Survival and response Flashcards
Define stimulus
a detectable change in the environment
Define response
a result of the stimulus that is detected by the receptor a response is caused.
Advantage to organisms of being able to respond to stimuli
-increases chance of survival
-move towards beneficial stimuli
-move away from harmful stimuli
-organisms that survive have a greater chance of raising offspring and of passing their alleles to next generation
-always a selection pressure favouring organisms with more appropriate responses
What are stimuli detected by
receptors that are specific to one type of stimulus
what does a coordinator do
formulates a suitable response to a stimulus
-may be at molecular level or involve behaviour of a whole organism
how does communication in animals happen
-nervous system
-have different receptors and control effectors
-each receptor and effector is linked to central coordinator which connects information from each receptor with the appropriate effector
Sequence of events in chemical control or nerve cells
stimulus > receptor > coordinator > effector > response
Describe tropism
-growth of part of a plant in response to a directional stimulus
-plants part grows towards stimulus (positive tropism ) or away from stimulus (negative tropism)
Examples of tropism
-plant shoots grow towards light (positive phototropism) and away from gravity (negative gravitropism) > so their leaves are in the most favourable position to capture light for photosynthesis
-plant roots grow away from light (negative phototropism) and towards gravity (positive gravitropism) > increase probability that roots will grow into the soil > absorb water and mineral ions better
Describe taxes
-single-celled algae move towards light (positive phototaxis) > this increases their chances of survival since, being photosynthetic , they require light to manufacture their food
-earthworms move away from light (negative phototaxis) > increases their chances of survival because it take them into the soil > better able to conserve water , find food and avoid some predators
-some bacteria (daphnia) move towards highly concentrated glucose region (positive chemotaxis) > increases chances of survival as they use glucose as a source of food
Describe kineses
response where organism doesn’t move towards/ away from stimulus, instead changes speed speed of movement and rate of directional change
-if organism crosses dividing line between favourable and unfavourable environment , its rate of turning increases. This raises its chances of quick return to a favourable environment
Examples of kineses
-woodlice lose water from their bodies in dry conditions.
-when move from dampt area into dry, they more more rapidly and change direction more often
-this increases their chance of moving back into damp area
-once back into damp area, they slow down and chance direction less often
-so means more likely to stay within damo area
-but if after some time spent changing direction rapidly they are still in the dry area, their behaviour chances.
-instead they move rapidly in straight lines, which increases their chances of moving through dry area and into a new damp one
-so they spend more time in favourable damp conditions than in less favourable drier ones
-prevents them drying out and so increases their chances of survival
