Tropisms Flashcards
What are tropisms?
Differential growth of plant cells triggered by chemical messages produced in response to particular stimuli
Chemotropism –> response to chemicals
Thigmotropism –>response to
touch.
What is phototropism?
Growth of plant in response to light
~> one direction
What is geotropism?
the response to gravity
What is positive phototropism?
Unilateral light causes auxins to move laterally in shoot tips to shaded side.
Higher auxin concentration on shaded side
Increase auxin promotes cell elongation on shaded side —>grows faster
Shoot bends towards light.
Why is phototropism a good evolutionary trait?
Ensures max rate of photosynthesis
Roots = grow away from light ~~>get water+minerals in soil
What is positive geotropism?
Auxins fall to bottom parts of shoots + roots due to gravity
Increase auxins = decrease in growth
.:top part grows faster
What is negative geotropism?
Increase in auxins = increase shoot growth
.:bottom part grows faster
What is the importance of geotropism?
Ensures shoots grow upwards for move light –> more photosynthesis
Ensure roots grow downwards to absorb water + minerals
What happens to the shoots if tipis removed?
No response
Tip must detect stimulus.
What happens to the shoots if mica is added?
Experiments by Darwin + Boysen-Jensen
–>Hormones pass only to shaded side.
–>increases growth and causes bending towards light
How is the ripening of plants controlled?
Ethene
Triggers series of chemical reactions.
Increases respiration rate
Oranges, strawberries —> do not produce large amounts of ethene
Unripened fruits –> easier to transport
When fruits ready for sale = exposed to ethene gas
Why is fruit ripening under such careful control?
Ensure each batch ripens at same rate
prevents food wastage
Increases time available to be sold
How does micropropagation occur?
Cutting = small piece of stem
Dipping cut stem in hormone rooting powder increases chance of root forming
–>successful propagation
Many plants now propagated on large scale micropropagation.
=100000s new plants from few cells of OG plant.
Hormones finely balanced to allow plant to grow.
Loss of balance = plant death
Good for weeds
~~>interfere with crop resources
Synthetic auxin = good weedkiller
Only affects broad-leaved dicot plants (weeds)
What are other uses of plant hormones?
*Production of seedless fruits
*Promote fruit dropping (cotton, walnuts, cherries)
*Gibberellin = delay ripening + ageing in fruits
~>improve size +shape of fruit
*Beer brewing = speed up malting process
*Cytokinins = prevent ageing of fruit (lettuce)
