he Fundamental Units of 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
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
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