Tropisms In Plants Flashcards
What is a tropism?
Plant growth responses to stimuli from one direction
Involve differential growth of plant cells triggered by chemical messages produced in response to a stimulus
What is plant growth in response to light?
Phototropism
What is plant growth in response to gravity?
Geotropism
What is plant growth in response to chemicals?
Chemotropism
What is plant growth in response to touch?
Thigmotropism
How do plants make to maximum use of the environmental conditions?
Grow and respond to variations in those conditions
Shoots of a seed grow up
Roots grow down= support, minerals, water
These take place in response to environmental factors
What does most of the research into tropisms use?
Germinating seeds and young seedlings
Easy to work with and manipulate
Grow and respond quickly= changes show quickly
Changes affect the whole organism, not just a part
Monocotyledons used, shoot emerges as single spike = coleoptile, easier to manipulate and observe, but this is relatively simple system and important to remember it may be more complex
How are phototropism’s investigates?
Shoots kept in dark or full illumination but this is rarely the case in real life
If plants are grown in all-round light= grow upwards
Even but low light= upwards
Light which is brighter on one side than other= shoots of plant grow towards light, if roots exposed they will grow away
What is positively phototropic and negatively phototropic?
Give examples
How can it aid survival?
Positively- grow towards light- shoots
Negatively- grow away from light- roots
Survival- ensure shoots receive as much light as possible, increasing photosynthesis
If roots emerge from soil (eg. Due to heavy rain) they will rapidly turn back to soil
How do phototropism’s work?
think auxins
Movement of auxins across the shoot or root if exposed to light stronger on one side than the other
when there is unilateral light, the shoot side exposed to the light contains less auxins than the side which is not illuminated.
light causes auxins to move across the shoot so theres greater conc on unilluminated side= stem elongation and growth on dark side, making plant grow towards light
once the shoot is growing towards the light, it grows straight and this diffrence in auxin conc stops
Describe an experiment that shows differing auxin concs, depending on light
what are 3 practical investigations into phototropisms?
germinate and grow seedlings in different conditions of dark, all-round light and unilateral light,
observe patterns of growth- could use time-lapse photography
germinate and grow seedlings in unilateral light with different colour filters to see which wavelength of light triggers the phototropic response
cover coleoptile with foil , remove tips of some coleoptiles , place auxin-impregnaed agar jelly blocks on decapitated coleoptiles, but on one side only
Why do plants grow quicker in the dark, than when illuminated?
grow rapidly upwards to try to reach light for photosynthesis
gibberellins responsible for this
levels of gibberellins decrease, once the stem is exposed to light
EG- a seed has to do this to compete with other seeds for light, this vertical growth slows when light is reached, as photosynthesis can construct leaves
what is a negative geotropism and a positive geotropism?
give examples
place seedling either in fully illuminated or dark conditions, place on sides. shoots are usually negatively geotropic (grow opposite to force of gravity), whereas roots are positively geotropic
to ensure roots grow down into soil and shoots grow up towards light
whats another word for geotropism?
gravitropisms
How do you investigate geotropisms?
investigated in roots and shoots using rotating drum (clinostat), plants can be grown on slowly rotating clinostat so gravity is applied equally to all sides of plant- should grow straight
