Final Exam - Plant Hormones

Question 1

What are the characteristics of meristems?

Answer 1

• perpetually undifferentiated tissues that allow a plant to have indeterminate growth
• active cell division
• cells are small and unexpanded
• plant development is plastic and represents responses to environment

Question 2

What are the three basic plant organs?

Answer 2

• roots
• stems
• leaves

Question 3

Where does primary growth of shoots occur?

Answer 3

from both the apical and axillary bud meristems

Question 4

What are the major plant hormones?

Answer 4

• auxin
• cytokinins
• gibberellins
• abscisic acid
• ethylene

Question 5

What is a tropism?

Answer 5

any response resulting in movement of organs toward or away from a stimulus

Question 6

What is phototropism/

Answer 6

• cells on shaded side expand more than those on the side exposed to sunlight
• plants bend toward the light

Question 7

What does most plant growth result from?

Answer 7

cell expansion due to the loosening of the cell wall

Question 8

What is the acid-growth hypothesis?

Answer 8

• auxins stimulate acidification of the cell wall using proton pumps
• proton pumps lower the pH in the cell wall, activating expansins
• once the cellulose is loosened the cell can elongate
• turgor pressure expands the cell

Question 9

How does auxin affect axillary and apical bud growth?

Answer 9

• inhibits axillary/lateral bud outgrowth

- promotes dominance of apical growth

Question 10

What are the characteristics of apical meristems?

Answer 10

• generate primary growth
• growth in length through cell expansion
• dominant over other meristems
• responsible for vertical growth

Question 11

What are the characteristics of axillary bud meristems?

Answer 11

• found above petiole/node junctions

- subordinate to apical meristems

Question 12

What are the characteristics of root apical meristems?

Answer 12

-increase root length through cell expansion

Question 13

What are the characteristics of cytokinins?

Answer 13

• stimulate cytokinesis
• produced in actively growing tissues
• stimulate growth of axillry/lateral buds

Question 14

How do auxins and cytokinins work together?

Answer 14

• with auxin alone, cells expand but do not divide

- when auxin and cytokinin work together, cells expand AND divide

Question 15

How do auxins and cytokinins play into apical dominance?

Answer 15

• auxins inhibit axillary bud growth, while cytokinins stimulate it
• competition between the two hormones contributes to apical dominance

Question 16

What are the characteristics of gibberellins?

Answer 16

• variety of effects, including stem elongation and seed germination
• promote stem elongation via cell elongation and cell division
• dwarf varieties of plants are gibberellin-deficient

Question 17

How does gibberellin deficiency occur in plants?

Answer 17

mutation in a gene which encodes a gibberellin biosynthesis enzyme

Question 18

How do gibberellins play a role in germination?

Answer 18

• produced by embryos upon imbibition (initial water uptake)

- stimulates production of enzymes which digest complex carbohydrates to simple sugars

Question 19

What is the main role of abscisic acid?

Answer 19

counteract the effects of other plant hormones

Question 20

What are the two critical processes abscisic acid is involved in?

Answer 20

• seed dormancy

- drought tolerance

Question 21

What are the characteristics of seed dormancy?

Answer 21

• ABA production occurs in dramatic increases during seed maturation
• ensures seed will germinate only in optimal conditions
• dormancy is broken when ABA is removed

Question 22

How does ABA play a role in drought tolerance?

Answer 22

• ABA is the major hormone regulating the opening and closing of the stomata
• increased ABA will keep stomata closed

Question 23

What are the characteristics of ethylene?

Answer 23

• simple, gaseous hormone

- associated with fruit ripening