Taxis and kinesis and response to the enviroment Flashcards
(20 cards)
what is a stimulus
detectable change in the enviroment that leads to a response
how does respondng lead to an increase of survival
move away from predator and survive por move towards food and survive
how does it influence natural selection
those best adapted to detecting and responding to changes in the enviroment are more likely to survive and reproduce passing on alleles to the offsprings
desribe a receptor
it is detects stimulus and is specific to one type of stimulus
what is a coordinator
formulates an appropriate response
what is an effector
a response producer at a molecular or larger level
what is taxis
directional movement of an organism body as a result of a directional stimulus towards favourable or away from unfavourable one
what is kinesis
change in speed and turning as a result of enviromental stimulus in order to find a more favourable enviroment
when does it occur
when the stimulus does not have a specific direction
what is tropism
directional growth in response to directional stimulus towards favourable condition
how to shoots grow
they are positive phototropism as they grow towards the light
how do roots grow
they are positive gravitropism as they grow towards the gravity
why do plants grow towards light
in order to maximise capturing of light for photosynthesis
why do plants grow towards gravity
they need to be firmly anchored into the soil
why do plants grow towards water
needed for photosynthesis
so how is directional growth achieved by plants
by a group of hormones called auxins iaa that act on the cells that release them
describe photropism
the iaa is produced in the growing part of the plant - the tip of the shoot
it then diffuses evenly throughout the plant
when the light hits the iaa moved to the shaded side of the plant
greater concentration of iaa in shaded side compared to lit side
in the shoots iaa promote cell elongation so the shaded side grows at a fster rate and bends towards the ligth
describe gravitropism
iaa is produced in the tip of the roots
distributed evenly throughtout the roots
then move to the lower side of the root as influenced by gravity
greater concentration of iaa in the root inhibit cell elongation \
upper side of the root grows at a faster rate compared to lower side and then bend towards gravity
what happens to young plants vs old plants
old plants are rigid and less flexible so cells cannot elongate
what is the acid hypothesis
the hydrogen ions are actively transported from the cytoplasm to the cell wall space and leads to the elongation of the cell walls
