Animal & Plant Tissues: Structure and Function

Posted on Nov 27, 2024 in Biology

Animal Tissues

Epithelial Tissue

Formed by closely packed flat, cubic, or cylindrical cells with short lifespans. Two main types:

  • Covering Epithelium: Forms a sheet covering body surfaces, cavities, and organ openings. Rests on a basement membrane. Three types:
    • Monostratified: Single layer of cells.
      • Squamous: e.g., alveoli lining.
      • Cuboidal: e.g., ovary wall lining.
      • Columnar: e.g., small intestine lining (with microvilli for absorption).
    • Pluristratified: Two or more cell layers.
      • Cuboidal: e.g., conjunctiva.
      • Squamous: e.g., mouth, esophagus, mammary gland ducts.
    • Pseudostratified Columnar: Appears layered but isn’t. Contains ciliated and goblet cells. e.g., trachea, bronchi.

Connective Tissue

Functions to unite, support, nourish, and protect other tissues. Various types:

  • Connective Tissue Proper: Connects and supports other tissues. Composed of collagen, elastic, and reticular fibers; fibroblasts; histiocytes/macrophages; mast cells; adipocytes; and blood cells.
  • Adipose Tissue: Primarily forms body fat. Adipocytes are large, spherical cells storing fat droplets in their cytoplasm.
  • Cartilaginous Tissue: Forms the skeleton and provides attachment for soft tissues. Solid, elastic matrix with chondrocytes in lacunae. Lacks blood vessels and nerve endings. Surrounded by perichondrium. Three types: hyaline, elastic, and bone.
  • Bone Tissue: Part of the vertebrate skeleton. Solid, rigid, mineralized extracellular matrix. Formed by osteoblasts, osteocytes (stellate cells in lacunae connected by canaliculi), and osteoclasts (multinucleated cells that absorb bone matrix).
  • Blood Tissue: Specialized connective tissue with a liquid matrix. Transports oxygen, nutrients, and waste products. Defends against foreign substances.
  • Blood Plasma: Yellowish, watery extracellular matrix of blood. Contains water, ions, proteins, lipids, glucose, amino acids, enzymes, hormones, and waste products.

Muscle Tissue

Main component of muscles, responsible for body movement. Three types:

  • Skeletal Striated Muscle
  • Cardiac Striated Muscle
  • Smooth Muscle

Nervous Tissue

Main component of the nervous system. Transforms stimuli into nerve impulses. Two main cell types:

  • Neurons: Transmit nerve impulses. Composed of perikarya, dendrites, and axons.
  • Glia: Supporting cells. Includes astrocytes, microglia, oligodendrocytes, and Schwann cells.

Plant Tissues

Meristematic Tissues

Derived from embryonic cells, retain the capacity for division, enabling continuous plant growth. Composed of small cells with thin walls, large nuclei, few vacuoles, and compact arrangement. Give rise to primary (from embryonic cells) and secondary (from dedifferentiated adult cells) meristems, such as cambium and phellogen.

Adult Tissues

Parenchyma

Most abundant plant tissue, poorly differentiated living cells with various shapes, thin cell walls, plastids, and a large central vacuole. Types:

  • Chlorenchyma: Photosynthetic, rich in chloroplasts. Found in green stems and leaves (mesophyll), including palisade and spongy parenchyma.
  • Storage Parenchyma: Stores starch reserves, mainly in seeds and tubers.
  • Aerenchyma: Contains large intercellular spaces for air storage, promoting gas exchange in aquatic plants.
  • Vascular Parenchyma: Accompanies vascular tissue.

Protective Tissues

Cover plant surfaces, protecting against desiccation and external agents.

  • Epidermis: Covers young plant parts. Usually a single layer of flattened living cells without intercellular spaces.
  • Endodermis: Located inside the root, separating vascular tissue from the cortex. Single layer of living cells with Casparian strips on radial and horizontal walls.
  • Suber (Cork): Replaces epidermis in secondary growth. Multiple layers of dead cells filled with air, arranged without intercellular spaces.

Supporting Tissues

Provide mechanical resistance.

  • Collenchyma: Found in young, growing parts. Elongated living cells with chloroplasts and thickened cellulose walls. Three types: angular, annular, and lacunar.
  • Sclerenchyma: Located in mature, non-growing organs. Dead cells with thick, lignified walls. Two types: sclereids and fibers.

Vascular Tissues

Specialized cells forming vessels for sap transport.

  • Xylem: Transports raw sap from roots to leaves. Primary and secondary xylem, each with vascular and non-vascular components.
  • Phloem: Transports prepared sap from leaves to other plant parts. Primary phloem with vascular and non-vascular components.

Secretory Tissues

Produce waste or useful substances.

  • External Secretory Tissues:
    • Located in the epidermis, expelling substances.
    • Nectaries: Secrete nectar to attract pollinators.
    • Hydathodes: Secrete water (guttation).
    • Stinging Hairs: Secrete irritants.
  • Internal Secretory Tissues:
    • Laticiferous Tubes: Elongated, branched, multinucleate cells throughout the plant.
    • Resin Canals: Cavities accumulating resin, defending against insects and fungi.