The concentration of potassium is higher in red blood cells than in the surrounding blood plasma. this higher concentration is maintained by the process of: ) circulation
(2) diffusion
(3) excretion
(4) active transport

Option 4, active transport

Explanation:

In active transportation, external force is used to move any substance against the concentration gradient. .This active transportation leads to movement of potassium in into the cell where the concentration of potassium ion is already high. While the sodium starts moving out of the cell. The energy for active transport is provided by the ATP. When the level of ATP reduce, the red blood cells attain spherical shape as the water and sodium move into RBCs.

Hence, option 4 is correct

"a.) well–developed vascular system."

the answer is "a.) well–developed vascular system."

explanation: