Oxygen is recycled in the

a nitrogen cycle
b carbon cycle
c none of these
d water cycle

6. in the dna double helix, how are the two strands of dna held together? a. chemical bonds between base pairs hold the two strands of dna together. b. hydrogen bonds between the base pairs hold the two strands of dna together. c. hydrogen bonds between sugar groups and phosphate groups hold the two strands of dna together. d. chemical bonds between sugar groups and phosphate groups hold the two strands of dna together.

Has regulatory areas for thirst, hunger, body temperature, water balance, and blood pressure

Organisms may contain up to five levels of organization within their bodies. which level of organization is shown by the liver? a. tissue b. organ c. organism d. organ system