Today we started the final module- inheritance and selection. We learned that variations in humans are called characteristics and that these can have inherited or environmental causes ( or both) .

We also found out the definition of a species, and that genetic differences are caused by the genes that we inherit from our parents. These genes (over 30,000 in all) are found in the 46 chromosomes in every nucleus of every cell.  It is the genes that are responsible for characteristics such as eye colour. The genes themselves are made of a chemical that contains coded information called DNA. We also talked briefly about cloning – more on this later.

Today 7WD completed the unit on reactions by looking at what happens when we burn fuels. Burning is known as combustion. We found out that water, energy and carbon dioxide are always released.

http://picasaweb.google.com/griggans/BurningFuel/photo#5039569054295316946

On Wednesday we looked at how it used to be thought that atoms were like plum puddings – they contained a sphere of positive charge which had embedded within it negative electrons.

This model was proved wrong by Rutherford when he fired alpha particles at some very thin gold leaf. He expected all the heavy particles to go straight through but amazingly, about 1 in 8000 bounced right back! ( about 1 in 2000 where also deflected off course)

This proved that atoms contain a central nucleus which is positively charged ( it repels the positive alpha particles) but that this nucleus is very tiny compared to the whole of the atom. In fact, atoms are mostly just empty space!

Now imagine that Wembley stadium is an atom. You are an electron sitting the furthest you can away from the pitch. Some of your mates (more electrons) are sitting in the stadium but they are all a long way from you. In the centre circle is a pea. The pea represents the nucleus. There is no crowd or players in the stadium, just a lot of empty space. This model would be OK, except that really you and your mates should be a lot smaller than the pea!

Every year questions are asked about the charges and masses of the 3 particles in an atom (protons, neutrons & electrons)- so make sure you learn this (check your revision book)