31. In the autumn, the amount of ____ increases and the amount of ____ decreases in fruit and leaf stalks, causing a plant to drop fruit and leaves.
(a) ethylene . . . auxin
(b) gibberellin . . . abscisic acid
(c) cytokinin . . . abscisic acid
(d) auxin . . . ethylene
32. Plant hormones act by affecting the activities of
(a) genes. (b) genes and enzymes.
(c) enzymes. (d) genes, membranes, and enzymes.
33. _______ appear to be responsible for gravitropism.
(a) Statoliths (b) phytochromes
(c) Gibberellins (d) Cytokinins
34. A rapid loss of water in specialized cells in the sensitive plant Mimosa pudica causes
(a) the plant to bend toward light.
(b) stomatal opening so photosynthesis can begin.
(c) stress that results in the production of PR proteins.
(d) leaves to droop.
35. A biological cycle with a period of about 24 hours is called
(a) thigmotropism. (b) a circadian rhythm.
(c) photoperiod. (d) abscission.
36. An Rajasthani hunter was worried about being attacked by grizzly tigers, so he left the lights in his cabin on all the time. Plants near the cabin flowered a month early. Which of the following best explains this?
(a) They must have been long-night plants.
(b) The lights must have emitted far-red light.
(c) They must have been long-day plants.
(d) They must have been short-day plants.
37. Most plants flower when
(a) the soil reaches a certain temperature.
(b) the days are of right length.
(c) a certain number of days have passed since they last flowered.
(d) the nights are of right length.
38. A certain short-day plant flowers when days are less than 12 hours long. Which of the following would cause it to flower?
(a) a 9-hour night and 15-hour day with 1 minute of darkness after 7 hour.
(b) an 8-hr day and 16-hour night with a flash of white light after 8 hr.
(c) a 13-hour night and 11-hour day with 1 minute of darkness after 6 hr.
(d) a 12-hour day and 12-hour night with a flash of red light after 6 hr.
39. A chemical change in a substance called phytochrome
(a) causes a plant to bend toward light.
(b) triggers fruit drop.
(c) enables a plant to respond to the presence of light.
(d) is responsible for gravitropism.
40. Which of the following tissues produces voluntary body movements?
(a) smooth muscle (b) simple cuboidal epithelium
(c) cardiac muscle (d) skeletal muscle