<meta http-equiv="refresh" content="1; url=/nojavascript/"> Exocytosis and Endocytosis ( Read ) | Biology | CK-12 Foundation
Dismiss
Skip Navigation
You are viewing an older version of this Concept. Go to the latest version.

Exocytosis and Endocytosis

%
Progress
Practice Exocytosis and Endocytosis
Practice
Progress
%
Practice Now
Exocytosis and Endocytosis

What does a cell "eat"?

Is it possible for objects larger than a small molecule to be engulfed by a cell? Of course it is. This image depicts a cancer cell being attacked by a cell of the immune system. Cells of the immune system consistently destroy pathogens by essentially "eating" them.

Vesicle Transport

Some molecules or particles are just too large to pass through the plasma membrane or to move through a transport protein. So cells use two other active transport processes to move these macromolecules (large molecules) into or out of the cell. Vesicles or other bodies in the cytoplasm move macromolecules or large particles across the plasma membrane. There are two types of vesicle transport, endocytosis and exocytosis (illustrated in Figure below ). Both processes are active transport processes, requiring energy.

Process of vesicle transport for exocytosis and endocytosis

Illustration of the two types of vesicle transport, exocytosis and endocytosis.

Endocytosis and Exocytosis

Endocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane. The membrane folds over the substance and it becomes completely enclosed by the membrane. At this point a membrane-bound sac, or vesicle, pinches off and moves the substance into the cytosol. There are two main kinds of endocytosis:

  • Phagocytosis , or cellular eating, occurs when the dissolved materials enter the cell. The plasma membrane engulfs the solid material, forming a phagocytic vesicle.
  • Pinocytosis , or cellular drinking, occurs when the plasma membrane folds inward to form a channel allowing dissolved substances to enter the cell, as shown in Figure below . When the channel is closed, the liquid is encircled within a pinocytic vesicle.

Electron microscope of pinocytosis

Transmission electron microscope image of brain tissue that shows pinocytotic vesicles. Pinocytosis is a type of endocytosis.

Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell, as shown in Figure below . Exocytosis occurs when a cell produces substances for export, such as a protein, or when the cell is getting rid of a waste product or a toxin. Newly made membrane proteins and membrane lipids are moved on top the plasma membrane by exocytosis. For a detailed animation of cellular secretion, see http://vcell.ndsu.edu/animations/constitutivesecretion/first.htm .

Axon signaling using exocytosis

Illustration of an axon releasing dopamine by exocytosis.

Summary

  • Active transport is the energy-requiring process of pumping molecules and ions across membranes against a concentration gradient.
  • Endocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane, and bringing it into the cell.
  • Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell.
  • Both endocytosis and exocytosis are active transport processes.

Practice

Use this resource to answer the questions that follow.

  1. Compare endocytosis to exocytosis.
  2. Describe the process of endocytosis.
  3. What are the differences between phagocytosis, pinocytosis, and receptor-mediated endocytosis?
  4. How are hormones released from a cell?

Review

  1. What is the difference between endocytosis and exocytosis?
  2. Why is pinocytosis a form of endocytosis?
  3. Are vesicles involved in passive transport? Explain.

Vocabulary

active transport

active transport

Energy requiring movement of substances across a plasma membrane.
endocytosis

endocytosis

Type of vesicle transport that moves substances into a cell.
exocytosis

exocytosis

Type of vesicle transport that moves substances out of a cell.
phagocytosis

phagocytosis

Process in which leukocytes engulf and break down pathogens and debris.
pinocytosis

pinocytosis

Type of vesicle transport that occurs when the plasma membrane folds inward to form a channel, allowing dissolved substances to enter the cell.

Image Attributions

Explore More

Sign in to explore more, including practice questions and solutions for Exocytosis and Endocytosis.

Reviews

Please wait...
Please wait...

Original text