keep the stomates closed during hot, dry daylight
hours and allow the stomates to open and function at
night. Certain other plants have mechanisms that
( 35 )cause stomates to remain closed for much longer
periods of time—for days and weeks, even months at
a time—until environmental conditions become more
favorable.
21. Which of the following best tells what the passage is about?(A) the discovery of stomates
(B) the process of photosynthesis
(C) how desert plants adapt to survive
(D) competition between plants in the desert
(E) the shortage of water in the desert22. The passage suggests that most successful desert plants must be able to(F) reach deep sources of groundwater.
(G) survive in loose, sandy soil.
(H) adapt to very low levels of rainfall.
(J) withstand frigid nighttime temperatures.
(K) destroy potential competitors.23. In comparison to the root systems of desert plants, the root systems of tropical rain forest plants will probably be(A) similar, because tropical rain forests are also hot.
(B) more widespread, in order to absorb the excess moisture in the soil.
(C) smaller, because large root systems are less necessary in wet rain forest soil.
(D) larger, because little sunlight reaches the forest floor.
(E) more complex, because the rain forest is a more complex environment than the desert.24. What is the function of stomates in desert plants?