The cycle that involves the conversion of nitrogen gas into a usable form by bacteria is the:
a.
carbon cycle
b.
nitrogen cycle
c.
water cycled.
d.
none of the above

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.