Chapter 5: Response in Plants Flashcards
Plants can respond to external stimuli such as ___, ___, ___, ____ and ____.
- light
- gravity
- water
- temperature
- touch
What are the two types of response in plants?
- tropism
- nastic response
What is meant by tropism?
- growth response of root tip or shoot tip towards or away from a stimulus
What are the characteristics of tropism?
- stimulus is from one direction
- growth response depends on the direction of the stimulus
- not reversible
- slow and not apparent
What is negative and positive tropism?
- positive tropism is the growth towards the stimulus
- negative tropism is the growth away from the stimulus
What are the five types of tropism?
- thigmotropism
- geotropism
- phototropism
- chemotropism
- hydrotropism
What is nastic movement?
- plant movement that occurs at any part of the plant in response to external stimuli
What are the characteristics of nastic response?
- non-directional
- does not depend on the direction of the stimulus
- does not lead to growth and is irreversible
- fast and apparent
What are the five types of nastic response?
- photonasty
- seismonasty
- thermonasty
- nyctinasty
- thigmonasty
Explain photonasty, seismonasty, and thermonasty.
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
Explain nyctinasty and thigmonasty.
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
What are the similarities between tropism and nastic response?
- both are plant responses
- both respond towards stimuli
What are the differences between tropism and nastic response?
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
What are phytohormones?
- stimulate and coordinate responses in plants, at low concentrations
What are the five main types of phytohormones?
- Auxin, gibberellin and cytokinin stimulate growth
- Abscisic acid and ethylene inhibit the growth
What are the functions of auxin?
- 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 )
What are the functions of gibberellin?
- stimulates cell elongation in the shoot ( growth of stem )
- stimulates germination of seeds
What are the functions of cytokinin?
- stimulates cell division
- delays aging and death of leaves
What are the functions of abscisic acid and ethylene?
Abscisic acid - inhibits the growth of shoots and promotes dormancy in seeds - stimulates abscission Ethylene - stimulates the ripening of fruits - stimulates abscission
What are the characteristics of auxin?
- 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
Auxin is also known as ______ ___.
- indoleacetic acid
Explain the response of the shoot tip in unilateral light.
- 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
What are the applications of auxin in agriculture?
- 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
What are the applications of gibberellin?
- produce larger grapes
- promotes germination of oats seeds during low temperatures
- treats mutated dwarf plants
What are the applications of cytokinin, abscisic acid, and ethylene?
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
