definition of tropism = a plant growth to a one-sided stimulus
positive tropism = plants grow towards a one sided stimulus
negative tropism = plants grow away from a one-sided stimulus
tips of shoot grow...?
towards light
tips of roots grow...?
away from light
positive phototropism = grow towards light
negative phototropism = grow away from light
roots grow down towards gravity
why do roots grow down towards gravity?
to ensure they have enough water from soil
roots = positive gravitropism
shoots = negative gravitropism
negative gravitropism = grow away from gravity
positive gravitropism = grow towards gravity
auxins = plant hormones that cause the response
auxins accumulate on side of plant where there is no light -> this side grows -> plant ends up growing towards light
accumulation of auxin molecules:
accumulation of auxin molecules on side of plant with no light = cell elongation
how to get seedlings to grow upwards?
place on a rotating plate where one rotation=20 minutes, illuminate from one side only by powerful bench lamp -> seedlings receive equal amount of light -> so auxin is distributed equally -> seedlings grow upwards
