Plant hormones Flashcards
what are tropisms?
responses to help ensure plants grow towards sources of light and water.
what are the two main types of tropisms?
what do they cause the plant to do?
positive tropisms - the plant grows towards the stimulus
negative tropisms - the plant grows away from the stimulus
what is phototropism?
growth of plant shoots towards the light
what are responses to light known as in the plant stem?
-what does this mean?
- positive phototropism,
-stem grows towards the light.
what are responses to light known as in the plant roots?
-what does this mean?
-negative phototropism
-root grows away from the light.
what are auxins?
what do they control?
a family of plant hormones
-control growth of stems and roots
where are auxins produced?
what can they do?
-tips of the growing stems and roots (apical meristems)
-diffuse to other parts of the stems or roots.
what does unequal distribution of auxins result in?
unequal growth rates in plants and shoots.
how do cells in stem and root cells react differently to high concentrations of auxins?
cells in stems grow more
cells in roots grow less
in a stem, which side grows longer and towards the light?
the shaded side which contains more auxins (the auxins diffuse towards the shaded side)
why does the stem grow towards the shaded side?
-because the auxin causes the cells to elongate on the shaded side, so this side grows more
what does the unequal growth of both sides result in?
the growth of the stem towards the light.
what effect do auxins have on root cells (about phototropism)?
explain why this occurs: (2)
the opposite effect
-the shaded side contains more auxin and grows less
- causing the root to bend away from the light.
what is gravitropism?
a response to the stimulus of gravity
what is positive and negative gravitropism?
-positive gravitropism= when a root grows in the direction of the force of gravity
-negative gravitropism= when the stem grows against the force of gravity
what would happen to a root placed horizontally? (2)
bottom side contains more auxin and grows less - causing the root to grow in the direction of the force of gravity. (pg)
what would happen to a shoot placed horizontally? (2)
bottom side contains more auxin and grows more - causing the stem to grow upwards against the force of gravity. (ng)
what are auxins often commercially used as? (2)
weed killers
rooting powders
what does selective weed killer contain?
a growth hormone that causes the weeds to grow too quickly and die
why is selective weed killer effective on weeds?
Because they have broader leaves, the weed killer is absorbed in larger quantities by the weeds than it is by the grass
why could selective weed killer be potentially harmful?
it can reduce biodiversity within treated areas due to specific plants being killed.
what does rooting powder contain?
plant hormones to promote growth
how could plant rooting powder be used?
Plant cuttings can be dipped in hormone rooting powder before planting
what are Gibberellins responsible for?
growth and development
why are gibberellins important within a plant?
they initiate seed germination
what can low concentration of gibberellins be used for? (2)
increase the speed of germination,
-stimulate cell elongation so plants grow taller.
4 main usages of gibberellins?
end seed dormancy
promote flowering
increase fruit size
seedless fruit
what is ethene and what does it do?
hydrocarbon gas that speeds up ripening in fruit
