BFG Ch 7

Question 1

Name the five major plant hormones

Answer 1

auxin
gibberellin
cytokinin
ethylene 
abscisic acid

Question 2

What is phototropism

Answer 2

When plant stems grow towards the light. Common response in sun loving species. Shade lovers do not do this

Question 3

Where are plant hormones made

Answer 3

Cells of general organs such as stems, leaves, roots and flowers

Question 4

what happens to seedlings that grow up in darkness

Answer 4

They have been colorless stems and undeveloped leaves. this is called etiolation

Question 5

Etiolation

Answer 5

when a seedling grows up without light and doesn’t develop colored stems and has undeveloped leaves.

Question 6

What does gibberellin do primarily?

Answer 6

Promote stem growth at internodes

results in space at the leaves
more active in low light (of high-light lovers)
shade-loving sp. don’t show elongation sensitivities

etiolated plants use gibberellin to try to reach the sun.

Question 7

What is geotropism? What hormone controls this?

Answer 7

When a part of the plant responds to gravity’s force

Stems have negative geotropism (grow UP), roots have positive geotropism (grow DOWN)

Auxin controls it.
-cell elongation to turn stems up (accumulates in lower side of stems)

roots respond to lower amounts of auxin in upper cells to allow growth downward

Question 8

What is thigmotropism?

Answer 8

The response to touch. Controlled by auxin; mechanisms unknown

Question 9

What are nastic movements?

Answer 9

controlled by hormones but not the direct result of outside stimulus like geotropism, phototropism, and thigmotropism

Cell growth at changing positions across the stem tip

seen in twiners; ivy; opening/closing flowers; fly traps

all movements require growth and are expensive and essentially irreversible.

Question 10

What does auxin as a plant hormone do?

Answer 10

The hormone stimulates an increase in cell length. Especially near stem and root tips

Distribution changes in response to light; allows plants to elongate toward the sun.

Question 11

senesence

Answer 11

irreversible plant ripening

it is closely regulated by opposing hormones: Ethylyne gas; abscisic acid promote it
Auxin/gibberellin/cytokinin inhibit senesence

Question 12

What hormones oppose senesence

Answer 12

Auxin
Gibberellin
Cytokinin

Question 13

Cytokinin

Answer 13

plant hormone that stimulates cell division

Question 14

What hormones promote senesence

Answer 14

Ethylene gas: used to commercially ripen fruit.

Abscisic acid

coupled with external environmental cues such as shorter days.

Question 15

What changes occur during fruit ripening?

Answer 15

Chlorophyll breakdown (color change)
tannins switch to sugars = promote predation
membrane softening and cell breakdown (via ethylene)
fungi growth on overripe things

Question 16

Describe leaf senesence prior to abscission

Answer 16

chlorophyll breakdown, weakening cell walls at base of petioles (“abscission zone”)

decrease auxin, increase ethylene

• due to low night temps and shorter days
• ethylyne=enzymatic breakdown of cellulose and pectin in walls of middle lamellae

similar process in evergreens, fruits, and flowers that undergo periodic abscission

Question 17

What is apical dominance? What hormone controls it?

Answer 17

apex growth suppresses the growth of axillary buds

Auxin controls this- it suppresses growth of axillary buds

Question 18

How do adventitious roots occur?

Answer 18

after cutting or layering
grow on cut stems/leaves; controlled by auxin

sometimes they’ll cut the plant and leave it on the parent plant while the adventitious roots draw nutrients until it’s good to go for moving. (this is called layering)

Question 19

Synthetic growth regulators

Answer 19

defoliants: promote leaf abscission
disbudders: cause flower buds to fall off (rid them of unwanted future fruits)

growth retardents: production of dwarfed potted plants

herbicides: weed killers

Question 20

What is plagiotropism?

Answer 20

when branches grow oblique to gravity

Question 21

What is diageotropism?

Answer 21

when branches/roots grow horizontal to gravity

Question 22

Additional roles of gibberellin

Answer 22

controls seed germination
revives plants from winter sleep

non-universally increases flower formation and fruit size

Question 23

Additional roles of ethylene

Answer 23

stem thickening (esp in seedlings)
initiates flowers (pineapple, not universal)

Question 24

Abscisic acid

Answer 24

promotes dormancy as well as aids in ripening and abscission

Question 25

What happens to buds when winter is coming?

Answer 25

Temperature cues lead to packing them with growth hormone as they are chilled. (auxin?)

After the long period of cold they will begin to develop (some plants require these long periods of cold for the plants to flower)

Question 26

What is vernalization?

Answer 26

the acquisition of a plant’s ability to flower in the spring by exposure to the prolonged cold of winter, or by an artificial equivalent. After vernalization, plants have acquired the ability to flower, but they may require additional seasonal cues or weeks of growth before they will actually flower.

may germinate before winter

required by many biennials

ex. cabbage doesn’t flower till 2nd year after winter.

Question 27

What is photoperiodism?

Answer 27

Response of plants to changing days (actually responding to night lengths)

Most flowers initiated by this

Angiosperms require:
-short day, long day, or day neutral timing

They must have “ripeness-to-flower” size before this photoperiodism kicks in

Question 28

What response to the external environment is most useful to plants?

Answer 28

photoperiodism because it allows them to achieve proper timing of seed maturity (flower at the right time in spring; have mature seeds by autumn)

Question 29

Once a meristem makes a flower…

Answer 29

it cannot make leaves again.

Question 30

Define meristem

Answer 30

A meristem is the tissue in most plants containing undifferentiated cells (meristematic cells), found in zones of the plant where growth can take place.

Meristematic cells give rise to various organs of the plant and keep the plant growing. The Shoot Apical Meristem (SAM) gives rise to organs like the leaves and flowers, while the Root Apical Meristem (RAM) provides the meristematic cells for the future root growth. The cells of the shoot and root apical meristems (SAM and RAM) divide rapidly and are considered to be indeterminate, in that they do not possess any defined end fate. In that sense, the meristematic cells are frequently compared to the stem cells in animals, which have an analogous behavior and function.

Question 31

What is florigen

Answer 31

the hormone thought to be involved in flowering

may just be a combination of other hormones we already know about