Understanding Plant Hormones and Their Functions in Plants

undefined
 
KNOWLEDGE AREA:
Life Processes in Plants and
Animals
 
TOPIC 3.3:  Responding to the
Environment
 
Plant Hormones
 
Some examples of plant hormones are…
a)
Auxins
b)
Gibberellins
c)
Abscisic Acid
These substances are 
not true hormones 
because
they 
work in the part of the plant 
where they are
produced
.
Therefore they are also referred to as 
plant growth
substances
.
 
Lets look at the functions of each of these plant growth
substances.
 
a)
Auxins
 
Auxins  bring about 
bending reactions in plants
.
These 
bending reactions 
are called 
tropisms
.
Some 
examples of tropisms 
are 
geotropism and
phototropism
.
They 
promote cell division
.
They are also 
responsible for cell elongation
.
They bring about 
apical dominance
.  This means
that the 
auxin
 found in the 
apical bud will promote
vertical growth
 and 
reduce growth of the lateral
branches
.
 
When the 
apical bud is removed then apical
dominance is lost
.  This mean that the 
lateral
branches will grow
.
The auxins also 
promote root development
.
 
b)
Gibberellins:
 
They have the following functions…
1.
They cause the 
internodes of the stem to
elongate
.
2.
They 
stimulate root growth
.
 
3.
They 
promote the development of flowers
.
4.
Brings about 
germination of seeds
, this means
the 
gibberellins stimulate the growth of the
seed
.
5.
They also 
increase fruit size
.
6.
It is also thought that they 
promote the
sprouting of dormant buds
.
 
 
 
c)
Abscisic Acid
 
Abscisic acid has the following functions…
 
1.
It 
slows down germination 
and therefore is able
to 
bring about dormancy of seeds
.
2.
Its brings about 
dormancy of apical buds
.
3.
Responsible for the 
onset of flowering in some
plants
.
4.
It 
promotes the aging of leaves
.
 
5.
It helps to 
close the stomata 
in 
times of drought
therefore 
reducing water loss by transpiration
.
 
Controlling Weeds using Plant Hormones:
 
Hormone weed killers 
are 
auxin-based selective
herbicides
.
The 
auxins used 
in these 
weed killers 
are made by
chemical synthesis
.
The 
main factor 
that 
controls the weed growth in
these herbicides
 are the 
auxins
.
These 
herbicides can only kill weeds
.
 
 
But they must be 
used in the correct dosage
.
However the 
plants that are similar to the weeds
can be damaged
, but 
they are not killed
.
The 
plants that are similar to the weeds 
are
called 
broad-leaved plants
.
 
 
 
 
Symptoms of Damage
to Broad-leaved
plants caused by
hormone weed
killers…
 
1.
Distorted or twisted
leaf stalks
2.
Swollen stems
3.
Warts or galls on
plants
 
Damage caused by hormone
weed killers
 
If the 
weed killer 
is used in 
large quantities it
can caused reduced plant growth
.
And can 
result in death of the plant
.
Therefore it is important to 
follow the dosage
suggested by the manufacturer
.
 
Advantages of Hormone Weed-killers…
 
1.
They are 
non toxic to animals and humans
.
2.
There is 
no longer the need for weeding the
garden
.
 
Tropisms:
 
As mentioned earlier 
tropisms are bending reaction in
plants in response to a stimulus
.
The tropism is 
brought about by auxins
.
The 
direction of the tropism 
is 
dependent on the
direction of the stimulus
.
These 
auxins are found at the tip of roots and shoots
.
Indole-acetic acid (IAA) 
is the most well known auxin.
We shall look at 2 types of tropisms.
 
These are 
geotropism and phototropism
.
Geotropism
 is a 
bending reaction in plants
to the stimulus of gravity
.
Phototropism
 is a 
bending reaction in
plants in reaction to the stimulus of light
.
 
We shall look at the role of auxins in each of these
tropisms.
 
