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 to the stimulus, to produce an effect
where does a receptor and effector link to?
a central coordinator
what is a taxis?
directional movement is response to a 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?
non-directional movement in response to a stimulus
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
what is an example of a plant growth factor?
- indoleacetic acid (IAA)
- a type of auxin
what does IAA control?
cell elongation
explain the sequence of events for the phototropism in flowering plants.
- cells in the rip of the shoot produce IAA, which is transported down the shoot
- IAA is transported evenly throughout all regions as it begins to move down the shoot
what are tropisms?
plants grow via growth to stimuli
where is IAA produced?
- made in the roots and shoots of plants and diffuse to other cells
what happens to a plant if there is higher levels of concentration of IAA in the shoots?
promotes cell elongation
what is a simple reflex?
- quick and involuntary response to a stimulus
