Transcript hormonal-control-of-growth-plants2

Higher Biology
Hormonal Control of Growth in
Plants -part 2
Hormonal Control of Growth 2
By the end of this lesson you should be
able to:
 Know the name of a 2nd plant growth substance.
 Know the effects of GA:
o on cells
o on stems
o on dormancy
o in inducing a-amylase in barley grains
 Describe practical applications of plant growth
substances.
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Introduction
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In the 1920s Japanese rice farmers
noticed that some of their rice seedlings
started to grow abnormally tall.
It was found that these plants were
infected with a fungus which secreted
substances.
They called these substances gibberellins.
It is now known that there are more than
70 different types of gibberellin- many of
them occurring naturally in plants.
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Gibberellic Acid (GA)
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GA is the most important gibberellin.
GA (like IAA) promotes cell elongation, but
only in the stems of plants.
Low concentrations of GA have this effect.
It does this by increasing the length of
the internodes (not their number).
GA and internodes
An internode is a space between 2 sets of
leaves on a stem.
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Effect of GA on germination
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1.
internal structure of barley grain
Copy this diagram and label:
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Starchy endosperm
Embryo (young plant)
Aleurone layer
Cotyledon
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Gibberellic Acid (GA) & Germination
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1.
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Read pages 257-258, “Effect of GA on
germinating barley grains” of Torrance,
then answer the following questions:
What carbohydrate is found in the
endosperm?
What carbohydrate is required for barley
seeds to germinate?
What enzyme converts the carbohydrate
in the endosperm into the carbohydrate
needed for germination?
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Gibberellic Acid (GA) & Germination
Stages in GA action:
 Water is absorbed by the seed.
 The embryo produces GA which diffuses to
the aleurone layer.
 GA stimulates the aleurone layer to
synthesise and secrete a-amylase into the
endosperm.
 a-amylase breaks down the starch in the
endosperm to maltose.
 Maltose diffuses into the embryo and is
used for respiration.
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Summary
Put the following stages into the correct
order:
GA stimulates
GA is transported
to
the aleurone
layer
GA is breaks
transported
a-amylase
down to
the aleurone
cells to synthesise
aleurone
starchthe
to maltose
a-amylaselayer
layer
GA stimulates
GA is produced
the aleurone layer
GAby
is the
produced
embryo
cells tobreaks
synthesise
down
by the embryo a-amylase
starcha-amylase
to maltose
a-amylase travels
travels
toa-amylase
the endosperm
to the endosperm
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Gibberellic Acid (GA) & Germination
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Insert and complete the “Germination”
summary into your notes.
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Bud Dormancy
1.
2.
3.
Read pages 258-259 on “GA and Bud
Dormancy” in Torrance, and then answer the
following questions:
What is meant by “bud dormancy”?
What effect does GA have on dormant buds?
When would this effect normally happen?
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Rooting Powder
1.
2.
Read page 255 on “Rooting Powders” in
Torrance, and then answer the following
questions:
What is present in rooting powder?
What effect does this have on the roots?
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Herbicides
1.
2.
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Read page 256 on “Herbicides” in Torrance,
and then answer the following questions:
Explain how auxins are used to kill weeds.
Explain why auxins can be used as selective
weedkillers on lawns.
Insert and complete the “IAA v GA”
summary.
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Practice Questions
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1.
2.
3.
Torrance
TYK page 259 Q1 and 2
AYK pages 260-262 Q2,3 and 7
You will need graph paper for Q2 on page
260!
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Hormonal Control of Growth 2
Can you do it?
 Know the name of a 2nd plant growth substance.
 Know the effects of GA:
o on cells
o on stems
o on dormancy
o in inducing a-amylase in barley grains
 Describe practical applications of plant growth
substances.
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