chapter 14 Flashcards
taxes and kinesis
simple responses that help organisms to remain in the favourable conditions of their environment e.g. light or dark, certain moisture levels , in the presence of certain chemicals.
what is a stimulus and what is a receptor?
stimulus- detectable change in the environment
receptor- cell that identifies the stimulus.
what are kinesis?
simple response in which organism moves its entire body towards a favourable stimulus or away from an unfavourable stimulus.
negative photototaxis
positive chemotaxis
earthworms are involved in negative phototaxis- move away from the light and into dark conditions- to avoid predators and dehydration and to find food.
bacteria are involved in positive chemotaxis- they move towards chemicals to help them survive.
kinesis
when an organism changes the speed of its mvoement or the rate at which it changes direction.
e.g. if organism moved from area of favourable stimuli to area of unfavourable stimuli, its kinesis response would be to increase the rate at which it changes direction to reneter the environment with favourable stimuli
if organism is surrounded by negative stimuli- its kinesis response will be to decrease the rate at which it changes direction- so the organism will follow a straight path until it reaches a favourable stimuli.
woodlice kinesis example
woodlice stay in damp areas to prevent their surface from drying out
if they are in an environment surrounded by negative stimuli, their kinesis will be to reduce the rate at which the change direction- they follow a straight path- try to find damp area
if they move from a damp to dry area they kinesis will be to increase the rate at which they change direction- increased probability that they will re enter damp area.
what are tropisms?
plant growth in response to a stimuli
plants can respond to light, water and gravity
this is controlled by a form of auxin- IAA indoleaceticacid
positive phototropism
plant grows towards a light source.
IAA is produced in the tip of the shoots.
it diffuses through the plant
if there is a unilaterla/equal distribution of light, the IAA will move to the shaded region and cause cells in the shaded region to elongate- so the plant bends towards the light.
negative phototropism
roots do not need light and do not photosynthesis
can better anchor the plant if they are deep in soil, away from the light.
in roots, a high concentration of IAA inhibits cell elongation so causes the root cells to elongate more on the lighter side, so the root bends away from light.
stimulus
receptor
stimulus- detectable change in the environment
stimulus is detected by receptor cells.
receptors
each receptor only responds to a specific stimuli- which leads to the establishment of a generator potential- leads to a response.
3 receptors-
rods
cones
pacinian corpuscle.
gravitropism
negative gravitropism- IAA moves from upper to lower side in shoot.
If plant is vertical, shoot cells elongate and plant grows upwards
if plant is on its side, it will cause the shoot to bend upwards.
positive gravitropism
IAA moves to lower side of root- causes cells on upper side to elongate more- root bends towards gravity and anchors plant in
where is the pacinian corpuscle found?
in the skin of the fingers and feet
joints, ligaments and tendons- allows organism to know when joints are changing direction.
pacinian corpuscle and stretch mediated sodium ion channels
at rest, the sodium ion channels are too narrow for sodium ions to pass through.
in the cell, there is a resting potential (balance of sodium ions inside and outside the cell)
when the pressure is changed, this causes a change in the shape of the corpuscle
the sodium ion channels stretch
so the sodium ions diffuse into the nerve cell
the influx of sodium ions changes the potential of the cell, leading to the creation of a generator potential.
this creates an action potential- passed along the nerve cell
what is the resting potential?
difference in electrical charge between the inside and outside of the nerve cell when it is at rest.
