4. orientation responses in plants Flashcards
what are tropsims?
directional response to an external stimuli
what are nastic responses?
non-directional responses based on the intensity of a stimulus (sudden and reversible)
phototaxis/nasty
light
chemotaxis/nasty
chemicals
hydrotaxis/nasty
water
thermotaxis/nasty
temperature
thigmotaxis/nasty
touch
nyctinasty
closing of flower petals
what is phototropism?
growth response of plants to grow towards or away from light
what is auxin/where is it produced?
a hormone that causes cells to elongate and is produced at the apical meristem of a plants’ shoot
is auxin soluble?
it can diffuse down stems through agar (not mica/glass)
how does the auxin work in phototropism?
- mitosis occurs at the apical meristem and auxin produced here
- auxin diffuses down dark side of plant when exposed to light
- cells on dark side elongate and the difference in cell size causes the stem to bend towards the light
survival advantage of auxin/phototropism?
by bending towards the light the plant inc its rate of photosynthesis = grow quicker and higher chance of survival
what is geotropism?
when a seed germinates its auxin stimulates directional growth so roots grow downwards and shots grow upwards
what happens in roots for geotropism?
high conc auxin = NO elongation
high conc auxin = elongation
roots bend to the ground
