LS2_Ch4Outline - Chapter 4: Cells: The Working Units of...

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Chapter 4: Cells: The Working Units of Life 4.1: What features of cells make them the fundamental unit of life? Cell theory: - Cells are the fundamental units of life. - All organisms are composed of cells. - All cells come from preexisting cells. I. Cell size is limited by the surface area-to-volume ratio A. Small cell size is a practical necessity arising from the change in the surface area-to-volume ratio of any object as it increases in size. 1. Volume : determines amount of chemical activity a cell carries out per unit of time. 2. Surface area : determines amount of substances a cell can take in from outside environment and waste products it can release to the environment. B. Cells must be small in volume to maintain a large enough surface area-to-volume ratio and ideal internal volume. 1. Chemical activity, rate of waste production, and need for resources increases faster than surface area in a growing cell. 2. Smaller cells distribute substances within themselves more easily. II. Microscopes are needed to visualize cells A. Resolution: distance apart two objects must be in order for the eye to distinguish them as separate. 1. Human eye: ~0.2 mm. B. Microscopes : improve resolution to see cells and their internal structures. 1. Light microscope : uses glass lenses and visible light to form a magnified image. a. Resolution: ~0.2 m or 1,000x human eye. 2. Electron microscope : uses electromagnets to focus an electron beam where electrons are being directed at a fluorescent screen or photographic film to create a visible image. a. Resolution: ~0.2 nm or 1,000,000x human eye. III. Cells are surrounded by a plasma membrane A. Plasma membrane: surrounds each cell separating it from its environment to create a segregated compartment. 1. Composed of a phospholipid bilayer : hydrophilic heads of lipids (embedded with proteins and other molecules) face cell’s aqueous interior on one side of the membrane and extracellular environment on the other. 2. Allows cell to maintain a constant internal environment ( homeostasis ). 3. Acts as a selectively permeable barrier by regulating what substances enter and leave the cell. 4. Is the cell’s boundary with the outside environment important in communication with adjacent cells and receiving signals from the environment . 5. Has protruding proteins that are responsible for binding and adhering to adjacent cells . IV. Cells are prokaryotic or eukaryotic A. Prokaryotes: organisms in domain Archaea and Bacteria. 1. Have in common a prokaryotic cell organization. 2. Do not typically have membrane-enclosed internal compartments. B. Eukaryotes: members in domain Eukarya (protists, plants, fungi, animals). 1. Eukaryotic cell organization. 2.
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This note was uploaded on 05/07/2008 for the course LIFESCI 2 taught by Professor Pires during the Spring '08 term at UCLA.

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LS2_Ch4Outline - Chapter 4: Cells: The Working Units of...

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