Plant Hormones (paper 2) Flashcards
2 factors
plants produce hormones to coordinate and control:
- groth and response to light - phototropism
- growth responses to gravity - gravitropism / geotropism
what causes unequal growth rates in plant roots and shoots
unequal distribution of auxin
what is the effect of auxin on shoots
to grow / elongate more quickly
what is the effect of auxin on roots
causes cells in roots to grow more slowly
name 3 plant hormones:
- auxin
- gibberellins
- ethene
what ae gibberellins used for
important in initiating seed germination
what is ethene used for
controls cell division and ripening of fruits
what is positive tropism
growth towards a stimulus
what is negative tropism
growth away from a stimulus
plant shoots and roots respond to which 3 stimuli
- light
- gravity
- water
phototropism =
plant shoots bend / grow in response to light
describe the stages of phototropism
- when light falls evenly on the shoot –> auxin is spread evenly through the tissues
- when light falls on shoots from one direction –> auxin moves away from light - accumulates on the shaded side of the shoot = now an uneven distribution of auxin
- auxin causes cells on shaded side to grow faster than cells on the side in the light –> causes shoot to bend towards the light
- when ** light falls evenly** on shoots again, –> auxin becomes evenly distributed = growth on all side of the root and shoot will be equal
gravitropism =
the response of a plant to gravity
describe the process of gravitropism when a young plant is laid on its side.
- auxin accumulates on the lower side of both the root + shoot = uneven distribution of auxin
- Roots: cells elongate faster on the side will less auxin - causes the roots to bend downwards - direction of the force of gravity
- Shoots: cells elongate faster on the side with more auxin - shoots bend upwards - away from gravity
- once roots is growing towards gravity + shoots is growing away from gravity - auxin becomes evenly distributed = growth on all side of the root + shoot will be equal
RPA 8 investigate the efffect of light / gravity on the growth of newly
describe the stages of phototropism
- auxin is produced in the shoot tips
- ausin diffuses to the shaded dise
- the concentration of auxin on the shaded side increases - unequal aucin distribution
- the higher concentration of auxn causes the cell on the shaded side to increas their length
- causes shoot tipe to bend towards light - shoot tips shows positive phototropism
RPA 8
there are 3 groups of seeds in a cardbaord box, with a hole that allows light into the box from one side onlyL=:
- Group A has had shoot tips removed
- Group B has had shoot tips covered
- Group c is left untouched
What will be the growth results of each seed group?
A = no auxin is made so stems do not grow
B - auxin moves to all part of the stem causing all parts to grow equally - grows straight up
C - auxin acculumates on the shaded side causing it to grow more than the illuminated side - grows towards light
where are plant growth hormones used
in agriculture and horticulture
3 ways in which auxin is used and how:
-
weed killers
- very high doses causes plants to grow too quickly + die
-
rooting powder
- encourage meristem in cuttings to grow into new roots
-
promoting growth in tissue culture
- encourage formation of rootlets + shootlets
what is ethene used for
- in the food industry to control ripening of fruit during storage + transport
what effect does ethene have on agriculture, transportation, sale
- unripe fruit can be picked + transported –> damages less easily + lasts longer
- fruit can be ripened with ethene at its destination so that it is ready to eat + look appealing for sale
what are gibberellins used for
- end seed dormancy
- promote flowering
- increase fruit size
how does the use hormones as weed killers has an effect on biodiversity.
selective weedkillers kill specific plants that some species of animals rely on as a food source –> reduction of biodiversity
