All living things are made of cells. Unicellular organisms exist as one single cell while multicellular organisms are made of many cells. Just like the buildings in a city, the cells of a multicellular organism are not all the same. Each is specialized, meaning it has a specific function and a structure that matches its function. These cells have the same DNA as all of the other cells, however, only specific genes are "turned on" allowing them to differentiate.
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All of the cells in a single organism are not the same. Humans are to large to function with only one type of cell. Having specialized or differentiated cells allow an organism to delegate functions to specific cells or parts of the body. Just like how in a small town, one building can serve multiple purposes, but in a large city, their are individual buildings or offices for each city function.
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Specialized plant cells are different based on their "job." In the roots of a plant, root hair cells have a large surface area in order to absorb as much water and nutrients as possible through cell transport. Throughout the plant, acting as its circulatory system, xylem cells are specialized to transport water from the roots to the leaves of a plant and phloem cells are specialized to transport glucose and oxygen to from the leaves to the rest of the plant. In the leaves, guard cells are specialized to take in carbon dioxide, release oxygen, and prevent water loss. The outermost layer of the leaf has palisade cells which, have lots of chloroplasts to help the use the sun's energy to make food since, these cells receive the most sunlight.
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Specialized human cells include cells that provide protection, cells that send and receive messages, cells that provide structure, cells that fight infection, cells that provide movement, cells that do a lot of cell transport, and cells used in reproduction among other functions. Each forms from a different germ layer of the original gastrula as shown above.
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Stem cells are undifferentiated cells that can differentiate to become any cell in the organism. In mammals, there are two types of stem cells; embryonic stem cells and adult stem cells.
Embryonic stem cells are found in the blastocyst which is a ball of cells that occurs during human development about 4-5 days after fertilization. Because these cells are undifferentiated, they have to potential to become any human body cell. Futrther along during developement, this is precisely what happens naturally; that ball of cells becomes bones, blood, muscles, nerves, etc.
Scientist can extract some of these cells from a living blastocyst or living embryo (further along in developement) and use them to create new cells, tissues, and organs for a person. Stem cells can also be taken from the umbilical cord after a child is born. |
Adult stem cells are found in the bone marrow. The body is constantly replacing damaged cells. Having undifferentiated cells can allow the body to produce more specialized cells that cannot reproduce on their own. For example, red blood cells do not have a nucleus, so they are constantly produced by the bone marrow. When you break a bone, the undifferentiated stem cells can replace the broken bone cells.
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