Tuesday 13 October 2015

The Colours of Autumn - Part 2 Chromatography.

This weekend resulted in a trip to Grimley for a bit of birding. I really love this time of year as there is a real possibility of anything turning up. And with plenty of reports around the region of some interesting birds I was very hopeful of finding a rarity or two. However, I found very little. In fact from a birding point of view the highlights were simply a few shovelers, a collection of wigeon, 7 little egrets and a couple of stonechats.

Grimley - Camp Lane Pits


Stonechat

Despite this I still enjoyed my walk around the pits and along the river. The colours were incredible and there is a real sense of being stuck between two seasons. As the sun poked through the clouds I had a glimpse of a few butteries and the odd dragonfly. I also spent lots of time admiring the autumn colours. The full range of colours that the leaves go is staggering. I know this was the main feature of my last blog but the pure beauty of autumn is difficult to get over. As a result I was easily inspired to do more on the topic.

Grmiley - Camp Lane Pits

The task was to carry out some chromatography on the different pigments in the leaves. So I collected a range of different leaves and most importantly different colours. To show the different stages of Autumn. As we walked around the area we collected as much as we could. We wanted to see as many of the different pigments that were on show as possible. We were reminded of the compound interest graphic showing what causes the green, yellow, orange and red colours.
Compound Interests Chemistry of Autumn Colours


Our Leaf Collection
We wanted to show that the yellow pigment is always present in leaves, just not visible due the the abundance of chlorophyll. Chlorophyll is the green pigment that absorbed sun light that the plant then uses to carry out photosynthesis. It is green because it absorbs the red and blue parts of the spectrum and reflects the green. We also wanted to show that the red pigment develops later in autumn as a result of chemical reactions in the leaves after the leaf has lost its chlorophyll. The pigment is found in the cell sap and is formed when proteins react with the sugars in the cell sap. The reaction requires light and high concentrations of sugars.

Cutting and Crushing the leaves
The changing of the leaf colours is driven by a number of factors. Firstly the low temperatures cause the plant to break down the chlorophyll. Then the yellows are visible. The reds come from further chemical reaction (hence not see in green leaf chromatography). The leaf needs dry weather to help concentrate the cell sap and then warm sunny days to accelerate the chemical reaction between the sugar and cell sap. So if the conditions are right you will get some stunning colours in the woodlands.

A bit of Careful Warming to Extract the Pigment

Left Over Night 

When we got home we couldn't wait to get started on the chromatography. The first stage was to crush the leaves and soak them in a solvent. We initially warmed the mixture before leaving it over night to extract as much of the pigments as possible. Chromatography is a separation technique. This means that we can separate out all the different chemical found in the leaf. It uses to phases. First the stationary phase – the paper – which holds onto the different chemicals. The second stage is the mobile phase – the solvent – which carries the chemicals trough the stationary phase. The result is that in the green leaves you can see two colours: green and yellow. In the yellow leaves you can only see yellow and in the red leaves you can not see any green, just red and a little yellow.

The First Chromatogram - Both Green and Yellow Pigments


Our Full Results

The results of this investigation confirm our hypothesis but more than that it was a lot of fun. It was great to do some science as a family and get some colourful results. In addition, we managed to connect nature with scientific ideas.