Paper 2: Topic 5 Homeostasis & response - Plant hormones (LV) Flashcards
State an example of a plant growth hormone
Auxin
Describe the role of growth hormones in plants
To co-ordinate and control plant growth in response to light, water and gravity
AND
to control responses such as flowering and fruit production
State where in a plant auxin is produced
Shoot tips
Root tips
Hint: do not just say shoot and root
Describe 3 roles of auxin in plants
It controls the direction of growth of plants in response to light, water and gravity
Define the term phototropism
The directional growth of plants in response to light
Define the term geotropism
The directional growth of plants in response to gravity
Define the term gravitropism
The directional growth of plants in response to gravity
Define the term hydrotropism
The directional growth of plants in response to water
Describe the how different parts of a plant respond to light
- Shoot tips grow towards the light
- Root tips grow away from the light
Describe the how different parts of a plant respond to gravity
- Root tips grow in the same direction of gravity (positive geotropism)
- Shoot tips grow away from the direction of gravity (negative geotropism)
Explain how a shoot tip grows towards the light
- Auxin is produced in the shoot tip
- The auxin diffuses to the shaded side of the shoot tip
- This casues unequal distrbution of auxin in the shoot tip
- The high concentration of auxin causes the cells just below the shoot tip on the shaded side to elongate faster
- This causes the shoot tip to curve towards the light
Explain how a shoot tip grows away from gravity
- Auxin is produced in the unequally in the shoot tip
- The auxin collects on the lower side of the shoot tip
- This causes unequal distribution of auxin in the root tip
- The high concentration of auxin causes the plant cells on the underside of the shoot tip on the lower side to elongate faster
- This causes the shoot tip to curve upwards away from gravity
Explain how a root tip grows away from gravity
- Auxin is produced in the unequally in the shoot tip
- The auxin collects on the lower side of the shoot tip
- This causes unequal distribution of auxin in the root tip
- The high concentration of auxin inhibits growth in roots
- This causes the plant cells on the top of the root tip to elongate faster
- This causes the root tip to curve downwards towards gravity
Describe how plant cells in the root and shoot tip respond differently to auxin
- Auxin stimulates plant cells to elongate in shoot tips
- Auxin inhibits elongation in plants cells found in root tips
State 5 variables that must be controlled during an investigation studying the effect of light on plant growth
- Type of seeds
- Number of seeds
- Volume of water added to the seeds
- Temperature
- Light intensity and duration
State independent variable in an investigation studying the effect of light on plant growth
Direction of the light
State dependent variable in an investigation studying the effect of light on plant growth
The angle of the seedling
Describe and explain what happens if a shoot tip is removed from a seedling
Description:
- No directional growth occurs
Explanation:
- If the shoot tip is removed no auxin is produced
- Plant cells on both the lit and shaded side of the seedling elongate at the same rate
- The seedling grows straight (with no curvature)
State the term used to describe plant growth towards a stimulus
Positive tropism
State the term used to describe plant growth away from a stimulus
Negative tropism
State the term used to describe plant growth towards the light
Positive phototropism
State the term used to describe plant growth away from the light
Negative phototropism
State the term used to describe plant growth towards gravity
Positive geotropism / positive gravitropism
State the term used to describe plant growth away from gravity
Negative geotropism / negative gravitropism
State the term used to describe plant growth towards water
Positive hydrotropism
State the term used to describe plant growth away from water
Negative hydrotropism
Name the plant hormone important in initiating seed germination
Gibberellins
Name the plant hormone important in controlling cell division and ripening of fruits
Ethene
Give 3 uses of auxins in agriculture and horticulture
- Weed killers
- Rooting powders (to promote root formation)
- Promoting growth in tissue cultures
State the use of ethane in the food industry
To control the ripening of fruit during storage and transportation
Give 3 commercial uses of gibberellins in agriculture
- To end seed dormancy (i.e. promote germination)
- To promote flowering
- To increase fruit size
Describe how auxins can be used as selective weed killers
- Specialised auxins have been developed that only affect broad-leaved plants
- If these auxins are applied to fields with crops in only the broad-leaved plants are affected
- The broad-leaved plants dies as a result of disrupted growth
- Narrow-leaved crop are unharmed
Explain the benefits of using auxins as a selective weed killer
- Selective weed killers only disrupt the growth of broad-leaved plants
- This kills the broad-leaved plants
- This means there is now more light and mineral ions available for the narrow-leaved plants
- So the narrow-leaved plants now grow faster
Describe how auxins can be used to stimulate root growth
- The tip of a cutting can be dipped in rooting hormone powder
- The auxins in the rooting hormone powder quickly stimulates root growth
Describe how auxins are used in tissue culture
- Auxins are added to the growth medium used in tissue culture
- The auxins simulate the plants cells to divide to produce roots and shoots
Give 2 techniques that involve the use of auxins to produce cloned plants
- Tissue culture
- Cuttings
Explain the advantages of using gibberellins to control seed germination
- Seeds can be forced to germinate at different times of the year
- This means plants can be grown ‘out of season’
- Using gibberellins ensures all the seeds in one batch will germinate at the same time (time efficient and cost effective for the gardener)
Explain the advantages of using gibberellins to control flowering
- Some types of plants require short days to stimulate flowering, other types of plants require long days
- By using gibberellins plants can be forced to flower without any changes in their environment
- The use of gibberellins can also result in larger flowers
Describe how gibberellins can be used in fruit production
The application of gibberellins causes seedless fruit to be larger than it would be naturally (so that the seedless fruit is a similar size to the seeded fruit)
Describe 2 effects ethene can have on plants
- Ethene stimulates cell division causing increased plant growth
- Ethene stimulates enzymes that cause fruit to ripen
How can ethene be used commercially in controlling fruit ripening
- Fruit can be picked in an unripe (harder) state
- Ripening can be delayed by exposing the unripe fruit to chemicals that block ethene’s effect
- This means the fruit can be stored or transported easily (less bruising and damage)
- On arrival at the destination e.g. supermarket the fruit can be exposed to ethene to promote ripening
- This make the fruit more desirable by the customer
Explain what is happening in eaach area of the plant
