B14 - Response to stimuli Flashcards
What is a stimulus?
A change in the environment
What is a receptor?
Detects different types of stimuli
What is an effector?
Production of an appropriate source
What is kinesis?
A non-directional response to a stimulus. The rate of movement of an organism is affected by the intensity of the stimulus
What is taxis?
A directional response to a stimulus. The organism moves directly away from or towards the stimulus
What does Indoleacetic acid (IAA) do in shoots?
In shoots, higher concentrations of IAA on the shaded side results in a greater rate of cell elongation. The shoot bends towards the light which is positive phototropism
What does Indoleacetic acid (IAA) do in roots?
In roots, higher concentrations of IAA results in a reduced cell elongation on the lower side of the root. The upper side of the root grows, and bends in the direction of gravity which is positive gravitropism. Opposite to in shoots
What is the reflex arc?
Reflex arc is a pathway along which impulses are transmitted from a receptor to an effector without involving ‘conscious’ regions of the brain. The response is very quick and is a protective response
What are the steps to the reflex arc?
- A stimulus is detected by a receptor
- The sensory neurone sends electrical impulses to the spinal cord (the coordinator)
- Electrical impulses are passed on to relay neurone in the spinal cord
- The relay neurone connects to the motor neurone and passes the impulses on
- The motor neurone carries the impulses to the effector
- The impulses cause the effector to act in a response
What do Pacinian corpuscles do and what is their structure?
It is a type of receptor found deep in the skin and responds to changes in pressure. These receptors are stimulated by pressure, and leads to a generator potential being established
Found at the ends of sensory neurone axons and are made of layers of membranes, separated by a gel which contains Na+ ions. The axon membrane contains stretch-mediated Na+ ion channels which open when sufficient pressure is applied which then forms a generator potential
How does the generator potential of Pacinian corpuscles work?
There is an excess of Na+ ions surrounding the axon
1. Pressure is exerted on the Pacinian corpuscle
2. Membrane layers become distorted
3. Stretched-mediated Na+ channels open
4. Na+ ions enter the axon via facilitated diffusion
5. Influx of ions changes the potential difference (voltage) of the membrane
6. Depolarisation occurs
What are rod cells sensitive to?
Light intensity
Rod cells contains rhodopsin. Breakdown of these pigments results in a generator potential being produced. Rhodopsin breaks downs in dim light
Rods are very sensitive to low-intensity light - allows humans to distinguish between light and dark objects in dim light
How does the brain receive signals from rod cells?
Multiple rod cells synapse with a single bipolar cell. Multiple bipolar cells synapse with a single ganglion cell, which connects to the optic nerve. The brain is not able to interpret which impulses are sent by specific rods. The brain receives a general, not specific, understanding of the fields of vision that are light or dark
What is the summation effect?
When a group of rods are stimulated at the same time the combined generator potentials are sufficient to reach the threshold. This effect is called summation, and enables organisms to see in much dimmer light than cone cells allow
What are cone cells sensitive to?
Cone cells are less sensitive to light but are sensitive to the different wavelengths of visible light (colour)
Cone cells contains iodopsin. Breakdown of these pigments results in a generator potential being produced. Iodopsin breaks down in bright light
There are three cone types found in human eyes, each containing a different optical pigment:
- Red sensitive cones are sensitive to wavelengths of light that correspond to the colour red
- Bluesensitive cones are sensitive to wavelengths of light that correspond to the colour blue
- Green sensitive cones are sensitive to wavelengths of light that correspond to the colour green
