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Cytoplasm - Filling Fluid

Cytoplasm is the fluid that fills a cell. Scientists used to call the fluid protoplasm. Early on, they didn't know about the many different types of fluids in the cell. There is special fluid in the mitochondria, endoplasmic reticulum, Golgi apparatus, and nucleus. The only two 'plasms' left are cytoplasm (the fluid in the cell also called cytosol) and nucleoplasm (the fluid in the nucleus). Each of those fluids has a very different composition.

The cell organelles are suspended in the cytosol. You will learn that the microfilaments and microtubules set up a "skeleton" of the cell and the cytosol fills the spaces. The cytoplasm has many different molecules dissolved in solution. You'll find enzymes, fatty acids, sugars, and amino acids that are used to keep the cell working. Waste products are also dissolved before they are taken in by vacuoles or sent out of the cell.

Special Fluids in the Nucleus

Nucleoplasm has a little different composition. Nucleoplasm can only be found inside of the nucleus. It doesn't have big organelles in suspension. The nucleoplasm is the suspension fluid that holds the cell's chromatin and nucleolus. It is not always present in the nucleus. When the cell divides, the nuclear membrane dissolves and the nucleoplasm is released. After the cell nucleus has reformed, the nucleoplasm fills the space again.

More than Filling

The cytosol in a cell does more than just suspend the organelles. It uses its dissolved enzymes to break down all of those larger molecules. The products can then be used by the organelles of the cell. Glucose may exist in the cytosol but the mitochondria can't use it for fuel. The cytosol has enzymes that break glucose down into pyruvate molecules that are then sent to the mitochondria.

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