THE CELL

🦠The cell is the fundamental unit of biological life-the common denominator of all living things. Any structure in the body more complex (e.g., bigger) than a cell is simply a collection of cells. Together, cells form tissues, tissues form organs, organs form organ systems, and organ systems combine to form an organism.

🦠A cell is the anatomical sum of its parts. The parts involved in some basic task necessary for cell operation are called organelles. The parts that are products of cellular metabolism are called inclusions. Organelles and inclusions are made up of organic chemical compounds. The following classes of organic compounds are found in the cells: nucleic acids, proteins, lipids (fats), carbohydrates, and conjugated compounds. Inorganic compounds found in cells are generally salts, such as sodium chloride, potassium chloride, and calcium nitrate.

🦠The cell is "ruled" by the nucleus, which is surrounded by a porous membrane. It is the administrative center in which the metabolic and synthetic activities of the cell are organized, initiated, and directed. The "blueprint" of every cell is the DNA (deoxyribonucleic acid) and this determines the size, shape, and function of a cell.

The outer part of the structure is the cell or plasma membrane. Each cell takes in substances with a cellular process called endocytosis through its membrane to form a vacuole. Exocytosis is a process by which a cell transports secreted material through the cytoplasm (the fluid that fills the cells) to the cell/plasma membrane.

🦠The nuclear membrane encloses the nucleus of the cell, and also connects the inner membrane with the outer membrane.

🦠The nucleoplasm is a type of protoplasm, and is enveloped by the nuclear membrane. The nucleoplasm includes the chromosomes and nucleolus. The nucleolus, a round body located inside the nucleus, makes ribosomal subunits from proteins and ribosomal RNA, also known as rRNA. These rounded bodies, known as ribosomes, are derived from RNA of the nucleolus and are distributed throughout the cytoplasm.

🦠Within the cytoplasm there is a network of tubules known as the endoplasmic reticulum, believed to serve as a mechanism for the movement of materials through the cell. They may be of a smooth or rough nature. The Golgi Complex (when the endoplasmic reticulum is near a complex of tubules and vesicles) is believed to receive newly synthesized protein from the endoplasmic reticulum and concentrate, package, store, and release it for final discharge in membrane-lined containers called vesicles or vacuoles. The secretory material in vesicles is moved through the cytoplasm to the free (unattached) border of the cell where, between fingerlike extensions (microvilli and microfilament) of the plasma membrane, it is released. These microvilli and microfilaments serve to increase the absorptive surface of the cell.

🦠Foreign matter that crosses the cell membrane is met by lysosomes, which contain digestive materials and aid the cell in removing the unwanted particles.

🦠Centrioles are shaped like small barrels. They are found in the cytoplasm in pairs. Their main function is to help with cell division, or mitosis. The centrioles help in the formation of the spindle fibers that separate the chromosomes during mitosis.

🦠The energy for all cell activity comes from the structures called mitochondria (mitochondrion, sing.) which are found close to the site of any energy-consuming activity. Mitochondria are complex in organization and the site of enzymatic activity. They are the powerhouse of the cell and are responsible for cellular respiration and production. The mitochondria act like a digestive system that takes in nutrients, breaks them down, and creates energy-rich molecules for the cell.

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