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Earlier in this SparkNotes, we described several types of organelles that exist within eukaryotic cells. This system of organization within the cell is termed compartmentalization. Compartmentalization enables the cell to isolate different cellular processes and enzymatic reactions, allowing them to occur simultaneously and within specialized environments. For instance, energy production occurs in mitochondria, protein and lipid synthesis occurs in the endoplasmic reticulum, and photosynthesis occurs in chloroplasts. Since these organelles are bound by internal membranes, they can regulate the entry and exit of molecules just like the plasma membrane does for the cell as a whole. This selective permeability creates controlled environments in each organelle. This is beneficial as some processes operate more efficiently in environments with specific solute concentrations, certain ions present, or pH levels. Internal membranes also increase the surface area where some reactions can occur. For example, the many folds of the inner membrane of a mitochondrion, allow for more reactions to take place and more ATP synthesized. The organization also separates processes that may interfere with one another, such as protein synthesis and degradation.
