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