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Plants respond to stimuli
Directional growth responses to stimuli in plants
are called tropisms. There are several forms of
tropisms.
Tropisms-
Phototropisms- where the plant grows towards a
light source
Geotropism- where roots grow towards the pull
of gravity
Chemotropism- on flowers, pollen tubes grow
down the style, towards the ovary where
fertilisation can take place
Thigmotropism- shoots of climbing plants grow
around solid structures to gain support.…read more

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What controls these responses?
Hormones!
Plant hormones are chemical messengers that
can be transported away from their site of
manufacture to act in other parts of the plant.
They are often referred to as plant growth
regulators because they aren't produced in
endocrine glands like in animals.
Hormones move about by active transport,
diffusion, or mass flow in the phloem sap or in
xylem vessels.…read more

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Types of hormones in plants
Hormone Effects
Auxins Promotes cell elongation and inhibits side
shoot growth, and leaf abscission
Gibberellins Promote cell division (growth)
Cytokinins Promote seed germination and growth of
stems
Abscisic acid Inhibits seed germination and growth, and
causes stomatal closure when the plant has
low amounts of water.
Ethene Promotes fruit ripening.…read more

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How do they respond to the
environment?
Growth only happens in particular parts of the
plant. These places are called meristems- they're
the only places where there are immature cells
that are still capable of dividing (stem cells).
Apical meristems: at the tip of shoots, make the
shoots get longer.
Lateral bud meristems: found in buds, that could
form side shoots.
Lateral meristems: found in a cylinder near the
outside of roots and shoots, and make them get
wider.…read more

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Phototropisms
This refers to plants growing towards light.
Auxins are responsible for this kind of
tropism. Auxins cause cells to elongate. Auxins
are transported to the side of the plant that is
shaded, so cell elongation occurs in that side
rather than the brighter side. This means faster
growth occurs on the shady side of the plant,
resulting in the plant bending over towards
the direction of the light.…read more

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