Cytoplasmic organellesĬytoplasmic organelles are "little organs" that are suspended in the cytoplasm of the cell. Within the cytoplasm, materials move by diffusion, a physical process that can work only for short distances. All of the functions for cell expansion, growth and replication are carried out in the cytoplasm of a cell. It provides a platform upon which other organelles can operate within the cell. The cytoplasm is the gel-like fluid inside the cell. The nucleus determines how the cell will function, as well as the basic structure of that cell. The nucleolus is a dense region of ribonucleic acid ( RNA) in the nucleus and is the site of ribosome formation. Threads of chromatin in the nucleus contain deoxyribonucleic acid ( DNA), the genetic material of the cell. The nucleus, formed by a nuclear membrane around a fluid nucleoplasm, is the control center of the cell. Proteins in the cell membrane provide structural support, form channels for passage of materials, act as receptor sites, function as carrier molecules, and provide identification markers. The cell membrane is a double layer of phospholipid molecules. All materials within a cell must have access to the cell membrane (the cell's boundary) for the needed exchange. It maintains the integrity of a cell and controls passage of materials into and out of the cell. The cell membrane separates the material outside the cell, extracellular, from the material inside the cell, intracellular. Cell membraneĮvery cell in the body is enclosed by a cell ( Plasma) membrane. Within the cytoplasm lie intricate arrangements of fine fibers and hundreds or even thousands of miniscule but distinct structures called organelles. A cell consists of three parts: the cell membrane, the nucleus, and, between the two, the cytoplasm. It includes features from all cell types. For descriptive purposes, the concept of a "generalized cell" is introduced. There are many different types, sizes, and shapes of cells in the body. Today's biologists know that cells are infinitely more complex than this. Early biologists saw cells as simple membranous sacs containing fluid and a few floating particles. Ideas about cell structure have changed considerably over the years.
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