Unit 1.1: Cell Theory

Cells

  • Cells are the structural and functional units of life

Cell Theory

Cell theory states:

  1. Living organisms are composed of cells (or cell products)
  2. The cell is the smallest unit of independent life
  3. Cells can only arise from pre-existing cells
  • Cell theory is proved through:
    • microscopic evidence
    • cells replicate in the right conditions
    • organelles don’t survive outside of the cell

Atypical Cells

  1. Striated muscle cells: can be up to 300mm long, and is multi-nucleated
  2. Giant algae: very large unicellular organisms (challenges idea that cells are small)
  3. Aseptate hyphae: long, multinucleated fibers without partitioning and have complete cytoplasm

Functions of Life

  • Metabolism
  • Response (to stimuli)
  • Homeostasis
  • Growth
  • Reproduction
  • Excretion
  • Nutrition

Cell Size

  • Surface area to volume ratio is important in determining the size limitation of cells.
  • Cells need to exchange materials with the environment to survive
    • rate of metabolism is determined by the SA:V ratio
  • Small SA:V ratio
    • higher metabolic rate
    • lower material exchange
  • Large SA:V ratio
    • lower metabolic rate
    • higher material exchange
  • As a cell grows, volume increases faster than surface area
    • therefore, cells must stay as small as possible to keep the SA:V ratio high

Magnification

  • Magnification = Image Size / Actual Size
  • Actual Size = Image Size / Magnification

Cellular Organization

  • Organisms → Organ Systems → Organs → Tissues → Cells → Organelles

Stem Cells

  • Maturing stem cells can show how diseases/conditions occur in humans
  • Can be used in regenerative medicine/testing for drug safety
    • Stargardt’s Disease
    • A genetic disease that causes blindness in children
    • Injecting stem cells can cause retina cells to redevelop in the eye
    • Leukemia
    • Caused by a genetic mutation that causes an abnormal amount of white blood cells
    • Bone marrow transplants (hemapoietic stem cells get translpanted into the bone marrow of the patient)
  • Cell Types
    • Germinal Cells (sperm and egg cells)
    • Somatic Cells (anything that aren’t germinal cells)
    • Embryonic stem cells
      • stem cells from an embryo that can differentiate into any cell type (totipotent)
    • Umbilical cord stem cells
      • stem cells obtained from the umbilical cord (pluripotent)
    • Adult stem cells
      • obtained from adult tissues such as bone marrow (difficult to obtain and limited capacity to differentiate but are fully compatible with other adults)