Well lets see Mr sgvaibhav's hard questions.
Plants again? Oh God! I hate plants. Okay.
Wait....
What did you mean by (water in the cell moves from cell to cell
and from cell wall to cell wall)? I didnot get it at all. Please tell me what you mean so I can help with that..
For germenation..Germenation? Auxins and those things are not about germenation ?! Its about sensetivity and movement in plants.
Listen, plants respond to a certain stimuli..What we are concerned about are light( photo-stimulus) and gravity( geo-stimulus) A growth response carried out by a plant in response to the direction of a stimulus is called a tropism..Easy for now?
A +ve response is a growth movement towards the stimulus and a negative response is a growth movement away from the stimulus. For example:
-a stem growing towards light is a +ve phototropism
-a stem growing upwards (away from gravity) is a -ve geotropism.
-a root growing downwards(away from light but towards gravity) is a +ve geotropism but a -ve phototropism
*Roots are positively geotropic:
-they grow into the soil which provides a source of water and mineral ions
-they provide an extensive system of support and anchorage for the plant
*Shoots are positively phototropic:
-leaves are in the optimum position to absor light energy for photosynthesis
-flowers are lifted into the position where they are most likely to recieve pollen. They will be held out into the wind or may be more visible to pollinating insects
NOW..! Auxins!
Phototropism is controlled by auxin..Auxin is simply a "growth substance"..
Here are some simple observations about it:
-if the tip of the shoot is cut off the shoot can no longer respond to stumuli.This suggests that the tip produces the auxin
-a shoot responding to a stimulus always bends just behind the tip. The auxin appears to travel from the tip(where it is made) to a region behind the tip(where it has its action)
-auxin can diffuse back from the tip and can be collected in blocks of agar jelly(allows the diffusion of auxin).These blocks can then allow the tip to resond to the light
-when shoot tips are exposed to light from one side auxing accumelates on the "dark" side of the shoot.The auxin is somehow affecting the growth of the dar side of the shoot.
Imagine now the sun light is distrbuted from all directions..the auxin will be prodeuced at the tip and diffuses slowly down the plant.Cells on both sides are affected equally and the shoot grows straight upwards.Got it?
But when the light comes from one of the sides only..the light reduces the concentration of auxin on the "light" side.The cells absorb less water and so swell less than normal.The light side therefore grows less quickly and the shoot bends towards the light.While the cells on the dark side recieve more auxin . they absorb more water and so increase the size more that normal. The dark side therefore grows more quickly and the shoot bends away from the dark i.e towards the light.
Now auxin thing in geotropism..you just have to know that when the pull of gravity occur..more growth substances"auxin"reaches the lower side..and stops it extending as much as the top side...
Take as a note that auxin inhibits(slows down) the cell growth in roots but stimulates(speeds up) cell growth in shoots.
NOW ANOTHER EXPLANATION IF YOU WISH:
Auxin is produced by cells at the tips of stems and roots. It speeds up growth ain stems.It slows down growth in roots.
Phototropism and auxin:
*When light comes from above auxin spreads evenly down the stem.The stem grows straight.
*When light comes from one side auxin spreads down the shaded side of the stem.
*Auxin makes stem cells grow faster.this causes the stem to bend towards the light.
Geotropism and auxin:
*If a plant is laid on its side auxin gathers in the lower half of the stem and root.
*Auxin at the root slows down the growth of root cells.The root curves downwards.
*Auxin at the shoot speeds up growth of stem cells.The stem curves upwards
Pay attention that both explanations should be taken into consideration, as both are so important. If you like print what I wrote and study it because its very useful.
About your last question about the experiment, from your understanding and knowledge of the above thing, you should be able to answer it. The rolling jar means that auxin will be spread on the whole of the plant equally and it will grow in a straight way. Study the notes above and still if you have any question please ask.
I hope you'll understand.
sweetsh
