Levels of Biological Organization and Tissues

Posted on Dec 1, 2024 in Biology

Levels of Biological Organization

Abiotic: Particles / Atomic / Molecular / Organelle

Biotic: Cells / Tissues and Organs / Systems / Population / Ecosystem / Biosphere

Bioelements and Biomolecules

Bioelements: Chemical elements forming living beings, present in specific proportions and combinations.

  • Primary: Most abundant (C, H, O, N)
  • Secondary: Less abundant but crucial (Na, K, Mg)
  • Trace elements: Present in small amounts but essential (Fe, I, Mn)

Bioelements combine to form Biomolecules:

Inorganic: Present in both living and non-living matter.

  • Water: Drives metabolic reactions, constitutes 70% of the body.
  • Mineral salts: Precipitates (skeletal features), dissolved (ions, nerve impulses).
  • Gases: CO2 (cellular respiration).

Organic: Exclusive to living matter.

  • Carbohydrates: Energy source.
  • Lipids: Energy reserve and other functions.
  • Proteins: Various functions (structural/collagen, regulatory/insulin, defense/antibodies).
  • Nucleic Acids: DNA and RNA (protein synthesis).

Histology: Embryonic Development

  1. Segmentation: Zygote divides into undifferentiated cells (morula).
  2. Gastrulation: Morula forms three layers (ectoderm, mesoderm, endoderm), initiating cell differentiation and tissue formation.
  3. Organogenesis: Formation of organs and systems.

Tissue Classification

Poorly Differentiated Cells

Epithelial Tissue

Covers and protects the body’s exterior and internal cavities. Classified by cell shape and layers:

  • Shape: Squamous (flat) or Cuboidal (cubical)
  • Layers: Simple (1 layer) or Stratified (+1 layer)
  • Examples: Simple squamous (endothelium – heart, blood vessels), Stratified squamous (epithelium/epidermis).

Glandular Tissue

Secretes substances. Can be isolated cells or grouped into glands:

  • Exocrine glands: Secrete externally (e.g., sweat glands).
  • Endocrine glands: Secrete internally (e.g., pituitary gland).
  • Mixed glands: Secrete both internally and externally (e.g., pancreas).

Connective Tissue

Binds organs, fills spaces, provides support. Intercellular substance varies in consistency:

  • Loose Connective Tissue: Semi-liquid intercellular substance with collagen, elastic, and reticular fibers. Cells include fibrocytes (produce fibers), melanocytes (contain melanin), and adipocytes (contain fat).
  • Fibrous Tissue: More fibers and fibrocytes than loose tissue (e.g., tendons).
  • Adipose Tissue: Many adipocytes, few fibers. Food reserve, found under skin, around organs, in yellow bone marrow.
  • Cartilaginous Tissue: Protein intercellular substance (chondrin) with collagen fibers and chondrocytes. Supports cartilage, found in joints, ears, and nose.

Highly Differentiated Cells

Nervous Tissue

Composed of neurons for nerve impulse transmission. Neurons have a cell body, dendrites, and an axon. Glial cells nourish neurons and remove waste.