Download TROPIC RESPONSES

Merighi Pietro
What is a Geotropism?
A geotropism is the
growthof living plants in
response to gravity.
It is given by the downward
of the plant roots
What is a Phototropism?
It is the directional growth in which the direction of
the growth is determined by the direction of the
light source.
In other words it is the growth and response to a
light stimulus.
Plant Auxins
As with animals , plants also use a variety of
hormones to control their growth and development.
A family of hormones called auxins are commonly
found in plants, and promote (and sometimes inhibit)
growth.
What are Auxins?
Auxins are produced in the meristems (tissue that
grows) of plants
Auxins are responsibile in promoting cell elongation,
a process that is required before differentiation of a
cell. It is able to this by promoting the intake of
water, increasing the elasticity of the cell to cope
with the increase of water taken in by the cell.
(One of the most common auxins is indole acetic
acid.)
Phototropism in Auxins.
Auxins also play a part in phototropism, an occurance thay
involves plants bending or moving away from light. The
shoot tip is responsible for directional movement by the
plant in response to sunlight, as this is the area where
auxins can be found.
Sunlight eradicates auxin, meaning that the part of the
shoot tip of the plant which is reaciving direct sunlight wil
have the least amount of auxin
The extra auxin present on the shaded side promotes
more cell division and elongation, causing the plant to
bend towards the sunlight after this lop-sided growth.
Geotropism in Auxins.
Geotropism is a similar occurance to the
phototropism where the plant exihibits directional
growth in response to gravity. The shoot tip
illustrates negative geotropism (grows against force
of gravity) while the root tip exhibits positive
geotropism (grows in the same direction as gravity).
Questions…..
What is a geotropism and a phototopism?
What are Auxins?