Chapter 14 - Response to stimuli Flashcards
What is a stimulus?
A noticeable change in the external or internal environment that leads to a response
What are stimuli detected by?
Receptors
How many stimuli does each receptor detect?
1
What is the name of the molecule that generates a response?
Effector
Describe the sequence of events in the nervous system
Stimulus - receptor - coordinator - effector - response
What is a taxis?
A response whose direction is determined by the stimulus
What is a kinesis?
A response where the organism changes the speed at which it moves and direction
What is a tropism?
The growth of part of a plant in response to a directional stimulus
Why are plant growth factors not described as hormones?
They may be made throughout the plant, not just in organs
Some factors impact the tissues that release them rather than acting on a distant organ
What hormone controls plant cell elongation?
IAA
Describe how plants respond to unilateral light
Cells in the tip produce IAA, which is transported throughout the plant
Light causes the IAA to move to the unshaded region
A greater concentration of IAA builds up on the shaded region than the unshaded one
IAA causes the elongation of cells - cells on the shaded side grow more
This causes the tip to bend towards the light
What impact does IAA have on roots?
It inhibits cell elongation
Describe how plants respond to gravity
Cells in the root tip produce IAA, which is distributed throughout the root
It is transported to all sides of the root
Gravity means that a higher concentration of IAA gathers on the lower side
Cells on this side grow more slowly than those on the upper side
This causes the root to bend downwards
What happens as plant cells mature?
Their responsiveness to IAA decreases - they become more rigid
What is the Central Nervous System?
The brain and spinal cord
What is the Peripheral Nervous System?
Made of pairs of nerves that originate from the brain or spinal cord
What are the two neurones found in the peripheral nervous system?
Sensory and motor neurones