🧬 Chapter 6: Tissues – CBSE Class 9 Science Notes
🔹 What is a Tissue?
- A tissue is a group of similar cells performing a specific function.
- Tissues make the functioning of organs more efficient in multicellular organisms.
🪴 Plant Tissues
🔹 6.2.1 Meristematic Tissue
- Meristematic tissues are actively dividing cells found in growing regions of plants.
- Types of Meristematic Tissue:
- Apical meristem – at the tips of roots and shoots → increases length.
- Intercalary meristem – at internodes or base of leaves → length.
- Lateral meristem (Cambium) – along sides of stem → girth (thickness).
🧪 Cells are small, with dense cytoplasm, thin walls, large nuclei, and no vacuoles.
🔹 6.2.2 Permanent Tissue
Formed when meristematic cells lose ability to divide and differentiate.
🔸 (i) Simple Permanent Tissue
- Parenchyma
- Living cells, thin-walled, loosely packed with intercellular spaces.
- Stores food; may do photosynthesis (chlorenchyma) or help in floating (aerenchyma).
- Collenchyma
- Living, elongated cells with thick corners.
- Provides flexibility and mechanical support (e.g., leaf stalks, tendrils).
- Sclerenchyma
- Dead cells with thick lignified walls, no internal space.
- Provides rigidity (e.g., coconut husk).
🔸 (ii) Complex Permanent Tissue
Made up of more than one type of cell.
- Xylem – transports water & minerals upward.
- Components: Tracheids, Vessels, Xylem Parenchyma, Xylem Fibres
- Phloem – transports food from leaves to plant parts.
- Components: Sieve tubes, Companion cells, Phloem Parenchyma, Phloem Fibres (only dead cells)
🔹 Epidermal Tissue
- Protective outer covering of plant body.
- May have:
- Stomata: pores for gaseous exchange and transpiration.
- Guard cells: control stomatal opening.
- Root hairs: increase absorption surface area.
- Cuticle (wax layer): prevents water loss in desert plants.
🔹 Cork (Protective Tissue)
- Replaces the epidermis in older stems/roots.
- Made of dead cells with suberin in walls (water & gas resistant).
🧍♂️ Animal Tissues
🔹 6.3.1 Epithelial Tissue
- Covers organs & lines body cavities.
- Tightly packed, no intercellular spaces.
- Types:
- Squamous Epithelium – flat cells (e.g., blood vessels, alveoli)
- Stratified Squamous – layered for protection (e.g., skin)
- Cuboidal – cube-shaped (e.g., kidney tubules)
- Columnar – tall cells (e.g., intestine)
- Ciliated Columnar – with cilia, in respiratory tract
- Glandular Epithelium – secretes substances (e.g., glands)
🔹 6.3.2 Connective Tissue
- Connects different parts of body.
| Type | Features & Function |
|---|---|
| Blood | Fluid matrix (plasma), transports materials |
| Bone | Hard matrix of calcium & phosphorus; supports body |
| Cartilage | Flexible, smoothens joints, in ear, nose, etc. |
| Ligament | Connects bone to bone, elastic |
| Tendon | Connects muscle to bone, strong & stiff |
| Areolar tissue | Fills space, supports internal organs |
| Adipose tissue | Fat storage, insulation, under skin |
🔹 6.3.3 Muscular Tissue
- Responsible for body movement.
| Type | Features | Control | Location |
|---|---|---|---|
| Striated (skeletal) | Long, cylindrical, multinucleate, striated | Voluntary | Limbs |
| Smooth (unstriated) | Spindle-shaped, uninucleate | Involuntary | Walls of organs (intestine, blood vessels) |
| Cardiac | Branched, striated, uninucleate | Involuntary | Heart |
🔹 6.3.4 Nervous Tissue
- Neurons are nerve cells that transmit messages (nerve impulses).
- Structure: cell body, axon (long fibre), dendrites (short branches).
- Forms brain, spinal cord, nerves.
📌 Key Terms to Remember
- Differentiation: Process of cells becoming specialised.
- Intercellular Space: Space between cells.
- Meristem: Growth tissue in plants.
- Contractile Proteins: In muscles for contraction.