Plant responses (chpt. 32) Flashcards
Stimulus
Something that causes a reaction in an organism
Response
The activity of an organism in response to a stimulus
↳ animals modify behaviour
↳ plants modify growth
Tropism
Change in the growth of a plant in response to a stimulus
↳ ensure a plant is positioned most favourably for its growth
Positive tropism
Towards stimulus
Negative tropism
Away from stimulus
Phototropism
Response to light
Geotropism
Response to gravity
Thigmotropism
Response to touch
Hydrotropism
Response to water
Chemotropism
Response to chemicals
Growth regulator
Chemical that controls the growth of a plant
Where are growth regulators produced?
Meristematic regions (root/shoot tips)
How are growth regulators transported around the plant?
Mostly in xylem and phloem
Example of a growth regulator and its effect
auxin
↳ small amounts → root promoter & shoot inhibitor
↳ large amounts → root inhibitor & shoot promoter
Mechanism of phototropism
• IAA produced in meristem
• auxin diffuses down shaded side
• higher concentration of auxin on shaded side causes cells on this side to elongate
• as a result of uneven elongation, cell bends towards the light
Commercial uses of plant regulators
Fruit harvesting: spray with auxins to prevent fruit drop, allows fruit to grow larger
Rooting powders: auxins used to stimulate plant cuttings to grow quicker
Adaptations of plants for protection (x4)
PHYSICAL:
• thorns - cactus
• epidermis/bark - prevent entry of pathogens, reduce water loss
CHEMICAL:
• tannins - make bark bitter tasting to prevent being eaten by caterpillars
• heat shock proteins - surround plant enzymes during high temperatures to prevent denaturing
What is a benefit to the plant that the shoot is positively phototropic?
Absorbs more light for photosynthesis
State why the action of an auxin is considered to be similar to the action of a hormone in the human body
Chemical action
Prolonged effect
Produced in one place and act in another
State an inhibitory function of auxin
Slows mitosis
Give an example of a growth regulator which has a negative effect on plant growth
IAA
Ethene
Give two examples of auxins which inhibit growth
IAA
Ethene
What is the role of the vascular system in tropic response?
Transport growth regulators
Advantage of tropisms
Plants can achieve more favourable conditions for growth
What are growth regulators transported in?
Vascular tissue
