Suppose there are 2.0 x 109 microvilli per cm2 of intestinal epithelium. calculate the total surface area of the microvilli in one cm2 of intestinal epithelium.

I have an article here that might help you understand more about villis and also aid you in answering your question:

"Intestinal villi (singular: villus) are tiny, finger-like projections that come out from the wall of the small intestine and have additional extensions called microvilli (singular: microvillus) which protrude from epithelial cells lining villi. They increase the absorptive area and the surface area of the intestinal wall. It is important that the food is absorbed at a considerably fast rate so as to allow more food to be absorbed. (If the process is too slow, the concentration of the blood in the blood vessels and the food will be equal, thus, diffusion will not occur.) Digested nutrients (including sugars and amino acids) pass into the villi through diffusion. Circulating blood then carries these nutrients away. 

In all humans, the villi and microvilli together increase intestinal absorptive surface area 30-fold and 600-fold, respectively, providing exceptionally efficient absorption of nutrients in the lumen. This increases the surface area so there are more places of food to be absorbed. 

Villi are made up of several cells."



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D)can be increased in a closed system