Semester 1 Final: Plant Responses to Internal and External Signals

Question 1

Light Receptors

Answer 1

Two major classes
 Blue-Light Photoreceptors
 Phytochromes

Question 2

Photoperiodism

Answer 2

Plants use environment stimuli to detect time of year & then provide a physiological response
 Flowering is regulated by this method

Question 3

Tropism

Answer 3

Plant growth which results in the curvature of whole organism towards or away from stimuli

Question 4

Heliotropism

Answer 4

The diurnal or seasonal movements of plants parts in the direction of the sun

Question 5

auxins

Answer 5

plant growth hormones that helps regulate shoot growth through the elongation of the shady side so plant grows in the direction of the light stimulus

Question 6

Long-day plants

Answer 6

flower in summer when nights are shorter than the critical time
 Ex: Red clover, spinach, lettuce
- large enough amounts of PFR remain at the end of short nights to bind to the
receptor
 This receptor promotes the transcription of genes needed for flowering

Question 7

Short-day plants

Answer 7

flower in autumn when nights are longer than the critical time
At the end of long nights there is little PFR left to bind to the receptor
 Here, the receptor inhibits the transcription of the genes needed for flowering when PFR binds to it

Question 8

Phytochrome

Answer 8

a pigment in the leaves of plants that measures the length of dark periods
two forms: inactive PR and active PFR
- Regulates seed germination
- Relays information about quality of light
- Provides biological clock
- Controls photoperiodism

Question 9

Inactive, PR

Answer 9

PR absorbs red light (660 nm) & is converted into the active form PFR
 Sunlight contains more light with a wavelength of 660 nm, therefore, in sunlight phytochrome (PR) is rapidly converted into PFR

Question 10

Active, PFR

Answer 10

PFR absorbs far-red light (730 nm) & is converted into PR
 PR is more stable than PFR therefore, in darkness PFR very gradually changes to PR

Question 11

Environmental stress

Answer 11

 Drought
 Flooding
 Salt stress
 Heat stress
 Cold stress

Question 12

Blue-Light Photoreceptors

Answer 12

• Initiate phototropism
• Control light induced opening of stomata
• Slow hypocotyl growth as seedling breaks ground

Question 13

Environmental stress: drought

Answer 13

• reduce rate of transpiration by closing the stomata
• inhibit growth of young leaves and slow increase of leaf surface
• inhibits growth of shallow roots while deeper roots continue to grow, maximizing exposure to soil water

Question 14

Environmental stress: flooding

Answer 14

oxygen deprivation stimulates the production of hormone ethylene, which causes some of the cells to undergo apoptosis to create air pockets that store oxygen

Question 15

Environmental stress: salt stress

Answer 15

produce solutes to moderate soil salinity and prevent water loss

Question 16

Environmental stress: heat stress

Answer 16

synthesize heat-shock proteins to prevent denaturation and membrane from dissociating

Question 17

Environmental stress: cold stress

Answer 17

take excess water into cytoplasm to prevent crystallization

-alter lipid composition (increase proportion of unsaturated fatty acids)