Chapter 5: Response in Plants

Question 1

Plants can respond to external stimuli such as ___, ___, ___, ____ and ____.

Answer 1

• light
• gravity
• water
• temperature
• touch

Question 2

What are the two types of response in plants?

Answer 2

• tropism

- nastic response

Question 3

What is meant by tropism?

Answer 3

• growth response of root tip or shoot tip towards or away from a stimulus

Question 4

What are the characteristics of tropism?

Answer 4

• stimulus is from one direction
• growth response depends on the direction of the stimulus
• not reversible
• slow and not apparent

Question 5

What is negative and positive tropism?

Answer 5

• positive tropism is the growth towards the stimulus

- negative tropism is the growth away from the stimulus

Question 6

What are the five types of tropism?

Answer 6

• thigmotropism
• geotropism
• phototropism
• chemotropism
• hydrotropism

Question 7

What is nastic movement?

Answer 7

• plant movement that occurs at any part of the plant in response to external stimuli

Question 8

What are the characteristics of nastic response?

Answer 8

• non-directional
• does not depend on the direction of the stimulus
• does not lead to growth and is irreversible
• fast and apparent

Question 9

What are the five types of nastic response?

Answer 9

• photonasty
• seismonasty
• thermonasty
• nyctinasty
• thigmonasty

Question 10

Explain photonasty, seismonasty, and thermonasty.

Answer 10

Photonasty

• non-directional movement of a plant in response to light
• petals of flowers open at day and close at night such as dandelion and morning glory

Seismonasty

• caused by mechanical stimuli such as shock or touch
• parts of the plats that show response: stigma, stamens and leaves
• Mimosa pudica and neptunia

Thermonasty

• occurs due to change in temperature
• open when temp.rises and closes when temp.drops
• tulip

Question 11

Explain nyctinasty and thigmonasty.

Answer 11

Nyctinasty
- due to circadian rhythm that responds towards the
onset of darkness
- seen in leguminous plants such as long bean and river tamarind
- leaves fold at night and open up in the day

Thigmonasty

• due to vibration
• some are carnivorous
• venus flytrap and pitcher plant

Question 12

What are the similarities between tropism and nastic response?

Answer 12

• both are plant responses

- both respond towards stimuli

Question 13

What are the differences between tropism and nastic response?

Answer 13

Tropism

• respond to directional stimuli
• irreversible
• a growth response
• slow and not apparent
• occurs at the shoot and root tip

Nastic response

• respond to non-directional stimuli
• reversible
• not a growth response
• fast and apparent
• occurs at any part of the plant

Question 14

What are phytohormones?

Answer 14

• stimulate and coordinate responses in plants, at low concentrations

Question 15

What are the five main types of phytohormones?

Answer 15

• Auxin, gibberellin and cytokinin stimulate growth

- Abscisic acid and ethylene inhibit the growth

Question 16

What are the functions of auxin?

Answer 16

• stimulates cell elongation at the shoot and root tip
• stimulates the growth of adventitious roots
• inhibits the growth of weeds
• prevents fruit or leaves from falling off prematurely
• inhibit growth of lateral buds into shoots ( prevents from branching out of the plants, so that the plant grows tall and straight )

Question 17

What are the functions of gibberellin?

Answer 17

• stimulates cell elongation in the shoot ( growth of stem )

- stimulates germination of seeds

Question 18

What are the functions of cytokinin?

Answer 18

• stimulates cell division

- delays aging and death of leaves

Question 19

What are the functions of abscisic acid and ethylene?

Answer 19

Abscisic acid
- inhibits the growth of shoots and promotes dormancy in seeds
- stimulates abscission
Ethylene
- stimulates the ripening of fruits
- stimulates abscission

Question 20

What are the characteristics of auxin?

Answer 20

• produced in the apical meristem
• moves away from light
• in shoot tip, high concentration stimulates cell elongation
• in the root tip, high concentration inhibits cell elongation

Question 21

Auxin is also known as ______ ___.

Answer 21

• indoleacetic acid

Question 22

Explain the response of the shoot tip in unilateral light.

Answer 22

• auxin is produced in the apical meristems
• auxin diffuses into the zone of elongation
• distribution of auxin is uneven
• more auxin accumulates in the shaded region
• high concentration stimulates cell elongation
• bends and grows towards the light
• shows positive tropism

Question 23

What are the applications of auxin in agriculture?

Answer 23

• sprayed onto fruits to make fruits develop and ripen at the same time
• (parthenocarpy) sprayed on the ovaries of the flowers which stimulates ovaries to develop into fruits without fertilization - seedless fruits are formed as ovules do not develop into seeds
• inhibit the growth of lateral buds - used on potatoes during shipment and also to produce bushy plants

Question 24

What are the applications of gibberellin?

Answer 24

• produce larger grapes
• promotes germination of oats seeds during low temperatures
• treats mutated dwarf plants

Question 25

What are the applications of cytokinin, abscisic acid, and ethylene?

Answer 25

Cytokinin
- used in tissue culture 
- delay leaf senescence
Abscisic acid
- inhibits germination and growth
Ethylene
- sprayed in fruit storage rooms to stimulate ripening of bananas
- promotes simultaneous flowering in plants