1.2 Tissues: The Fabric of Life

Introduction to Tissues

• Definition: Groups of cells with similar structure and function.
• Histology: The study of tissues.
• Purpose: Division of labor, specialized functions, increased efficiency in multicellular organisms.

Plant Tissues

• Meristematic Tissues (Growth Tissues): Actively dividing cells.
  • Apical: Tips of roots/shoots (length).
  • Lateral: Sides of stems/roots (girth).
  • Intercalary: Base of leaves/internodes (length of leaves/internodes).
• Permanent Tissues (Specialized Tissues): Differentiated cells, lost ability to divide.

Plant Tissues: Permanent Tissues

Simple Permanent Tissues (Single cell type)

• Parenchyma: Storage, photosynthesis, buoyancy (chlorenchyma, aerenchyma).
• Collenchyma: Flexible support to young stems/leaves.
• Sclerenchyma: Rigid mechanical strength (fibers, sclereids).

Complex Permanent Tissues (Multiple cell types)

• Xylem: Conducts water and minerals (tracheids, vessels, parenchyma, fibers).
• Phloem: Transports food (sugars) (sieve tubes, companion cells, parenchyma, fibers).

Animal Tissues

• Classified into four main types:
  1. Epithelial Tissue: Covering and lining.
  2. Connective Tissue: Support and binding.
  3. Muscular Tissue: Movement.
  4. Nervous Tissue: Control and communication.

1. Epithelial Tissue (Covering Tissue)

• Function: Protection, absorption, filtration, secretion, sensation.
• Types:
  • Squamous: Thin, flat (filtration, diffusion).
  • Cuboidal: Cube-shaped (secretion, absorption).
  • Columnar: Tall, pillar-like (secretion, absorption).
  • Ciliated: With cilia (moves substances).
  • Glandular: Modified for secretion.

2. Connective Tissue (Supporting Tissue)

• Function: Connects, supports, binds other tissues/organs.
• Types:
  • Areolar: Loose packing, support.
  • Adipose: Fat storage, insulation.
  • Fibrous: Strong connection (tendons, ligaments).
  • Cartilage: Flexible support.
  • Bone: Rigid support, protection, movement.
  • Blood: Transport (fluid matrix).

3. Muscular Tissue (Movement Tissue)

• Composed of elongated cells (muscle fibers) capable of contraction.
• Types:
  • Striated (Skeletal): Voluntary, attached to bones.
  • Unstriated (Smooth): Involuntary, walls of internal organs.
  • Cardiac: Involuntary, branched, in heart wall.

4. Nervous Tissue (Control Tissue)

• Main component of nervous system (brain, spinal cord, nerves).
• Function: Generation and transmission of nerve impulses.
• Structure: Composed of neurons (cell body, dendrites, axon) and glial cells (supporting cells).