(3) Red blood cells receive oxygen from what organ system? A. Immune
B. Digestive
C. Respiratory
D. Cardiovascular

How does the study of genetic disorders such as pku biologists understand normal alleles?

Number and variety of living organisms includes genetic, species, and ecological types

The greenhouse effect a. something that has occurred for millions of years b. an unnatural phenomenon caused by humans that maintains earths temperature range. c. the results of the differences in the angle of the suns rays d. an unnatural phenomenon that causes heat energy to be radiated back into the atmosphere