Paper 2: Topic 5 Homeostasis & response - Plant hormones (LV)

Question 1

State an example of a plant growth hormone

Answer 1

Auxin

Question 2

Describe the role of growth hormones in plants

Answer 2

To co-ordinate and control plant growth in response to light, water and gravity

AND

to control responses such as flowering and fruit production

Question 3

State where in a plant auxin is produced

Answer 3

Shoot tips

Root tips

Hint: do not just say shoot and root

Question 4

Describe 3 roles of auxin in plants

Answer 4

It controls the direction of growth of plants in response to light, water and gravity

Question 5

Define the term phototropism

Answer 5

The directional growth of plants in response to light

Question 6

Define the term geotropism

Answer 6

The directional growth of plants in response to gravity

Question 7

Define the term gravitropism

Answer 7

The directional growth of plants in response to gravity

Question 8

Define the term hydrotropism

Answer 8

The directional growth of plants in response to water

Question 9

Describe the how different parts of a plant respond to light

Answer 9

• Shoot tips grow towards the light
• Root tips grow away from the light

Question 10

Describe the how different parts of a plant respond to gravity

Answer 10

• Root tips grow in the same direction of gravity (positive geotropism)
• Shoot tips grow away from the direction of gravity (negative geotropism)

Question 11

Explain how a shoot tip grows towards the light

Answer 11

• 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

Question 12

Explain how a shoot tip grows away from gravity

Answer 12

• 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

Question 13

Explain how a root tip grows away from gravity

Answer 13

• 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

Question 14

Describe how plant cells in the root and shoot tip respond differently to auxin

Answer 14

• Auxin stimulates plant cells to elongate in shoot tips
• Auxin inhibits elongation in plants cells found in root tips

Question 15

State 5 variables that must be controlled during an investigation studying the effect of light on plant growth

Answer 15

1. Type of seeds
2. Number of seeds
3. Volume of water added to the seeds
4. Temperature
5. Light intensity and duration

Question 16

State independent variable in an investigation studying the effect of light on plant growth

Answer 16

Direction of the light

Question 17

State dependent variable in an investigation studying the effect of light on plant growth

Answer 17

The angle of the seedling

Question 18

Describe and explain what happens if a shoot tip is removed from a seedling

Answer 18

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)

Question 19

State the term used to describe plant growth towards a stimulus

Answer 19

Positive tropism

Question 20

State the term used to describe plant growth away from a stimulus

Answer 20

Negative tropism

Question 21

State the term used to describe plant growth towards the light

Answer 21

Positive phototropism

Question 22

State the term used to describe plant growth away from the light

Answer 22

Negative phototropism

Question 23

State the term used to describe plant growth towards gravity

Answer 23

Positive geotropism / positive gravitropism

Question 24

State the term used to describe plant growth away from gravity

Answer 24

Negative geotropism / negative gravitropism

Question 25

State the term used to describe plant growth towards water

Answer 25

Positive hydrotropism

Question 26

State the term used to describe plant growth away from water

Answer 26

Negative hydrotropism

Question 27

Name the plant hormone important in initiating seed germination

Answer 27

Gibberellins

Question 28

Name the plant hormone important in controlling cell division and ripening of fruits

Answer 28

Ethene

Question 29

Give 3 uses of auxins in agriculture and horticulture

Answer 29

1. Weed killers 2. Rooting powders (to promote root formation) 3. Promoting growth in tissue cultures

Question 30

State the use of ethane in the food industry

Answer 30

To control the ripening of fruit during storage and transportation

Question 31

Give 3 commercial uses of gibberellins in agriculture

Answer 31

1. To end seed dormancy (i.e. promote germination) 2. To promote flowering 3. To increase fruit size

Question 32

Describe how auxins can be used as selective weed killers

Answer 32

* 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

Question 33

Explain the benefits of using auxins as a selective weed killer

Answer 33

* 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

Question 34

Describe how auxins can be used to stimulate root growth

Answer 34

* The tip of a cutting can be dipped in rooting hormone powder * The auxins in the rooting hormone powder quickly stimulates root growth

Question 35

Describe how auxins are used in tissue culture

Answer 35

* Auxins are added to the growth medium used in tissue culture * The auxins simulate the plants cells to divide to produce roots and shoots

Question 36

Give 2 techniques that involve the use of auxins to produce cloned plants

Answer 36

* Tissue culture * Cuttings

Question 37

Explain the advantages of using gibberellins to control seed germination

Answer 37

* 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)

Question 38

Explain the advantages of using gibberellins to control flowering

Answer 38

* 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

Question 39

Describe how gibberellins can be used in fruit production

Answer 39

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)

Question 40

Describe 2 effects ethene can have on plants

Answer 40

* Ethene stimulates cell division causing increased plant growth * Ethene stimulates enzymes that cause fruit to ripen

Question 41

How can ethene be used commercially in controlling fruit ripening

Answer 41

* 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

Question 42

Explain what is happening in eaach area of the plant

Answer 42