First organisms to inhabit the Earth 3.5 billion years ago. Prokaryotes are subjected to natural selection (reason for them being so diverse).

Prokaryotes are unicellular, much smaller than eukaryotic cells, have variety of shape, well organized within organism's cells.

The structure of a prokaryotic cell starts with the cell wall, which protects the cell and maintains the shape of the cell. Hypertonic environments allow prokaryotic cells to shrink and lose their water and with that lose of water, it can inhibit cell reproduction. With this action, salt can enter the cell, preserving the food, and allowing the cell to "die" from not reproducing (multiply) properly

Peptidoglycan - polymer composed of modified sugars linked by short polypeptides.

Gram stain - technique used to color and categorize cells. Gram positive - has a thick layer of peptidoglycan, which can hold the color well enough used to stain the cells. Gram negative - has less of the "gel" and has an outer membrane that contains carbohydrates.

Capsule - sticky layer of polysaccharide or protein. This layer allows prokaryotes to adhere to their substrates. Some protect the cell from dehydration and some shield pathogens from attacking the host's immune systems.

Endospores - resistant cells developed by bacteria when it lacks water or nutrients. Cell produces a copy of its chromosome and surrounds that copy with a structure to form the endospore. Most are durable and can survive in hot temperatures and conditions.

Fimbriae - stick to substances by this hairlike appendage. Used to fasten the cell to the membranes of the host. Similar is structure to pili, fimbriae are shorter and more numerous.

Taxis - directed movement toward or away from a stimulus (nutrients or oxygen)

Flagella - movement of the cell. Differ in prokaryotes and eukaryotes based on size and length, composition, and propulsion. Flagella is scattered all around the membrane or concentrated at one end.

Nucleoid - region of cytoplasm not enclosed by a membrane.
Plasmid - smaller rings of replicating DNA

Single prokaryotic cell can divide into 2, and then 4,6,8 and so on. Most can dive within 1 to 3 hours, and some even in 20 minutes. However, cells will eventually exhaust themselves of nutrients, poison themselves with waste, and would be consumed by others (similar to to human nature: birth and death.)

Phototrophs - organisms that obtain energy from light
Chemotrophs - organisms that obtain energy from chemicals
Autotrophs - organisms that only need CO2 or related source
Heterotrophs - require at least one organic nutrient

Obligate aerobes - must use O2 for cellular respiration and can't grow without it
Obligate anaerobes - poisoned by O2; live by fermentation and extract energy by anaerobic respiration, which uses any substance other than O2
Facultative anaerobes - uses O2 if present but can also use anaerobic respiration

Eukaryotes can only obtain Nitrogen - essential for amino acid production, from limited groups, while prokaryotes can metabolize nitrogen in many forms.

Nitrogen fixation - cells use the "fixed" nitrogen to form amino acids and other molecules.

Nitrogen fixed prokaryotes can increase nitrogen available in plants. Also uses compounds that ammonia is produced from

Cooperation that takes place between specialized cells of filament. Most cells carry out photosynthesis, but there are few that use heterocysts that use a different process

Heterocysts - specialized cells that use nitrogen fixation. Structure of a heterocyst: surrounded by a thick wall, which restricts entry of O2, produced by neighboring photosynthesis cells.

Biofilms - metabolic cooperations occurring between these surface-coating colonies. This causes colonies to grow. However, biofilms help with attracting nutrients and discarding waste.