Topic 5 - Homeostasis and Response - Plant Hormones

Question 1

What is auxin?

Answer 1

• auxin is a plant homrone - controls growth near tips and shoots of roots
• controls growth of plant in response to light (phototropism) and gravity (geotropism)

Question 2

Where is auxin produced?

Answer 2

• tips and moves backwards to stimulate cell elongation process
• if tip of shoot removed - no auxin available - shoot may stop growing
• extra auxin promotes growth in shoots but inhibits growth in roots

Question 3

How do shoots grow toward light?

Answer 3

• when shoot tip is exposed to light - more auxin accumulates on side thats in shade than side in light
• makes cell elongate faster on shaded side - shoot bends toward light

Question 4

How do shoots react to gravity?

Answer 4

• when shoot is growing sideways - gravity produces unequal distribution of auxin in the tip - more auxin on lower side
• causes lower side to elongate faster - bending shoot upwards

Question 5

How do roots react to gravity?

Answer 5

• when root is growing sideways - gravity produces unequal distribution of auxin in the tip - more auxin on lower side
• extra auxin inhibits growth in roots - cells on top elongate faster - root bends downward

Question 6

Uses of auxin in killing weeds?

Answer 6

• selective weedkillers developed using using auxins
• disrupt normal growth patterns - sends plants into rapid uncontrolled growth - killing them

Question 6

Investigating plant growth responses method?

Answer 6

• put 10 cress seeds into three different petri dishes - each lined with moist filter paper
• shine light onto one of the dishes from above - shine light on 2 other dishes from different directions
• leave cress seeds alone for a week - observe their responses
• control: number of seeds, type of seed, temperature, water, light intensity

Question 7

Uses of auxin in growing from cuttings with rooting powder?

Answer 7

• a cutting is part of plant that has been cut off it - normally wont grow if stuck into soil
• if add rooting powder that contains auxins to cuttings - produce roots rapidly - grow as new plants
• enables growers to produce lots of clones

Question 8

Uses of auxin in growing cells in tissue culture?

Answer 8

• tissue culture can be used to grow clones of plant from its cells
• auxin added to growth medium with nutrients to stimualte cells to divide and form roots and shoots

Question 9

What is gibberellin?

Answer 9

• type of plant hormone
• promotes seed germination - stem growth - flowering

Question 10

How is gibberellin used in controlling dormancy?

Answer 10

• lots of seeds wont germinate until they have been through certain conditions - this is dormancy
• seeds can be altered with gibberellin to alter dormancy - make them germinate at times of year they normally wouldnt

Question 11

How is gibberellin used in inducing flowering?

Answer 11

• plants that rely on certain conditions to flower can be treated with gibberellin - they will flower without any change in environment
• can be used to grow bigger flowers

Question 12

How is gibberellin used in growing larger fruit?

Answer 12

• seedless varieties of fruit often do not grow as large as seeded fruit
• gibberellin can be added so they grow larger than normal

Question 13

What is ethene?

Answer 13

a gas that stimulates enzymes that cause the fruit to ripen

Question 14

How is ethene used?

Answer 14

• speeds up the ripening of fruit