hormonal control in plants requirements for growth & reproduction 2010
TRANSCRIPT
![Page 1: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/1.jpg)
Hormonal Control in Plants
Requirements for Growth & Reproduction
2010
![Page 2: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/2.jpg)
Why would plants need hormones? Controlling growth Responses to environmental changes Controlling reproductive cycles Responses to competition for
resources
![Page 3: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/3.jpg)
When a seed begins to grow into a plant, why does the root grow downwards and the shoot grow upwards?
![Page 4: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/4.jpg)
Gravitropism Heavier organelles settle on the lower
side of cells Auxin concentrates in cells on lower
side, causing differential growth
![Page 5: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/5.jpg)
Mechanism of Action loosens cell wall cells elongate
auxin stimulates proton pumps pump protons (H+) into cell wall expansins modify hydrogen bonds between
cellulose molecules molecules slide past one another, allowing for
elongation
![Page 6: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/6.jpg)
Phototropism Photo=light Tropism=growth Plants grow towards a
light source. Charles Darwin and his
son carried out a series of experiments to determine what controlled phototropism (1881)
![Page 7: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/7.jpg)
Experiment 1 Oat shoots were used A light source was
placed on one side The top of one shoot
was covered with tinfoil to keep out the light
![Page 8: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/8.jpg)
Write down your predictions: Why was the top of the shoot covered with
tinfoil?
![Page 9: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/9.jpg)
Results The uncovered shoot
bends towards the light
The covered shoot remains straight
Therefore the tip of the shoot is required to detect the light stimulus
![Page 10: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/10.jpg)
In another experiment, they covered the tip with a transparent glass tube. Predict what occurred.
![Page 11: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/11.jpg)
Experiment 2 a) the tip was cut off b) the tip was cut off,
then replaced c) the tip was cut off,
then replaced on a block of agar
d) the tip was cut off, then replaced on a metal disc
![Page 12: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/12.jpg)
Write down your predictions: a)
b)
c)
d)
![Page 13: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/13.jpg)
Results The tip is required for growth The hormone was able to
diffuse through the agar and cause growth
The metal disc prevented growth from occurring
Therefore the tip produces a hormone which diffuses downwards and promotes growth
![Page 14: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/14.jpg)
Experiment 3 This experiment was
carried out by Frits Went in 1926
He placed tips of shoots on blocks of agar, so that the hormone diffused into them.
He than placed the agar blocks on different areas of the cut tips.
![Page 15: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/15.jpg)
Write down your predictions:
![Page 16: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/16.jpg)
Results The growth hormone
diffused into the agar Uneven
concentrations on one side of the shoot caused bending
![Page 17: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/17.jpg)
The hormone involved is a member of a group of hormones called auxins.
The specific hormone is IAA (indole acetic acid).
If the tip is exposed to light on one side, the IAA drifts to the darker side. This prompts that side to grow more, bending the tip towards the light source.
![Page 18: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/18.jpg)
![Page 19: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/19.jpg)
Questions What is the advantage of phototropism? What would happen to a plant placed
under lights which shone on it from all directions?
![Page 20: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/20.jpg)
Photoperiodism Photo=light Period=time Why do flowers
which are open during the day close at night?
What controls the time of year when plants flower?
![Page 21: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/21.jpg)
Circadian rhythms The plants’ biological clock
is set to a 21-27 hour cycle. Some plants close their
flowers or leaves at night. This prevents loss of heat
and frost damage. Photosynthesis, auxin
production and cell division also rise & fall with the circadian rhythm.
![Page 22: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/22.jpg)
Long day plants Long days of
sunlight and short nights stimulate flowering
E.g. lettuce, clover
Short day plants Short days and
long nights stimulate flowering
E.g. dahlias, chrysanthemums
![Page 23: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/23.jpg)
Questions At what time of the year would long day
plants flower? What is the advantage of this? At what time of the year would short day
plants flower? What is the advantage of this? What about tropical plants growing on the
equator? When would they flower?
![Page 24: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/24.jpg)
Phytochrome A pigment called phytochrome detects the
amount of daylight in each diurnal (day/night) cycle.
It has two forms Pr (biologically inactive) Pfr (biologically active)
Pr is converted into Pfr by exposure to light It is involved in seed germination, leaf growth,
flowering and dormancy. Inhibits flowering in short day plants Induces flowering in long day plants
![Page 25: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/25.jpg)
![Page 26: Hormonal Control in Plants Requirements for Growth & Reproduction 2010](https://reader035.vdocument.in/reader035/viewer/2022062423/5697bfc31a28abf838ca55db/html5/thumbnails/26.jpg)
(note: Northern hemisphere data)