Which gas forms less than one percent of the atmosphere, but is essential to life?

a. carbon dioxide
b. oxygen
c. hydrogen
d. nitrogen

Question 1 which of the following allows cells to take in fluids? a. phagocytosis b. pinocytosis c. exocytosis d. receptor-mediated endocytosis question 2 molecules move along their concentration gradient (from areas of high concentration to low concentration) using active transport mechanisms. a. true b. false question 3 which of the following powers active transport (ie. provides the energy for)? a. glucose b. transport proteins c. atp d. phospholipids question 4 what type of lipid is a major component of the plasma membrane? a. cholesterol b. phosopholipids c. proteins d. triglycerides