Modeling Endocytosis and Exocytosis

By Laura Hospitál on Jan 12, 2015

Students of biology learn about the movement of various substances into and out of cells.  This is done either utilizing energy from the cell (active transport) or not requiring energy of the cell (passive transport). 

Some particularly large molecules are moved across the cell membrane by a membrane-bound sac called a vesicle.  Movement into the cell in this manner is called endocytosis and movement out of the cell in this manner is called exocytosis. This movement in a vesicle requires energy from the cell and is therefore considered active transport.

Using this model, the student with a visual impairment will be able to experience and model this movement into and out of the cell within a vesicle.

Pictures by Ditmar



 The cell membrane is modeled by a circle of string while the substance entering or exiting the cell is modeled by a marble. The vesicle is modeled by a smaller circle of string.

  1. Cut a piece of string 2.5 ' long.
  2. Tie the ends together into a tight knot. 
  3. Cut a second piece of string 6" long.
  4. Tie the ends of the second string together as well.


  • Thin white string
  • White marble - large
  • Pair of scissors


  1. Model of a substance entering  the cell by endocytosis

    Place the cell membrane model (larger string) and the marble on the desk for the students prior to their entrance to class.

  2. When the students enter class, explain that the string is a model of the cell membrane and that unlike a cell membrane it is 2-dimensional rather than 3- dimensional. Tell the students that the marble represents a polysaccaride or protein that needs to enter or exit the cell.

  3. Explain to the students that some substances must cross the cell membrane in a vesicle as they are very large.  As endocytosis is described, have the students model this movement using the string and marble.  (See picture.)  

    Model is used to describe exocytosis.

    Note that the cell membrane surrounds the substance and forms a pouch.  The pouch pinches off to make a vesicle (membrane-bound sac).  This is not shown using the model and should be described.
  4. After students are comfortable with endocytosis, describe the movement of substances out of the cell by exocytosis.  For this model, give the students each the small circle made of string and explain that it represents a vesicle.  During exocytosis, vesicles within the cell fuse with the cell membrane and release their contents outside of the cell.



For students with low vision with particular color preferences, the color of the string and/or the marble may be modified. 


NGSS Standards:

Middle School - Structure, Function, and Information processing

LS1.A: Structure and Function

  • All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular). (MS-LS1-1)
  • Within cells, special structures are responsible for particular functions, and the cell membrane forms the boundary that controls what enters and leaves the cell. (MS-LS1-2)


endocytosis and exocytosis collage



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