A Tour of the Cell

The Fundamentals Unit of Life

What do a small compartment in a honeycomb, a

prison room, and the area covered by a mobile

phone tower have in common with a microscopic

part of your body? Each is the simplest unit of function

in a larger system, and each is described by the word cell.

The cell is as fundamental to the living systems of biology as

the atom is to chemistry: All organisms are made of cells.

In the hierarchy of biological organization, the cell is the

simplest collection of matter that can live. Indeed, there are di·

verse forms of life existing as single-celled organisms. More

complex organisms, including plants and animals, are multicellular;

their bodies are cooperatives of many kinds of specialized

cells that could not survive for long on their own.

However, even when they are arranged into higher levels oforganization,

such as tissues and organs, cells are an organism's

basic units of structure and function. The contraction of mus·

cle cells moves your eyes as you read this sentence; when you

decide to turn the next page, nerve cells will transmit that decision

from your brain to the muscle cells of your hand. Each

action of an organism begins at the cellular level.

The cell is a microcosm that demonstrates most ofthe themes

introduced in Chapter L Life at the cellular level arises from

structural order, reflecting emergent properties and the correlation

between structure and function. For example, the movement

of an animal cell depends on an intricate interplay of the

structures that make up a cellular skeleton (the colored fibers in

the micrograph in Figure 6.1). Another recurring theme in bioI·

ogy is the interaction oforganisms with their environment. Cells

sense and respond to environmental fluctuations. And keep in

mind the one biological theme that unifies all others: evolution.

AU ceUs are related by their descent from earlier cells. However,

they have been modified in many different ways during the long

evolutionary history of life on Earth.

Although cells can differ substantially from one another,

they share certain common characteristics. In this chapter,

we'll first examine the tools and experimental approaches that

allow us to understand subcellular details; then we'll tour the

cell and become acquainted with its components.

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