B3.2 The Endocrine System - Plant Hormones Flashcards
What is a tropism?
A growth response made by a plant in response to a particular stimuli in their environment.
What is the difference between a positive and negative tropism?
- Positive = growing towards stimulus
- Negative = growing away from stimulus
Define โphototropismโ.
- Growth in response to light
- Stems = positively phototropic
- Roots = negatively phototropic
Define โgravitotropismโ.
- Growth in response to gravity
- Stems = negatively gravitrophic
- Roots = positively gravitrophic
Another term used for gravitropism.
Geotropism
A plant hormone that enables a plant to grow towards, or away from a stimulus.
Auxin.
Where is auxin made?
Roots and shoots.
How does auxin cause a response to a stimulus?
The stimulus causes an uneven distribution of the hormone auxin, which causes an unequal growth rate, causing the root or shoot to bend.
How does the response to auxin differ between roots and shoots?
- Auxin causes increased growth in shoots
- Auxin causes decreased growth in roots
How do plants respond to light?
- When light hits one side of a shoot the auxin on that side both moves away from the light, and is broken down (denatured) by the light
- This lead to a build up on the shaded side
- The cells on the shaded side elongate
- The shoot bends towards the light
How do plants respond to gravity?
- Gravity causes auxins to gather on the lower side of the root and shoot
- In roots auxins inhibit growth so the side with the least auxins elongates and grows down towards the force of gravity.
- In shoots auxins stimulates growth so the side with the most auxins elongates and grows down away from the force of gravity.
State three plant hormones commonly used in agriculture and horticulture?
- Auxins
- Ethene
- Gibberellins
Why is ethene unique to the other two hormones?
It is a gas.
This hormone is used to help to regulate fruit development, without it fruit is often small.
Auxins.
What is ethene?
- Ethene is a hormone that stimulates the conversion of starch into sugar which causes fruit to ripen โ this is why unripe fruit is not as sweet as ripe fruit.
- This hormone is the only plant hormone that is a gas