Symmetry and function

In practice, the symmetry class of an object is often related to the way it is used. Spherical symmetry, for example, predominates in objects that are used with little or no constraint from any specific direction, as with soccer balls that roll around in any way we choose. Radial symmetry, on the other hand, is common in cases where constraints operate along one major axis. Bottles and stools, for instance, are designed to withstand the effects of gravity bottles prevent liquids being spilt...

A pattern of hidden colours

You have been invited to a football stadium with lots of other people to send a birthday message to someone flying overhead in a helicopter. The stadium has already been carefully marked out with a grid of squares, each square being painted a distinct colour, making the stadium look like a colourful patchwork. You are given two pages of instructions and a large piece of card, black on one side and white on the reverse, and told to go and stand on a square. After choosing a square, you look at...

Proteins as guiding shapes

The properties of every plant or animal cell depend on the types of protein it contains. We normally come across proteins as part of our diet. Proteins, though, play a much more pervasive role in our lives than this might lead us to believe. All the processes in the body, such as digestion, secretion, moving, sensing and thinking, depend on the activity of different types of protein molecule. Without proteins we would not be able to do anything. The most important feature of protein molecules...

Multicellular organisms

Fascinating though the reproduction of microbes might be, it seems to be a far cry from the way you or I reproduce. We cannot go forth and multiply by splitting ourselves in half. Our style of reproduction is more complex than that of a unicellular microbe, but nevertheless there is a common element that links the two. Both microbes and ourselves are based on the same type of building blocks, cells, but whereas individual microbes may comprise a single cell, we are made of many billions of...

Reproduction through development

We can now return to the problem of how multicellular organisms, such as humans, mice and oak trees, reproduce. Like unicellular organisms, their reproduction is based on cell division but instead of making many separate individuals, the cells stay together to gradually build up a multicellular individual. We can summarise the whole process with a life cycle. In the case of humans, for example, parents each contribute a cell a sperm cell from the father and an egg cell from the mother. These...