Drawings should follow Figures 38.16 to 38.19. Several answers may be possible but all should include the reabsorption of water by the system as it follows a concentration gradient. Answers will vary. List could be quite long. ADH enhances water reabsorption.
Aldosterone increases the kidneys' salt retention.
Answers will vary. Survival of the fittest. High salt concentration in sea water would cause water to leave your cells thus increasing dehydration. Dehydration can be deadly. Renin boosts aldosterone levels.