BackA Tour of the Cell: Structure, Function, and Microscopy
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Chapter 6: A Tour of the Cell
Cells: The Fundamental Units of Life
Cells are the basic structural and functional units of all living organisms. Despite their diversity, all cells share certain fundamental characteristics that allow them to perform the essential functions of life.
Definition of a Cell: The smallest unit of life that can carry out all life processes.
Origin: All cells arise from pre-existing cells by division.
Common Features: All cells have a plasma membrane, cytoplasm, genetic material (DNA), and ribosomes.
Internal Organization: Eukaryotic cells contain internal membranes that compartmentalize functions, allowing for specialized chemical reactions.
Energy and Matter Transformations: Organelles such as mitochondria and chloroplasts convert energy into usable forms (e.g., ATP, chemical energy).
Interactions with the Environment: The plasma membrane controls the movement of substances in and out of the cell.
Example: Plant cells have a rigid cell wall in addition to the plasma membrane.
Concept 6.1: Biologists Use Microscopes and Biochemistry to Study Cells
Understanding cells requires specialized tools, including various types of microscopes and biochemical techniques.
Microscopy: The use of microscopes to visualize cells and their components.
Magnification: The ratio of an object's image size to its real size.
Resolution: The measure of the clarity of an image; the minimum distance two points can be separated and still be distinguished as separate points.
Contrast: The visible differences in brightness between parts of the sample.
Scale: Cells and their components vary greatly in size, from atoms and small molecules to entire cells (see diagram for scale of biological structures).
Types of Microscopy
Light Microscopy (LM): Visible light passes through a specimen and then through glass lenses. The lenses refract (bend) the light so that the image is magnified. Useful for viewing live cells and tissues.
Electron Microscopy: Uses beams of electrons for much higher resolution imaging.
Scanning Electron Microscopes (SEMs): Focus a beam of electrons onto the surface of a specimen, providing detailed 3-D images of the surface.
Transmission Electron Microscopes (TEMs): Pass a beam of electrons through a thin section of a specimen, revealing detailed internal structures.
Example: SEM images show the 3-D surface of cells, while TEM images show the internal ultrastructure.
Microscope Type | Principle | Best For | Example Image |
|---|---|---|---|
Light Microscope (LM) | Visible light passes through specimen | Live cells, tissues | Cell shapes, nuclei |
Scanning Electron Microscope (SEM) | Electron beam scans surface | 3-D surface structure | Cell surface, cilia |
Transmission Electron Microscope (TEM) | Electron beam passes through thin section | Internal cell structure | Organelles, membranes |
Key Formulas
Magnification:
Additional info:
Biochemical techniques such as cell fractionation are also used to study cell components by separating them based on size and density.
