Living cells exist on this planet in two basic patterns: procaryotes
and eucaryotes. As we saw in Chapter 23, procaryotes are older and
simpler in design, and are represented today only by bacteria and
blue-green algae. The eucaryotic pattern is newer and more complex
and is found in every other type of living cell: green, red, and
other algae, fungi, protozoa, and higher plants and animals.
Both kinds of cells carry out the essential functions outlined at
the beginning of Chapter 22: They propagate, grow, metabolize at
the expense of their surroundings, use and protect themselves from
their environment, and evolve in response to slow changes in the
environment. They may go about things in different ways, but they
all face similar challenges and have similar goals: to meet those
challenges well enough to survive.
Right: Electron micrograph of a bacterium (staphylococcus
aureus). Notice the cell wall outside the bacterial membrane.