 
Role of Auxins in Geotropism:
 
In the 
root auxins 
are 
produced at the tip of the
root
.
If the 
auxins are evenly distributed 
around the
root then the root grows straight downwards
.
But…
If a 
root is placed horizontally
, 
gravity pulls the
auxins to the lower side of the root
.
 
 
Therefore there is an 
uneven distribution of
auxins
.
One side has more auxins 
than the other.
In 
roots a high concentration 
of 
auxins inhibits
growth
.
Therefore the 
upper side with less auxins will
grow faster
.
The 
upper side will therefore bend downwards
.
That is 
towards gravity
.
Since the 
roots grows towards gravity 
we say that
it is 
positively geotropic
.
 
 
Role of Auxins in Phototropism:
 
Auxins
 are 
produced at the tips of the stem
.
They then 
move down evenly 
which 
causes even
growth
.
This ensures the 
stem grows straight upright
.
Sometimes  the 
auxins are exposed to light from
one side only
.
This is known as 
unilateral light
.
Auxins
 are 
destroyed by light
.
 
Therefore we find that the 
side exposed to
unilateral light has less auxins
.
This is because the 
auxins are destroyed y the
light or they move to the darker side
.
In 
stems more auxins promotes growth
.
Therefore the 
darker side will grow faster than
the lighter side
.
This is because the 
darker side has more auxins
.
Since the 
darker side grows faster
 it causes the
stem to grow towards light
.
Therefore we say that the 
stems are positively
phototrophic 
because they 
grow towards light
.
 
A 
defense mechanism 
is required by plants to
protect themselves against attacks by herbivores
and from pathogens
.
Some examples of these 
pathogens are fungi,
bacteria and viruses
.
Plants are able to 
protect themselves using
chemicals and thorns
.
 
Lets look at these defense mechanisms
 
1.
Thorns:
 
Thorns may be 
found on the leaves and stems
of some plants
.
Thorns are 
evolutionary developments
.
Some examples of 
plants that have thorns 
are
the 
cacti, roses and lemons
 
 
 
 
Functions
They function to 
protect the plant from
herbivores
.
When plants 
grow in bunches
, then the 
thorns
work together to bring about group defense
.
Thorns also help to 
disperse the plants over wide
areas
, because the 
vegetation becomes attached
to animals by their thorns 
and are 
carried to
other areas
.
 
2.
Chemicals
 
Some plants secretes chemicals.
Sometimes these 
chemicals can be poisonous
to other organisms
.
One example is the 
high vitamin C  and
bioflavonoid content of some plants
.
These chemicals are 
anti-bacterial and anti-
viral
.
This means that these 
chemicals are harmful to
bacteria and virus
.
 
Other plants have 
sticky secretions
.
The 
sticky secretions makes it difficult for insects
and animal to eat the plant
.
Some chemicals are used as 
chemical messengers
between the plants
.
These chemicals release an 
odor
.
Other 
plants detect this odor 
and can 
strengthen
their defense mechanism
.
On example  is the 
sage bush
.
When the bush is 
attacked by insects, it releases
a chemical
.
 
This chemical is called 
methyl jasmonate
.
 
Other  plants detect this chemical 
and 
increase
the levels of a certain enzyme
.
This enzyme is called 
PPO
.
PPO 
prevents the leaves from being attacked by
many different parasite
.
Other plants 
secrete a chemical that attracts
insects that feed on the larva of the pest or
parasite
.
 
Tropisms
:  refers to bending movements in plants
that are brought about by a response to a certain
external stimuli.
Phototropism
:  this is when the plant grows
towards the stimulus of light.
Geotropism
:  is a bending movement in response
to the stimulus of gravity
 
 
 
 
 
 
1.
A chemical substance that causes plants to
increase the secretion of a particular enzyme is…
 
A.  PPO
 
B.  Methyl jasmonate
 
C.  Both A and B
 
D.  Neither A nor B
 
 
 
 
2.
The enzyme that is responsible to protect the
leaves against attack of parasites is called
 
A.  PPO
 
B.  Methyl jasmonate
 
C.  Both A and B
 
D.  Neither A nor B
 
 
 
