biology 25.1

25-1 HORMONES AND PLANT GROWTH

Ch. 25 Plant and Responses and Adaptations

HORMONE Substance produced in one part of an

organism that affects another part of the same organism

TARGET CELL Cell that has a receptor for a particular

hormone

PHOTOTROPISM Tendency of plants to grow toward a

source of light

AUXIN Substance produced in the tip of a

seedling that stimulates cell elongation

GRAVITROPISM Response of a plant to the force of

gravity

LATERAL BUD Meristematic area on the side of a stem

that gives rise to side branches

APICAL DOMINANCE Phenomenon in which the closer a bud

is to the stem’s tip, the more its growth is inhibited

HERBICIDE Compound that is toxic to plants

CYTOKININ Plant hormone produced in growing

roots and in developing fruits and seeds

GIBBERELLIN Growth-promoting substance produced

by plants

ETHYLENE Plant hormone that stimulates fruits to

ripen

KEY CONCEPT Plant hormones are chemical

substances that control a plant’s patterns of growth and development, and the plant’s responses to environmental conditions.

KEY CONCEPTS Auxins are produced in the apical

meristem and are transported downward into the rest of the plant. They stimulate cell elongation.

KEY CONCEPTS In plants, cytokinins stimulate cell

division and the growth of lateral buds, and cause dormant seeds to sprout.

KEY CONCEPTS Gibberellins produce dramatic increases

in size, particularly in stems and fruit.

KEY CONCEPTS In response to auxins, fruit tissues

release small amounts of the hormone ethylene. Ethylene then stimulates fruits to ripen.