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The first cells were not specialized • Organisms were unicellular Cell Specialization • The cell performed all cell functions Multicellular organisms have specialized cells • Each cell has a specific job • Cells have special shapes and structures that relate to function This cell has to get its energy, get rid of its waste, reproduce, make everything it needs to make, regulate everything it needs to regulate, and do everything! All by itself! Think of an analogy to compare and contrast unspecialized and specialized cells. This cell is specialized to do one job. This is a neuron – it receives and sends messages. Notice the long thin extensions – these help connect this cell to other cells so that they can communicate with each other. How do you get from one cell to a multi-cellular animal? An organism starts off as one cell. That cell divides by mitosis during development. If all of the cells expressed all of the genes in the DNA, the organism would grow up to be a blob. But it doesn’t… Fully developed Sea Urchin See… its already starting to look like something… Specialized cells develop from unspecialized STEM CELLS When a cell divides, the new cells don’t get the same stuff Each cell gets different chemicals & cells can affect their neighbors When a cell gets its job (becomes specialized), some genes are turned on in that cell and others are turned off. Not specialized Your Turn - Write in Your Notebook: • How are unicellular organisms different from multi-cellular organisms? Not specialized yet… • How do cells in multi-cellular organisms become specialized? Specialized! • What is the advantage of being multicellular? The “on” genes make their proteins which give the cell its special structures Cells are arranged to form multicellular organisms For now, tell me how you think this structure is related to its function: • Tissues – made of cells working together – Skin – Connective – Muscle • Organs – made of tissues working together – Heart – Lungs – Stomach This is a crosssection of your intestines. • Organ systems – made of organs working together – Digestive system – Endocrine system – Circulatory system • Organism – made of organ systems working together – Human What about this: This is the lining of your wind pipe (trachea) What about this? How does structure relate to function? These cells transport water through a plant (remember xylem?)