 
3.
Plant structure that is able to protect the plant
against attack from herbivores is/are…
 
A.  Sticky secretion
 
B.  Thorns
 
C.  Both A and B
 
D.  Neither A nor B
 
 
 
 
4.
Auxin based selective herbicides…
 
A.  Are made using auxins
 
B.  Only kill weeds if they are used in the correct
 
dosage
 
C.  Both A and B
 
D.  Neither A nor B
 
 
 
 
5.
The advantage of auxin based herbicides is/are…
 
A.  No need to weed
 
B.  They are pet and children friendly
 
C.  Reduces labour because there is no need to
 
weed
 
D.  All of the above
 
 
 
 
6.
In roots a high concentration of auxins
 
A.  Promotes growth
 
B.  Inhibits growth
 
C.  Both A and B
 
D.  None of the above
 
 
 
 
7.
Auxins are produced at the tip and then moves
evenly upwards in the…
 
A.  Stem
 
B.  Leaves
 
C.  Roots
 
D.  All of  the above
 
 
 
8.
Auxins are produced at the tip and then moves
evenly downwards in the…
 
A.  Stem
 
B.  Leaves
 
C.  Roots
 
D.  All of  the above
 
 
 
 
9.
In stems a high concentration of auxins…
 
A.  Promotes growth
 
B.  Inhibits growth
 
C.  Both A and B
 
D.  Neither A nor B
 
 
 
 
10.  In roots a low concentration of auxins…
 
A.  Promotes growth
 
B.  Inhibits growth
 
C.  Both A and B
 
D.  Neither A nor B
 
 
 
 
11.
When the root bends towards gravity this is
known as…
 
A.  Positive geotropism
 
B.  Negative geotropism
 
C.  Positive phototropism
 
D.  A and C
 
 
 
 
12.
When the stem grows towards the sun this is
known as…
 
A.  Positive geotropism
 
B.  Negative geotropism
 
C.  Positive phototropism
 
D.  A and C
 
 
 
 
 
13.
Roots and stems grow evenly if there is…
 
A.  An even distribution of auxins
 
B.  An uneven distribution of auxins
 
C.  An uneven distribution of gibberellins
 
D.  None of the above
 
 
 
 
14.
Bending reactions in plants are called…
 
A.  Plasticity
 
B.  Tropism
 
C.  Guttation
 
D.  Transpiration
 
 
 
 
15.
Light from one side is called…
 
A.  Bilateral light
 
B.  Mono-lateral light
 
C.  Unilateral light
 
D.  Both B and C
 
 
 
 
16.
The plant growth substance that brings about
elongation of the internodes and increases fruit
sizes is…
 
A.  Auxins
 
B.  Gibberellins
 
C.  Abscisic acid
 
D.  None of the above
 
 
 
 
17.
Growth of the lateral braches is inhibited when…
 
A.  Apical bud is removed
 
B.  Axillary bud is removed
 
C.  Apical bud stays intact
 
D.  None of the above
 
 
 
 
18.
Abscisic acid is responsible for…
 
A.  Apical dominance and cell enlargement
 
B.  Development of flowers and increase in fruit
 
size
 
C.  Ageing of the leaves and closing of the
 
stomata during drought.
 
D.  Germination of seeds and flowering in some
 
plants
 
 
 
 
19.
Gibberellins are responsible for…
 
A.  Apical dominance and cell enlargement
 
B.  Development of flowers and increase in fruit
 
size
 
C.  Ageing of the leaves and closing of the
 
stomata during drought.
 
D.  Germination of seeds and ageing of leaves
 
 
 
 
20.
Auxins are responsible for…
 
A.  Apical dominance and cell enlargement
 
B.  Development of flowers and increase in fruit
 
size
 
C.  Ageing of the leaves and closing of the
 
stomata during drought.
 
