Cell Theory and Levels of Organization Notes

Cell Theory

• Cell Theory is a basic principle in biology.
• Developed by German scientists: Theodor Schwann, Matthias Schleiden, and Rudolph Virchow.
• Cell Theory states:
  • All living organisms are composed of one or more cells.
  • The cell is the basic unit of structure and organization in all living organisms.
  • Cells arise from pre-existing cells (not spontaneous generation).

Modern Version of the Cell Theory

• Energy flow occurs within cells.
• Hereditary information (DNA) is passed from cell to cell.
• All cells have the same basic chemical composition.
• Basic principles that form the foundation for the study of life:
  • Cell theory
  • Gene theory
  • Evolution
  • Homeostasis
  • Laws of thermodynamics

Levels of Organization

• From simplest to most complex:
  • Atom
  • Molecule
  • Macromolecule
  • Organelle (e.g., Mitochondria)
  • Cell (e.g., Epithelial cells)
  • Tissue (e.g., Epithelial tissue)
  • Organ (e.g., Stomach)
  • Organ System (e.g., Digestive System)
  • Organism

Levels of Organisation (Multicellular Organisms)

• Five levels, from simplest to most complex:
  • Cells
  • Tissues
  • Organs
  • Organ Systems
  • Organism

Cells

• Basic unit of structure and function in living things.
• May serve a specific function within the organism.
• Examples: blood cells, nerve cells, bone cells, etc.

Specialised Cells

• Cells are differentiated to carry out specific functions.
• Examples:
  • Erythrocytes (red blood cells):
    • Flattened biconcave shape increases surface area to volume ratio.
    • Lack nuclei and many organelles to increase space for haemoglobin.
    • Flexible to squeeze through narrow capillaries.
  • Neutrophils (white blood cells):
    • Essential to the immune system.
    • Multi-lobed nucleus facilitates movement through small gaps to reach infection sites.
    • Cytoplasm contains enzymes to attack pathogens.
  • Sperm Cell:
    • Male gametes that deliver genetic information to the ovum.
    • Possess a flagellum (tail) for movement and many mitochondria for energy.
    • Head contains digestive enzymes to penetrate the ovum's protective layers.

Tissues

• Composed of similar cells working together to perform a specific activity.
• Examples: blood, nervous, bone.
• Four basic human tissues: connective, epithelial, muscle, and nerve.

Tissue Types (Animals)

• Nervous tissue: supports the transmission of electrical impulses.
• Epithelial tissue: covers body surfaces (internal and external).
• Muscle tissue: adapted to contract.
• Connective tissue: holds other tissues together or acts as transport medium.

Organs

• Composed of tissues working together to perform a specific activity.
• Examples: heart, brain, skin.
• Skin: The largest organ in the human body.

Organ System

• Groups of two or more organs working together for a specific function.
• Examples: circulatory system, nervous system, skeletal system.
• Eleven organ systems in the human body: circulatory, digestive, endocrine, excretory (urinary), immune (lymphatic), integumentary, muscular, nervous, reproductive, respiratory, and skeletal.

Organism

• Entire living things capable of carrying out all basic life processes.
• Processes: taking in materials, releasing energy from food, releasing wastes, growing, responding to the environment, and reproducing.
• Usually made up of organ systems, but may be unicellular (e.g., bacteria).
• Examples: bacteria, amoeba, mushroom, sunflower, human.