Extracting The Best From The Week

Another good week – worked our way through the rest of the experiments I’d planned to do, from seeing how yeast reacts to different environments to extracting DNA from a kiwi fruit and having a look under the microscope…

First we had a quick look at osmosis, using cucumber slices in distilled water and a saline solution. Osmosis is “the spontaneous net movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, in the direction that tends to equalise the solute concentrations on the two sides”. in this case water moving through cell walls to equalise both sides. The distilled water moves into the cucumber cells, the water in the cells moves out into the saline solution, making one slice turgid and the other squishy and reduced.

Next we looked at the properties of water and other liquids by freezing water, salt water, olive oil and tomato sauce, then placing them in their liquid form. The ice floated, the others sank. We were unsure of the sauce – it sort of hovered – but it was very slowly sinking. We put it in water just to see what would happen, and it sank…

Ice floats, unlike the other liquids, because the molecules freeze in a hexagonal structure, spacing them apart and making the solid less dense than the liquid.

Next was looking at the growth of yeast.

We put yeast in four glasses – hot water, tap water, warm water and warm water covered in cling wrap. As yeast is a living organism the hot water killed it and nothing happened. The tap water didn’t do much – it would have needed more time to activate.

The warm water was the best environment, and there wasn’t much difference in growth. Given more time we may have seen a difference, as the plastic kept the carbon dioxide that was being given off inside the glass, and it would eventually kill the yeast.

The final experiment – DNA!
The kiwi fruit was mashed and mixed with salt and washing up liquid, then warmed. This was to disrupt the cells and extract the DNA. DNA is soluble in water, but not in alcohol, so we added methylated spirits to precipitate the DNA. This made it possible to pull some out with a paper clip.