Investigating Tropisms Notes - UNIT 14 Flashcards
set-up A: light-proof box, unilateral light
results?
- seedlings grow towards the light source, to the side
set-up B: clinostat (rotating around), unilateral light
results?
- effect of the light only coming from one direction has been cancelled out by using a clinostat (it revolves slowly and repeatedly,
so the shoots are evenly exposed to light)
equal amount of light so they do not curve towards the light source but grow straight up
set-up C: in complete darkness
results?
the seedlings grow straight up looking for light and the plant becomes tall and slender with yellowing leaves due to the lack of light
Investigating Gravitropisms
equipment
- radicle (develops into primary root) RADROOT
- plumule (develops into the shoot) - PLUMSHOOT
- moist cotton wool
- petri dish
also:
- each seedling should point in a different direction
- both set-ups should be placed in complete darkness
set-up A:
results?
A) petri dish is on its side, support
all radicles have grown downwards (positive gravitropic response)
all plumules have grown upwards (negative gravitropic response)
set-up B:
results?
B) clinostat
all radicles and plumules have continued to grow in whichever direction they were placed
effect of gravitropism was cancelled out by the rotating clinostat
steps:
Add some damp cotton wool to two petri dishes
Place 3 bean seedlings in the cotton wool in each petri dish
A - radicle facing downwards ⬇
B - horizontally →←
C - radicle (root grows from here) facing upwards ⬆
Cover each dish with a lid
Attach one petri dish to a support so that it’s on its side
Attach the second petri dish to a clinostat
Place both in a light-proof box (so that the seedlings are in complete darkness), leave for two days and then observe growth of the seedlings
The experiment needs to be done in a lightproof box in order to
to cancel out the effect of light on the growth of the seedlings
When light shines on the shoot predominantly from one side though, the auxin produced in the tip concentrates on the shaded side, ……..
making the cells on that side elongate and grow faster than the cells on the sunny side
!!!!!! AUXIN ON SIDE WITHOUT LIGHT, SIDE ELONGATES
unequal growth on either side of the shoot causes the……..
shoot to bend and grow in the direction of the light
role of auxin can be tested using………
using seedlings placed in a box that has a slit on one side, only allowing light in from one direction:
recall ;; hard to rmbr
In roots, higher concentrations of auxin results in a lower rate of cell elongation
The auxin that accumulates at the lower side of the root inhibits cell elongation
As a result, the lower side grows at a slower rate than the upper side of the root
This causes the root to bend downwards
