3.6 organisms respond to changes in their internal and external environments Flashcards
why do organisms respond toc changes in their environment
to increase their chance of survival
what can affect the cell elongation in the roots and shoots of flowering plants
different concentrations of indoleacetic acid- IAA
explanation of gravitropism and phototropism in flowering plants
due to the effect of different concentrations of IAA on cell elongation in the roots and shoots of flowering plants
simple responses
- simple responses keep mobile organisms in a favourable environment
- present in simple mobile organisms e.g woodlice
- their responses can either be tactic or kinetic
tactic response verb
taxis
tactic response
- directional movement in response to a stimulus; direction of stimulus affects response
- positive taxis = towards light
kinetic response verb
kinesis
kinetic response
- ## non directional movement in response to a stimulus; intensity of stimulus affects response
simple reflex
- rapid and involuntary response
- communication goes through spinal cord and not through concious part of brain
- simple reflexes are protective; they help organisms avoid damage
role of simple reflexes
- help organism avoid damage
role of receptors
- they’re specific cells that detect a particular stimulus
variation in types of receptors + examples
- some receptors are cells
- e.g photoreceptors = receptors that connect to nervous system
- some receptors are proteins on the cell surface membranes e.g glucose receptors = proteins found in cell membranes of pancreatic cells
what do receptors in the NS convert energy of stimulus into
electrical energy which is used by neurones
what is resting potential
potential difference when a cell is resting
difference in charge when a receptor is in resting state
- inside is negatively charged, relative to its outside
- means that there is a voltage or potential difference across the membrane
how is the resting potential generated
- by ion pumps and ion channels
what is generator potential
change in potential difference due to a stimulus
how is a generator potential generated
- when a stimulus is detected, the cell membrane is excited and becomes permeable
- this allows more ions to move in and out of the cell; altering the potential difference
- bigger stimulus excites membrane more, causing a bigger movement of ions and therefore a greater change in potential difference; hence a bigger generator potential
what is an action potential
- an electrical impulse along a neurone
- it is only triggered if the generator potential reaches the threshold level
how is an action potential triggered
- if the generator potential is big enough, it will trigger an action potential
how are action potentials measured
- they are all one size, so the strength of the stimulus is measured by the FREQUENCY of action potential (number of action potentials at a time)
- if stimulus is too weak, the generator potential won’t reach the threshold, so there is no action potential
what do mechanoreceptors detect
changes in pressure
example of a specific mechanoreceptor
pacinian corpuscle
structure of pacinian corpuscle
- receptors that occur deeply in skin
- its a sensory neurone surrounded by layers of connective tissue separated by viscous gel
how is a generator potential established in the pacinian corpuscle
what does the pacinian corpuscle act as and why
- acts as a transducer
- converts mechanical energy (pressure) into energy of a nervous impulse
