Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells.

Figure 6 shows an image from an optical microscope of meiosis occurring in a flower bud of a flowering plant. W and Z are undergoing meiosis.

Explain the appearance of W and Z.

An environmental scientist investigated a possible relationship between air pollution and the size of seeds produced by one species of tree.

He was provided with a very large number of seeds collected from a population of trees in the centre of a city and also a very large number of seeds collected from a population of trees in the countryside.

Describe how he should collect and process data from these seeds to investigate whether there is a difference in seed size between these two populations of trees.