D.  Germination of seeds and flowering in some
 
plants
 
1.
B
2.
A
3.
C
4.
C
5.
D
6.
B
7.
C
8.
A
9.
A
10.
A
 
11.
A
12.
C
13.
A
14.
B
15.
C
16.
B
17.
C
18.
C
19.
B
20.
A
Slide Note
Embed
Share

Plant hormones play crucial roles in various plant processes such as growth, development, and response to environmental stimuli. Auxins, gibberellins, and abscisic acid are key plant hormones that regulate tropisms, cell division, elongation, flowering, seed germination, and dormancy. Understanding the functions of plant hormones helps in comprehending how plants respond and adapt to their surroundings.


Uploaded on Jul 16, 2024 | 1 Views


Download Presentation

Please find below an Image/Link to download the presentation.

The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author. Download presentation by click this link. If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.

E N D

Presentation Transcript


  1. LIFE SCIENCES GRADE 12 CAPS STRUCTURED, CLEAR, PRACTICAL - HELPING TEACHERS UNLOCK THE POWER OF NCS KNOWLEDGE AREA: Life Processes in Plants and Animals TOPIC 3.3: Responding to the Environment Plant Hormones

  2. SUMMARY OF THE PRESENTATION: Plant Hormones Plant Defense Mechanisms

  3. PLANT HORMONES Some examples of plant hormones are Auxins Gibberellins Abscisic Acid These substances are not true hormones because they work in the part of the plant where they are produced. Therefore they are also referred to as plant growth substances. a) b) c) Lets look at the functions of each of these plant growth substances.

  4. PLANT HORMONES Auxins a) Auxins bring about bending reactions in plants. These bending reactions are called tropisms. Some examples of tropisms are geotropism and phototropism. They promote cell division. They are also responsible for cell elongation. They bring about apical dominance. This means that the auxin found in the apical bud will promote vertical growth and reduce growth of the lateral branches.

  5. PLANT HORMONES When the apical bud is removed then apical dominance is lost. This mean that the lateral branches will grow. The auxins also promote root development. Gibberellins: b) They have the following functions They cause the internodes of the stem to elongate. They stimulate root growth. 1. 2.

  6. PLANT HORMONES They promote the development of flowers. Brings about germination of seeds, this means the gibberellins stimulate the growth of the seed. They also increase fruit size. It is also thought that they promote the sprouting of dormant buds. 3. 4. 5. 6.

  7. TERMINOLOGY: TERM: Tropisms DEFINITION: USE IN SENTENCES: Refers to bending movements in plants that are brought about by a response to a certain external stimuli. The tropsims can be brought about by a response to light or gravity.

  8. PLANT HORMONES Abscisic Acid c) Abscisic acid has the following functions It slows down germination and therefore is able to bring about dormancy of seeds. Its brings about dormancy of apical buds. Responsible for the onset of flowering in some plants. It promotes the aging of leaves. 1. 2. 3. 4.

  9. PLANT HORMONES It helps to close the stomata in times of drought therefore reducing water loss by transpiration. 5.

  10. PLANT HORMONES Controlling Weeds using Plant Hormones: Hormone weed killers are auxin-based selective herbicides. The auxins used in these weed killers are made by chemical synthesis. The main factor that controls the weed growth in these herbicides are the auxins. These herbicides can only kill weeds.

  11. PLANT HORMONES But they must be used in the correct dosage. However the plants that are similar to the weeds can be damaged, but they are not killed. The plants that are similar to the weeds are called broad-leaved plants.

  12. PLANT HORMONES Symptoms of Damage to Broad-leaved plants caused by hormone weed killers Distorted or twisted leaf stalks Swollen stems Warts or galls on plants 1. 2. Damage caused by hormone weed killers 3.

  13. PLANT HORMONES If the weed killer is used in large quantities it can caused reduced plant growth. And can result in death of the plant. Therefore it is important to follow the dosage suggested by the manufacturer.

  14. PLANT HORMONES Advantages of Hormone Weed-killers They are non toxic to animals and humans. There is no longer the need for weeding the garden. 1. 2.

