Plants - Chapter 13

Question 1

Plant growth regulators

Answer 1

plant hormones affect the rate of division, elongation, and differentiation of plant cells
five well-characterized groups = auxins, gibberellins, cytokinins, abscisic acid, ethylene

Question 2

Auxins

Answer 2

produced in plants at the apical meristem
cause apical dominance, plant grows upward with few to no side branches
promote elongation of cells, stimulate growth and ripening of fruit, inhibit the dropping of fruits and leaves
synthetic auxins can stimulate growth of fruit from unpollinated plants, such as seedless tomatoes

Question 3

Gibberellins

Answer 3

promote cell division and elongation
sometimes cause a process calling bolting, the stem of a plant rapidly grows taller before flowering
many dwarf varieties of plants stay small because they do not produce normal levels of gibberellin

Question 4

Cytokinins

Answer 4

stimulate cell division and leaf growth

commercially, they are used to extend the life of cut flowers

Question 5

Abscisic acid

Answer 5

coordinates responses to stress in plants
usually inhibits growth
can induce dormancy of seeds to protect them from harsh conditions and also regulates rate of transpiration

Question 6

Ethylene

Answer 6

gas produced in many of the plant’s tissues
it plays a role in flower death, fruit ripening, and fruit loss
commercially, growers can delay ripening of fruit until they are about to be sold by controlling the levels of ethylene

Question 7

Tropism

Answer 7

a change in the growth pattern or movement of a plant in response to an external stimulus
positive tropism = growth towards
negative tropism = growth away from

Question 8

Nastic response

Answer 8

plant’s response to a stimulus independent of the direction of the stimulus
example = flower opening petals during the day and closing them at night

Question 9

Thigmotropism

Answer 9

a change in the growth pattern or movement of a plant in response to touch
for example, the tendrils of pea plants will grow around a supporting structure at the point of contact

Question 10

Phototropism

Answer 10

a change in the growth pattern or movement of a plant in response to light
for example, a plant growing in uneven light will lean and bend its stem in order to become better exposed to the light

Question 11

Gravitropism

Answer 11

a change in the growth pattern or movement of a plant in response to gravity
if plants could not detect and respond to gravity, their roots would be as likely to grow up into the air as down into the ground

Question 12

Photoperiodism

Answer 12

plants in regions where there are two or more seasons control their reproductive cycles based on the duration of daylight
plants flower in the spring because it allows for the most time available for seed and fruit development before winter
trees drop their leaves in the fall because it allows for protection from the cold, dry conditions of winter

Question 13

Nutrients

Answer 13

carbon dioxide and water = needed for photosynthesis
nitrogen (from organic material) = needed to produce proteins, nucleic acids, chlorophyll and leaf growth
NH3 from animal water, NO2 and NO3 from decayed material, nitrogen fixing bacteria contain nitrogen gas and convert it to nitrates