Symposium…

My neighbouring village, Foussais Payré, has just held its fifth annual Symposium de Sculpture à la Tronçonneuse. I thought that the standard was the highest yet and I much enjoyed seeing the sculptors in action and admiring some of their finished items.

One of the organisers has produced this nice video, which is also on the website for the symposium.

I don’t know what kind of wood the sculptors were using, it may have varied from artist to artist, but there is no shortage of trees in this part of the Vendée. Just a few miles north of the village is the Mervent Forest which is about 5000 hectares of beech, oak and sweet chestnut trees – it is a pretty impressive site. Beech, oak and sweet chestnut, like most of the trees around here, are deciduous meaning that they drop their leaves to conserve resources during the winter. Their wood is hard, excellent for making furniture and in construction, and produces splendid firewood. They are quite easy to distinguish by their leaves.

Commercial forests are managed to encourage the growth of straight, tall trees from which decent logs and planks can be cut. This is achieved through coppicing (selective cutting of poorer trees to allow the better ones more space and light) and careful monitoring of the woodland ecosystem.

 

You may remember from our biology lessons that plant stems contain two types of transport vessels called xylem and phloem. Xylem carries water up the stem from the roots and phloem carries glucose down from the leaves to the roots. The sapwood in the diagram above is the xylem. The heartwood used to be xylem but it has now become clogged with resins so it no longer transports any water. Wood is composed of cells surrounded by cellulose interspersed with lignin. Lignin increases the strength of the wood and reduces its tendency to rot. Cellulose has a hydrophilic chemical structure which makes it hold on to water. The lignin (which is hydrophobic) makes it possible for water to move freely from cell to cell.

Glucose produced during photosynthesis has to be delivered to the roots because, being underground, they receive no light and cannot produce sugar for themselves. The phloem, found just inside the bark layer, carries sap down to the roots. A tree may be killed by removing a very thin layer all the way around the trunk. This is known as girdling and, because it prevents the phloem from doing its job, it will eventually kill the roots. Some trees sprout shoots below the cut that then produce leaves so that sugar can be produced for the roots. Girdling is often done intentionally to thin out trees in a forest, to remove specific branches of a tree or sometimes as a way of encouraging some orchard trees to produce larger fruit. It can also happen as the result of attack by deer (who love to eat the bark of young trees), rabbits and some birds.

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Questions…

1. Suggest three structures that you might find in a plant cell but not in an animal cell.
2. For what process do the roots require the glucose delivered to them by the phloem and with what does this supply the roots?
3. Water evaporates from trees through tiny pores in the underside of their leaves. What are these called?
4. Name a dissolved mineral present in the water absorbed by the roots and a function that this mineral serves in the plant.
5. What is une tronçonneuse in English?
6. Cellulose has the general formula (C₆H₁₀O₅)_n and lignin has the formula (C₃₁H₃₄O₁₁)_n where the n refers to some large number of these units stuck together. Given this information, what two molecules would you expect to be produced when a piece of wood burns in an ample supply of oxygen?
7. For one of the products in your answer to Q6, give me a chemical test, and its positive outcome, that you could perform in the lab.
8. What is the meaning of the words hydrophobic and hydrophilic?