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Cells & Cell Organelles. The Building Blocks of Life. Cell Theory. Cells first described by Hooke – 1665 First LIVING cells described by Leeuwenhoek Schleiden – all plants made of cells Schwann – all animals made of cells Virchow – all cells come from pre-existing cells

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Cells & Cell Organelles

The Building Blocksof Life

cell theory
Cell Theory
  • Cells first described by Hooke – 1665
  • First LIVING cells described by Leeuwenhoek
  • Schleiden – all plants made of cells
  • Schwann – all animals made of cells
  • Virchow – all cells come from pre-existing cells
  • Principles of Cell Theory
    • cells are the basic units of life
    • all living things are composed of cells
    • cells come only from other cells
types of cells


Types of cells


- no organelles


- organelles

animal cells

plant cells

cell size comparison

Animal cell

Bacterial cell

Cell size comparison

most bacteria

  • 1-10 microns

eukaryotic cells

  • 10-100 microns


  • micron = micrometer = 1/1,000,000 meter
  • diameter of human hair = ~20 microns
prokaryote eukaryote dna comparison
Prokaryote/Eukaryote DNA comparison
  • Prokaryotes lack internal organization – NO organelles
  • Prokaryote DNA shaped as a closed ring floating in cytoplasm
    • Nucleoid region
  • Eukaryote DNA in linear chromosomes enclosed in a nucleus
prokaryote eukaryote cell wall comparison
Prokaryote/Eukaryote Cell Wall Comparison
  • Prokaryotes all have cell walls
    • Unique composition - peptidoglycan
  • Eukaryotes may or may not have cell walls
    • Animal cells – none
    • Plant cells – cell walls made of cellulose
    • Fungal cells – cell walls made of chitin
prokaryote vs eukaryote
Cell Wall of peptidoglycan

No membrane bound organelles

Ribosomes are present

DNA in a ring, floating in the cytoplasm

May or may not have cell walls

Membrane bound organelles

DNA enclosed in a nucleus and arranged in linear chromosomes

Prokaryote vs. Eukaryote
plant cell vs animal cell
Cell Wall of cellulose

Large Central Vacuole


No cell wall

Vacuoles are small and transient

No chloroplasts

Plant Cell vs. Animal Cell
observing cells how we know what we know
Observing Cells – How We Know What We Know…
  • Light Microscopes
    • Remember Hooke and Van Leeuwenhoek
    • Magnification
      • Size of image
    • Resolving power
      • Clarity of image
  • Observing Organelles
    • Too small for light microscope
  • Electron Microscope
    • Scanning EM
      • External views
    • Transmission EM
      • Thin sections of specimen – internal views
tem vs sem both are images of cells from a rabbit trachea windpipe cilia are visible
TEM vs SEM – both are images of cells from a rabbit trachea (windpipe). Cilia are visible.
why are cells small
Why are cells small?
  • With size increase, volume grows more than surface area.
  • Small objects have larger surface area:volume ratio
  • Cell/Plasma membrane functions as selective barrier
    • Enough oxygen, nutrients, wastes must pass in to service entire volume of the cell
    • Only so much “stuff” can pass through at a time.
    • Need a surface large enough to accommodate volume, thus cells have to be small.
eukaryotic cells and complex internal membranes
Eukaryotic Cells and Complex Internal Membranes
  • Membranes create ORGANELLES
    • Partition cells into compartments
    • Provide separate “little rooms” so that incompatible processes can go on at the same time in the cell
  • Internal membranes of cells participate directly in metabolism
    • Enzymes are often built directly into membranes
    • Chemical reactions occur at such sites
  • All membranes are similar, but different
    • All made of phospholipid bilayer
    • But suited to specific functions due to embedded enzymes, etc.
why study cells
Why study cells?
  • Cells  Tissues  Organs  Bodies
    • bodies are made up of cells
    • cells do all the work of life!
the work of life
The Work of Life
  • What jobs do cells have to do for an organism to live…
    • “breathe”
      • gas exchange: CO2 vs. O2
    • eat
      • take in & digest food
    • make energy
      • ATP
    • build molecules
      • proteins, carbohydrates, fats, nucleic acids
    • remove wastes
    • control internal conditions
    • respond to external environment
    • build more cells
      • growth, repair, reproduction & development



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Tour of the Eukaryotic Cell!