Bright pink cells under Gram stain are characteristic of Gram negative status. This is associated with an outer lipid membrane and reduced peptidoglycan. The reduction in peptidoglycan is what leads to a failure to retain the Gram stain, which would have colored the cells purple.

Gram-positive bacteria are able to retain the crystal violet stain found in gram stain because of their thick peptidoglycan cell walls. Consequently, these bacteria stain dark blue or purple by gram staining. Alternatively, gram-negative bacteria appear red or pink because they are unable to retain the dye due to thinner cell walls and less peptidoglycan.

No animal cells will have cell walls. Trichocytes are specialized to be hard and resilient, but do not have cell walls.

Fungi, plants, and bacteria do use cell walls. The distinction between gram positive and gram negative bacteria refers to the composition of the cell wall only; both positive and negative bacteria have a cell wall present.

Bacterial cells are prokaryotic and lack all membrane-bound organelles. We can thus eliminate mitochondria and nucleus as answers. These structures are not found in bacterial cells or in mature erythrocytes.

All cells, regardless of origin, are surrounded by a cell membrane. This structure is present in both prokaryotes and erythrocytes.

DNA is used to code for the genome of the organism and is found in both prokaryotes and eukaryotes. Bacteria contain a cytsolic genome known as the nucleoid. Red blood cells, however, lack DNA. This is partly due to their lack of a nucleus, and is considered evolutionarily advantageous because no viruses can target red blood cells.

The technique explained in the question is the "Gram stain". Bacteria that are Gram-positive will stain a bluish-purple color, while Gram-negative bacteria will stain a red or pink color. This difference in color occurs because of the large cell wall present on Gram-positive bacteria, and is a response to increased peptidoglycan expression. Additionally, some bacteria (such as mycobacteria and helicobacter) are not easily stained using this method.

Bacilli are rod-shaped bacteria and "strepto" indicates organization in a chain. Streptobacillus bacteria are a class of bacteria that are rod-like in shape and tend to congregate in chains of cells.

Cocci are spherically shaped, and spirilli are rigid helices. Spirochetes are non-rigid helices.

Since the obligate anaerobe grows well, we know that both bacteria are grown in an anaerobic environment.

A facultative anaerobe can grow in an aerobic or anaerobic environment. It simply grows better when oxygen is present; therefore, we would see slower growth from a facultative anaerobe than an obligate anaerobe when there is no oxygen present. If the bacteria were aerobic, it would not grow at all in the anaerobic environment.

In order for the bacteria to be distributed throughout the liquid, it must be able to survive in either the presence or absence of oxygen. Facultative anaerobic bacteria can surive in both cases, although, they prefer oxygen. In the absence of oxygen, they can produce energy through fermentation. Both microaerophiles and obligate aerobic bacteria require oxygen to survive and, in this experiment, would be found near the top of the tube. Oxygen is toxic to obligate anaerobic bacteria, which would be found at the bottom.

Anaerobic environments lack oxygen, while aerobic environments contain oxygen. Generally, aerobic respiration is more energetically efficient than anaerobic respiration mechanisms. Aerotolerant organisms, however, will continue to use anaerobic means of energy production, even in the presence of oxygen. These are a special class of organism that can survive in either an aerobic or anaerobic environment.

Obligate anaerobes require an anaerobic environment and find oxygen to be toxic. These organisms will not be able to produce ATP in the presence of oxygen. Obligate aerobes require the presence of oxygen in order to survive and cannot produce ATP without oxygen utilization. Facultative anaerobes can switch between metabolism mechanisms, using cellular respiration in the presence of oxygen and fermentation or anaerobic respiration in its absence. Microaerophiles are aerobic organisms, but require a particularly low level of oxygen in order to survive.

Obligate anaerobes are incapable of producing energy in the presence of oxygen, and can only metabolize compounds via fermentation and anaerobic respiration. Oxygen acts as a toxin to obligate anaerobes.

In contrast, obligate aerobes are only capable of aerobic cellular respiration and cannot survive in the absence of oxygen. Facultative anaerobes are capable of multiple respiration mechanisms and can continue to generate energy in a fluctuating atmosphere, in either the presence or absence of oxygen.