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Endocytosis and Exocytosis
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If cells are alive, do they eat? Cells are the fundamental units of life and exhibit the same properties as multicellular organisms. Individual cells reproduce and maintain a fairly constant internal environment. They also take in energy and nutrients and excrete waste. Cells in a multicellular organism generally transport individual molecules across the cellular membrane to accomplish the equivalent of eating and excretion. However single celled organisms may not encounter food in the form of individual molecules. Therefore cells have evolved mechanisms for moving objects larger than individual molecules across cellular membranes. The mechanisms are endocytosis and exocytosis for moving material into and out of cells, respectively.

View the animation below, then complete the quiz to test your knowledge of the concept.






1Exocytosis is a process by which cells
A)release substances from the cell through pores in the cell membrane.
B)release substances from the cell via vesicles.
C)release substances from the cell via carrier proteins.
D)bring in substances from the outside via vesicles.
E)bring in substances from the outside via pores in the cell membrane.



2Certain white blood cells engulf microorganisms and bring them in to digest them. This process is best described as
A)pinocytosis.
B)osmosis.
C)receptor-mediated exocytosis.
D)phagocytosis.
E)diffusion.



3Which of the following statements about receptor-mediated endocytosis is TRUE?
A)it is used to transport material out of the cell
B)it is not specific
C)it involves clathrin-coated pits
D)it involves transport of material into the cell through pores in the cell membrane
E)none of the above



4If the material the cell takes in is liquid, the process is termed pinocytosis.
A)True
B)False



5Low-density lipoprotein is brought into the cell by receptor-mediated endocytosis.
A)True
B)False







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