Trophism

Question 1

What is trophism?

Answer 1

• The growth of part of an organism in response to a directional stimulus
• In most cases, the plant will grow towards or away from the stimulus

Question 2

What is phototropism?

Answer 2

• Response to light
• Positive phototropism = growing towards light
• Negative phototropism = growing away light

Question 3

What is gravitropism?

Answer 3

• response to gravity
• Positive gravitropism = growing toward gravity
• Negative gravitropism = growing away from gravity

Question 4

What tropism occurs in shoots?

Answer 4

• Positive phototropism = Shoots grow towards light to maximise sunlight for photosynthesis
• Negative phototropism = So their leaves are in a favourable position for photosythesis

Question 5

What tropism occurs in roots?

Answer 5

• negative phototropism = roots grow away from the light to access nutrients and water in soil
• Positive gravitropism = roots grow in soil

Question 6

What stimuli to plants respond to?

Answer 6

• light
• gravity
• water

Question 7

What do plant growth factors do?

Answer 7

• They exert their influence by affecting growth and act on tissues rather than a specific target organs

Question 8

What is IAA?

Answer 8

• Indoleactic acid
• This belongs to auxins and specifically controls cell elongation

Question 9

How does phototropism in flowering plants in unilateral light occur

Answer 9

• Cells in the tip of the shoots produce IAA
• IAA is then evenly distributed by diffusion down the shoot
• Light causes the IAA to diffuse to the shaded side of the shoot
• The greater concentration of IAA on the shaded side of the shoot, causes cell elongation
• This means the shaded side elongates more than the lighter side, causing the shoot to bend towards light
• This is positively phototropic

Question 10

Why are roots negatively phototropic

Answer 10

• The IAA would diffuse to the shaded side and inhibit cell elongation. This means the lighter side would elongate more than the shaded side and bend away from light

Question 11

What does IAA do to roots?

Answer 11

• IAA inhibits elongation in roots

Question 12

What is the response of roots to gravity?

Answer 12

• Cells in the root tip produce IAA which is then transported along the root
• AT first, IAA is initially transported to all sides of the root
• however, due to gravity IAA diffuses to lower sides of the root
• This means that a greater concentration of IAA builds on the lower side and inhibits growth on the lower side of the root
• This means that the upper part of the root grows faster than the lower side, this causes the upper side to outweigh the lower side and the root will bend toward the force of gravity

Question 13

What is the response of shoots to gravity?

Answer 13

• IAA accumulates on the lower side and promotes cell elongation
• This then means the lower side elongates more than the upper side and the shoots grow toward gravity
• this is positively gravitropic

Question 14

What are the roles of IAA?

Answer 14

• IAA promotes cell elongation and plascity of cell walls
• However, this only occurs to young cell walls
• As cells mature, they grow rigid and respond less