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Specialized Cells • Cells can vary in the shape, size, and content. • Each type of cell is specialized to perform a different function. • Structure determines function. Nerve Cells or Neurons • Neurons are cells of the nervous system and are specialized to carry "messages" through an electrochemical process. Neurons are similar to other cells in the body because: • Neurons are surrounded by a cell membrane. • Neurons have a nucleus that contains genes. • Neurons contain cytoplasm, mitochondria and other organelles. • Neurons carry out basic cellular processes such as protein synthesis and energy production. Neurons differ from other cells in the body because: • Neurons have specialize cell parts called dendrites and axons. Dendrites bring electrical signals to the cell body and axons take information away from the cell body. • Neurons communicate with each other through an electrochemical process. Nerve Cell Sperm Cell • A sperm cell is the male reproductive cell that carries the male portion of chromosomes, DNA or hereditary information to be fused with the female egg, or ovum. • The sperm cell is composed of three main parts: the head, middle piece and tail. Parts • The head contains enzymes near the tip, used to penetrate the egg; contains the nucleus and all hereditary information needed to successfully reproduce once the sperm cell has fertilized an egg. • The middle piece contains mitochondria which provides energy to move the cell. • The flagellating tail propels the sperm cell. Sperm Cell Guard Cell • Guard cells are cells surrounding each stoma in plants. They help to regulate the rate of transpiration by opening and closing the stomata. Guard Cell Xylem and Phloem • Vascular tissue in plants; contain several types of specialized cells. • Xylem – made up of tracheid and vessel elements, carry water from the roots to the rest of the plant • Phloem – made up of sieve tube elements and companion cells; transports food Xylem and Phloem • Multicellular organisms begin as undifferentiated masses of cells • Variations in DNA expression and gene activity determine cell specialization • During differentiation, only specific parts of DNA are activated which determine the function and specialized structure of a cell • All cells contain the same DNA; all cells have the potential to become any type of cell • Depends on the genetic instructions • Stem cells – unspecialized cells which can differentiate into other types of cells (can be manipulated in laboratories under the right conditions) • Stem cells→DNA→cell differentiation→specialized cells