Tissues: Quick-Revision Notesh

Tissue Concept

• tissue = group of similar cells with common origin & function.

• In multicellular organisms tissues establish $\text{division of labour}$ → higher efficiency & survival.

Plant Tissues

1. Meristematic (dividing)

• General traits: thin cell wall, large nucleus, no/ small vacuole, no inter-cellular spaces, active mitosis.

• Types (by position)

  • Apical – tips of root & shoot; length growth.

  • Intercalary – at nodes/leaf bases; local elongation.

  • Lateral (cambium) – parallel to axis; $\text{girth}$ increase.

2. Permanent (non-dividing)

• Formed via differentiation of meristem.

• Categories:

  • Simple (one cell-type)

  • Parenchyma – thin wall, large vacuole; storage, photosynthesis (chlorenchyma), buoyancy (aerenchyma).

  • Collenchyma – cellulose/pectin thickenings at corners; flexibility, mechanical support, photosynthesis.

  • Sclerenchyma – dead, lignified; fibres & sclereids; hardness, strength.

  • Complex / conducting

  • Xylem – tracheids, vessels, fibres (dead); parenchyma (living); upward transport of water & minerals, support.

  • Phloem – sieve tubes, companion cells, parenchyma (living); fibres (dead); bidirectional food translocation.

3. Protective

• Epidermis – single layer, cuticle, root hairs, stomata; reduces water loss, gas exchange, absorption.

• Cork (phellem) – dead, suberised; formed by cork cambium; insulation & protection in older stems.

Animal Tissues

1. Epithelial

• Compact cells on basement membrane; no blood vessels.

• Types & locations

  • Squamous – alveoli, capillaries; diffusion, protection.

  • Cuboidal – kidney tubules, glands; secretion, absorption.

  • Columnar – stomach, intestine; absorption, secretion.

  • Ciliated – trachea, oviduct; propulsion.

  • Glandular – gastric / intestinal glands; secretion.

  • Stratified – skin, mouth lining; wear & tear protection.

2. Connective

• Cells + fibres in matrix; binding & support.

• Connective proper

  • Areolar – “packing”; joins skin to muscle, fills spaces.

  • Adipose – fat storage, insulation, shock absorption.

  • Tendon – dense collagen; muscle ↔ bone.

  • Ligament – elastic+collagen; bone ↔ bone.

• Supportive

  • Cartilage – chondrocytes in lacunae; nose, ear, trachea; flexibility.

  • Bone – osteocytes in lamellae, $\text{Ca}^{2+}$ salts; rigid endoskeleton.

• Fluid

  • Blood – plasma (≈$90\%$ water), RBCs (no nucleus, haemoglobin), WBCs (defence), platelets (clotting).

  • Lymph – plasma + WBCs; exchange & immunity.

3. Muscular (contractile)

• Striated (skeletal) – multinucleate, voluntary, rapid; attach to bones.

• Smooth (visceral) – spindle, uninucleate, involuntary, slow; walls of organs.

• Cardiac – branched, intercalated discs, rhythmic, non-fatigable; heart only.

4. Nervous

• Neuron = cyton + dendrites (receive) + axon (transmit); impulse across synapse.

• Types: apolar, unipolar, bipolar, multipolar (common).

Key Comparisons

• Plant vs Animal Tissues

  • Plants largely supportive, many dead cells; growth localized & indefinite.

  • Animals active, mostly living cells; growth definite & uniform.

• Xylem vs Phloem

  • Water/mineral vs food; upward only vs both directions; mainly dead vs living elements.

• Meristem vs Permanent

  • Dividing, thin-walled, dense cytoplasm vs differentiated, variable wall, large vacuole, specialized functions.

Crucial Figures / Values

• Blood composition: plasma $\approx55\%$, cells $\approx45\%$; RBC count $\approx5\times10^{6}\, \text{mm}^{-3}$, WBC $\approx4–11\times10^{3}\, \text{mm}^{-3}$.

• Human blood volume ≈ $5\,\text{L}$.

Take-home Points

• Meristems drive plant growth; cambium adds girth.

• Simple permanent tissues differ by wall thickening and living status.

• Xylem & phloem form vascular bundles (transport + support).

• Four basic animal tissues underpin all body structures and functions: epithelial (cover), connective (bind/support), muscular (movement), nervous (control).