Due to the fluid mosaic nature of membranes, cell membranes can fold outward or inward   and engulf particles or fluid droplets. These membranes can than pinch off  and form   vesicles with the particle or fluid inside. This process is called endocytosis.  Read the pages indicated  by B-5 and study behavioral objectives 4. In your notes draw figures showing endocytosis and write a paragraph comparing  three types of  endocytosis: pinocytosis, phagocytosis, receptor-mediated endocytosis. 
 

  
 
 
                              Contrast between the following processes. 
 

pinocytosis	phagocytosis	receptor- mediated endocytosis

 

 During pinocytosis the unit membrane simply folds inward forming small vesicles containing extracellular fluid which may merge together forming a water vacuole. Water vacuoles store water soluble molecules and provide a means for the cell to  control its turgidity (tightness of a cell due to the taking up of water). 

During phagocytosis solid  particles (living and nonliving ) are engulfed  into the cell's cytoplasm. Read the pages concerning the immune system and phagocytotic cells (B-5)  White blood cells (macrophages)  in your body move to a site of  infection  where in engulfs and digests  bacteria and foreign  material which enters your body.  The white pus which forms on an uncleaned cut is an accumulation of the white blood cells.  Cells lining your small intestine engulf  particles of  lipids located in the lumen of the intestine and hydrolyzes these into fatty acids and glycerol which can be transported  to other parts of the body via blood stream. 
 

Mediated  endocytosis  allows specific particles  (cholesterol, for example) to be placed in food vacuoles to be processed. The cell membrane bears many receptor proteins on the outside  surfaces , each bearing a binding site for a particular molecule. These receptor proteins  will bind to only specific molecules which are than engulfed by phagocytosis. 
 
 

12. What is the relationship between phagocytosis and leukemia? 
 
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13. Which structures in the cell membrane act as the receptors during mediated endocytosis? 
        a) phospholipids                                      c)  cytoskeleton 
        b) transport protein                                 d)   receptor proteins 

 
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14. Which of the following  processes is responsible the event described below? 
 
      a)  pinocytosis          b) phagocytosis           c) mediated phagocytosis 

Formation of a food vacuole by an Amoeba when it surrounds a Paramecium with its pseudopodia and brings the organism into the interior by fusing the outer membranes together. 

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15. Which of the following  processes is responsible the event described below? 
 
      a)  pinocytosis              b) phagocytosis            c) mediated phagocytosis 

Formation of water vacuoles which contain the same a solution the same as the extracellular fluid. 

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 Waste substances formed in the vacuoles after digestion must be expelled to the outside. This is accomplished by exocytosis.  In your notes draw a figure showing exocytosis and explain how it is accomplished. 
 
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16. Which of the following  processes is responsible the event described below? 
 
      a)  pinocytosis    b) phagocytosis      c) mediated phagocytosis   
      d) exocytosis 

A vesicle  created by the Golgi complex moves to the cell surface, where the membrane of the vesicle fuses with the plasma membrane. The vesicle opens to the extracellular  fluid and its contents diffuse out. 
 
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 Multicellular organism's  cells are held together by special connections and the cytoplasm of their cells  communicate using various types of channels. Click here to study connections and communication.  click 
 
 
 
 
 
 
 

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