Answer to Question 1
A healthy GI tract is home to a vibrant community of some 100 trillion microbes-bacteria, viruses, fungi, protozoa, and other microorganisms, collectively known as the human microbiome. The prevalence of different microbes in various parts of the GI tract depends on such factors as pH, peristalsis, diet, and other microbes. Relatively few microbes can live in the low pH of the stomach with its somewhat rapid peristalsis, whereas the neutral pH and slow peristalsis of the lower small intestine and the large intestine permit the growth of a diverse and abundant population. Bacteria digest and metabolize fibers and other nutrients that cannot be digested by the human body, producing compounds such as short fragments of fat, which can influence energy metabolism and immunity. Bacteria in the GI tract also produce several vitamins. Fibers and some other food components are called prebiotics because they encourage the growth and activity of bacteria. Some foods contain probiotics, live microbes that change the conditions of the GI tract in ways that seem to benefit health, including helping to alleviate diarrhea, constipation, inflammatory bowel disease, ulcers, allergies, lactose intolerance, and infant colic; enhance immune function; and protect against colon cancer.
Answer to Question 2
A
Using a microscope to study the human body
Respiration in human
Important Human Viral Table
Three phylogenetic representations of modern human origins.
Human Visual System
A transgenic mouse carrying a mutation in the human SOD1 gene that causes paralysis of the limbs. In