![]() ![]() Some other cells also have cell walls, but they are generally made of different materials. The cell wall keeps plant cells from bursting. Under healthy conditions for plant cells, the central vacuole is large and produces turgor pressure against the cell wall, which is located outside the cell membrane. Often, other organelles found in plant cells are located adjacent to the plasma membrane because the central vacuole takes up so much space within the cell. The central sap vacuole often occupies a large space within the cytoplasm of plant cells, but may be small or absent in other types of cells. Other kinds of plastids include chromoplasts, which contain pigments other than chlorophyll, and amyloplasts which store starch. ![]() The green pigment, chlorophyll, is located in special photosynthetic plastids called chloroplasts. Some organic compounds are produced and stored in plastids. Plastids are organelles found in plants and algae. These organelles are roughly the size of many bacteria and can only be seen at higher magnifications in specially prepared slides. The minute “power-plants” in the cytoplasm of cells are called mitochondria. It contains fluid, ribosomes, the cytoskeleton, and, in eukaryotes, other membrane-bound organelles. The cytoplasm is the region of the cell outside the nucleus. When stained, the nucleus appears darker than the surrounding cytoplasm. The nucleus in living cells is sometimes indistinguishable from the cytoplasm unless the cell is stained. This chromosome, which may be visible as a dark spot in the nucleus, is called a Barr body. An exception is one inactivated and condensed chromosome in female mammals. When cells are not dividing, chromosomes are seen as chromatin. Chromosomes can be seen only after special staining procedures applied to dividing cells. The nucleus also contains a number of structures called chromosomes, which are composed of DNA and proteins. Ribosomal RNA (rRNA) is transcribed within the nucleolus. In some stained preparations the nucleus may contain one or more darker-stained bodies, the nucleoli (singular-nucleolus). In eukaryotes, DNA is located within the nucleus whereas, prokaryotes lack a nucleus. Eukaryotic cells are compartmentalized by membrane-bound organelles with specialized functions. Prokaryotic cells lack a nucleus and membrane-bound organelles. While there are several characteristics that are common to all cells, such as the presence of a cell membrane, cytoplasm, DNA and ribosomes, not all cells are the same. Cells Lab from Lumen Learning IntroductionĬells are the fundamental unit of life. ![]()
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