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Plant Behaviour

External factors, such as light, gravity and

touch have an influence on plant growth

and development.

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Plant Behaviour

External factors, such as light, gravity and

touch have an influence on plant growth

and development.

The growth of a plant in response to a

stimulus such as light or water is called a

tropism.

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Types of TropismTypes of Tropism

stimulusgravity

tropism

response

shoot

root

geotropism

negative

positive

unilateral light

phototropism

positive

negative

water

hydrotropism

no response

positive

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Tropisms

Growth of a plant in a specific DIRECTION

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Tropisms

Growth of a plant in a specific DIRECTION

Positive tropism =TOWARDS THE

STIMULUS

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Tropisms

Growth of a plant in a specific DIRECTION

Positive tropism =TOWARDS THE

STIMULUS

Negative tropism =AWAY FROM THE

STIMULUS

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Importance of PhototropismImportance of Phototropism

Enables leaves to be in a position to

receive as much sunlight as possible for

photosynthesis

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Tropisms

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Auxin

Commonest plant hormones

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Auxin

Commonest plant hormones

Regulates growth & other physiological

processes in plants

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Auxin

Commonest plant hormones

Regulates growth & other physiological

processes in plants

Produced by root tip / shoot tip

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Auxin

Commonest plant hormones

Regulates growth & other physiological

processes in plants

Produced by root tip / shoot tip

They affect the elongation region of the tip

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Auxin

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Auxin

If light is concentrated on one side of the

plant, then auxin moves awayfrom the

light source to the darker side of the tip

and becomes more concentrated in thecells in that region.

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Auxin

If light is concentrated on one side of the

plant, then auxin moves awayfrom the

light source to the darker side of the tip

and becomes more concentrated in thecells in that region.

The increased concentration of auxin

means they grow more quickly than cellsnearer the light.

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Auxin

If light is concentrated on one side of theplant, then auxin moves awayfrom thelight source to the darker side of the tip

and becomes more concentrated in thecells in that region.

The increased concentration of auxinmeans they grow more quickly than cellsnearer the light.

The uneven growth results in the bending

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Phototropism in ShootPhototropism in Shoot

The shoot tip produces auxin which diffuse

downward

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Phototropism in ShootPhototropism in Shoot

The shoot tip produces auxin which diffuse

downward

The auxin diffuse to the

shaded side due to the presence

of unilateral light

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Phototropism in ShootPhototropism in Shoot

The shoot tip produces auxin which diffuse

downward

The auxin diffuse to the

shaded side due to the presence

of unilateral light

High auxin concentrationstimulates growth in shoot

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Phototropism in ShootPhototropism in Shoot

The shoot tip produces auxin which diffuse

downward

The auxin diffuse to the

shaded side due to the presence

of unilateral light

High auxin concentration

stimulates growth in shoot The shaded side grows

fasterthan the lighted side

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Phototropism in ShootPhototropism in Shoot

The shoot tip produces auxin which diffuse downward

The auxin diffuse to the

shaded side due to the presence

of unilateral light

High auxin concentrationstimulates growth in shoot

The shaded side grows

fasterthan the lighted side

The shoot bends towards

the light

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Geotropism in RootGeotropism in Root

The root tip produces

auxin which diffuse to

the elongation region

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Geotropism in RootGeotropism in Root

The root tip produces

auxin which diffuse to

the elongation region

The auxin diffuse tothe lower side due to

gravity

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Geotropism in RootGeotropism in Root

The root tip produces

auxin which diffuse to

the elongation region

The auxin diffuse tothe lower side due to

gravity

High auxin

concentration inhibits

growth in root

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Geotropism in RootGeotropism in Root

The root tip produces

auxin which diffuse to the

elongation region

The auxin diffuse to the

lower side due to gravity

High auxin concentration

inhibits growth in root

The lower side grows

slowerthan the upper

side

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Geotropism in RootGeotropism in Root

The root tip producesauxin which diffuse to theelongation region

The auxin diffuse to the

lower side due to gravity High auxin concentration

inhibits growth in root

The lower side growsslowerthan the upperside

The root bendsdownward

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The End