What maintains the concentration gradient across respiration membranes?
A. Ventilation
B. Cartilage
C. Spiracles
D. Cohesion

Amino acids contain the elements carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. of the 20 amino acids found in humans, 11 are called "nonessential" because they can be manufactured by the body when needed. which elements in these 11 amino acids are commonly obtained from the metabolism of sugar molecules?

Why do some dna fragments move farther than others during gel electrophoresis? a. because their shapes are different b. because they are different types of molecules c. because the samples are different colors d. because their masses are different

Using the gas pedal analogy explain the impact on the cell cycle of one mutated tumor suppressor gene allele versus two mutated tumor suppressor alleles