Difference Between Endocytosis and Exocytosis

The key difference between endocytosis and exocytosis is that endocytosis brings substances into the cell while exocytosis transports substances to the outside of the cell.

A cell has a cell membrane that acts as a barrier between the cell interior and the external environment. Therefore, having such a membrane, cells need some kind of transportation mechanism to connect with the external environment. For example, cells need to obtain nutrients and excrete waste from the cell. For this purpose, cells have four basic mechanisms of transportation: diffusion, osmosis, active transport, and bulk transport. Diffusion and osmosis are passive processes whereas active transport and bulk transport are active processes that consume energy.  Endocytosis and exocytosis are two types of bulk transportation mechanisms, which transport big particles through the plasma membrane, either from cell to the external environment or from the external environment to the cell. Both these mechanisms form membrane-bound vesicles as the mean of transportation.

CONTENTS

1. Overview and Key Difference
2. What is Endocytosis 
3. What is Exocytosis
4. Similarities Between Endocytosis and Exocytosis
5. Side by Side Comparison – Endocytosis vs Exocytosis in Tabular Form
6. Summary

What is Endocytosis?

Endocytosis is the transportation of macromolecules, large particles, and polar substances that cannot enter the cell through the non-polar membrane. In this process, the material that has to enter the cell is surrounded by an area of the plasma membrane, which then buds off inside the cell to form a vesicle containing the ingested material. Then, the vesicle enters into the cytoplasm with the substances. After it has entered the cytoplasm, this vesicle binds with another membrane-bound organelle such as vacuole or Endoplasmic Reticulum (ER).

There are four types of endocytosis as clathrin-mediated endocytosis, caveolae, macropinocytosis, and phagocytosis. Endocytosis occurs in immune responses, in signal transduction, in neural function, and in pathological conditions. This is harder in plant cells than in the animal cells, since they have a cell wall covering the cell membrane.

What is Exocytosis?

The opposite of endocytosis process is exocytosis. Cells transport unwanted materials from the cell through exocytosis. The main materials that are transported via exocytosis are waste materials cells such as solid, undigested remains and useful materials such as materials needing to produce the cell wall. In the cytoplasm, these materials are packed into a vesicle and directed to the plasma membrane. When the vesicle comes in contact with the plasma membrane, it fuses with the plasma membrane and releases those wastes into the external environment. During exocytosis, vesicle becomes part of the plasma membrane.

Exocytosis is important in making the cell wall after the nuclear division of the cell. Exocytosis also transports necessary polysaccharides and proteins to the cell wall. Furthermore, plants use exocytosis to release nectar to attract pollinators. For example, mustard plants emit oil through exocytosis to irritate herbivores and carnivorous plants release enzymes through exocytosis. Another importance of exocytosis in plants is that the plants release root exudates due to environmental stress using exocytosis.

What are the Similarities Between Endocytosis and Exocytosis?

• Endocytosis and exocytosis are forms of active transport.
• Both methods facilitate the transportation of macromolecules that are unable to pass through the cell membrane.

What is the Difference Between Endocytosis and Exocytosis?

Endocytosis is the transport of macromolecules, large particles, and polar substances that cannot enter the cell through the non-polar membrane whereas exocytosis is the transport of molecules or particles outside of the cell. Therefore, we can consider this as the key difference between endocytosis and exocytosis. Besides this, functionally, the difference between endocytosis and exocytosis is that endocytosis involves in up-taking nutrients into the cell, but exocytosis involves in removing waste from the cell.

Moreover, exocytosis helps in the making of the cell wall, but not endocytosis. Also, at the end of endocytosis, vesicle binds to the cellular membrane-bound organelles, while at the end of exocytosis vesicle is bound with the cellular membrane. Therefore, this is an additional difference between endocytosis and exocytosis.

Below infographic on the difference between endocytosis and exocytosis tabulates more differences between both.

Summary – Endocytosis vs Exocytosis

Endocytosis and exocytosis are two types of bulk transportation mechanisms. Both methods carry out the transportation of macromolecules to and from the cell. Endocytosis refers to the transportation of macromolecules into the cell while exocytosis refers to the transportation of macromolecules from the cell to the outside of the cell. There are four types of endocytosis mechanisms while there are only two types of exocytosis mechanisms. At the end of endocytosis, vesicle fuses with the membrane-bound organelles while at the end of exocytosis, vesicle fuses with the cell membrane. This summarizes the difference between endocytosis and exocytosis.

Reference:

1. Cooper, Geoffrey M. “Endocytosis.” Current Neurology and Neuroscience Reports., U.S. National Library of Medicine, 1 Jan. 1970, Available here.
2. “Exocytosis.” NeuroImage, Academic Press, Available here.

Image Courtesy:

1. “0310 Exocytosis” By OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “A depiction of various types of Endocytosis” By Manu5 – (CC BY-SA 4.0) via Commons Wikimedia