plants and tropisms Flashcards
what is a positive tropism
when plants grow towards a stimulus
what is a negative tropism
when plants grow away from a stimulus
what is the response to gravity known as
gravitropism
what is positive gravitropism
when plants grow towards the force of gravity (eg toward roots)
what is negative gravitropism
growth away from gravity (eg towards roots)
what is the response to light known as
phototropism
what is positive phototropism
growth towards light
what is negative phototropism
growth away from light
how must shoots grow
upwards
away from gravity
towards light
so that leaves are able to absorb sunlight
how must roots grow
downwards into the soil
away from light and towards gravity
in order to anchor the plant and absorb water and minerals from the soil particles.
what does this say about roots tropic responses
roots have a negative phototropic response and a positive gravitropic response
what does this say about shoots tropic responses
shoots are negatively gravitropic and positively phototropic
what is auxin
Plants respond to stimuli by producing a growth hormone called auxin which controls the direction of growth of roots or stems
how do plants control their growth
chemically
where is auxin mostly produced
Auxin is mostly made in the tips of the growing stems and roots
how does auxin travel
through diffusion
high concentration in shoot tips down the shoot to an area of low concentration
where does auxin stimulate growth
Auxin stimulates the cells behind the tip to elongate
the more auxin there is the faster they will elongate
what is the part of the plant in which auxin grows the most called
Only the region behind the tip of a shoot is able to contribute to growth by cell division and cell elongation. This part of a shoot is called the meristem.
when light shines on a plant where does the auxin form
auxin forms in the shaded region (the side where light is not shone) making the cells on that side grow faster and longer
this unequal growth causes the shoot to bend and grow in the side of the light
how does auxin affect gravitropism in shoots
Gravity modifies the distribution of auxin so that it accumulates on the lower side of the shoot
As seen in the phototropic response, auxin increases the rate of growth in shoots, causing the shoot to grow upwards
negative phototropism
how does auxin affect gravitropism in roots
In roots, higher concentrations of auxin results in a lower rate of cell elongation
The auxin that accumulates at the lower side of the root inhibits cell elongation
As a result, the lower side grows at a slower rate than the upper side of the root
This causes the root to bend downwards
Explain how auxins control the growth response of seedlings
auxins made in tip diffuse down the stem auxins collect in the side away from the light, greater elongation in the side in the dark
explain the role of auxins in phototropism
auxin stimulates cell elongation, auxin accumulates on shaded side which causes bending on non-shaded side
