The difference between gram-positive and gram-negative bacteria is the thickness of the peptidoglycan protein layer. Gram-positive bacteria have a thick peptidoglycan layer that retains the gram stain well, making it purple under a microscope. Gram-negative bacteria have a thinner peptidoglycan layer, and do not retain the stain as well as gram positive bacteria. This makes it pink when viewed under a microscope. 

Leukocytes can be broken down into the following categories and cells types.

We need to know the different between hypertonic, hypotonic, and isotonic. An environment is said to be hypertonic is there are more solute outside of the cell than inside. Since these solutes do not cross the cellular membrane very easily, but water can cross, water will travel out of the cell to balance the concentrations. This would cause the cell to shrink and shrivel.

The opposite is true for a hypotonic scenario, in which the cell will swell and maybe burst as water flows from the environment into the solute-filled cell. An isotonic environment is one in which solute concentrations are even, so there is no net movement of water into or out of the cell.

The two most common bacterial arrangements are Staph- and Strep-. Staph- is a non-symmetrical arrangement like a cluster of grapes. Strep- indicates a chain of bacteria.

The three most common bacterial shapes are listed below.

Coccus—round or oval

Bacillus—rectangular or rod-shaped

Spirilla (spirochete)—spiral

By breaking down names into arrangement and shape, students can predict or identify the appearance of an organism by its name. In the example Staph indicates arrangement in a chain. Coccus indicates round or oval in shape. Therefore, Staphylococci are round or oval-shaped organisms arranged in a cluster.

Aldehydes are powerful, toxic chemicals which work by denaturing DNA and RNA (nucleic acids).

Modern antibiotics are less toxic and work by disrupting cells' production of ribosomes. Common household cleaners, containing chlorine, work by oxidizing cell membranes. Older antibiotics, such as penicillin, work by dissolving cell walls. These modes of destruction are also known as mechanisms of cell death.

Spores can survive most methods of control and are resistant to cold and heat. Pasteurization is a heating process that destroys some pathogenic microorganisms in foods and beverages, but does not kill spores. Boiling is not considered a reliable lethal control because the destruction of bacterial spores cannot be guaranteed. Cold temperature is a non-lethal means of microbial control that can slow multiplication or induce stasis, but cold is only effective while conditions are maintained.

Incineration is the use of extreme temperature to reduce matter to ash and is an effective means of sterilization.

Detergents, or soaps, are non-lethal microbial controls. They emulsify lipids and oils, making it easier to wash them away. The action of washing away substances is strictly a mechanical mode of action. Detergents provide only static control, and have no killing power.

Prokaryotes create their own proteins, which means that ribosomes are present in the cell. Viruses, however, rely on the ribosomes of the host cell in order to create proteins. This means that ribosomes are not present in viruses, but are present in prokaryotes.

DNA and RNA will both be found in prokaryotes. Some viruses will contain DNA, while others will contain RNA. Attachment proteins allow viruses to bind to cell membranes, but also can allow one cell to bind to another.

Recall that bacterial ribosomes contain a 30S and a 50S subunit. The ribosome itself is a 70S ribosome, as the combination of the two subunits results in a smaller mass than the two separate units. Eukaryotic ribosomes contain a 40S and 60S subunit and form an 80S ribosome.

Flagella are used for mobility by both prokaryotes (bacteria) and eukaryotes. In humans, you can find these structures in sperm cells, which are propelled by the motion of flagella. Similarly, bacterial cells move through the environment with the aid of flagella. The key difference between a bacterial and eukaryotic flagellum is its composition. Bacterial flagella are made up of a protein called flagellin, whereas eukaryotic flagella are made up of microtubules, formed from the protein tubulin.