  15. PLANT HORMONES Tropisms: As mentioned earlier tropisms are bending reaction in plants in response to a stimulus. The tropism is brought about by auxins. The direction of the tropism is dependent on the direction of the stimulus. These auxins are found at the tip of roots and shoots. Indole-acetic acid (IAA) is the most well known auxin. We shall look at 2 types of tropisms.

  16. PLANT HORMONES These are geotropism and phototropism. Geotropism is a bending reaction in plants to the stimulus of gravity. Phototropism is a bending reaction in plants in reaction to the stimulus of light. We shall look at the role of auxins in each of these tropisms.

  17. TERMINOLOGY: TERM: Phototropism DEFINITION: USE IN SENTENCE: This is when the plant grows towards the stimulus of light. When stems are phototrophic because they grow towards light.

  18. TERMINOLOGY: TERM: Geotropism DEFINITION: USE IN SENTENCE: Is a bending movement in response to the stimulus of gravity Roots are geotropic because they grow towards gravity.

  19. PLANT HORMONES Role of Auxins in Geotropism: In the root auxins are produced at the tip of the root. If the auxins are evenly distributed around the root then the root grows straight downwards. But If a root is placed horizontally, gravity pulls the auxins to the lower side of the root.

  20. PLANT HORMONES Therefore there is an uneven distribution of auxins. One side has more auxins than the other. In roots a high concentration of auxins inhibits growth. Therefore the upper side with less auxins will grow faster. The upper side will therefore bend downwards. That is towards gravity. Since the roots grows towards gravity we say that it is positively geotropic.

  21. PLANT HORMONES Role of Auxins in Phototropism: Auxins are produced at the tips of the stem. They then move down evenly which causes even growth. This ensures the stem grows straight upright. Sometimes the auxins are exposed to light from one side only. This is known as unilateral light. Auxins are destroyed by light.

  22. PLANT HORMONES Therefore we find that the side exposed to unilateral light has less auxins. This is because the auxins are destroyed y the light or they move to the darker side. In stems more auxins promotes growth. Therefore the darker side will grow faster than the lighter side. This is because the darker side has more auxins. Since the darker side grows faster it causes the stem to grow towards light. Therefore we say that the stems are positively phototrophic because they grow towards light.

  23. PLANT DEFENSE MECHANISMS A defense mechanism is required by plants to protect themselves against attacks by herbivores and from pathogens. Some examples of these pathogens are fungi, bacteria and viruses. Plants are able to protect themselves using chemicals and thorns. Lets look at these defense mechanisms

  24. PLANT DEFENSE MECHANISMS Thorns: 1. Thorns may be found on the leaves and stems of some plants. Thorns are evolutionary developments. Some examples of plants that have thorns are the cacti, roses and lemons

  25. PLANT DEFENSE MECHANISMS Functions They function to protect the plant from herbivores. When plants grow in bunches, then the thorns work together to bring about group defense. Thorns also help to disperse the plants over wide areas, because the vegetation becomes attached to animals by their thorns and are carried to other areas.

  26. PLANT DEFENSE MECHANISMS Chemicals 2. Some plants secretes chemicals. Sometimes these chemicals can be poisonous to other organisms. One example is the high vitamin C and bioflavonoid content of some plants. These chemicals are anti-bacterial and anti- viral. This means that these chemicals are harmful to bacteria and virus.

  27. PLANT DEFENSE MECHANISMS Other plants have sticky secretions. The sticky secretions makes it difficult for insects and animal to eat the plant. Some chemicals are used as chemical messengers between the plants. These chemicals release an odor. Other plants detect this odor and can strengthen their defense mechanism. On example is the sage bush. When the bush is attacked by insects, it releases a chemical.

  28. PLANT DEFENSE MECHANISMS This chemical is called methyl jasmonate. Other plants detect this chemical and increase the levels of a certain enzyme. This enzyme is called PPO. PPO prevents the leaves from being attacked by many different parasite. Other plants secrete a chemical that attracts insects that feed on the larva of the pest or parasite.

