I need help this is due In 30 minutes

Describe the response the kidneys have to dehydration and excessive water intake. what happens to the concentration of urine in each case ?

Which of the following observation darwin shape his concept of descent with modification? a) species diversity declines farther from the equator. b) fewer species live on islands than on the nearest continents. c) birds live on islands located farther from the mainland than the bird's maximum nonstop flight distance. d) south american temperate plants are more similar to the tropical plants of south america than to the temperate plants of europe. e) earthquakes reshape life by causing mass extinctions.

Why are current extinctions of concern to enviromentalists?