The region between the nucleus and the plasma membrane is the cytoplasm All the

The region between the nucleus and the plasma

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The region between the nucleus and the plasma membrane is the cytoplasm. All the material within the plasma membrane of a prokaryotic cell is cytoplasm. Within the cytoplasm of a eukaryotic cell are a variety of membrane-bound organelles of specialized form and function. These membrane-bound organelles are absent in prokaryotes. Eukaryotic cells are generally much bigger than prokaryotic cells. The logistics of carrying out metabolism set limits on cell size. At the lower limit, the smallest bacteria, mycoplasmas, are between 0.1 to 1.0 micron. Most bacteria are 1–10 microns in diameter. Eukaryotic cells are typically 10–100 microns in diameter. Metabolic requirements also set an upper limit to the size of a single cell. As a cell increases in size, its volume increases faster than its surface area. Smaller objects have a greater ratio of surface area to volume. The plasma membrane functions as a selective barrier that allows the passage of oxygen, nutrients, and wastes for the whole volume of the cell.
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The volume of cytoplasm determines the need for this exchange. Rates of chemical exchange across the plasma membrane may be inadequate to maintain a cell with a very large cytoplasm. The need for a surface sufficiently large to accommodate the volume explains the microscopic size of most cells. Larger organisms do not generally have larger cells than smaller organisms—simply more cells. Cells that exchange a lot of material with their surroundings, such as intestinal cells, may have long, thin projections from the cell surface called microvilli. Microvilli increase surface area without significantly increasing cell volume. Internal membranes compartmentalize the functions of a eukaryotic cell. A eukaryotic cell has extensive and elaborate internal membranes, which partition the cell into compartments. These membranes also participate directly in metabolism, as many enzymes are built into membranes. The compartments created by membranes provide different local environments that facilitate specific metabolic functions, allowing several incompatible processes to go on simultaneously in a cell. The general structure of a biological membrane is a double layer of phospholipids. Other lipids and diverse proteins are embedded in the lipid bilayer or attached to its surface. Each type of membrane has a unique combination of lipids and proteins for its specific functions. For example, enzymes embedded in the membranes of mitochondria function in cellular respiration. Concept 6.3 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes The nucleus contains most of the genes in a eukaryotic cell.
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