Mass Transport: Types & Explanation |

Imagine that the cells of the body are small factories surrounded by a high wall. There are various gates in this wall. These ensure that the right raw materials get to the factory and that processed and superfluous raw materials can be transported out of the factory. The factory only works if a regulated transport of raw materials is possible through its delimitation.

In reality, of course, the cells in our bodies are not separated by a wall, but by a biomembrane. As in our example, the cell depends on nutrients and other molecules to pass through the biomembrane. An exchange of substances within the cell and between the cells is essential for a functioning organism. This is ensured by a regulated transport of substances through the membrane.

Definition of mass transport

A human body consists of an estimated 30 trillion body cells. In order for these to be able to function together as an organism, an exchange of substances and mass transport between them essential.

mass transport (in biology) describes the transport of inorganic and organic substances within organisms. This includes, for example, the transport of water, salts, nutrients and metabolic products.

This article is specifically about molecular mass transport at the cellular level. This can basically be divided into two types.

  • Transport of substances through the biomembrane
  • Mass transport by cytosis

Of the Transport of substances through the biomembrane describes the transport of molecules from one side to the other side of the biomembrane. Depending on the type of substance transport, the help of proteins or the provision of energy is required.

Material transport by means of cytosis are transport processes of larger particles. Corresponding particles are enclosed by the biomembrane. The particles are then transported within the resulting coating (vesicle).

Transport of substances through the biomembrane

Mass transport is one of the most important functions of the biomembrane. The decisive factor here is that not just any substance can pass through the membrane, but that the transport of substances is regulated. The biomembrane is not equally permeable for all molecules. are biomembranes semipermeable (semipermeable).

The biomembrane is semipermeable (semi-permeable) because it is permeable to some particles but not to others. Here the size and the charge of the particles play a major role.

Furthermore, it is possible to increase the permeability for substances that normally cannot pass through the biomembrane. Through so-called transmembrane proteins larger and charged molecules can also be transported across the membrane. Think of these proteins as tunnels or passageways that are integrated into the biomembrane.

transmembrane proteins (also integral proteins) are proteins, which over the entire cross-section of a biomembrane are embedded in her. This includes among other things channel proteins (transport proteins).

Of course, the substances do not move through the biomembrane on their own. A driving force is needed to make the molecules move from one side of the membrane to the other. Here he plays concentration gradient of the particles play a crucial role.

concentration gradient

Particles naturally have their own motion. The direction in which the particles move depends on the concentration. Particles usually move from places of high concentration to places of low concentration. You strive for a concentration balance. One speaks of a so-called diffusion.

Since diffusion is the movement of the particles themselves, no additional energy is required when molecules move through the membrane from the high concentration to the low concentration. They move along the concentration gradient, more precisely the concentration gradient.

Figure 1: Diffusion of particles

Now you have already learned a lot about the permeability of membranes and the driving force of mass transport. Depending on whether the mass transport takes place with the help of transmembrane proteins and whether the particles move with or against the concentration gradient, a distinction is made between different types of mass transport through the biomembrane.

Passive mass transport

Passive transport is mass transport along the concentration gradient. The driving force here is the movement of the particles. No additional energy needs to be provided. Passive mass transport includes the simple and the facilitated diffusion.

Easy diffusion

the easy diffusion describes the passive transport (diffusion) of small particles, which due to their size and charge, the biomembrane without the help of Transmembrane proteins can happen (this includes, among other things, the particle movements of water molecules and gases such as oxygen and carbon dioxide). The particles migrate along the concentration gradient.

Facilitated Diffusion

the facilitated diffusion describes passive transport (diffusion) across a biomembrane using transmembrane proteins. Transport proteins are always required for mass transport when particles cannot easily pass through the biomembrane due to their size and charge. The particles migrate along the concentration gradient.

You can find more detailed information on passive mass transport in a separate article.

