Response To Stimuli Flashcards
Define stimulus
A detectable change in the internal/ external environment of an organism that leads to a response
What is response and what are the advantages of being able to respond to stimuli
it increases the chances of survival in an organism which increases the likelihood of reproducing and passing alleles onto the next generation. Examples: phototaxis (worms and algae moved towards light for food, chemotaxis where bacteria move towards glucose)
Define taxis and the different types
The movement of a motile organism in response to a stimulus, a simple directional response & direction is determined by direction of stimulus (+= towards stimulus and -= away from stimulus)
Define kinesis
A motile organism doesn’t move towards or away from a stimulus so movement is non directional and random. Organism changes speed and rate of turning in response to a stimulus to remain in favourable conditions. In unfavourable= rate of turning deceases and speed increases to move in straight line back to favourable
How does taxis and kinesis increase organisms rate of survival
Taxis- move to positive stimuli such as food or humidity if dry out easily and move away from predators in light, low food source) kinesis- stay in more favourable Areas and move away from unfavourable
Define tropism
The growth of plants in response to a directional stimulus, plant grows towards (positive) or away (negative) from stimulus
Describe the stimuli plants respond to
Light (in shoots there is + phototropism), gravity (in roots + gravitropism), water ( positive hydrotropism). Also temp, touch, atmospheric gases, pathogens, chemicals from other plants
Can you describe plant growth factors such as IAA
affect growth and diffuse down shoot. Main growth factor is IAA which increases flexibility of cell walls, allowing cell elongation. (This done by acid growth hypothesis where IAA stimulates H+ pump so H+ move into cellulose and weaken it)
What did Darwin originally find when investigating phototropism
When there is a unilateral light source, the shoot bends towards the light but there is no growth when the tip is removed and when there is a cover over the tip
How do roots and shoots respond differently to IAA
In shoots, IAA stimulates cell elongation so high concs of IAA promote growth but in the roots, IAA inhibits cell elongation so high concs limit growth
Explain phototropism in flowering plants
- Cells in tip produce IAA, which diffuses down the shoot 2. Light causes movement of IAA to shaded side of shoot 3. Increased IAA causes cell elongation on shaded side, so shoot bends towards unilateral light source
Explain gravitropism in flowering plants
In horizontal roots, the tips produce IAA which diffuses to the lower side due to gravity 2. The IAA inhibits cell elongation on the lower side (less inhibition on upper side) so lower side grows less and upper side grows more, bending down 1. In horizontal shoots, tips produce IAA which diffuses to the lower side due to gravity 2. IAA stimulates cell elongation so lower side grows more as upper side less stimulated
Explain how a simple reflex arc works
- A stimulus is a change in the internal or external environment of an organism 2. Receptor cells detect a stimulus and the nerve impulse is passed along a sensory neurone into the spinal cord/cns/control system 3. The impulse is taken up by a relay neurone and then the impulse leaves the spinal cord via a motor neurone which carries the impulse to an effect or which produces a response
Outline the importance of reflex arcs
They are an involuntary and rapid response to changes in the environment which prevents injury/damage to tissues. Reflexes are important for homeostasis, balance, to escape from predators or for finding food
The main features of sensory reception
Stimuli are detected through receptors and each receptor responds to a single specific stimulus. Receptors are found at the end of sensory neurones and act as transducers which convert stimulus into an electrical signal (first a generator potential and then an action potential)
