Plant hormones B11

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What is phototropism?
How plants respond to light (plant shoots grow towards the light)
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What is auxin?
A plant hormone
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How do shoots use auxin to grow towards the light?
Auxin is produced at tip of shoot, where it triggers cell growth. Light causes auxin to conc. on darker side of shoot tip. Auxin now spreads down shoot. Cells on darker side grow faster than cells on lighter side. This causes shoot to grow towards light
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What is gravitropism/geotropism?
How plants respond to gravity (plant roots grow towards the force of gravity)
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How do roots use auxin to grow towards the force of gravity?
Auxin is produced in the root, but gravity causes the auxin to concentrate on the lower side. In the roots, auxin inhibits cell growth. The lower side grows more slowly than the upper side, and this causes the roots to grow towards the force of gravity.
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What happens if there are unequal distributions of auxin?
It causes unequal growth rates in plant roots and shoots.
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What other chemicals do plants use to regulate their behaviour?
Gibberellins and ethene
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What do gibberellins do in plants?
Gibberellins are important in starting seed germination.
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What does ethene do in plants?
Ethene controls cell division and ripening of fruits.
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Required Practical 8: Plant Responses
Investigating the effect of light/gravity on the growth of newly germinated seedlings
What is the method for the light intensity practical?
1. Place cotton wool in 3 Petri dishes + soak w equal vols of water
2. Place 10 mustard seeds in each dish. Leave dishes in warm place+allow to germinate.
3. Water seeds everyday w same vol of water
4. After some days, seeds will germinate.
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Required Practical 8: Plant Responses
Investigating the effect of light/gravity on the growth of newly germinated seedlings
What is the method for the light intensity practical? (cont.)
5. Make sure 3 dishes have same no. of seedlings + use ruler to measure height of each seedling (hold stems to straighten)
6. Place dishes in 3 diff conditions (full sunlight, partial light, darkness)
7. Measure height of seedlings everyday for a week
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Required Practical 8: Plant Responses
What should you do after you finish the light intensity practical?
1. Record the results in a table
2. Calculate a mean seedling height for each day
3. Draw diagrams to show the effects of different light intensities on seedlings
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Required Practical 8: Plant Responses
What are the variables for the light intensity practical?
IV: light intensity
DV: height of the seedlings
CV: volume of water, type of seed, number of seedlings
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Required Practical 8: Plant Responses
What are the typical results of the light intensity practical?
Full sunlight and partial light: the height of the seedlings is similar. Seedlings have grown towards light source.
Darkness: have grown the longest. The leaves are small and yellow.
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1. Why are the heights of the full sunlight and partial light similar?
2. Why have the ones in the dark grown the longest?
3. Why do the ones in the dark have small, yellow leaves?
1. Chlorophyll=efficient at absorbing light energy
2. Seeds usually germinate underground + grow rapidly to reach the light
3. Once the seedlings have used all their energy stores, they cannot carry out photosynthesis in the dark
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Required Practical 8: Plant Responses
Investigating the effect of light/gravity on the growth of newly germinated seedlings
What do you do for the gravity practical and what does it show?
Dish of seedlings is placed on its side in the dark
The shoots grow upwards, against the direction of gravity, and the roots have grown downwards towards the direction of gravity.
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What can plant hormones be used for?
Agriculture and horticulture
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What are the three main uses of auxins?
Auxins are used:
• as weed killers
• as rooting powders
• for promoting growth in tissue culture.
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What are the three main uses of gibberellins?
Gibberellins can be used to:
• end seed dormancy (forces seeds to germinate earlier than they would)
• promote flowering
• increase fruit size.
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What is the main use of ethene?
Ethene is used in the food industry to control ripening of fruit during storage and transport.
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Other cards in this set

Card 2

Front

What is auxin?

Back

A plant hormone

Card 3

Front

How do shoots use auxin to grow towards the light?

Back

Preview of the front of card 3

Card 4

Front

What is gravitropism/geotropism?

Back

Preview of the front of card 4

Card 5

Front

How do roots use auxin to grow towards the force of gravity?

Back

Preview of the front of card 5
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