How many species of animals and plants are estimated to go extinct in our lifetimes?
A. 500
B. 10,000
C. 25
D. one-fifth of the world's species
Answer: D
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Which respiratory surface lacks physical protection from the external environment?
a. tracheal system tubes b. human lungs c. external gills d. internal gills e. bird lungs
The sliding filaments that move relative to each other during muscle contraction are ________.
Fill in the blank(s) with the appropriate word(s).
It is difficult to make a vaccine against HIV because
a. the virus mutates rapidly. b. it is too expensive. c. it is a retrovirus. d. not enough is known about it. e. it contains reverse transcriptase.
Which of the following statements about energy metabolism is false?
-The energy that powers living systems ultimately comes from the sun. -All animals in some way rely on producers for their energy. -Plants provide the water and carbon dioxide that animals need to carry out cellular respiration. -Most eukaryotic organisms carry out cellular respiration in the presence of oxygen. -The main objective of cellular respiration is to break down glucose and make ATP.