When is S-phase complete? O A. When two nuclei have formed
O B. When two daughter cells are produced
O C. When the spindle fibers dissolve
O D. When each chromosome has been duplicated

Which of these is not a function of some membrane proteins ? a. allowing polar molecules to enter the cell b. recognizing other types of cells c. receiving messeges from other cells b. carrying messages to oher cells

Molecular models of two different substances are shown below. in the molecule on the left, the oxygen atom pulls on electrons more strongly than the hydrogen atoms. in the molecule on the right, the two oxygen atoms pull on the shared electrons with the same strength. water molecule, h, o oxygen molecule, oz when the two substances are put in the same container, they do not attract each other. why does this happen? a. they both contain oxygen. b. one is polar and one is nonpolar. c . they are both polar. d. they contain different elements.

Which of the following is a reason why early living organisms on earth could not have survived on the surface? 1. the lack of an ozone layer 2. the lack of oxygen in the atmosphere 3. the fact that these organisms were single-celled