Tuesday, 24 July 2007

SXR270 - day 4

Day four - and we move on to theme 3, the plants one.

After the briefing the night before, we were urged to find some interesting plant leaves from anywhere we could to compare carbon uptake. This is a recurring idea in the course. Unlike SXR103 where you sort of just follow a script, here you have to make your own hypotheses and can even devise your own experiments within certain boundaries.

Anyway, Cheryl had this great idea to find some holly and some ivy, and then we could make a bit of a theme if we wrote it up as a poster. However it took a while to track down some ivy. We eventually found some half way to the lab.

In the lab after a briefing we decided to subject the variegated holly to the carbon 14 test. We picked bits of the leaf that were yellow to compare with green bits. After a few background counts we subjected the leaf discs to about 20 mins of 14C exposure, and then started to look at the results with a GM tube. The discs we had cut were quite small so the results were not much above background rates. Background was around 30, and we were getting 50-60 on the green bits. The t-test showed these results as significant.

After this, we tried some lime leafs - one of which was growing in sunlight, the other in shade. This was far more dramatic. The shaded leafs gave counts of 3600, and those in the light around 700. After we did the maths the results were highly significant. Some good results!
We finished up the morning by looking at leaf impressions that showed the stomata under a microscope to see if we could see the structures.

So the holly and the ivy theme sort of disappeared.

After lunch, we moved onto stomatal control, looking at the effects of light, dark, CO2 and ABA on the opening of stomata. We had to peal epidermal layers off a leaf and then subject them to the various conditions. Results were rather disappointing not really leading to very solid conclusions. Some of them went the way the text book and tutors expected, but with quite small margins. Others went the opposite way. We weren't really clear what went wrong, or if we had discovered something new! However it seemed it wasn't the first time this had happened.

The tea, and a debrief on the days experiments, followed by a briefing on the next days experiment. Then a session roughing out a design for a scientific poster to be done tomorrow. Rachel the activity tutor was like a walking encyclopaedia of latin names for plants. She just kept reeling them off.

Then to the bar for further discussion!

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