RESPONDING TO THE ENVIRONMENT: PLANTS Flashcards
What are plant hormones?
Chemicals that regulate plant growth, development, and differentiation of cells and tissues and occur in extremely low concentrations
what is the major means of response to stimuli by plants?
Plant hormones
How are plant hormones produced
Each cell in the plant is capable of producing hormones. They usually interact with each other to bring about the necessary responses
What do plants have to respond to ?
They respond to stimuli in their environment as a safety measure to ensure their survival. They respond to stimuli more slowly than animals.
Examples of stimuli from the environment
Light
Gravity
Chemicals
etc.
What are auxins
One of the most important group of plant hormones
Most common naturally occurring auxin
Indoleacetic acid (IAA)
Where are auxins made and how are they distributed in the plant?
Auxins are made by cells in the tip of a shoot, the apical bud (meristem). Very small amounts are also produced in the root tip. The auxins then diffuse downwards towards the roots. This creates a gradient down the main axis of the plant, the concentration being highest at the tip and lowest at the root.
Functions of Auxins
- Promote growth
- Cause apical dominance
- Play a part in tropic movements
How do auxins promote growth?
Auxins stimulate both cell division and cell elongation which will bring about growth (these cells can then differentiate and develop into various tissues).
How does the auxin concentration affect growth in different parts of the plant?
The further the stem tissue is from the shoot tip, the more sensitive they become to auxin concentrations (need less auxins to bring about elongation.) If the concentration of auxins is too high cell elongation will stop. Root elongation requires much less auxin than stems; higher concentrations will inhibit cell elongation in the roots.
