BIO 1140 - Cell Structure & Varieties

a small membrane bound unit filled with a concentrated aqueous solution of chemicals with reproduction capacity

• Prokaryotic cells range from 0.2 to 2.0 µm in diameter • Eukaryotic cells range from 10-100 µm in diameter

• The cell surface area determines the amount of substances entering and exiting the cell • To function, cells must maintain a large surface area to volume ratio

Energy Source: - Phototroph = Light - Chemotroph = Chemical Compounds (Lithotroph & organotroph) Carbon Source: - Photoautotroph = Inorganic - Photoheterotroph = Organic - Chemoautotroph = Inorganic - Chemoheterotroph = Organic

Robert Hooke (1665) built the first compound microscope - two converging lenses - coined the term ‘cell’

Anton Van Leeuwenhoek (1670) observed living microorganisms - Called them animalcules - 200x magnification

• Cells are the fundamental units of life • All living organisms are composed of cells • All cells come from preexisting cells

• Modern cells evolved from a common ancestor

Unless natural pigments are present, there is little contrast and details are not distinguished - light passes directly through the cells

contrast is increased by emphasizing differences in refractive index (the capacity to bend light) - enhances light and dark regions in the cell

The combined images look as if the cell is casting a shadow on one side - two beams of polarized light are used

Stains differ greatly in their chemistry and their capacity to bind to cell materials. - A stain enhances contrast and reveals details not otherwise visible

a natural substance in the cell or a fluorescent dye that binds to a specific cell material is stimulated by a beam of light - the longer wavelength florescent light is observed coming directly from the dye

• fluorescent materials are used • adds a system of focusing both the stimulating and emitted light so that a single plane through the cell is seen • The result is a sharper two-dimensional image than with standard fluorescence microscopy

• 1931 • Max Knoll and Ernst Ruska invented electron microscope

The electron microscope directs electrons through a vacuum at a fluorescent screen or digital camera to create a visible image

The resolution of electron microscopes is about 2nm (100,000x greater than the eye).

• Transmission Electron Microscope (TEM) • Scanning Electron Microscope (SEM)

• a beam of electrons is focused on the object by magnets • Objects appear darker if they absorb the electrons • If the electrons pass through they are detected on a fluorescent screen

• electrons aredirected to the surface of the sample where they causeother electrons to be emitted • These electrons are viewedon a screen • The tree-dimensionalsurface of the samplecan be seen

Everything inside the cell, except for the nucleus of the cell has one, is termed the cytoplasm

The cytosol is the fluid cytoplasm not contained inside another compartment

• A prokaryotic cell does not have a nucleus or any other membrane-enclosed internal compartments • Eukaryotic cells contain membrane-enclosed compartments called organelles • Nucleus is the most noticeable organelle in eukaryotes

• A cell membrane • A nucleoid • A cytoplasm • Ribosomes (25 nm in diameter)