar-like; aids absorption and secretion (e.g., intestines). 5. **Ciliated Columnar:** Has cilia for moving substances (e.g., respiratory tract). 6. **Glandular:** Secretes substances (e.g., salivary glands). #### B. **Connective Tissue** - **Function:** Supports, connects, or separates different types of tissues and organs. - **Types:** 1. **Blood:** - Liquid matrix (plasma); transports gases, nutrients, and waste. 2. **Bone:** - Hard matrix of calcium and phosphorus; provides structural support. 3. **Cartilage:** - Flexible matrix; smoothens joint surfaces (e.g., nose, ear). 4. **Tendons:** - Connect muscles to bones; strong but less elastic. 5. **Ligaments:** - Connect bones to bones; elastic and strong. 6. **Areolar Tissue:** - Found between skin and muscles; fills spaces and supports organs. 7. **Adipose Tissue:** - Stores fat; acts as an insulator. #### C. **Muscular Tissue** - **Function:** Responsible for movement in the body. - **Types:** 1. **Striated (Skeletal) Muscles:** - Voluntary; attached to bones; show striations. - Structure: Long, cylindrical, multinucleate cells. 2. **Smooth (Involuntary) Muscles:** - Found in organs like the stomach; spindle-shaped, uninucleate cells. 3. **Cardiac Muscles:** - Found in the heart; involuntary, branched, and striated. #### D. **Nervous Tissue** - **Function:** Transmits signals across the body. - **Structure:** - Composed of neurons. - Parts: Cell body, dendrites (receive signals), and axon (transmits signals). - **Location:** Brain, spinal cord, and nerves. --- ### Summary Chart: **Plant Tissues** - **Meristematic:** Apical, lateral, intercalary. - **Permanent:** Simple (parenchyma, collenchyma, sclerenchyma), complex (xylem, phloem), protective (epidermis, cork). **Animal Tissues** - **Epithelial:** Simple squamous, stratified squamous, cuboidal, columnar, ciliated, glandular. - **Connective:** Blood, bone, cartilage, tendons, ligaments, areolar, adipose. - **Muscular:** Striated, smooth, cardiac. - **Nervous:** Neurons.