Tutor profile: Benjamin P.

How is the letter "v" pronounced in Spanish?

In Spanish, the letter "v" is pronounced the same as the letter "b." However, in some instances, the pronunciation of the letters "b" and "v" is "hard" (think of the "b" sound in English) and in some instances it is "soft." The "hard" pronunciation is used if the letter begins the phrase or follows "l," "m," "n," or "s;" otherwise, the "soft" pronunciation is used. For example, the hard "b" is used in the words "verdura," "convento," and "alba," while the soft "b" is used in the words "abuela" and "abogado."

Ascaris lumbricoides and Trichinella spiralis are similar in that they are both intestinal nematode parasites that affect the small intestine. However, adult T. spiralis stimulates inflammation and is cleared from the intestine by the immune system, while A. lumbricoides does not. Why is this?

A. lumbricoides is able to evade the immune system because it stays in the intestinal lumen, feeding off the food that the host has eaten. It does not invade the intestinal tissue, and therefore stimulates little to no immune response. T. spiralis, on the other hand, invades the intestinal mucosa and feeds on the intestinal tissue, causing inflammation. However; T. spiralis has its own methods of outsmarting the immune system, because adult females produce offspring before being cleared from the intestine; the larvae then enter the bloodstream and encyst in skeletal muscle tissue.

What is the difference between eubacteria and archaebacteria?

Bacteria and archaea were once considered to belong to the same kingdom (Bacteria) because scientists originally classified organisms based on their morphology. Bacteria and archaea are both prokaryotes, meaning they lack membrane-enclosed organelles, and are therefore morphologically similar. However, improvements in genomic analysis technology showed that bacteria and archaea are as genetically distinct from one another as each is from eukaryotes, hence the new three-domain system. Physiologically, bacteria differ from archaea in that their cell walls are usually composed of peptidoglycan, while archaeal cell walls are not. Additionally, the bacterial cell membrane contains ester-linked lipids, while the archaeal cell membrane contains ether-linked lipids.