2) oxygen constantly diffuses from air or water into a animal's bloodstream. for this to happen, the concentration of oxygen in the blood must be
a. greater than the concentration of oxygen in the air or water.
b. greater than the concentration of carbon dioxide in the air or water.
c. lower than the concentration of oxygen in the air of water.
d. lower than the concentration of carbon dioxide in the air or water

Cladistics is a way of classifying organisms by examining the characteristics of their ancestors and descendants and depicting the relationships in a cladogram. which of the following best describes a challenge in classifying organisms this way? a. there are millions of species on earth, and a cladogram is not a practical means for classifying all of them. b. it is impossible to tell which organisms are most closely related to each other using a cladogram. c. cladograms are detail-oriented and do not provide a useful understanding of evolutionary relationships. d. there is a limited number of ways to organize the information, so most cladograms end up looking very similar.