What percentage of air is oxygen?
A) 79%
B) 6%
C) 12%
D) 21%
E) < 1%
Ans: D) 21%
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Consider the global nitrogen cycle depicted in the figure above. How are humans altering this cycle?
A) industrial nitrogen fixation B) nitrogen lost to the atmosphere C) reduction of nitrogen available to terrestrial ecosystems D) reduction of nitrogen fixation by bacteria E) permanent burial of nitrogen in coastal environments through runoff
Our sense "fullness" after a big meal is due to
A. mechanoreceptors. B. thermoreceptors. C. stretch receptors. D. electromagnetic receptors. E. chemoreceptors.
The organisms that cause ringworm, or tinea, use keratin protein as their growth substrate. This is why these infections
A. have a high mortality rate. B. cause a discoloration of the skin by damaging skin pigment protein. C. produce a rash all over the body during an infection. D. are restricted to superficial skin layers.
How does carbon move through the carbon cycle?
A) Carbon flows one way from volcanoes to plants to consumers and then to the atmosphere. B) Carbon is recycled among plants, animals, water, soil, and the atmosphere. C) Carbon dioxide (CO2 ) is the only carbon-containing compound involved in the carbon cycle. D) Exhaled carbon dioxide becomes trapped in the atmosphere, adding to the greenhouse effect.