21. After fertilization, the _____ develops into a seed and the _____ develops into a fruit.
(a) ovule . . . ovary
(b) pollen grain . . . ovule
(c) ovary . . . ovule
(d) egg . . . ovule
22. Plants growing in harsh environments such as deserts, sand dunes, and arctic tundra often reproduce vegetatively. This is because
(a) there are few animals available to pollinate them.
(b) they are members of plant families that only reproduce asexually.
(c) fruits would freeze or dry out in these environments.
(d) vegetative reproduction is not as risky as making seeds.
23. In contrast to animals, plants exhibit ______ and _____.
(a) determinate growth . . . persistent morphogenesis
(b) indeterminate growth . . . are not capable of morphogenesis throughout their lifespan
(c) indeterminate growth . . . persistent morphogenesis
(d) growth . . . morphogenesis
24. Which of the following seedlings will probably bend toward the light?
(a) tip covered with a cap made of black plastic
(b) tip separated from base by a gelatin block
(c) tip separated from base by aluminum foil
(d) tip cut off and place a block of agar over half of the cut portion; the side with the agar block will bend towards the light
25. In shoots, branching is inhibited by _____ from the tip of a growing shoot, but this
effect is countered by _____ from the roots.
(a) cytokinins . . . auxins
(b) gibberellins . . . ethylene
(c) auxins . . . cytokinins
(d) gibberellins . . . abscisic acid
26. As leaf lettuce matures, the basal edible leaves suddenly send up a tall flowering shoot. After the plant bolts like this, it no longer produces broad, tasty leaves. Suppose you wanted to prevent bolting so that you could harvest lettuce longer. You might look for some way to interfere with the effects of
(a) abscisic acid. (b) gibberellins.
(c) cytokinins. (d) ethylene.
27. Seeds of many desert plants will not germinate until a heavy rain washes away their
(a) phytochrome. (b) abscisic acid.
(c) gibberellins. (d) auxins.
28. The abscission layer
(a) causes a shoot to bend toward light.
(b) secretes cytokinin.
(c) is the location of the biological clock in a plant.
(d) is where a leaf separates from a stem.
29. When a plant structure such as a leaf is injured, it produces ______, which may cause the part to age and drop off.
(a) cytokinins (b) ethylene
(c) auxins (d) abscisic acid
30. Once a flower is pollinated, changes occur that make it less attractive to insects. Its petals, for example, shrivel and fall off. Pollination must
(a) increase the output of cytokinins in the flower.
(b) block the flow of auxins from the roots.
(c) trigger the release of ethylene in the flower.
(d) increase the formation of phytochrome, which sets the biological clock.