Which characteristic is necessary for natural

selection to occur in a species?

(1) stability

(2) variation

(3) complex cellular organization

(4) a very low mutation rate

Why is circulation in humans called closed double circulation?

What is antigenic variation and how is it beneficial to pathogens? Give an example of two pathogens that demonstrate antigenic variation.

The simplest structured unit of a compound is a (n): electron atom proton molecule

DNA would be found in which classification of biological molecules? A) Lipids B) Carbohydrates C) Nucleic acids D) Proteins

Latrotoxin, produced by the poisonous black widow spider, increases the release of acetylcholine. how do muscle cells respond?

Probably the main reason Africans, rather than Native Americans, became slaves in America was that? A. Indians passed North American diseases to the Europeans. B. Africans and Europeans shared immunities to Old World diseases. C.

Structures through which conduction impulses pass, in sequential order, causing the heart to contract:

When a river or stream flows downward into a basin that is surrounded by high ground on all sides, what can form a. a lake b. a creek c. a sinkhole d. a delta

Is groundwater a renewable or nonrenewable resource? what are the consequence of drought or overpumping?

Which of these explains why deletion of an imprinted gene can be a dominant mutation?