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Anatomy of an Analogy
The membrane of a cell has a similar function to our skin. It keeps the cell's interior on the inside and protects it from harm. A cell's membrane is different from ours in that it is much simpler, and is capable of absorbing nutrients through the entirety of its surface. Human skin is too thick to allow materials to cross its barrier, so we have a mouth to take in nutrients.
The nucleus of a cell functions much like our own brain.It commands the cell and the nucleolus produces ribosomes to execute the commands. This can be compared to the way our brains manipulate our bodies through signals sent down the spinal cord and nerves. The nucleus also contains the cell's genetic information in the form of DNA. Our brains, unlike the nucleus, are not essential to our reproduction, as you know if you have ever watched "Sixteen and Pregnant".
The cytoplasm is the medium in which all the organelles exist. It gives the cell structure and allows the cell to function efficiently. Without the ciytoplasm, the organelles would drift aimlessly, and would not be able to carry out tasks. Without our muscles, our organs would be useless blobs of tissue. Cytoplasm is a simple, but very necessary part of the cell.
The bones of the cell are its cytoskeleton, an internal structure of fibers. The cytoskeleton holds the cell together and promotes efficiency. The purpose of the cytoskeleton can be compared to the purpose of the heart. Just as the heart pumps blood around the body, carrying nutrients, oxygen and glucose, the cytoskeleton ensures that all the materials in the cell get where they are supposed to go. It provides structure and transportation.
The digestive system is a network of organs whose primary function is to obtain and deliver energy for the body to use. The entire gastro- intestinal tract, or alimentary canal, measures about thirty feet in length, but is tightly compressed inside the abdominal cavity. The mitochondria that produce energy for the cell are very similar. They have a very wrinkled inner membrane, allowing them to pack a lot of surface area into one small structure. The mitochondria process glucose to provide ATP, the energy that drives all the functions within the cell.
After it leaves the stomach, the food is delivered to the small intestine where lipids and proteins are processed and absorbed. The intestines are lined with villi, tiny projections into the intestine that increase its surface area. The villi absorb nutrients and deliver them into the bloodstream and from there on to where ever they need to go. These villi may be compared to an organelle called the Golgi apparatus whose function is to package and send out vesicles to the rest of the cell.
Though digestion takes place in the alimentary canal, many organs contribute to the process. The liver breaks down toxins, the gallbladder helps digest lipids and the pancreas secretes enzymes to break down carbohydrates. The smooth endoplasmic reticulum can be compared to all these digestive accessories because its functions are varied, depending on where the cell is located in the body. Lysosomes can also be compared to digestive accessories because they contain enzymes that the cell uses in intracellular digestion.
The rough endoplasmic reticulum can be compared to the small intestine. The small intestine processes and absorbs protein, then transports the protein to the rest of the body where it can be used for a variety of different things. The rough ER manufactures proteins using the many ribosomes that are imbedded in its surface. The proteins it produces are then transported in vesicles to where they are needed.
The nucleolus is the primary and most essential structure inside the nucleus, kind of like the brain stem and cerebellum are the most vital parts of the brain. The function of the nucleolus is similar to that of the pituitary gland. The pituitary gland produces chemicals that the body needs in order to perform essential functions.The nucleolus produces the ribosomes that the endoplasmic reticulum uses to synthesize proteins. Without the nucleolus, the cell would not be able to function.
Vacuoles are the orifices of the cell. They eject products from the cell including wastes and take in materials from the outside of the cell. They do not actively absorb or excrete, they merely contain and release.