16.4 Tropisms in plants Flashcards
what is a tropism?
plant growth repsonses to stimuli
what is phototropism?
growth of plants in response to light
what is geotropism?
growth of plants in response to gravity
what causes phototropism?
diffusion of auxin across roots and shoots due to varying exposures to light
how is auxin transported over short distances?
diffusion
how is auxin transported over long distances?
by the phloem
how does auxin cause growth in the roots and shoots?
it causes cell elongation on the side it is most present on
are shoots positively or negatively phototropic?
POSITIVELY
as the shoots grow TOWARDS the stimuli
are roots positively or negatively phototropic?
NEGATIVELY
as they grow away from the stimuli
what causes a plant to grow towards light?
auxin on the the side exposed to the light diffuses laterally to the shaded side
as there is more auxin on the shaded side there is more growth which leads to the shaded side elongating and causing it to bend towards the light
how do auxin concentrations change with light?
THEY STAY THE SAME
no auxin is destroyed
auxin moves by diffusion
what happens to a plant’s response to light when the shoot tip is removed?
there is not shoot growth
as the shoot tip detects the stimuli, and produced the auxin needed for growth
what happens to a plant’s response to light when the shoot is covered?
there is no shoot growth
as the shoot tip cannot detect the light as it is covered
what is mica?
impermeable gel which prevents hormones passing through
what happens to a plant’s response to light when mica is added to the illuminated side?
shoot bends towards the light
as the auxin cannot pass down the illuminated side to the mica, it passes down the shaded side which causes elongation and growth
what is a gelatin block?
permeable gel which allows hormones to pass through
what happens to a plant’s response to light when a gelatin block is added?
normal phototropic response
bends towards light
what was the original theory about the affect of light on auxin?
originally thought that auxin was BROKEN DOWN by light
what has disproved the original theory on light’s affect on auxin?
auxin levels regardless of the direction of light stay the same
which hormone causes plants to grow in the dark?
gibberellins as they lead to extreme elongation of the internodes
what is etiolation?
growth of a plant in the dark
what is geotropism?
growth of a plant in response to gravity
are shoots positively or negatively geotropic?
NEGATIVELY
as they grow away from gravitational pull UPWARDS
are roots positively or negatively geotropic?
POSITIVELY
as they grow towards gravitational pull DOWNWARDS
what does geotropism ensure?
roots grow down into the soil
shoots grow up into the sky
why is it important for roots to grown into the soil?
can reach water stores in the soil
why is it important for shoots to grow up into the sky?
can reach more light for photosynthesis
