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2: Cellular Level of Organization
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2.1: Introduction to the Cellular Level of Organization
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The human body consists of trillions of cells, all derived from a single fertilized egg cell. Through the process of mitosis and differentiation, this single cell becomes many specialized cells that all work together to carry out the functions of human life.
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2.2: The Cell Membrane
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All living cells in multicellular organisms have a surrounding cell membrane. This cell membrane provides a protective barrier around the cell and regulates which materials can pass in or out.
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2.3: The Cytoplasm and Cellular Organelles
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The intracellular components of a cell, that is the materials contained inside the cell membrane, can vary drastically from cell to cell depending on their function. A prototypical cell can be studied to learn about all of the internal components, and their functions, that may be found in a human body cell.
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2.4: The Nucleus
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The nucleus is the largest and most prominent of a cell’s organelles. The nucleus is generally considered the control center of the cell because it stores all of the genetic instructions.
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2.5: Cell Growth and Division
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Human body cells must constantly replace themselves when they become worn out (e.g. red blood cells), worn off (e.g. skin cells), or damaged. However, this process of replacement must be closely monitored, to avoid the replacement of too many cells too fast (which leads to cancer). The cell cycle is the sequence of events that a cell goes through in its lifetime, that ultimately leads to cell division.
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2.6: Cellular Differentiation
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How does a complex organism such as a human develop from a single cell—a fertilized egg—into the vast array of cell types such as nerve cells, muscle cells, and epithelial cells that characterize the adult? Throughout development and adulthood, the process of cellular differentiation leads cells to assume their final morphology and physiology. Differentiation is the process by which unspecialized cells become specialized to carry out distinct functions.