Q3: Plant growth hormones, IAA

Question 1

Tropism

Answer 1

The growth of part of a plant in response to a directional stimulus.

Question 2

Positive response tropism

Answer 2

plant grows towards the stimulus

Question 3

Negative response tropism

Answer 3

plant grows away from the stimulus

Question 4

Plant shoots grow towards light

Answer 4

positive phototropism

Question 5

Negative phototropism

Answer 5

plant roots grow away from light

Question 6

Negative gravitropism

Answer 6

plant shoots grow away from gravity

Question 7

Plant roots grow towards gravity

Answer 7

positive gravitropism

Question 8

Why do plant shoots act with positive phototropism and negative gravitropism?

Answer 8

so their leaves are in the most favourable position to capture light for photosynthesis

Question 9

Why do plant roots act with negative phototropism and positive gravitropism?

Answer 9

increases the probability that roots will grow into the soil, where they are better able to absorb mineral ions and water

Question 10

Plants respond to changes in…

Answer 10

their external and internal environments

Question 11

Plants respond to external changes such as,

3

Answer 11

light
water
gravity

Question 12

Why do plant respond to light?

Answer 12

needed for photosynthesis

Question 13

Why do plant respond to gravity?

Answer 13

plants to need to be firmly anchored in the soil,

roots are sensitive to gravity

Question 14

Why do plant respond to water?

Answer 14

in order to absorb it for photosynthesis and other metabolic processes

Question 15

Plant responses to external stimuli involve?

and name

Answer 15

hormone-like substances,

plant growth factors

Question 16

Characteristics of plant growth factors

2

Answer 16

1. Exert their influence by affecting plant growth and may be made by cells located throughout the plant rather than specific organs.
2. Some affect the tissues that release them rather than distant target organs.

Question 17

IAA

Answer 17

indoleacetic acid

Question 18

IAA is a type of

Answer 18

auxin

Question 19

What is one thing IAA controls?

Answer 19

plant cell elongation

Question 20

Unilateral light

Answer 20

Light directed from one side

Question 21

In roots does IAA increase or inhibit cell elongation?

Answer 21

inhibit

Question 22

In shoots does IAA increase or inhibit cell elongation?

Answer 22

increase

Question 23

IAA increases plasticity of plant cells

meaning

Answer 23

increase the ability to stretch of plant cell walls

Question 24

Which type of plant cell walls are able to elongate?

Answer 24

young

Question 25

Acid growth hypothesis

Answer 25

Active transport of hydrogen ions from the cytoplasm into spaces in the cell wall causing the cell wall to become more plastic allowing the cell to elongate by expansion.

Question 26

Proposed explanation of how IAA increases the plasticity of cells

Answer 26

acid growth hypothesis

Question 27

Relative speed of plant response to environmental stimuli

Answer 27

relatively quickly

Question 28

Stimuli and IAA relationship

Answer 28

stimuli causes uneven distribution of IAA

Question 29

How is IAA exported from cells?

Answer 29

IAA carrier proteins

Question 30

Gravity effect on IAA carrier proteins

Answer 30

changes their distribution