Water Type Effects on Organism Growth

Arabidopsis vs Tobacco Seeds: A comparison

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I took some macro- and microscopic images to show the size difference between the arabidopsis and the tobacco seeds. While microscopically, the arabidopsis is roughly the same size as the tobacco seed in 1 dimension, the arabidopsis is actually much smaller volume wise. While I have no concrete numbers (because I have no way to measure this stuff), it is obvious that the width and height of the tobacco seed are much greater (probably twice as wide and tall).

The scale rectangles in the microscopic images are 100um meaning each hash mark is 25um apart. These images were taken at 10x magnification on our Olympus IX71. The scale is built into a coverslip called Cellattice (which I really don’t like at all, they are made of plastic and bend very easily and thus make it hard for microscopy).

The reason that I’m showing all this is to get a sense of how difficult it is to work with these seeds. First they are small (tobacco is ~.6mm a side, and arabidopsis is ~.3mm on its smallest side). Second there is the static thing. I mentioned this before, but for some reason the seeds become charged and are repelled by the tweezers. I thought the tobacco seeds were hard to handle, but the arabidopsis go flying when I try to pick them up.

In trying to rationalize why there is a more profound effect on the smaller seeds, I thought we’d look at this physically speaking (don’t worry only basic math):

  • Electric Force is proportional to the charge of the objects divided by the distance between the objects. F_{E} = kq_{1}q_{2}/d
  • Let’s assume the charge on both the arabidopsis and tobacco seeds are the same. Then q_{1} is your seed charge and q_{2} is the charge on your tweezers. If the charges are both positive or both negative then you will get a repulsion, otherwise you get an attraction.
  • To find out which one will get flung farther if there is a repulsion then you need another equation. We can say that F_{E} = F_{a} = ma Where F_{a} is just a force due to acceleration. Both seeds will have the same F_{a} because they have the same F_{E}. This means that the tobacco seed, which has more mass (m) will have less acceleration (a) than the arabidopsis which will have a much higher acceleration.

That means less fun for me šŸ™