Plant hormones

Question 1

What is a plant hormone

Answer 1

• Substance produced in small quantities in one part of organism and then transported to another part where it performs its function
• Stimulate or inhibit certain physiological processes
• Time taken by plants to react to hormone concentrations is much longer than in the case of animals

Question 2

What are the types of plant hormones

Answer 2

Auxins
Gebberellins
Abscisic acid

Question 3

Explain auxins fully

Answer 3

• Prod in root tip and growing point of stems ( ie. shoot tip; apical bud and auxiliary bud)
• Involved in phototropism and geotropism
• Promotes cell division and elongation
• Promotes apical dominance and suppression of lateral buds
  Promotes development of adventitious roots in stem cuttings

High concentration in stems = promotes growth

High concentration in roots = inhibits growth

Sensitive to light and are repelled by it

Pulled down by gravity

Question 4

Explain gibberellins fully

Answer 4

• Promote cell elongation
• Stimulate cell division
• Control cell enlargement
• Plays a role in cell germination

Question 5

Explain abscisic acid fully

Answer 5

• Responsible for retardation of growth
• Stops winter bud growth thus promotes dormancy of buds
• Inhibits seed growth

Question 6

Explain phototropism

Answer 6

• Plant growth response to light
• Stems = towards light thus are + phototrophic
• Roots = away from light thus - phototrophic

Question 7

Explain geotropism

Answer 7

• Plant growth response to gravity
• Stems = grow away from gravity thus - geotropic
• Roots = grow towards gravity thus + geotropic

Question 8

Explain plant defence mechanisms fully

Answer 8

1) Thorns
- Prevents herbivores from eating / damaging the plant or slow down the rate at which they eat the plant

2) Chemical Secretions
- Secrete chemicals that are harmful to herbivores as they taste bad or are poisonous
- Bitter and difficult to digest

Question 9

What are tropisms

Answer 9

• Plant responses either towards or away from stimuli

   - brought about by hormones

Question 10

Explain auxin apical dominance

Answer 10

• High conc near apical buds suppress growth of higher lateral buds
• Growth of plant is conc on the main shoot

Question 11

Explain pruning

Answer 11

• Removing apical dominance
• Lateral buds develop
• Bushier plant

Question 12

Explain geotropism summary

Answer 12

• Auxins move towards gravity thus higher conc on lower side of root tip
• High auxin conc in roots inhibits growth thus less cell elongation on lower side than upper side
• Tip curves down

Question 13

Explain unilateral light on stem

Answer 13

• Auxins move away from light thus higher conc on shady side of stem tip
• Higher auxin conc in stems promotes growth thus more cell elongation on shady side
• Results in stem tip curving towards light