Shaped for the job
Cells are not all alike. They vary in shape, size and activity — and they do so because they are shaped to carry out different jobs.
Shape follows the job
A red blood cell that has to carry oxygen and a nerve cell that has to send an impulse a long way are doing quite different jobs, so they are quite different shapes. Take any job in the body and you will find cells shaped for that job in particular.
How are they seen?
Apart from a few special cases, cells are not normally visible to the naked eye. They therefore have to be observed under a light microscope.
A limit worth remembering
Not seeing a cell is not the same as there being no cell. Every piece of living material you can see with your eyes is made of cells; you cannot pick them out individually only because they are small.
Where this goes next
The rest of the chapter does one thing: it looks inside a cell under the microscope and asks what each part is and what it does. Section 6.3 starts with the structure.