Life in multicellular organisms begins as a single cell and develops into about 100 trillion cells. These cells are responsible for everything from weight to shape to movement. Information necessary for an organism to develop is contained in the single cell. A typical cell can be compared to a factory. Each worker in the factory has a specific job and like a factory, the cell performs many functions so it is organized so that each part carries out a different function. The specialized areas found throughout the cytoplasm of a cell are called organelles. “ The organization of cell parts for specific jobs is known as division of labor- each part carries out its own functions. However it depends on other parts as well. The cell operates and survives only if all parts work together”(4)
Most cells have similar characteristics. The outer covering of an animal cell is the cell membrane and the outer covering of a plant cell is the cell wall, inside which is the membrane. The membrane’s job is to provide protection and support for the cell. It also contains tiny openings, which control the amount of materials, which enter and leave the cell. Everything the cell needs or needs to get rid of must enter or leave here. The nucleus (which will be discussed in greater detail) is a large structure found in the center of the cell. This structure controls all of the cell’s activities. It also contains chemical substances that determine the inherited characteristics of the cell. The cytoplasm is the area of the cell between the cell membrane and the nucleus. Although jellylike and consisting of about 70% water it contains proteins, sugars, starches, fats, salts, vitamins and minerals which interact with each other. This is the site of metabolism and the site where organelles are stored. Within the cytoplasm lies the endoplasmic reticulum, which are tubular passageways serving as a transportation system for protein delivery. Ribosomes, which are found on the endoplasmic reticulum, are the protein making sites for RNA. Once the protein is made, it is then delivered to other cell parts via the endoplasmic reticulum. The golgi apparatus is where proteins made by ribosomes are delivered to needed areas. Other structures, which supply energy to the cell, are called mitochondria. These constructs break down sugars into water and carbon dioxide causing the release of energy. They are often called “the powerhouse of the cell” (5). Large fluid filled sacs also are floating in the cytoplasm. These storage bins for food and other materials are called vacuoles. Small structures called lysosomes contain enzymes, which help in the digestion of certain food molecules and the removal of undigested wastes.
The cell needs a number of different molecules to work efficiently. Nucleic acids DNA and RNA are the cell’s blueprints carrying all information for inheritance. Proteins serve as enzymes that run chemical reactions in cells. They are built from smaller molecules called amino acids. Carbohydrates provide the fuel supply for the cell. They include glucose, sucrose, fructose, starch and cellulose. Lipids, which are found in fats and oils, help the cell store energy for future use and are a major component of membranes.
Growth is one of the basic characteristics of all living things and cells begin to grow by reproducing and dividing. The process of producing new cells occurs during cell division. During this process one cell divides into two cells, which are called daughter cells, identical to the other and to the parent cell. This happens in a series of 6 phases. Phase one is called interphase. During the beginning of this phase, the cell is performing all functions except the division. This stage is where chromosomes are copied. Phase two, called prophase, is where mitosis begins. The nucleus divides into two nuclei and the formation of two new daughter cells begins. Phase three, metaphase, is the phase where chromosomes attach to a meshlike spindle at the center of the cell. Phase four, the point at which the chromosomes begin to separate is called anaphase. Phase five is the telophase stage. Here two new nuclei form and mitosis is completed. However cell division goes through a sixth phase called cytokinesis, which is the division of the cytoplasm and the formation of two new daughter cells.
As stated earlier, the nucleus is the control center of the cell and the site of the structures, which determine chemical characteristics. These structures, called chromosomes, are visible during the cell’s reproductive phase. Forty-six chromosomes are found in humans - 22 matched pairs and 2 sex chromosomes. Each chromosome is made up of either a single or double cord of DNA, deoxyribonucleic acid, the molecule containing the genetic instructions for making protein. Genes are located on the chromosomes. After cell division chromosomes are copied and passed on to offspring. The science, which studies how these traits are passed from parent to offspring, is called genetics.