Modern Cell Theory

 The smallest units of life, cells, are described by the Modern Cell Theory. It is composed of several points, such as that all living things are composed (made) of a cell (single-celled) or multiple cells (multicellular). Secondly, a cell is the most basic complete unit within living organisms, and it is made from atoms of different elements that combined to make molecules. Next, every existing cell comes from older cells that reproduced. Finally, cells perform the functions that sustain life. In the case of a single-celled organism, the cell may belong to one of two categories, prokaryote or eukaryote. If a cell is a prokaryote, then the cell is much simpler, and it will not have a nucleus. A eukaryotic cell, on the other hand, does have a nucleus, along with other organelles that help the cell to function.



Parts of the cells
The cell membrane is the thin skin that controls what goes in and out of the cell, such as food and waste products. In the case of plant cells, the cell membrane is supported and protected by a cell wall. Any items inside the cell are surrounded by a liquid gel material called cytoplasm. These items include the organelles that perform the cell’s functions, such as chloroplasts in plants, which gather energy from the sun for photosynthesis, mitochondria, which act as “power plants” in cells, and the endoplasmic reticulum, which works to fold and move proteins in the cells. Other examples are the Golgi complex, which sorts and packages proteins like a post office, the vacuole, which works to store and transport materials, as well as make sure the right amount of water is in the cell, the lysosomes, which digest some items and get rid of waste products. Around the center of the cell is the nucleus, which is surrounded by the nuclear membrane. The nucleus contains most the cell’s DNA, which is the genetic material that acts as the recipe with which the cell was made, and from which new cells will be made. Other organelles are the centrioles, which work to keep the cell organized by forming spindles when a cell divides, the nucleolus, an organelle inside the nucleus that prepares the RNA that acts as the recipe for ribosomes, which produces protein for the cells.

Looking at cells
In order to see most kinds of cells, you need to use a microscope, which is a tool that makes small items easier to view. When teaching students about Life Science (Biology), one way to teach students to use a microscope is to take a sample of water from a pond or lake and observe the tiny organisms that are swimming in the water. An example of a much larger cell is the yolk, or yellow part of an egg. The largest single cell is the yolk of an ostrich egg, which is about the size of a baseball.

Working together
When a group of cells that work together to perform the same task are tissues. If two or more tissues work together, they form an organ. For example, groups of cells work together to form epithelial tissue, which is what the body’s largest organ, skin, is made from. A collection of organs and tissues that are working together create an organ system. Continuing with the skin example, the integumentary system include that organ along with other parts of the body that help protect it from wear and tear.

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