I. Cell Theory
A. Three part theory about cells
1. All living things are made of cells
2. All cells arise from existing cells
3. All cells come from pre-existing cells
Red Blood Cells
Onion Skin Cells
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B. Who came up with this theory circa 1838?
Schleiden
(all plants are made of cells)
Schwann
(all animals are made of cells)
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Virchow
(all cells come from pre-existing cells)
II. How do we study cells?
A. Light Microscopes
1. Light passes through lenses to magnify image up to 1000X
2. Can observe living cells
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B. Electron Microscopes
1. Uses a beam of electrons to magnify image > 1000X
2. Kills cells being observed
III. Common features of all cells
A. Small size – allows materials to move via diffusion
Diffusion = process by which molecules move from
levels of high concentration to levels of low
concentration until equilibrium is reached
B. Cell Membrane – selectively/differentially permeable (lets some
things in and out)
C. Cytoplasm – semi-fluid material in which cell organelles float
D. Cytoskeleton – proteins that support the cell
E. Ribosomes – make proteins
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