Organisms Respond to Changes in their Internal and External Environments: Stimuli, Both Internal and External, are Detected and Lead to a Response - Survival and Response in Plants

Question 1

Define the term tropism

Answer 1

• A tropism is the directional growth response of a plant to a directional stimulus

Question 2

Describe the direction of plant growth in relation to a stimulus in positive tropisms

Answer 2

• In positive tropisms, growth is towards the stimulus

Question 3

Describe the direction of plant growth in relation to a stimulus in negative tropisms

Answer 3

• In negative tropisms, growth is away from the stimulus

Question 4

What is phototropism?

Answer 4

• The growth of a plant in response to light

Question 5

Are shoots positively or negatively phototropic?

Answer 5

• Shoots are positively phototropic and grow towards light

Question 6

Are roots positively or negatively phototropic?

Answer 6

• Roots are negatively phototropic and grow away form light

Question 7

What is gravitropism?

Answer 7

• The growth of a plant in response to gravity

Question 8

Are shoots positively or negatively gravitrophic?

Answer 8

• Shoots are negatively gravitrophic and grow upwards

Question 9

Are roots positively or negatively gravitrophic?

Answer 9

• Roots are positively gravitrophic and grow downwards

Question 10

What are growth factors?

Answer 10

• Chemicals that regulate speed of plant growth in response to directional stimuli
• Made in growing regions of plant (shoot and root tips) and move to where they’re needed in a plant

Question 11

What are auxins?

Answer 11

• Type of growth factor that stimulate growth in shoots but in high concentrations, inhibit growth in roots

Question 12

Where are auxins produced?

Answer 12

• In tips of shoots

Question 13

How do auxins work?

Answer 13

• From tips of shoots, they diffuse backwards to stimulate cells just behind the tips to elongate
• Cell walls become loose and stretchy, so cells get longer

Question 14

What happens to growth when the tip of a shoot is removed?

Answer 14

• No auxin will be available so shoot stops growing

Question 15

What is indoleacetic acid (IAA)?

Answer 15

• A plant growth factor that is a type of auxin that moves around the plant to control cell elongation

Question 16

Where is indoleacetic acid (IAA) produced?

Answer 16

• In tips of roots and shoots of flowering plants

Question 17

How does indoleacetic acid (IAA) move around a plant?

Answer 17

• By diffusion and active transport over short distances

- Via phloem over long distances

Question 18

Describe how indoleacetic acid (IAA) affects phototropism in shoots

Answer 18

• In response to unilateral light, IAA concentration increases on shaded side
• Cells on shaded side elongate so shoot bends towards the light

Question 19

Describe how indoleacetic acid (IAA) affects phototropism in roots

Answer 19

• In response to unilateral light, IAA concentration increases on shaded side
• Growth of cells on shaded side is inhibited so root bends away from light

Question 20

Describe how indoleacetic acid (IAA) affects gravitropism in shoots

Answer 20

• IAA concentration increases on lower side

- Cells elongate so shoot grows upwards

Question 21

Describe how indoleacetic acid (IAA) affects gravitropism in roots

Answer 21

• IAA concentration increases on lower side

- Growth is inhibited so root grows downwards

Question 22

Which parts of the shoots and roots does indoleacetic acid (IAA) move to in phototropism?

Answer 22

• IAA moves to more shaded parts of roots and shoots

Question 23

Which parts of the shoots and roots does indoleacetic acid (IAA) move to in gravitropism?

Answer 23

• IAA moves to underside of shoots and roots

Question 24

What effect does indoleacetic acid (IAA) have on growth of shoots and roots?

Answer 24

• IAA increases growth in shoots

- IAA inhibits growth in roots