The days are getting shorter and colder. these trees are responding to the change. their leaves change color and will soon fall off. losing leaves during the winter is the response to the external environment called
a) dormancy.
b) hibernation.
c) hydrotropism.
d) phototropism.

Which of the following is the best definition of a eukaryota? a. a one-celled organism that does not have a membrane-bound nucleus b. a one-celled organism that does not have a cell wall c. an organism whose cells each contain a membrane-bound nucleus d. an organism whose cells each have a cell wall