In the last 20 years one concern of scientists who study amphibians is that
A. DDT is affecting reproduction by thinning the egg membranes.
B. genetic diversity is being increased too rapidly for proper maintenance.
C. the edge effects are causing declines in species numbers.
D. many species are declining or have gone extinct in recent years.
E. populations are diversifying rapidly and speciation is occurring.
Answer: D
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At the genetic level, evolution is
A. a change in fitness over time. B. a population change over time. C. a change in the frequency of an allele or genotype over time. D. an increase in fitness over time. E. natural selection.
Why does an action potential travel in one direction down an axon?
A. because it needs to reach the synapse to trigger release of neurotransmitter B. because voltage-gated sodium channels cannot immediately reopen C. because voltage-gated potassium channels remain open longer D. because the diffusion of charge can only occur in one direction
Calculate the estimated population size, N, given a study that initially marked 100 animals and subsequently captured 50, of which 25 were marked
A) 25 B) 100 C) 50 D) 200
What region of the heart acts as the heart's pacemaker?
A) sinoatrial (SA) node B) atrioventricular (AV) node C) semilunar valve D) ventricle