Organisms Response to Change - Taxis and Kinesis Flashcards
what is phototropism?
the growth of a plant in response to light
what are the two types of phototropism?
positive and negative phototropism
what part of a plant is positively phototrophic?
shoots
what part of a plant is negatively phototropic?
roots
what is positive phototropism?
growth towards light
what is negative phototropism?
growth away from light
what is a tropism?
the response of a plant to a directional stimulus
what is gravitropism?
the growth of a plant in response to gravity
what part of a plant is postively gravitopic?
roots
what part of a plant is negatively gravitropic?
shoots
what are growth factors?
hormone like chemicals that speed up or slow down plant growth
where are growth factors produced?
in the growing regions of the plant
which growth factor brings about tropism?
IAA
what does IAA stand for?
indoleacetic acid
where does IAA promote growth?
shoots
where does IAA inhibit growth?
roots
how does IAA promote plasticity of cells?
by actively transporting hydrogen ions from the cytoplasm to spaces in the cell wall, allowing cells to expand
describe the process of phototropism in the shoots
IAA concentration increases on the shaded side of the plant
cells on the shaded side elongate and so the shoot bends towards the light
describe the process of phototropism in the roots
IAA concentration increases on shaded side of the plant
growth inhibited so the root bends away from the light
describe the process of gravitropism in the shoots?
gravity causes IAA to accumulate at lower side of shoots
elongation promoted so shoot grows upwards
describe the process of gravitropism in roots
promotes elongation on lower side of roots - bending them downwards so the root grows towards down
what is a taxis?
a simple response where the direction is determined by the direction of the stimulus
what type of organism uses taxes?
simple and mobile organisms
what is a positive taxis?
organism moves its whole body towards a stimulus
what is a negative taxis?
an organism moves its whole body away from a stimulus
what is kinesis?
stimulus response where speed and rate of change of direction change in response to a stimulus
movement is random and related to intensity of stimulus
what happens during kinesis when the organism is in a favourable environment?
speed slows down
rate of change of direction increases
what happens during kinesis when the organism is in an unfavourable condition?
speeds up
rate of change of direction decreases
