Making a potometer

I had to make a potometer for biology class in 2014 and measure the transpiration rates of plants under different environments. The biology was utterly boring.  But the engineering was far more interesting.

Image result for measuring transpiration rates
Schematic of a potometer

Here is a simple schematic for a potometer. As the plant takes up water, it moves the air bubble along and we can measure how far it has moved and meaure its water consumption. Simple enough on paper.

Testing if it will all fit together.

I was rather cash strapped and not willing to spend for somthing as miserable as biology so I built my own simpler version of a potometer. Instead of using a glass capillary tube, emptied out the contents of a pen refill(the plastic bit) and used that as a capillary tube. Its inner diameter is around 1 mm so it shows the bubble pretty well.

MK 1

This was my first working prototype. Water rises up the green tube, through the pen refill and into the plant. The syringe was the reservior to  reset the position of the air bubble.

Then I made the more robust, compact MK 2 of the potometer. Here are some close ups and labels.

MK 2
MK 2 close up

Repeatablity is very importantant with when applying the scientific method. So I made 5 of these potometers and tested all the plants parallely.

It was surely the best design the class could create for this project. However, there was some exprimentation to do with placing the plants under different conditions and seeing how their transpiration was affected. I tried to see if different coloured light would affect transpiration.  In retrospect this might be  a bit of a bogus science because its quite difficult to ensure consistent intensity of different coloured lights. I wrapped a floroscent bulb with this coloured film and shined it on the plants for around and hour and checked to see if different colours affect transpiration rates. It did not really make a difference.

Wrapping the coloured plastic film around the white bulb
Shining the red tinted light.

From an engineering perspective, I quickly found out that the heat from the lamp was melting the plastic film. There was a terrible smell. Anyway, it did not really cause any major problem.

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