Q3: Plant growth hormones, IAA Flashcards
Tropism
The growth of part of a plant in response to a directional stimulus.
Positive response tropism
plant grows towards the stimulus
Negative response tropism
plant grows away from the stimulus
Plant shoots grow towards light
positive phototropism
Negative phototropism
plant roots grow away from light
Negative gravitropism
plant shoots grow away from gravity
Plant roots grow towards gravity
positive gravitropism
Why do plant shoots act with positive phototropism and negative gravitropism?
so their leaves are in the most favourable position to capture light for photosynthesis
Why do plant roots act with negative phototropism and positive gravitropism?
increases the probability that roots will grow into the soil, where they are better able to absorb mineral ions and water
Plants respond to changes in…
their external and internal environments
Plants respond to external changes such as,
3
light
water
gravity
Why do plant respond to light?
needed for photosynthesis
Why do plant respond to gravity?
plants to need to be firmly anchored in the soil,
roots are sensitive to gravity
Why do plant respond to water?
in order to absorb it for photosynthesis and other metabolic processes
Plant responses to external stimuli involve?
and name
hormone-like substances,
plant growth factors
Characteristics of plant growth factors
2
- Exert their influence by affecting plant growth and may be made by cells located throughout the plant rather than specific organs.
- Some affect the tissues that release them rather than distant target organs.
IAA
indoleacetic acid
IAA is a type of
auxin
What is one thing IAA controls?
plant cell elongation
Unilateral light
Light directed from one side
In roots does IAA increase or inhibit cell elongation?
inhibit
In shoots does IAA increase or inhibit cell elongation?
increase
IAA increases plasticity of plant cells
meaning
increase the ability to stretch of plant cell walls
Which type of plant cell walls are able to elongate?
young
