GED Science Practice Test: Type of Cells

While all cells have certain structures in common (like the plasma membrane and the cytosol), categories of cells do differ in their structure in certain key ways.  One way to classify cells is by their complexity in terms of how their genetic material (DNA) is contained or stored.  Prokaryotic cells have genetic material that floats free in the cytoplasm. In fact, all of the contents of the cells of prokaryote organisms are contained within the cytoplasm. Eukaryotic cells have genetic information that is contained within a membrane-bound nucleus. The word “eukaryote” literally means true (eu-) nucleus (karyo). Eukaryotes have other membrane-bound organelles, which serve very specific functions. Prokaryotic cells lack many of these membrane-bound organelles, and instead, their cell functions mostly take place within the cytosol. Prokaryotes are typically single-celled organisms, such as bacteria.  For this reason, prokaryotes also contain a cell wall, located outside of the plasma/cell membrane, which provides some structural support to the cell. Below is a picture that demonstrates the relative simplicity of prokaryotic cells when compared to eukaryotic cells:


Eukaryotic cells possess membrane-bound organelles, some of which are described below:


Another way to categorize cells in order to understand their structure is to differentiate eukaryotic cells into plant and animal cells. Obviously, plant cells are found in plants, and animal cells are found in animals. Plant cells have additional organelles that animal cells do not have, such as cell walls and chloroplasts.  Cell walls are found outside of the plasma membrane, and serve to provide additional structure and support to a plant cell.  Chloroplasts are green structures, where photosynthesis takes place.  In addition to having a few extra organelles and structures, some structures within a plant cell are different than those in animal cells.  For example, vacuoles in plant cells tend to be much larger, also helping to support the structure of plant cells with water pressure.  The following diagram shows some of the differences between plant and animal cells:



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