Ch 31: Plant Responses to Internal and External Signals

Question 1

What is etiolation?

Answer 1

morphological adaptations for growing in darkness

Question 2

Effects of light on plants –

Answer 2

photosynthesis
etiolation/ de-etiolation
seed germination
shade avoidance
(the 3 above are sometimes referred to as photomorphogenesis)

Question 3

Photomorphogenesis

Answer 3

how plants change in response to light

Question 4

Plants have biological clocks, which regulate…

Answer 4

….responses to daily changes (circadian rhythms)
responses to seasonal changes (circannual ***

Question 5

One way plants avoid shade is with phototropism. Plants sense light with photoreceptors (blue-light photoreceptors include cryptochromes).

Answer 5

***

Question 6

When a shoot reaches light, the plant undergoes profound changes, collectively called __________ (informally known as greening).

Answer 6

de-etiolation

Question 7

Some plants have light-dependent flowering.
Plants whose flowering is NOT dependent on light are known as ___________ plants.

Answer 7

day-neutral

Question 8

The researchers called Maryland Mammoth a short-day plant because it apparently required a light period shorter than a critical length to flower. A better name for these type of plants is….
Why?

Answer 8

….long-night plant. If they are exposed to light during their night, it inhibits flowering.

Question 9

Long-day plants

Answer 9

8888

Question 10

_____ light is the most effective color in interrupting the dark portion of the photoperiod.

Answer 10

Red

Question 11

Auxins stimulate growth only over a certain concentration range: from 10^-8 to 10^-4 M. Auxin acts by _______ ______ _______ within young developing shoots. At higher concentrations, it may inhibit cell elongation by inducing the production of ethylene.

Answer 11

stimulating cell elongation

p. 652

Question 12

According to a model called the acid growth hypothesis, _____ _____ play a major role in the growth response of cells to auxin.

Acidification of the wall activates enzymes called ________ that break the cross-links (hydrogen bonds) between cellulose microfibrils and other cell wall constituents, loosening the wall’s fabric.

Answer 12

proton pumps

expansins

Question 13

A reduced flow of auxin from a branch indicates that the branch is not being sufficiently ________: New branches are needed elsewhere. Thus, lateral buds below the branch are released from _______ and begin to grow.

Answer 13

productive

dormancy

Question 14

The transport of auxin also plays a key role in establishing the pattern of ___ emergence from the shoot apical meristem. Polar auxin transport in the shoot tip generates local peaks in auxin concentration that determine the site of leaf primordium formation. If the apical bud, the _______ ______ of auxin is removed, the inhibition of axillary buds is removed and the plant becomes bushier.

Answer 14

leaf

primary source

p. 652

Question 15

A high level of abscisic acid (ABA) in maturing seeds _______ _________. Many types of dormant seeds germinate when ABA is removed or inactivated.

Answer 15

inhibits germination

Question 16

ABA plays a major role in _______ signaling. When a plant begins to wilt, ABA accumulates and causes stomata to _____ rapidly, preventing further water loss. ABA does this by causing _________ channels in the plasma membrane of guard cells to open, leading to a massive loss of potassium ions from the cells. The accompanying loss of water reduces guard cell turgor and closes the pore.

Answer 16

drought

CLOSE

potassium

Question 17

These morphological adaptations for growing in darkness, collectively referred to as etiolation, make sense if we consider that a young potato plant in nature usually encounters continuous darkness when sprouting underground. Under these circumstances, expanded leaves would be a hindrance to soil penetration and would be damaged as the shoots pushed through the soil. Because the leaves are unexpanded and underground, there is little evaporative loss of water and little requirement for an extensive root system to replace the water lost by transpiration. Moreover, the energy expended in producing green ________ would be wasted because there is no light for photosynthesis. Instead, a potato plant growing in the dark allocates as much energy as possible to elongating its _____. This adaptation enables the shoots to break ground before the nutrient reserves in the tuber are exhausted.

Answer 17

chlorophyll

stems