Cells are surrounded by a watery fluid, and they contain watery cytoplasm. explain how the structure of the lipid bilayer is related to these two watery environments.

Veins have a much lower blood pressure than arteries. which of these prevents backflow of blood in veins? a. pressure applied by the heart b. one–way valves in veins c. thin muscular walls of veins

Scientific evidence is most likely to be consistent if it is based on data from

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