Under anaerobic conditions, fermentation follows the process of glycolysis. While glycolysis is responsible for creating ATP, fermentation allows the body to regenerate the NAD⁺ that is reduced during glycolytic processes. This key step allows glycolysis to continue, and more ATP to be made.

Fermentation is a form of anaerobic respiration where there is no oxygen available as the final electron acceptor to the electron transport chain. As such, pyruvate is reduced, yielding lactic acid and, in the presence of lactate decarboxylase, ethanol. However, the products of fermentation do not undergo the Krebs cycle nor electron transport chain. The purpose of fermentation is to regenerate NAD⁺ so that glycolysis can continue. The cell does this by transferring the electron from NADH to pyruvate. Fermentation is less efficient per glucose than is aerobic oxidation, generating a fraction of the ATP. Lactic acid and ethanol are actually quite toxic to the cell (in humans they are immediately sent to the liver to be detoxified).

Either ethanol or lactic acid can be produced through fermentation depending on the organism. Ethanol fermentation only occurs in bacteria and yeast. Lactic acid fermentation has been found to occur in multiple kingdoms. 

Fermentation allows for the regeneration of  which can allow for glycolysis to continue. Butanol is a four carbon alcohol and aspartic acid is an amino acid found in proteins. 

Glycogen is the common form for storing glucose in animal cells, while starch is the common form for storing glucose in plant cells. These saccharides are very similar, but glycogen is more easily digestable due to its structure. Liver and muscle cells are the primary storage places for glycogen. Adipose cells are primarily known for the storage of fats.

When blood glucose levels are elevated, the liver will convert available carbohydrates into glucose, and then convert the glucose into glycogen. This allows for glucose to be stored in the liver until blood glucose levels drop, and it needs to be released. The act of converting glucose to glycogen in the liver is called glycogenesis. Glycogenolysis is the opposite reaction, in which glycogen is converted to glucose once again.

Glycolysis is a step in cell metabolism in which glucose is cleaved into pyruvate. Gluconeogenesis is the production of glucose from non-carbohydrate molecules when glycogen is unavailable.

There are many factors that determine the fluidity of cell membranes. Membranes that are composed of fully saturated, long fatty acid tails are generally less fluid then the opposite conditions. In addition, lower temperatures result in a less fluid membrane.

Membranes that have fatty acid tails with double bonds are more fluid because the double bonds make it difficult for multiple phospholipids to float next to one another. The shape of the double bond adds a another dimension to the lipid, preventing the tails from packing together. Unsaturated fatty acids are thus more fluid than saturated fatty acids.

In higher temperatures, the cell membrane is going to become increasingly fluid due to the increased movement of the phospholipids. The cell membrane can control its fluidity in high temperatures by both increasing the saturated fatty acid tail content of the phospholipids, as well as making the fatty acid tails longer. Cholesterol can also help by acting as a buffer at high temperatures.

Although cell walls often serve very similar functions for different species, the composition of the cell walls can vary significantly. Plant cell walls employ cellulose, while bacteria use peptidoglycan. Fungal cell walls use the polymer chitin.

The correct answer is peptidoglycan. Cellulose composes the cell walls of plants, whereas chitin composes the cell walls of fungi. Starch and glycogen are stored polymers of glucose in plants and animals, respectively.

A Gram-positive cell has the following basic structural characteristics: stains dark purple in the Gram stain, has a thick peptidoglycan layer, and possesses no outer membrane beyond this layer. Thus, there is also no periplasmic space. Acid-fast stains are only used for specific bacteria that have waxy cell walls.