  29. TERMINOLOGY: Tropisms: refers to bending movements in plants that are brought about by a response to a certain external stimuli. Phototropism: this is when the plant grows towards the stimulus of light. Geotropism: is a bending movement in response to the stimulus of gravity

  30. QUESTION 1 A chemical substance that causes plants to increase the secretion of a particular enzyme is A. PPO B. Methyl jasmonate C. Both A and B D. Neither A nor B 1.

  31. QUESTION 2 The enzyme that is responsible to protect the leaves against attack of parasites is called A. PPO B. Methyl jasmonate C. Both A and B D. Neither A nor B 2.

  32. QUESTION 3 Plant structure that is able to protect the plant against attack from herbivores is/are A. Sticky secretion B. Thorns C. Both A and B D. Neither A nor B 3.

  33. QUESTION 4 Auxin based selective herbicides A. Are made using auxins B. Only kill weeds if they are used in the correct dosage C. Both A and B D. Neither A nor B 4.

  34. QUESTION 5 The advantage of auxin based herbicides is/are A. No need to weed B. They are pet and children friendly C. Reduces labour because there is no need to weed D. All of the above 5.

  35. QUESTION 6 In roots a high concentration of auxins A. Promotes growth B. Inhibits growth C. Both A and B D. None of the above 6.

  36. QUESTION 7 Auxins are produced at the tip and then moves evenly upwards in the A. Stem B. Leaves C. Roots D. All of the above 7.

  37. QUESTION 8 Auxins are produced at the tip and then moves evenly downwards in the A. Stem B. Leaves C. Roots D. All of the above 8.

  38. QUESTION 9 In stems a high concentration of auxins A. Promotes growth B. Inhibits growth C. Both A and B D. Neither A nor B 9.

  39. QUESTION 10 10. In roots a low concentration of auxins A. Promotes growth B. Inhibits growth C. Both A and B D. Neither A nor B

  40. QUESTION 11 11. When the root bends towards gravity this is known as A. Positive geotropism B. Negative geotropism C. Positive phototropism D. A and C

  41. QUESTION 12 12. When the stem grows towards the sun this is known as A. Positive geotropism B. Negative geotropism C. Positive phototropism D. A and C

  42. QUESTION 13 13. Roots and stems grow evenly if there is A. An even distribution of auxins B. An uneven distribution of auxins C. An uneven distribution of gibberellins D. None of the above

  43. QUESTION 14 14. Bending reactions in plants are called A. Plasticity B. Tropism C. Guttation D. Transpiration

  44. QUESTION 15 15. Light from one side is called A. Bilateral light B. Mono-lateral light C. Unilateral light D. Both B and C

  45. QUESTION 16 16. The plant growth substance that brings about elongation of the internodes and increases fruit sizes is A. Auxins B. Gibberellins C. Abscisic acid D. None of the above

  46. QUESTION 17 17. Growth of the lateral braches is inhibited when A. Apical bud is removed B. Axillary bud is removed C. Apical bud stays intact D. None of the above

  47. QUESTION 18 18. Abscisic acid is responsible for A. Apical dominance and cell enlargement B. Development of flowers and increase in fruit size C. Ageing of the leaves and closing of the stomata during drought. D. Germination of seeds and flowering in some plants

  48. QUESTION 19 19. Gibberellins are responsible for A. Apical dominance and cell enlargement B. Development of flowers and increase in fruit size C. Ageing of the leaves and closing of the stomata during drought. D. Germination of seeds and ageing of leaves

  49. QUESTION 20 20. Auxins are responsible for A. Apical dominance and cell enlargement B. Development of flowers and increase in fruit size C. Ageing of the leaves and closing of the stomata during drought. D. Germination of seeds and flowering in some plants

  50. SOLUTION: B A C C D B C A A 11. A 12. C 13. A 14. B 15. C 16. B 17. C 18. C 19. B 20. A 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. A

Related


More Related Content

giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#