The microorganisms present on day 5 were
(1) newly added from the sterile culture medium
(2) offspring of antibiotic-resistant individuals
(3) organisms that were all present on day 1
(4) offspring with no resistance to the antibiotic

amber has allowed scientists to study dna that has been preserved over millions of years.

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms