In autumn, the amount of _________ increases and the amount of _________ decreases in fruits 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

What does reverse transcriptase do?

During winter or periods of drought, which one of the following plant hormones inhibits growth and seed germination?

a. Ethylene

b. Abscisic acid

c. Gibberellin

d. Auxin

Which of the following statements about hormones is correct?

a. They tend to be large molecules.

b. They exert their effects only on the same cells that produce them.

c. They can exert strong effects only when they are present in high concentrations.

d. They trigger a response by binding to target-cell receptors.

What evidence suggests that ABA from roots can signal guard cells to close?

a. If roots are given sufficient water, guard cells close anyway.

b. If roots are dry, guard cells begin to close—even though leaves may not be experiencing water stress.

c. Applying ABA to guard cells directly causes them to close.

d. If roots are dry, the ABA concentration in leaf cells drops dramatically.

Plant hormones act by affecting the activities of:

a. Genes

b. Membranes

c. Enzymes

d. Genes, membranes, and enzymes

Why was it logical to predict that amyloplasts function as statoliths?

a. They are dense and settle to the bottom of gravity-sensing cells.

b. They are present only in gravity-sensing cells.

c. They make a direct physical connection with membrane proteins that have been shown to be gravity-receptor molecules.

d. Their density changes in response to gravity.

Buds and sprouts often form on tree stumps. Which hormone would stimulate their formation?

a. Auxin

b. Cytokinin

c. Abscisic acid

d. Ethylene