WHAT IS DIRECT RESPIRATION AND IN WHICH ORGANISMS DOES IT OCCUR? - BIOLOGY - 2025

The direct breathing is occurring between the cells of a living being and the environment, without an organ needed breathing; that is, gas exchange occurs through a membrane. In these organisms, oxygen transport occurs by simple diffusion; Due to the fact that oxygen is in greater quantity outside, it diffuses into the body.

Direct respiration is one of several types of respiration along with blood diffusion respiration, tracheal respiration, gill respiration, and lung respiration. These are classified into simple or complex respiration, according to the different mechanisms for extracting oxygen from their environment.

Breathing is an involuntary process. Its main function is to deliver oxygen to the cells of the body and remove carbon dioxide. All living things have mechanisms to carry out this process.

In all cases, this gas exchange that occurs between an organism and its environment is carried out by means of diffusion, a physical process that allows this exchange.

In the case of humans, diffusion occurs in the lungs and in the case of simpler organisms, such as sponges or jellyfish, it occurs throughout the surface of their bodies.

The simplest creatures, such as single-celled organisms, depend entirely on diffusion for the movement and exchange of gases.

As the complexity of these organisms increases, cells move away from the cell layer where gas exchange with the environment occurs. In this way, it becomes more difficult to obtain and eliminate gases by diffusion.

Direct breathing or diffusion breathing

Despite the fact that specialized organisms have a great variety of cells with different functions, one structure is common to all cells: the cell membrane or plasma membrane.

This membrane forms a kind of barrier around cells and regulates everything that enters and leaves them.

The structure of the cell membrane is extremely important. It is composed mainly of two sheets of phospholipids and proteins that make it control what passes through it.

Phospholipid is a molecule made up of fatty acids, alcohol (glycerol), and a phosphate group. These molecules are in constant random motion.

The cell membrane is semi-permeable, which means that certain small molecules can pass through it. Because the membrane molecules are always in motion, it allows temporary openings to form that allow small molecules to cross from one side of the membrane to the other.

This constant movement, and the disproportionate concentration of the molecules inside and outside the cell, makes it easier for them to move across the membrane.

Substances within the cell also help determine the level of concentration between the cell and its surroundings.

Inside you can find cytosol, made up mostly of water; organelles and various compounds such as carbohydrates, proteins and salts, among others.

Oxygen diffusion

Molecules move below the concentration level. That is, its movement goes from an area of ​​higher concentration to one of lower concentration. This process is called broadcasting.

An oxygen molecule can pass through the plasma membrane of a cell since it is small enough and under the right conditions.

Most living things constantly use oxygen in the chemical reactions that occur in their cells. These chemical processes include cellular respiration and energy production.

Therefore, the oxygen concentration inside cells is much lower than the oxygen concentration outside them. So the molecules move from the outside to the inside of the cell.

Likewise, cells also produce more carbon dioxide than their environment, so there is a higher concentration inside the cell than outside.

So this carbon dioxide moves from the inside to the outside of the cell. This gas exchange is vital to survival.

Fick's Laws

There are organisms that do not have specialized respiratory organs like humans. Therefore, they have to take in oxygen and expel carbon dioxide through their skin.

For this simple gas exchange to happen, several conditions are needed. Fick's laws state that the proportion of diffusion through a membrane depends on the surface area, concentration difference and distance.

Therefore, their bodies have to be thin and long (low in volume but with a lot of surface area). In addition, they should secrete some wet and viscous substance that facilitates the exchange (as happens with the mucus found in the lungs).

Organisms with direct respiration

Organisms such as pinworms (nematodes), tapeworms (flatworms), jellyfish (coelenterates) and sponges (porifers) that breathe through diffusion, do not have a respiratory system, tend to have long and thin shapes, and always secrete viscous fluids or mucus.

Due to the shape and simplicity of these organisms, each cell in your body is very close to the external environment. Its cells are kept humid so that the gas diffusion is carried out directly.

Jellyfish

Tapeworms are small and flat. The shape of your body increases the surface area and area of ​​diffusion, ensuring that every cell within the body is close to the surface of the outer membrane to access oxygen.

If these parasites were cylindrical in shape, then the central cells of your body would not be able to obtain oxygen.

Finally, it should be noted that the diffusion process that allows the obtaining of oxygen and the expulsion of carbon dioxide is a passive process like any other respiratory mechanism. No body does it in a conscious way nor can it control it.

Breathing by blood diffusion

A more complex form of diffusion incorporates a circulatory system that allows greater displacement. It consists of transporting oxygen through a moist layer on the surface to the bloodstream.

Once oxygen is in the blood, it can spread through the body to reach all cells and tissues. This system is used by amphibians, worms and leeches, for example.

As with tapeworms, earthworms have a cylindrical but thin body that has a lot of surface area and little volume.

In addition, they keep your body humerus by secreting a viscous mucus in your epithelial glands that allows it to trap and dissolve oxygen from the air.

References

1. Beal, Lauren. "Wow! The Wonders of an Earthworm. How Diffusion Allows an Earthworm to Breathe ”. Retrieved June 5, 2017 at sas.upenn.edu.
2. Science Clarified (2017). "Respiration - How it works". Retrieved June 5, 2017 at scienceclarified.com.
3. Raven, P., Johnson, GB (2002) Biology, Sixth Edition. McGraw Hill, Dubuque, 11053-1070 pp.
4. Science Encyclopedia (2017). " Respiration - External Respiration ”. Retrieved June 5, 2017 at science.jrank.org.
5. Boundless. "The Respiratory System and Direct Diffusion". Retrieved June 5, 2017 at boundless.com.