28. Plant Response Flashcards
Stimulus def.
Any change in the environment which causes an organism to react/grow
Response def.
Is the reaction to the stimulus
eg. growth
Tropism def.
The change in growth of a plant in response to an outside stimulus.
Positive tropism
Growth is towards the stimulus
eg. shoot in response to gravity
Negative tropism
Growth is away from the stimulus
eg. root in response to gravity
Tropism types
Geotropism-gravity Phototropism-light Thigmotropism-touch Chemotropism-chemicals Hydrotropism-water
Phototropism def.
Negative/positive in shoots/roots
Growth response to light
Negative: Roots grow away from light
Positive: Shoots grow towards light
Geotropism def.
Positive/negative
Def: Growth response to gravity
Neg: Shoots
Pos: Roots
Thigmotropism def.
example
Growth response to touch/contact
Vines wrap around objects which help support the plant
Chemotropism def.
example
Growth response to chemicals
eg. Pollen tubes grow down carpel in response to chemicals released by ovule
- Roots towards fertilisers in the soil
Hydrotropism def.
example
Growth response to water
eg. roots grow towards water
Advantage of tropisms
Allows plants to have the best conditions for growing.
eg. growth towards light so more light, more photosynthesis
What are internal factors affecting growth n a plant
Growth regulators
either growth inhibitors or promoters
Plant growth regulator def.
produced
transported by
Def: A chemical that controls the growth in a plant
Produced: Meristems regions-tips of roots and shoots
Transported by the phloem
Growth promoter def.
Increase rate of growth
eg. auxins such as IAA
Auxin
produced
How it works
Effects/Roles
Produced: Tip of plants, young seeds, young leaves
Works by: Loosening cell walls causing expansion of cells and elongation and therefore growth.
Effects: Causes tropisms, causes apical dominance, causes seeds to develop into fruits.
How IAA controls phototropism
High IAA concentration on the shady side of shoot. Therefore cell elongation and quicker growth on shaded side. Which leads to bending due to uneven growth. Results in phototropism…plant growing in direction of light
IAA role in geotropism
Low IAA concentration in roots causes roots to grow
IAA role in apical dominance
Auxin produced at tip. Causes plant to grow up not sideways
IAA role in fruit formation
IAA produced in developing seeds stimulates food store in seeds to form into fruits
Examples of growth inhibitors
Abscisic acid
Ethene
Abscisic Acid
How it protects against harsh conditions
- Causes stomata to close saving water
- Causes bud scales to form to protect buds during winter
- Causes seed dormancy so stops germination in unfavourable conditions
Ethene
why different from other growth regulators
Only one that is a gas
Ethene where produced and role in plants
Produced: ripe fruits, decaying leaves
- Causes ripening of fruit, fruit flavour and colour to develop.
- Causes leaves to fall
- Causes ageing of plants
- Causes more ethene to be produced and further ripening of fruit.
Uses of plant regulators in commercial plants
- Rooting powders-artificial auxin used for rapid root growth
- Tissue Culturing-plant tissue grown in high auxin concentration to form new plant
- Artificial Ethene-ripening of fruit
Structural Adaptations in plants
- Bark/ Epidermis/ Cuticle-prevent entry of microbes and reduces water loss
- Thorns prevent plants from being eaten by herbivores
- Stinging cell in epidermis prevent plants being eaten
Chemical Adaptations in plants
- If infected by microorganisms produces stress proteins which attack cell wall of microorg, stimulates neighbouring plant to respond to microorg, produces specialised cell wall to prevent entry.
- Excessive heat: plants produce heat shock proteins to protect enzymes when temperatures are high
