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c. Gap junctions

Gap junctionsform channels between cells that allow the movement of ions and molecules from one to the other. (Similar to plasmadesmata).

B.Tissues

Tissuesare made of cells grouped together to form functional unit

1. Epithelium

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An epitheliumis a sheet of cells. Epithelia are classified based on the shape of the cells and the number of layers. Epithelia are found at the boundarybetween one compartment and another, for example between the inside of you and the outside world. They are generally linked to their neighbors by tight junctions, so they can form a selective barrier(like the endodermis) that restricts the passage of substances. In many cases, they are polarized, with apical and basolateral compartments that have different functions. Epithelial cells generally lay down a thick ECM along one surface that is known as a basement membrane. The lining of your lungs and intestines, and your skin are all epithelia.

a. Boundary b. Barrier c. Polarized d. Basement membrane

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1*. Cells that line ducts

The cells that line the insides of ducts are also consided epithelia.