Transcript Plant Growth - onlinebiosurgery

Tropic Responses
Objectives:
*Define geotropism and phototropism
**Explain role of auxin in plant growth
***Explain the use of synthetic plant hormones
as weedkillers
•
What is controlled by
hormones in plants?
Growth – roots and shoots, seed
germination, leaf fall, disease
resistance, fruit formation and
ripening, flowering time, bud
formation.
Sensitivity – Responding to the
environment
The way Plants grow is controlled
by Hormones. They are sensitive to
their environment and can make
adjustments to survive.
Copy and Complete
Tropism is how plants respond to their
environment.
When sunlight is the stimulus this is known as
______tropism.
Positive phototropism is where the plant grows
_______the light. This happens at the _____tip.
________ phototropism is where the plant grows
away from the______, this happens at the_____.
When gravity is the stimulus this is known as
______tropism.
________Geotropism is where the plant grows in
the direction of_______. This happens at the
roots.
Negative ___tropism is where the plant grows
apposing gravity, this happens at the _____tips.
.
Auxins
Auxins are one of the hormones used by plants for growth.
They have different effects depending where it is.
In the shoots any concentration promotes growth.
At the root, high concentration inhibits growth, small
concentration promotes growth.
• The Sunlight breaks down auxins, therefore the shoot tip
which has direct sunlight will have the least amount of
auxins. This means the area of the plant which is shaded
has a higher concentration of auxins, and so more growth
occurs, this leads to lop sided growth and the plant bends
towards the light
•
•
•
•
• diagram
Auxin in action
Cells become longer when they absorb water by
osmosis. The vacuole swells increasing the
turgor pressure inside the cell which causes the
cell wall to stretch. Auxins help by making it
easier for the walls to stretch.
Uses of Plant hormones
• Developed by scientists
• Plant cultivation and food production
•
•
•
•
•
Rooting powder
Selective weedkillers
Fruit ripening Ethene
Dormancy in seeds
Neater Hedges. Cutless hormone.
Match the correct scenario to the
tropism.
Roots Growing Downwards
into Dark Soil
Positive
Phototropism
Roots Growing Upwards
towards light.
Negative
Geotropism
Shoots Growing
Upwards
Negative
Phototropism
Roots Growing
Downwards.
Positive
Geotropism
Synthetic Plant Hormone
Synthetic auxins are very effective as weedkillers.
Crops like barley and wheat has narrow leaves whereas the weeds competing
with them for sunlight water and minerals have broad leaves. 2,4-D are
sprayed which runs off the narrow leaves because they are thin and pointed
upwards but absorbed by the broad leaves.
The auxins increase the growth rate of affected weeds by increasing the rate
of cell division. The weeds cannot provide enough food from photosynthesis
to maintain the growth rate and die.
• Homework – Revise Coordination and
response topic for test on 26/05/11