Survival and Response Flashcards
what is a stimulus?
a detectable change in the internal or external environment of an organisms that leads to a response in the organism
what does the ability to respond to a stimuli lead to?
increases the chances of survival for an organism
why do organisms want to survive?
- greater chance of raising offspring and of passing their alleles to the next generation
- selection pressure favours the organism with more appropriate responses
what are stimuli detected by?
receptors
what are receptors?
- receptors are specific to one type of stimulus
what are coordinators?
formulates a suitable response to a stimulus
- may be at a molecular level or involve a large organ (e.g. brain)
what does an effector produce?
a response
where does a receptor and effector link to?
a central coordinator
what is a taxis?
a simple response whose direction is determined by the direction of the stimulus
how are taxes classified?
- movement is towards the stimulus = positive taxis
- movement is away from the stimulus = negative taxis
what are examples of taxis movement?
- single-celled algae will move towards light (positive phototaxis) = increases chance of survival
- earthworms move away from light (negative phototaxis) = increases their chances of survival
what is kinesis?
form of response in which the organism does not move towards or away from a stimulus
- moves and changes direction
what are tropisms?
growth of a part of the plant in response to direction stimulus
where in flowering plants is there positive phototropism and negative gravitropism?
- plants SHOOTS grow TOWARDS the light and AWAY from gravity
- leaves are in a favourable position to capture light
where in flowering plants is there negative phototropism and positive gravitropism?
- plant ROOTS grow AWAY from light and TOWARDS gravity
- increases probability roots will grow into soil to better absorb water and mineral ions
