Biologi campbel : A cell in Life

Given the scope of biology, you may wonder sometimes how

you will ever learn all the material in this course! The answer

involves cells, which are as fundamental to the living systems

of biology as the atom is to chemistry. The contraction of muscle cells moves your eyes as you read this sentence. The words

on the page are translated into signals that nerve cells carry to

your brain. Figure 6.1 shows extensions from one nerve cell

(purple) making contact with another nerve cell (orange) in

the brain. As you study, your goal is to make connections like

these that solidify memories and permit learning to occur.

All organisms are made of cells. In the hierarchy of biological organization, the cell is the simplest collection of matter

that can be alive. Indeed, many forms of life exist as singlecelled 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. Even when cells are arranged into higher

levels of organization, such as tissues and organs, the cell remains the organisms basic unit of structure and function.

All cells are related by their descent from earlier cells. However, they have been modi ed in many different ways during

the long evolutionary history of life on Earth. But although

cells can differ substantially from one another, they share

common features. In this chapter, well rst examine the tools

and techniques that allow us to understand cells, then tour

the cell and become acquainted with its components