Summary study book Understanding Life Sciences of T. M. Thomas Isaac, S. Chetty, S. Naidoo (Chapter 9: Plant Responses to the Environment) - ISBN: 9781920192150 (Matric CAPS.)
Answer: auxins bring about a bending reaction due to tropisms
they promote cell division
they are responsible for cell enlargement
they are responsible for apical dominance
they promote root development
3.
What is the purpose of gibberellins
Answer: Helps with seed germination
Increases fruit size
Promotes floral development
Promotes sprouting of dormant buds
Elongates the internodes of stems
Stimulates root growth
4.
What is the purpose of abscisic acid
Answer: Promotes aging of leaves
closes stomata in periods of drought
Induces flowering
Brings about dormancy in apical buds and slows germination
5.
Explain phototropism
Answer: The growth movement in response to the stimulus of light
auxins are produced at the tip of the stem from where they move downwards evenly
The even distribution of auxins brings about equal growth on all sides of the stem
The stem grows straight upwards
when the stems are exposed to a unilateral light, the brightly lit side suffers from a shortage of auxins because they are destroyed by the light or because they move to the darker side
A high concentration of auxins promotes growth
Thus an uneven distribution causes an uneven growth, with the darker side growing faster
this causes the stem to bend towards the light
Content preview
CHAPTER NINE
PLANT RESPONSES TO THE
ENVIRONMENT
BASICS
Hormone: organic substance produced in small amounts. Controls growth and
development.
HORMONES
AUXINS
* Auxin has 5 letters, so there are 5 things that you need to remember:
1. Auxins bring about a bending reaction due to tropisms
2. They promote cell division
3. They are responsible for cell enlargement
4. They are responsible for apical dominance
5. They promote root development
GIBBERELLINS
* Change the b’s to p’s to form the word Gipper
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