chapter 26: flowering plants: control of growth responses

Question 1

what is signal transduction

Answer 1

process within a cell when a molecular signal (protein, hormone, etc.) initiates a response within interior of cell

Question 2

steps of signal transduction

Answer 2

1. Receptors
   -chemical change
2. Transduction pathway
   -series of relay proteins or enzymes that pass along signal until it reaches nucleus of cell
   -amplifying and transforming the signal
3. Cellular response
   -change in gene expression, etc
   -brings about an overall visible change in the plant
   -can be short term or long term

Question 3

characteristics of plant hormones

Answer 3

-Chemical signals to coordinate cell responses
-Produced in low concentrations, still bring about active change
-Active in another part of organism
-Travel within phloem or from cell to cell

Question 4

what are auxins

Answer 4

-Plant hormone regulating growth, particularly cell elongation - bend towards light
-Prevents loss of leaves & fruit
-Promotes positive phototropism
-Responsible for gravitropism - responding to gravity

Question 5

what are gibberllins

Answer 5

-hormones promoting increased stem growth; involved in flowering & seed germination
-Young leaves, roots, embryos, seeds, & fruits
-Breaks dormancy (period of time when plant growth is suspended) in seeds & buds when applied to the plant

Question 6

what are cytokinins

Answer 6

-hormone that promotes cell division
-Prevents senescence: Sum of processes involving aging, decline, & eventual death of a plant or plant part
-Organ formation (with interaction between auxin)
-Found in dividing tissues of roots, seeds, fruits

Question 7

what is abscisic acid (ABA)

Answer 7

-Produced in chloroplast
-Initiates and maintains seed & bud dormancy
-Closure of stomata in a plant under water stress

Question 8

what is ethylene

Answer 8

-Gas formed from amino acid methionine
-Ripening of fruit
-Inhibits plant growth
-Moves freely by diffusion
-Involved in abscission (dropping leaves and fruit)

Question 9

what are

Answer 9

Molecule not directly involved in growth, development, or reproduction of an organism; discourage herbivores, competition, or are used as a warning signa

Question 10

what is tropism

Answer 10

growth response toward or away from a directional stimulus; caused by external stimuli
-Positive tropism: growth toward stimulus
-Negative tropism: growth away stimulus

Question 11

what is phototropism

Answer 11

Growth response of plant stems to light
-Receptors called photoreceptors: proteins embedded with pigment molecules that respond to light wavelengths

Question 12

what is thigmotropism

Answer 12

Unequal growth due to contact with solid objects
-Slow & rapid responses
-Thigmomorphogenesis: plant changes overall shape due to an environmental touch stimulus (barrier, wind, rain)

Question 13

what is gravitropism

Answer 13

Growth response of roots and stems of plants to Earth’s gravity
-Specialized cells called statoliths: starch granules found within organelles called amyoplasts
-Settle to bottom of the cell
-Influences auxin

Question 14

what are turgor movements

Answer 14

-Internal signals cause nongrowth movements
-movement without growth
-may result from touch, shaking, thermal stimulation
-Both sensitive plants & Venus fly traps utilize turgor pressure to move

Question 15

what do phytochromes help plants know

Answer 15

-Daytime, nighttime, dawn/dusk
-Time of year
-seed germination
-breaking bud dormancy
-onset of senescence

Question 16

what is a phytochrome

Answer 16

-Blue-green leaf pigment present in cytoplasm of plant cells that alternately exists in two forms
-Conversion of forms allows plant to detect photoperiod changes
-Promotes seed germination, flowering, inhibits shoot elongation, & affects accumulation of chlorophyll in plant tissue

Question 17

what is photoperiodism

Answer 17

-phycological response promoted by changes in the length of day or night in a 24-hour daily cycle
-Requires biological clock and activity of phytochrome

Question 18

what are the categories of plants flowering utilizing photoperiodism

Answer 18

-Short-day plants: flower when day length is shorter than a critical length
-Long-day plants: flower when day length is longer than critical length
-Day-neutral plants: not dependent on day length for flowering

Question 19

what is critical length

Answer 19

Not based off an absolute number but a critical number of hours that either must be met or cannot be exceeded in order to flower
Ex: Spinach is a long-day plant that has a critical day length of 14 hours; only will flower when day lengths increases to 14+ hours

Question 20

what are circadian rhythms

Answer 20

-Rhythms tend to persist even in absence of daily light cues
-Entrained to daily cycle through phytochrome & blue-light receptors
-Measure day-length changes so plants respond appropriately to seasonal environmental changes

Question 21

what is a biological clock

Answer 21

Internal mechanism that maintains biological rhythm in absence of environmental stimuli
-Length of daylight compare to darkness, called photoperiod & influenced by phytochrome, sets clock
-Temperature has little to no effect
-Synchronization is adaptive as photoperiod indicates seasonal change better than temperature

Question 22

How does auxin actually cause stems to curve towards the light?
a.
In the presence of unidirectional light, auxin moves to the shady side and activates an ATP-driven proton pump that results in weakened cell walls and eventual elongation

b.
In the presence of light, auxin increases the formation of hydrolytic enzymes that release energy needed for growth purposes

c.
In the presence of light, auxin increases the turgor pressure of the cell and accelerates growth

d.
In the presence of light, auxin moves toward the light source and activates a protein that binds to DNA and starts enzyme production

e.
In the presence of blue light, auxin triggers additional photosynthesis and growth

Answer 22

a.
In the presence of unidirectional light, auxin moves to the shady side and activates an ATP-driven proton pump that results in weakened cell walls and eventual elongation

Question 23

Which of the following pertain to movement of plants?
a.
Phototropism

b.
Gravitropism

c.
All of the choices are correct

d.
Thigmotropism

Answer 23

c.
All of the choices are correct

Question 24

Plants could readily develop seasonal responses for flowering based on temperature changes but have “elected” through evolution to manage their rhythms based on a comparison of daylight and darkness. Why has the day-night ratio system been selected?
a.
Temperature has no effect upon plant biochemistry

b.
A plant’s nervous system is tuned to light stimuli and not to temperature stimuli

c.
Temperatures fluctuate widely across seasons and from year to year, but photoperiod comparisons are a more reliable indicator of season

d.
Temperature is a gradation but day/night is all-or-nothing

Answer 24

c.
Temperatures fluctuate widely across seasons and from year to year, but photoperiod comparisons are a more reliable indicator of season

Question 25

Which statement is not true about photoperiodism?
a.
A day-neutral plant flowers according to some form of regulation other than photoperiodism

b.
A long-day plant will flower when the day length is longer than a critical length

c.
The phytochrome form Pfr is converted to Pr in daylight, producing the active form that induces flowering in long-day plants

d.
A short-day plant flowers when the day length is shorter than a critical length

Answer 25

c.
The phytochrome form Pfr is converted to Pr in daylight, producing the active form that induces flowering in long-day plants

Question 26

Which of the following statements is not correct about a circadian rhythm?
a.
The primary usefulness of circadian rhythms seems to be to measure day-length changes so plants respond appropriately to seasonal environmental changes

b.
These rhythms tend to persist even in the absence of daily light cues

c.
An example is the opening of stomata in the morning and their closing at night

d.
If plants are maintained in total darkness or total light, their circadian rhythm acts on a faster time scale

Answer 26

d.
If plants are maintained in total darkness or total light, their circadian rhythm acts on a faster time scale