Wednesday, 25 July 2007

SXR270 - day 5

Wow - those days keep rolling by!

We started this morning after breakfast in the plant lab again. This time we ground up some plant leaves to extract the chloroplasts. This involved a pestle and mortar, an extraction buffer, a couple of trips to the centrifuge, and quite a lot of ice to keep them from degrading. It was also our first encounter with whizzy stirrers.

Once we had prepared the extraction, we used DCTIP to check that we had captured chloroplasts and that things were working. This is a die that is blue, but turns colourless as it hijacks the electrons produced from the photosystem electron transfer chains. Extremely convenient as it shows you photosynthesis in action.

First we measured the degradation of the die with white light. Then we tried a few different filters to see the effect red, green, blue, orange and yellow light had on the rate of photosynthesis.

Plotting these on a graph showed the light colours that were best absorbed with the steepest lines.

Red and blue are favourites, green not very good and orange, yellow and light somewhere in between. So that's why plants are green - they absorb the rest.

Other groups tried light intensity variations which showed an increase with increasing light - up to a point. Photooxidation then starts to kick in as the leaves get more light than they can handle. We have a debrief on this session which ends with Rachel posing us the question "why aren't plant leaves black and so absorbing all light wavelengths?"

Lunch was followed by a poster session. We had two hours to make a scientific poster on any of the activities we had done with plants. I did mine on the results from yesterdays lime leaves which gave some rather fine data. As usual, for me, I had about finished it after 30 minutes, but then all the little touching up and fiddling around and reprinting took another hour or so. I asked Rachel why plants are green, to which she suggested it was to do with not absorbing too much light and so causing overheating.
Eventually my poster was as done as it was ever going to be, and it was framed in a big sleeve and pinned up on a set of display boards.
I went back to Rachel unconvinced about the black/green plant leaf explanation, challenging her on plants in low light environments like forest floors and Arctic tundra. Finally I found something she couldn't answer! Boy that was hard work, she had an answer for everything else!!

Then back to the room to crash out for a while until tea, then its back to the QMC to do poster viewing.

We looked and commented on our own posters after a break, and also at all the others in the group. Then we went on to look at the other groups and see what they looked like. It was quite useful in some ways. You got to see posters with bits in that you thought you'd done better. You also saw some ideas you wish you'd have thought of too. Still - in the end I was satisfied with my efforts, and the feedback was fairly good too. I made some rather light hearted remarks on the feedback form, not realising they would be collected in. I hope it doesn't count against me!!

We decided to go to Lenton bar tonight and had a few drinks there. After we returned I thought I'd just poke my nose into Cripps bar to see what was going on, and somehow got into a discussion on Tim's view of exactly what risk assessment means to him (everything apparently!).

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