Transcript Tropisms[1] - missdannocksyear11biologyclass

Plant
responses
Plant Hormones
• Like animals, plants also use hormones to
control internal activities but unlike animals
they have no nervous system.
• The hormones they release are not from
glands but from different types of cells.
• Instead of blood the plant hormones travel
through a series of tubes called phloem.
How do plants always grow the
right way up?
What conditions will affect how a plant grows?
What do plants respond to?
Plants are very sensitive and their growth is affected by
their environmental conditions.
water
light
gravity
A condition that affects plant growth is called a stimulus.
What are the three types of stimuli that plants respond to?
What is a tropism?
Plants respond to stimuli by growing to or away from them.
A growth movement in response to a stimulus is a tropism.
water
light
gravity
Movement towards a stimulus is called a positive tropism.
What is a movement away from a stimulus called?
A negative tropism.
Different types of tropism
Plant responses to light, water and gravity are given
special names.
water
hydrotropism
light
phototropism
gravity
geotropism
The question is, which parts of a plant respond to these
different stimuli?
Plant
response to
Light
How do plants respond to light?
A plant’s response to light is called phototropism.
Is phototropism a positive or negative tropism?
light
Plants grow towards light, which is a positive tropism.
Why do plants grow towards light?
Plants need light for photosynthesis, so they respond
to light by growing towards it.
Phototropism and auxins
Which part of a plant is involved in phototropism?
A growing shoot on a plant responds to light.
light
Auxins are made in the
tip of a growing shoot
and move down the stem.
These plant hormones
speed up growth in
a growing shoot.
Phototropism and auxins
– light from above
light
When a shoot gets light
from above, the auxins
produced at the tip are
spread out evenly in
the shoot.
How will this affect the
growth of the shoot?
Phototropism and auxins – light from above
Why does a shoot grow straight up when light is from above?
There is an equal amount of auxins in all parts of the shoot,
which grow at the same rate, so the shoot grows straight up.
light
light
Phototropism and auxins
– light from one side
When a shoot gets
light from one side,
the auxins are not
evenly spread out in
the shoot.
light
How will this affect the
growth of the shoot?
Phototropism and auxins – light from one side
Why does the shoot bend towards the light when it gets
light from one side?
There are more auxins on the shaded side of the shoot,
so the shaded side grows faster making the bright side
bend towards the light.
light
light
Phototropism experiment
Plant
response to
Gravity
How do plants respond to gravity?
A plant’s response to gravity is called a geotropism.
Different parts of a plant have different responses to gravity.
shoots grow up
negative geotropism
gravity
roots grow down
positive geotropism
Are these responses positive or negative geotropisms?
Why is important that roots grow down into the soil?
Geotropism and auxins
Auxins speed up growth in shoots and slow growth in roots.
If a plant is laid on its side, the auxins produced collect
in the lower side of the root and stem.
How will the auxins affect the growth of the root and stem?
Geotropism and auxins
If a plant is laid on its side, why does the root grow down
and the stem grow up?
Auxins slow down growth on the lower side of the root,
so the root curves down.
Auxins speed up growth on the lower side of the stem,
so the stem curves up.
Plant
response to
water
How do plants respond to water?
A plant’s response to water is called hydrotropism.
Roots always grow towards water, a positive tropism.
dry soil
wet soil
Roots will grow sideways or even upwards, towards water.
Do roots have a stronger response to water or gravity?
Roots always have a stronger response to water than
gravity to ensure that a plant gets the water it needs.
Hydrotropism and auxins – water all around
When roots are well watered from all sides,
the auxins produced in the roots are spread out evenly.
How will this affect the growth of the roots?
wet
soil
wet
soil
Hydrotropism and auxins – water all around
Why do roots grow out in all directions when they are well
watered from all sides?
There is an equal amount of auxins in all parts of the roots,
which grow at the same rate, so the roots grow out in all
directions.
wet
soil
wet
soil
wet
soil
wet
soil
Hydrotropism and auxins
– more water on one side
When roots are in soil with more water on one side,
the auxins are not spread out evenly in the roots.
How will this affect the growth of the roots?
dry
soil
wet
soil
Hydrotropism and auxins – more water one side
Why do roots grow towards the wet side when they are
in soil with more water on one side?
There are more auxins on the wetter side of the roots,
which grows slower than the dryer side, so the roots bend
towards the water.
dry
soil
wet
soil
dry
soil
wet
soil
Plant Hormones
Hormone What it does
Auxins
Cytokinin
•Released by the tip of shoots
•Causes cell elongation (growth)
•Stops side branches growing to
near the tip.
•Involved in phototropism.
•Involved in geotropism
• Involved in plant cell division
Gibberellins
•Growth of stems when flowers
start to form.
•Involved in seed germination.
Aba
•Produced by chloroplasts.
•Inhibits the growth of the plant.
•Closes stomata in times of
drought.
•Produced in response to auxin
in ripening fruit.
•Promotes ripening.
•Inhibited by carbon dioxide.
•Makes starch turn to glucose.
Ethylene