IB Biology Topic 1: Cell Biology

Key Topics Covered

• Cell Theory
• Stem Cells
• Functions of Life
• Microscopes

Cell Theory

• Describes cells found in all living organisms
• Three Key Principles:
  1. Cells are the smallest unit of life
  2. All living organisms are made up of cells
  3. All cells come from pre-existing cells
• Atypical Cells (exceptions to the general trend):
  • Skeletal Muscle: Multi-nucleated
  • Septate Fungi: Contain hyphae but no septa
  • Acetabularia (Giant Algae): Very large but single-celled
• Surface Area to Volume Ratio:
  • As a cell grows, the surface area to volume ratio decreases
  • Limits speed of substance transport, energy transfer, and metabolism
  • Restricts cell size

Differentiation

• Differentiation: Development of cells in different ways to perform specific functions
  • Involves the expression of certain genes
  • Enables emergent properties (characteristics not evident at the cellular level)
• Stem Cells:
  • Can differentiate to form any cell
  • Types:
    • Pluripotent: Differentiate to form any cell in an organism
    • Multipotent: Differentiate to form many different cells but not any cell
  • Sources:
    • Embryonic Stem Cells: Pluripotent but not fully compatible with adults
    • Blood Stem Cells: Found in umbilical cord, multipotent, fully compatible with adults
    • Adult Stem Cells: Found in bone marrow, multipotent, fully compatible
  • Disease Treatment:
    • Stargardt's Disease: Stem cells form healthy retinal cells to cure blindness
    • Leukemia: Stem cells replace abnormal white blood cells with healthy ones

Functions of Life

• Mnemonic: MR G HEARN
  • M: Metabolism - Enzyme-catalyzed reactions
  • R: Reproduction - Production of offspring
  • G: Growth - Increase in mass/volume
  • H: Homeostasis - Maintaining internal environment
  • E: Excretion - Removal of metabolic waste
  • R: Response - Reacting to stimuli
  • N: Nutrition - Obtaining food for metabolism
• Examples:
  • Paramecium (Heterotroph):
    • Metabolism: Enzymatic reactions
    • Reproduction: Binary fission
    • Growth: Increase in size
    • Homeostasis: Maintains internal conditions
    • Excretion: Expulsion of waste
    • Response: Reacts to solids
    • Nutrition: Endocytosis
  • Chlamydomonas (Autotroph):
    • Metabolism: Enzymatic reactions
    • Reproduction: Binary fission
    • Growth: Increase in size
    • Homeostasis: Maintains internal conditions
    • Excretion: Expulsion of waste
    • Response: Responds to light
    • Nutrition: Photosynthesis

Microscopes

• Structure:
  • Lamp, condenser lens, stage, objective lens, nosepiece, eyepiece, focusing knob, diaphragm
• Resolution:
  • Ability to distinguish two close objects
  • Higher resolution with shorter wavelength
  • Light microscope: Uses light (long wavelength, low resolution)
  • Transmission Electron Microscope: Uses electron beams (short wavelength, high resolution)
• Calculating Magnification:
  • Formula: Magnification = Size of image / Size of specimen
  • Measurements must be in the same units
  • Example: Pollen grain 50 micrometers wide, image size 20 mm; Magnification = 400

Additional Resources

• Notes, flashcards, and questions available on the website for further study and reinforcement