Cell Theory and Biological Classification

Cell Theory

• Cells are the fundamental unit of life and smallest structure capable of performing life functions.
• Organisms consist of one or more cells and all cells originate from pre-existing cells.
• Key contributors to cell theory include:
  • Hans and Zacharias Janssen - developed the first optical microscope.
  • Anton Van Leeuwenhoek - discovered bacteria and coined the term “animalcules.”
  • Robert Hooke - first to use the term “cell” after observing cork.
  • Matthias Schleiden - all plants are made up of cells.
  • Theodore Schwann - concluded that all animals are composed of cells.
  • Rudolf Virchow - asserted that "Omnis cellula e cellula," meaning all cells arise from pre-existing cells.

Zygote

• Defined as a fertilized egg formed by the union of an egg cell and a sperm cell.

Levels of Organization

• Biological organization follows a hierarchy: Cells > Tissues > Organs > Organ Systems > Organisms.

Cell Classification

• Living organisms are classified based on the presence of a nucleus:
  • Prokaryotes - lack a defined nucleus (bacteria).
  • Eukaryotes - have a defined nucleus (plants, animals).

Cell Structures

• Organelles are specialized internal structures within cells, observable under an electron microscope.

Human Tissue Types

• Four main types: Connective Tissue, Epithelial Tissue, Nervous Tissue, Muscle Tissue.

Epithelial Tissue

• Serves as a protective layer covering body surfaces and lining cavities.
• Functions include lining, protection, and forming glands (e.g., saliva, sweat).
• Types of epithelial tissue are classified by cell layers and shapes:
  • Simple (one layer) vs. Stratified (multiple layers).
  • Squamous (tile-like), Cuboidal (cube-like), Columnar (rectangular).

Connective Tissue

• Connects and supports various body parts; types include:
  • Bones - provide structure and support.
  • Blood - fluid connective tissue crucial for transport of oxygen and cells.
  • Dense Connective Tissue - includes ligaments (bone to bone) and tendons (muscle to bone).
  • Adipose Tissue - serves as insulation and shock absorber.

Muscular Tissue

• Composed of muscle cells that facilitate movement.
• Types of muscle tissue:
  • Skeletal Muscle - voluntary movement, attached to the skeleton.
  • Smooth Muscle - involuntary, controls internal functions (e.g., digestion).
  • Cardiac Muscle - involuntary, responsible for heart contractions.

Nervous Tissue

• Comprises neurons that transmit electrical impulses, connecting the brain and spinal cord to the body.
• Key components include:
  • Neurons - transmit signals.
  • Axons - carry impulses away from the cell body.
  • Dendrites - receive impulses toward the cell body.

Human Organ Systems

• Integumentary System: Protects body, regulates temperature, comprises skin, hair, nails.
• Muscular System: Facilitates movement and physical support.
• Skeletal System: Provides structure, protects organs, produces blood cells.
• Respiratory System: Manages gas exchange (oxygen in, carbon dioxide out).
• Digestive System: Breaks down food, absorbs nutrients, and eliminates waste.
• Excretory System: Maintains osmotic balance and eliminates metabolic waste.
• Nervous System: Controls body functions using the brain, spinal cord, and nerves.
• Endocrine System: Regulates bodily functions through hormones.
• Lymphatic System: Transports lymph and helps eliminate waste.
• Circulatory System: Composed of the pulmonary and systemic systems to manage blood flow.

Skin Structure

• Comprises three layers:
  • Epidermis: Outer layer, protective, produced by keratinocytes.
  • Dermis: Middle layer, contains connective tissue, sensory structures, and sweat glands.
  • Hypodermis: Inner layer, stores energy and connects skin to muscles.

Key Functions of Skin Cells

• Keratinocytes: Produce keratin.
• Melanocytes: Generate melanin, protecting against UV radiation.
• Langerhans: Play a protective role against pathogens.