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General Biology
Prof. Bryan Cardella, M.Ed.

ap biology eaton

AP Biology 
Dr. Carleen Eaton, M.D.

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Cells: The Basics

  • The word "biology" means the scientific study of life and living organisms. But what, exactly, is life? There are many definitions, some of which are hotly debated by scientists, philosophers, and theologians. One definition is that life is any system that has three basic properties: Metabolism, Growth, and Reproduction

  • Metabolism is the sum of all the chemical reactions in an organism. Growth is the process of increasing in size. Reproduction is the process of producing new individuals of the same kind. Rocks, for example, aren't alive because they don't metabolize or reproduce. Rocks can grow by adding mineral deposits to their surface, but they must have all three properties in order to be considered "alive."

  • Earlier in the course, we learned that the cell is the simplest level of biological organization. By that, we mean it's the smallest unit of life that has all three of the properties listed above. We can think of it as the "atom" of biology. Some organisms consist of just a single cell, while most are far more complex. But even the most complex organisms begin their lives as single cells — including humans. By the time an embryo becomes an adult person, that single initial cell divided enough times to become 100 trillion cells!

  • In this Lesson, we're going to explore the basic structure and function of cells. We'll develop a better understanding of what cells are, then look at the two major classes of cells: prokaryotes and eukaryotes. We'll conclude by investigating several important tools biologists use to study cells.