Download Myelin Sheaths Plant Hormone Intro

Neurones
of Ranvier
•Most axons of the nervous
system are surrounded by a
myelin sheath (myelinated axons)
•The presence of myelin speeds
up the transmission of action
potentials along the axon
•Myelin will get laid down in
segments along the axon, leaving
unmyelinated gaps known as
“nodes of Ranvier”
A) Nucleus Of Schwann Cell
B) Cytoplasm
C) Myelin Sheath
D) Axon
How would we describe the role of the Myelin Sheath?
- Serves as an electrical insulator
- Allows depolarisation to occur at the nodes
- The impulse jumps from node to node
- Allowing faster conduction
- In a process known as saltatory conduction
Coordination in plants
Response of plants to the stimulus is much
slower and the usual response is growth.
Phototropism – response to light.
- positive phototropism- the shoot grows
towards the light.
Geotropism – response to gravity.
- negative geotropism – shoots tend to grow
away from pull of gravity.
- positive geotropism – roots tend to grow
towards the pull of gravity.
Why is it important for plants to root and stem
behave in this way?
Which part of a shoot is sensitive to light?
Which part of a shoot responds to light?
• The part of a shoot sensitive to light is the tip.
• The part of the shoot which responds to the
stimulus is the part just below the tip.
• These two parts of the shoot must be
communicating with one another by means
hormones.
• Plant hormones are chemical that affect the
activities of particular cells.
• They may move in the phloem (by diffusion or
active transport from cell to cell).
Auxin
- Made all the time by the cells in the tip of the
shoot
- Diffuses downwards from the tip
- Make the cells just behind the tip get longer
(stimulates cell elongation).
What would you expect to see if you mounted a plant pot on a
vertical disc and rotated it slowly over the course of it’s growth.