Active mass transport

If substances have to be transported through the membrane against the concentration gradient, additional energy must be provided. That is why this mass transport is also called active transport designated. As a rule, the cleavage of ATP molecules as an energy source to move molecules across a transmembrane protein against their concentration gradient.

ATP stands for adenosine triphosphate. This is a high-energy molecule equipped with three phosphate groups. The elimination of a phosphate residue releases energy. This can be used for a wide variety of processes. ATP is something like the fuel of living cells and plays an important role in providing energy in organisms.

In the following figure you will find an overview of the presented transport processes.

Figure 2: Representation of passive and active transport

Active mass transport will continue to be in primary-active and secondary-active transport divided.

Primary active transport

In primary active transport, the energy comes from ATP. The molecules to be transported are transported using so-called Transport-ATPases (transmembrane proteins) transported through the membrane. Figure 2 shows a primarily active transport.

Transport ATPases are transmembrane proteins that form a passageway through the cell membrane. They split ATP and use the released energy to transport particles through a membrane against their concentration gradient.

Secondary active transport

Transport proteins can transport individual molecules, but also coupled several molecules. Depending on the type of transport, a distinction is made between the following:

  • uniport: A molecule is in over the biomembrane transported.
  • symport: Two molecules are transported coupled in the same direction across the cell membrane.
  • antiport: Two molecules are transported in opposite directions.

Symport and antiport are usually about secondary active transport. This means that one of the two molecules is transported with the concentration gradient and the other molecule against the concentration gradient. The energy required for active transport is obtained from transport along the concentration gradient.

Figure 3: Representation of uniport, symport and antiport

Would you like to learn more about active mass transport? You will also find a suitable article on this topic at .

Mass transport cytosis

Material transport by means of cytosis are transport processes of larger particles. Corresponding particles are enclosed by the biomembrane. Subsequently, the particles within the resulting coating (vesicles) transported. Depending on whether the substances are taken up into the cell or transported out of the cell, between endocytosis and exocytosis distinguished.

exocytosis

Exocytosis describes the transport of substances from the inside of the cell (intracellular space) to the outside of the cell (extracellular space). The substances are packaged in transport vesicles in the Golgi apparatus. When the vesicles reach the cell membrane, they fuse with it and the contents of the vesicles are released.

endocytosis

Endocytosis describes the process when molecules are taken up from the outside of the cell into the inside of the cell. Endocytosis occurs through an invagination in the cell membrane. The biomembrane closes around the particles to be absorbed and forms a vesicle, which then separates from the biomembrane.

A distinction is made between special forms of endocytosis, depending on which type of particle is taken up by the cell through endocytosis.

phagocytosis

phagocytosis describes the absorption of large particles such as nutrients, but also pathogenic protozoa. In this case, the vesicle resulting from endocytosis becomes phagosome called. The absorbed particles are then digested in the phagosome by enzymes and acids and rendered harmless.

Phagocytosis plays a special role in protozoa. They use phagocytosis to absorb food particles and as a defense mechanism against other microorganisms.

pinocytosis

as pinocytosis refers to the absorption of liquid and dissolved substances through endocytosis.

Receptor-mediated endocytosis

the Receptor-mediated endocytosis enables the absorption of specific molecules. The corresponding molecules bind to the designated receptors using the key-lock principle. Endocytosis is initiated by binding to the receptor.

Receptor-mediated endocytosis has two key advantages. It ensures a targeted and regulated absorption of particles. Furthermore, it enables the absorption of substances that are only present in low concentrations outside the cell.

In the articles on endocytosis and phagocytosis you will get a deeper insight into the transport of substances via cytosis.

Get an overview of the explained transport processes using the following figure.

Figure 3: Types of endocytosis

Cloth transport – the most important thing

  • Mass transport is one of the most important functions of the biomembrane. The decisive factor here is that not just any substance can pass through the membrane, but that the transport of substances is regulated.
  • The biomembrane is semipermeable (semi-permeable) because it is permeable to some particles but not to others.
  • Passive transport is mass transport along the concentration gradient. No additional energy is required…