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CELL DIFFERENTIATION Cell differentiation: The process by which an undifferentiated cell reaches its specialized function. It occurs during histogenesis. Cell differentiation is stable. Most differentiated cells cannot transform into other cell types (it can happen during regeneration). As cell division proceeds, the cells not only increase in number but also undergo differentiation becoming specialized in structure and function. In the development of most multicellular organisms, a single cell (fertilized egg) gives rise to many different types of cells, each with a different structure and corresponding function. CHARACTERISTICS OF CELL DIFFERENTIATION There are four characteristics of cell differentiation. They are: 1. It is stable phenomenon 2. It is induced by specific stimuli 3. It precede morphological difference 4. It is controlled by genetic factors 1. It is stable phenomenon • One of the principle characteristics of cell differentiation in higher cells is that once established, the differentiated state is very stable and can persist throughout many cell generations. For example, a neuron will persist as such throughout the lifetime of an individual. 2. It is induced by specific stimuli • Another important characteristic of cell differentiation is that it is induced in the organism by various stimuli but once it has been established, it can persist even in the absence of the initial stimulus. For example, differentiated cloned cell lines, such as steroid-secreting cell lines are able to grow indefinitely in vitro. The differentiated state is maintained over many cell generations. 3. It precede morphological difference • In many cases before morphological difference appears, the cell is committed to a particular change due to cell differentiation process. 4. It is controlled by genetic factors • Genes (genetic factors) enacted crucial role in controlling and executing cell differentiation process. Key Concept • As multicellular organisms develop, their cells differentiate (change & separate) and form levels of organization • Why it Matters: so Humans (we are multicellular) can have different kinds of cells, tissues, organs, and organ systems Cells • Are the simplest form of life • Chemical elements organized into cells become living matter. • All organisms are made-up of cells • All the substances of an organism are the products of its cells. • The number of cells from any organism ranges from one to trillions. • However, even the most complex organisms have a relatively small (~200) catalog of differentiated cell types with specialized function (bone, muscle, nerve). Life is Cellular – – Some things are only one cell (unicellular) Some have many cells (multicellular) Unicellular Organisms may be Prokaryotic Eukaryotic Unicellular Organisms • “uni-” = one • Prokaryotes are unicellular organisms • Some algae, some protists, and some eukaryotes (yeasts), are unicellular • Can still do everything they need to stay alive • Benefits over multicellular organisms: – Need fewer resources – Can live in harsher conditions Multicellular Organisms • “multi-” = more than one • Plants, animals, some protists, and most fungi are multicellular • Start as a single cell many cells cells differentiate (change) into different types of cells cells group together •The fertilized egg gives rise to a large number of cells through cell division, but the process of cell division alone could only lead to increasing numbers of identical cells. Multicellular organisms depend on interactions among different cell types. CELL TISSUE stem shoot system leaf vascular tissue ORGAN lateral roots primary root root system • Tissues are groups of cells that perform a similar function. • Organs are groups of tissues that perform a specific or related function. • Organ systems are groups of organs that carry out similar functions. SYSTEMS •Nearly all of the cells of a multicellular organism have exactly the same chromosomes and DNA. •During the process of differentiation, only specific parts of the DNA are activated; the parts of the DNA that are activated determine the function and specialized structure of a cell. Specialized cells perform specific functions. • Cells develop into their mature forms through the process of cell differentiation. • Cells differ because different combinations of genes are expressed. • A cell’s location in an embryo helps determine how it will differentiate. Outer: skin cells Middle: bone cells Inner: intestines Levels of Organization • • • • 1st Level: Cells 2nd Level: Tissues 3rd Level: Organs 4th Level: Organ Systems • Cells Tissues Organs Organ Systems Level 1 : Cells • Cells can be specialized (have a certain function) • Function = job • Function is related to the cell structure • Structure = how parts of the cell are put together – Shape – Material it’s made from • Structure of a brain cell is different from muscle cell Cells Continued • Cells occur in many different shapes and sizes so they can perform many different functions. Level 2: Tissues • Tissue = group of cells that work together to do a specific job • Ex: Heart muscle tissue is made of heart muscle cells • Animals have 4 types of tissue: nerve, muscle, connective, protective • Plants have 3 types of tissue : transport, protective, ground Level 3: Organs • Organ = structure that is made up of 2 or more tissues working together to get a specific job done • Ex: Stomach – muscle tissue moves food, special tissues make chemicals to digest food, connective tissue holds stomach together, nervous tissue sends messages back and forth between the stomach and brain Level 4: Organ Systems • Organ system = group of organs working together to perform a specific function • Each organ system has a specific job • Ex: Digestive system is made of several organs including the stomach and intestines Structure of Animals Cells -basic unit of an animal’s structure -become specialized _______________________________ Tissues -made of cells that work together to perform a specific function __________________________________________ Organs -made of different types of tissues that work together to perform a specific function ____________________________________________________ Organ Systems -made of organs that work together to perform a specific function _____________________________________________________________ Organisms •The various types of cells (such as blood, muscle, or epithelial cells) arrange into tissues which are organized into organs, and, ultimately, into organ systems.