Cell: Basic unit Tissue: Group of cells –4 types Organ: Groups of tissue –Ex: lung contains each tissue Organ System: Group of organs working together –Digestive System Organism: all organ systems working together Muscle Tissue Contracting cells Skeletal, cardiac cells Connective Tissue Support the body Bone, fat, tendons Epithelial Tissue protection sheet of cells skin, stomach lining Nerve Tissue Transmit electric signals Brain & Spinal Cord

Zygote: fertilized cell created by the union of the egg and sperm Embryonic stem cells –Created during earliest divisions –Potential to become any type of cell Average human: –100 trillion cells –Over 200 types of human cells

Determination –Stem cell genes program the cell to be a specific type –Few weeks into development –Irreversible

Differentiation –Cells acquire the structures & functions of a specialized cell –Specific genes activated

Quick Questions Do your muscle cells have the same DNA as your skin cells? Yes Do your skin cells have the same DNA as your brain cells? Yes Do your brain cells have the same DNA as your liver cells? Yes So if all your cells have the same DNA, how do they know to do different jobs? Stay tuned for the answer

Stem cell programmed to become a muscle cell Stem cell programmed to become a nerve cell How will the top cell know to become a muscle cell…and the bottom to become a nerve cell if they have identical genes? Gene AGene BGene CGene DGene EGene FGene G Gene AGene BGene CGene DGene EGene FGene G If they have the same genes…how does one become a muscle and the other a nerve?

Stem cell programmed to become a muscle cell Stem cell programmed to become a nerve cell ON During “differentiation”, certain genes are activated in some cells, but deactivated in others. Gene AGene BGene CGene DGene EGene FGene G Gene AGene BGene CGene DGene EGene FGene G Remember that genes tell cells to create proteins. Muscle cells create different proteins from nerve cells based on the genes that are active and these proteins are what help the cell carry out their functions.

Programmed cell death (apoptosis) between the fingers

Webbed Toes

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1)What is a zygote? 2)What is the specific function of a stem cell? 3)How does “determination” differ from “differentiation”? 4)Cells are programmed to die during a process called ______. 5)From smallest to largest, name the 5 levels of organization. 6)Name the four types of tissues. 7)Which tissue is able to stretch and contract? 8)Which tissue transmits electric signals? 9)Which tissue covers and protects the body? 10)Which tissue connects the body?