Plant Responses Flashcards
Stimulus
Anything that causes a reaction in an organism
Response
The activity of an organism as a result of a stimulus
Tropism
A plants response to a stimulus
Structures required for response
Chemical or hormonal system
Sense organs/ Nervous system (a)
Ability to move and grow
Immune system
Phototropism
A plants response to light from a given direction
Positive tropism
Occurs when the plant grows in the direction of the stimulus eg:light for photosynthesis
Negative tropism
Occur when the plant grows away from the stimulus eg: chemotropism
Advantage of tropisms
Allow plant to obtain better growing conditions
Geotropism
Response to gravity
Thigmotropism
Response to touch
Eg: Venus fly trap
Hydrotropism
Response to water
Chemotropism
Response to chemicals
Positive: rooting powder
Negative: herbicides
Growth regulator
A chemical that controls the growth of a plant
Produced in the meristem and carried to their sites of action in vascular system
Examples of growth regulators:
(Positive)
Growth promotors
Examples of growth promotors
Auxin (IAA) - used for stem elongation, flower initiation and fruit growth
Gibberellin - used for stem cell elongation and seed germination
Cytokinin - used for cell division and differentiation
Examples of growth regulators:
(Negative)
Growth inhibitors
Growth inhibitors:
Reduce the growth of plants
Examples of growth inhibitors
Abscissic acid - inhibits growth in seeds and results in dormancy
Ethylene (ethene) - inhibits growth in petioles and results in leaf fall in autumn
(Can ripen veg, not organic)
Plant growth regulators (hormones) are…
Chemicals that interact with one another to control a particular development or response
Commercial use of growth promotors:
- Rooting powders (NAA, rapid root formation in stem cuttings)
- Banana ripening (ethene)
- Tissue culture (microprogation) (auxin promotes the formation of callus)
- Produce seedless fruits eg: grapes
Name a family of growth promoters
Auxins
IAA
Indolacetic acid
Production site for auxin
Mainly in shoot top meristem, young leaves and developing seeds
Meristem is
Tissue capable of mitosis
Effect of auxins
Cell enlargement and growth
Involved in phototropism and apical dominance
The mechanism of phototropism
- IAA is produced in the meristem and is passed down the stem
- If the stem is exposed to light from one side IAA will diffuse down the shaded side
- The cell on the shady side elongates, those on the bright side dont
- The difference in elongation caused the stem to grow towards the light
Apical dominance
Auxins are responsible for apical dominance, where the main Bud inhibits the growth of buds lower down the stem
Plants adaptation for protection:
Anatomical/structural
Protective epidermis or bark
Thorns
Stinging hairs
Guard cells shrivel in drought and close stomata to prevent further water loss
Plants adaptation for protection:
Chemical features:
Heat shock proteins (prevent denaturation)
Stress proteins (phytoalexins: attack cell walls of the infecting micro organisms)
