Response to stimuli Flashcards
What is kineses?
Not movement towards or away from the stimulus. Instead, it changes in speed and rate it changes direction.
What is a taxes?
Simple response where the direction of movement is determined by the direction of the stimulus.
What is tropism?
Growth of a plant in response to a directional stimulus
How do woodlice use kinesis to stay moist?
When in a dry area, they move rapidly and change direction a lot to increase chances of being in a moist area
What growth factor controls phototropism?
IAA
How does IAA control phototropism in flowering plants?
Cells in shoot tip produce IAA. Originally IAA is transported equally down the shoot. IAA moves away from light to a shaded area so the greater concentration of IAA means elongation of shoot cells on the shaded side causing it to bend towards the light.
How does IAA control gravitropism in flowering plants?
Occurs in roots. Cells in root tip produce IAA. Originally IAA is distributed evenly down the root but IAA moves to the pull of gravity. More IAA on lower side of the root, which inhibits cell elongation, causes the cells on the upper side to grow faster and the root bends downwards.
Compare the response to IAA in the root and in the shoot.
Shoot- promotes cell elongation
Roots- Inhibits cell growth
How does IAA cause cells to enlongate?
Increases the plasticity of cell walls using the acid growth hypothesis
What is the acid growth hypothesis?
Active transport of hydrogen ions from the cytoplasm into spaces in the cell wall causing the wall to become more plastic.
What are receptors?
Cells that can detect a specific stimuli
What does the Pacinian corpuscle detect?
Changes in mechanical pressure
What is the special type of sodium channel Pacinian corpuscles have?
Stretch-mediated sodium channels
How does the Pacinian corpuscle function?
At rest, the stretch mediated sodium channels are too narrow to allow sodium ions to diffuse across. When pressure is applied, the membrane becomes deformed and stretched causing the stretch mediated sodium channels to widen so the sodium ions can diffuse through. This causes the membrane to become depolarised and creates a generator potential.
What evidence do we have for tropisms in plants?
Removing or covering shoot tip prevents tropisms
