Cell Theory
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Transcript of Cell Theory
Cell Theory
1. All living things are composed of cells.
2. Cells are the simplest form of life
3. All cells come from preexisting cells.
Compound Light Microscope
Different methods for seeing cell structures.TECHNIQUE RESULT
Brightfield (unstained specimen). Passes light directly through specimen. Unless cell is naturally pigmented or artificially stained, image has little contrast.
(a)
Brightfield (stained specimen). Staining with various dyes enhances contrast, but most staining procedures require that cells be fixed (preserved).
(b)
Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining living, unpigmented cells.
(c)
50 µm
Scanning Electron Microscope
…provides for detailed study of the surface of a specimen
TECHNIQUE RESULTS
Scanning electron microscopy. Micrographs taken with a scanning electron microscope show a 3D imageof the surface of a specimen. This SEM shows the surface of a cell from a rabbit trachea (windpipe) covered with motile organelles called cilia. Beating of the cilia helps moveinhaled debris upward toward the throat.
(a)
Cilia1 µm
Transmission Electron Microscope
provides for detailed study of the internal structure of cells
Longitudinalsection ofcilium
Cross sectionof cilium
1 µm
All cells have several basic features in common.
1. bounded by a plasma membrane
2. contain a semi-fluid substance called the cytoplasm.
3. contain chromosomes
4. all have ribosomes
Prokaryote vs. Eukaryote Cells
prokaryotic• Do not contain a nucleus
• Have their DNA located in a region called the nucleoid
eukaryotic• Contain a true nucleus,
bounded by a membranous nuclear envelope
• Have extensive and elaborately arranged internal membranes, which form organelles
• Are generally quite a bit bigger than prokaryotic cells
Animal Cell
Plant Cell
Plant Cell Structure
Onion CellsElodea with chloroplasts
Surface to Volume Ratio• Smaller cells have a higher
surface to volume ratio.
• This facilitates the exchange of materials into and out of the cell.
Surface area increases whiletotal volume remains constant
5
11
Total surface area (height width number of sides number of boxes)
Total volume (height width length number of boxes)
Surface-to-volume ratio (surface area volume)
6
1
6
150
125
12
750
125
6
Cell Membrane
Phospholipid Bilayer w/ Proteins
Plasma (cell) Membrane
• Functions as a selective barrier
• Allows sufficient passage of nutrients and waste
Outside of cell
Inside of cell
Hydrophilicregion
Hydrophobicregion
Hydrophilicregion
(b) Structure of the plasma membrane
Phospholipid ProteinsTEM of a plasmamembrane. Theplasma membrane,here in a red bloodcell, appears as apair of dark bandsseparated by alight band.
(a)
0.1 µm
Mitochondria
Chloroplasts
Ribosomes in the Endoplasmic Reticulum
Ribosomes
other miscellaneous structures/functions
• golgi apparatus- distributes molecules within the cell.
• lysosomes- digest/recycle obsolete cell organelles. Not found in plant cells.
• vacuoles- store materials in the cell.
• cytoskeleton- “cyte” = cell – support, protein fiber construction.
Cytoskeleton