Which situation could cause an ecosystem to lose its equilibrium? A. Competition among species
B. Interdependence among species
C. Arrival of a nonnative species
D. An increase in the population of a keystone species

C

Explanation: the ecosystem is metastable, so an increase in the keystone species would be accommodated. Introductionof a nonnative species is likely to generate significant biotic change to the environment.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

the answer is d p: cell, q: organ, r: organ system, s: tissue