Tissues: Plant and Animal Tissues

• Meristematic Tissue: Composed of young, undifferentiated, actively dividing cells with thin cellulose walls, dense cytoplasm, large nuclei, and no vacuoles. Responsible for continuous growth.
• Permanent Tissue: Composed of mature, fully differentiated cells that have lost the power of cell division. Possess specialized shapes, thickened walls, large central vacuoles, and perform specific permanent functions (food storage, support, vascular transport).

• (i) Apical Meristem:
- Location: Tips of growing roots and main shoot stems.
- Function: Produces new cells to increase the height and length of the plant (Primary growth).
• (ii) Lateral Meristem (Cambium):
- Location: Beneath the bark in circular vascular cylinders of dicot stems and roots.
- Function: Produces secondary xylem and phloem, increasing the girth, thickness, and diameter of the stem/root (Secondary growth).

1. Parenchyma: Cells are living, thin-walled (cellulose), oval/spherical, with large intercellular spaces. Functions in food storage, photosynthesis (chlorenchyma), and buoyancy (aerenchyma).
   2. Collenchyma: Cells are living, elongated, with cell walls thickened at corners with pectin, minimal intercellular spaces. Imparts tensile mechanical strength and flexibility, allowing young stems and leaves to bend in wind without breaking.
   3. Sclerenchyma: Cells are dead at maturity, with uniformly thick, hard cell walls impregnated with lignin, no intercellular spaces. Imparts rigid mechanical protection and structural strength (e.g., coconut husk, grit of pear).

• The four constituent elements of xylem are:
1. Xylem Tracheids (Dead, elongated hollow cells with tapered ends)
2. Xylem Vessels (Dead, continuous open cylindrical pipes)
3. Xylem Fibres (Dead, providing mechanical support)
4. Xylem Parenchyma (The ONLY living element in xylem; functions in radial conduction and food storage).

• Translocation: The physiological process of transporting soluble organic food materials (primarily sucrose) manufactured by photosynthesizing leaves to all non-photosynthesizing tissues, growing tips, and storage organs (roots, fruits, seeds) of the plant.
• Responsible Tissue: Phloem (specifically through perforated sieve tubes assisted by companion cells).

1. Branched Fibers with Intercalated Discs: Cardiac muscle cells are cylindrical and branched, forming an interconnected meshwork joined by specialized intercalated discs that allow synchronized electrical conduction across the heart.
   2. Involuntary and Non-Fatiguing: Unlike voluntary skeletal muscles that tire quickly, cardiac muscle is involuntary and completely immune to fatigue, contracting and relaxing rhythmically non-stop from embryonic development until death.

• A typical motor neuron consists of:
1. Cyton (Cell Body / Soma): Contains a prominent nucleus and granular Nissl's granules.
2. Dendrites: Short, branched cytoplasmic projections radiating from the cyton that receive incoming nerve signals.
3. Axon: A single, long, cylindrical cytoplasmic extension that conducts the impulse away from the cell body.
4. Myelin Sheath & Nodes of Ranvier: Insulating lipid layer around the axon with gaps (nodes) for saltatory conduction.
5. Axon Terminals (Synaptic Knobs): Terminal branches that transmit signals to the next neuron across a Synapse.

• Type of Epithelium: Ciliated Columnar Epithelium (interspersed with mucus-secreting goblet cells).
• Protective Function: The microscopic hair-like cilia beat rhythmically in a continuous upward wave, sweeping trapped dust particles, foreign bacteria, and mucus out of the respiratory tract toward the throat to be expelled, keeping the lungs clean.