Response To Stimuli Flashcards
Stimulus
Detectable change in the internal and external environment of an organism that leads to a response in the organism
Ability to respond is necessary because
It increases chances of survival for organism - detect and move away from harmful stimuli or move towards a source (food)
Stimuli are detected by
Receptors
Receptors are
Specific to one type of stimulus
A coordinator
Formulates suitable response to a stimulus may be at a molecular level or involve a large organ like the brain
Response is produced by an
Effector
Hormones as a means of communication
Slow process via chemicals(hormones ), in large mulitcullular organisms, plants and animals
Animals have a more rapid means of communication
Nervous system
Central coordinator
Each receptor and effector is linked to one. It connects information from each receptor with the appropriate effector
Sequence of events
Stimulus - receptor - coordinator - effector- response
Taxis
Simple response whose direction is determined by the direction of the stimulus - an organisms moves whole body towards a favourable stimulus or away from unfavourable one
Towards stimulus
Positive taxis
Eg towards the light is
Positive phototaxis
Algae moving towards light advantage
Increases chances of survival as being photosynthetic they require light to manufacture there food
Earthworms moving away from the light is
Negative phototaxis
Earthworms moving away from light increases survival rate because
Takes them into the soil where they are better able to conserve water , find food and avoid some predators
Bacteria move towards region where glucose is more highly concentrated as it’s a source of food which is ?
Positive chemotaxis
Kinesis
Organism doesn’t move towards or away from stimulus instead it changes the speed at which it moves and the rate at which it changes direction
If an organism(kinesis)crosses a sharp dividing line between favourable and unfav environment what happens
It’s rate of turning increases raising its chances of a quick return to a fav environment
(Kinisis) if moves a considerable amount into unfav environment what happens to rate of turning
Decreases so that it moves in long straight lines before it turns sharply . This tends to bring the organism to a region favourable
When a stimulus is less directional (kinesis)
Humidity and temperature eg don’t always produce a clear gradient from one extreme to another
Example of kinesis - spend more time in damp than less fav dry preventing then drying out increase survival
Woodlice- lose water in dry conditions so when move from damp to dry move more rapidly to increase chance of getting back to damp. Once in damp they slow and don’t change direction as much so more likely to stay in damp. But if been in dry for a while and been changing direction they move rapidly in straight lines instead to increase chance of getting into damp quicker
Tropism
Growth of part of a plant in response to a directional stimulus (grows towards or away from stimulus- stimulus names the type of response )
Plant shoots response so that leaves are in most favourable position to capture light for photosynthesis
Shoots grow - towards light (positive phototropism) and away from gravity ( negative gravitropism)
Roots response to increase probability they’ll grow in soil and why need to
Grow away from light ( negative phototropism) and towards gravity(pos gravitropism) so there better able to absorb water and min ions
Example of a plant growth factor
Indoleacetic acid (IAA)
IAA
Controls plant cell elongation. Belongs to group called auxins
Unilateral light
Light directed at a shoot from one side
Phototropism in flowering plants process
Cells in the tip of the shoot produce IAA which is then transported down the shoot
Initially it’s transported evenly but then the light causes the movement of it from the light side to the shaded side of the shoot.
Greater conc builds up on shaded side and as they cause cell elongation the cells on shaded side elongate faster than the light side , causing the shoot to bend towards the light
Phototropism. High concentration of IAA in roots affect ?
Inhibits cell elongation so in roots the cell elongation is greater on the light side than the shaded so roots bend away from the light(neg)
Protein pigment in rod cells
Rhodopsin
Receptor
, detect stimulus if big enough create generator potential or action potential
Rod cells
Absorb light intensity and the protein pigment inside rhodopsin (if a big enough light intensity is absorbed) it will break down pigment and this triggers an action potential
How does an action potential occur in rod cells
If enough pigment has been broken down for threshold to be met in bipolar cell an action potential can occur
2 reasons we can see in dark
Not a lot of energy needed to break down rhodopsin and the Threshold can be reached in low light as there’s multiple rod cells connecting to 1bipolar cell (retinal convergence ) creates spatial summation
Spatial summation
Collectively all broken down pigment results in big enough stimulus to trigger action potential-rod cells
Rod cells accuracy of vision
Low visual acuity - can’t distinguish between separate light sources
Cone cells colour pigment
Iodopsin (3 types red green and blue )all absorb diff wavelengths of light
How do we perceive range of colours
Depending on proportion of each cone cell stimulated
No retinal convergence or special summation
Cone cells so can’t see colour in dark
Going towards Spinal cord
Afferent
Going away from spinal cord
Efferent
Macula
High density of rods and cones
