Learning Objectives
- Understand what tissues are and why multicellular organisms need them
- Classify plant tissues: meristematic and permanent
- Classify animal tissues: epithelial, connective, muscular, and nervous
- Relate tissue structure to their functions
Key Concepts
What are Tissues?
A tissue is a group of cells that are similar in structure and work together to perform a particular function. Multicellular organisms have division of labour among tissues, allowing specialisation and efficiency.
Plant Tissues โ Meristematic Tissue
Made of actively dividing cells. Cells are small, dense cytoplasm, thin cell walls, no vacuoles.
- Apical meristem: At tips of roots and stems โ increases length (primary growth).
- Lateral meristem (cambium): Increases girth of stem and root (secondary growth).
- Intercalary meristem: At base of leaves or internodes โ helps in elongation.
Plant Tissues โ Permanent Tissue
Cells that have lost the ability to divide. They are differentiated and specialised.
Simple Permanent Tissues:
- Parenchyma: Thin-walled, loosely packed cells with large intercellular spaces. Functions: storage, photosynthesis (chlorenchyma), buoyancy (aerenchyma). Found throughout the plant.
- Collenchyma: Irregularly thickened corners. Provides flexibility and mechanical support to growing parts like leaf stalks. Few intercellular spaces.
- Sclerenchyma: Uniformly thick, lignified cell walls. Cells are dead. Provides rigidity and hardness. Found in coconut husk, seed coats. No intercellular spaces.
Complex Permanent Tissues:
- Xylem: Conducts water and minerals from roots to leaves. Components: tracheids, vessels, xylem parenchyma, xylem fibres. Except xylem parenchyma, all are dead.
- Phloem: Transports food (sucrose) from leaves to other parts. Components: sieve tubes, companion cells, phloem parenchyma, phloem fibres. Except phloem fibres, all are living.
Animal Tissues
Epithelial Tissue: Covers body surfaces and lines organs. Cells tightly packed with no intercellular spaces. Types: squamous (flat โ skin), cuboidal (cube-shaped โ kidney tubules), columnar (tall โ intestinal lining), glandular (secretory), ciliated (with cilia โ respiratory tract).
Connective Tissue: Connects and supports organs. Has cells scattered in a matrix. Types: blood (fluid matrix โ plasma), bone (hard matrix โ calcium), cartilage (flexible matrix), ligament (connects bone to bone โ elastic), tendon (connects muscle to bone โ tough), areolar (fills spaces), adipose (stores fat).
Muscular Tissue: Responsible for movement. Types: striated/skeletal (voluntary, striped, attached to bones), smooth/unstriated (involuntary, no stripes, found in internal organs), cardiac (involuntary, striated, found only in heart, cells are branched).
Nervous Tissue: Transmits nerve impulses. Neuron is the structural and functional unit. Parts: cell body (cyton), dendrites (receive impulses), axon (transmits impulses). Found in brain, spinal cord, nerves.
Summary
Tissues are groups of specialised cells performing specific functions. Plant tissues include meristematic (dividing) and permanent (simple and complex) tissues. Animal tissues include epithelial, connective, muscular, and nervous tissues. Each tissue type has a distinct structure suited to its function.
Important Terms
- Tissue: A group of cells with similar structure and function
- Meristematic Tissue: Plant tissue composed of actively dividing cells
- Xylem: Vascular tissue that conducts water and minerals upward
- Phloem: Vascular tissue that transports food throughout the plant
- Neuron: Nerve cell; the basic unit of the nervous system
- Ligament: Connects bone to bone
- Tendon: Connects muscle to bone
Quick Revision
- Meristematic tissue divides continuously; permanent tissue does not
- Parenchyma: storage; Collenchyma: flexibility; Sclerenchyma: rigidity (dead cells)
- Xylem: water transport (mostly dead); Phloem: food transport (mostly living)
- Epithelial: covering; Connective: support; Muscular: movement; Nervous: signalling
- Three muscle types: skeletal (voluntary), smooth (involuntary), cardiac (involuntary)