Plant Growth Factors

Question 1

Tropisms

Answer 1

• Growth of part of a plant in response to a directional stimulus

Question 2

Plant roots grow

Answer 2

• Increase the probability that roots will be better able to absorb water and mineral ions
• Positive gravitropism
• Negative phototropism

Question 3

Plant shoots grow

Answer 3

• Leaves are in the most favourable position to capture light for LDRs of photosynthesis
• Positive phototropism
• Negative geotropism

Question 4

Phototropism

Answer 4

• Young shoot will grow towards the light that is directed at it from one (unilateral side)

Question 5

Gravitropism

Answer 5

• Root grow towards the earth gravitational pull

- Horizontal plant root will grow down in the light and dark.

Question 6

Hydrotropism

Answer 6

• Almost all plant roots grow towards water in order to absorb it for use in the LIR’s of PHS, other metabolic processes and for support

Question 7

Plant growth factors

Answer 7

• They affect growth
• May be made in cells located throughout the plant rather than in organs
• Some affect tissues the tissues that release them rather than acting on distant target organs

Question 8

Indoleacetic Acid

Answer 8

• Plant growth factor
• Belongs to a group of substances called auxins
• Controls cell elongation

Question 9

IAA response in plant shoots

Answer 9

• Cells in the tip of the shoot = IAA
  1. IAA transported down the shoot evenly
• Light causes IAA to move from the light side to shaded side of shoot = higher concentration of IAA.
• IAA = shoot cells on the shaded side to elongate more than on the light side
  = Shoot bends towards the light

Question 10

Roots

Answer 10

IAA’s inhibit growth

Question 11

Shoots

Answer 11

IAA’s encourage/ stimulate growth