HOW DO FUNGI BREATHE? TYPES, CLASSIFICATION AND STAGES - BIOLOGY - 2025

The respiration of the fungi varies depending on what type of fungus we are observing. In biology, fungi are known as fungi, one of the kingdoms of nature where we can distinguish three large groups: molds, yeasts and mushrooms.

Fungi are eukaryotic organisms composed of cells with a well-defined nucleus and chitin walls. In addition, they are characterized by the fact that they feed by absorption.

There are three main groups of fungi, yeasts, molds and mushrooms. Each type of fungus breathes in a certain way as seen below. You may be interested in How do mushrooms feed?

Types of fungal respiration

Cellular respiration or internal respiration, are a set of biochemical reactions by which certain organic compounds through oxidation are converted into inorganic substances that provide energy to the cell.

Within the fungi community we find two types of respiration: aerobic and anaerobic. Aerobic respiration is one in which the final electron acceptor is oxygen, which will be reduced to water.

On the other hand we find anaerobic respiration, which should not be confused with fermentation, since in the latter there is no electron transport chain. This respiration is one in which the molecule used for the oxidation process is not oxygen.

Mushroom respiration by classification

To make the explanation of the types of respiration easier, we will classify them according to the types of fungi.

Yeasts

This type of fungi are characterized by being unicellular organisms, which means that they are only composed of one cell.

These organisms can survive without oxygen, but when there is oxygen they breathe it anaerobically from other substances, they never take up free oxygen.

Anaerobic respiration consists of the extraction of energy from a substance, used to oxidize glucose, thus obtaining adenosine triphosphate, also known as adenosine phosphate (hereinafter ATP). This nucleodite is in charge of obtaining energy for the cell.

This type of respiration is also known as fermentation and the process that follows to obtain energy through the division of substances is known as glycolysis.

In glycolysis, the glucose molecule is broken down into 6 carbons and a pyruvic acid molecule. And in this reaction two molecules of ATP are produced.

Yeasts also have a certain type of fermentation, which is known as alcoholic fermentation. By breaking down glucose molecules for energy, ethanol is produced.

Fermentation is less effective than respiration since less energy is used from the molecules. All possible substances used for glucose oxidation have less potential

Molds and mushrooms

These fungi are characterized by being multicellular fungi. This type of mushroom has aerobic respiration.

Respiration makes it possible to extract energy from organic molecules, mainly glucose. To be able to extract the ATP, it is necessary to oxidize the carbon, for that, oxygen from the air is used.

Oxygen crosses the plasma membranes and then the mitochondrial. In the latter, it binds electrons and hydrogen protons, forming water.

Stages of fungal respiration

To carry out the respiration process in fungi, it is carried out in stages or cycles.

Glycolysis

The first stage is the glycolysis process. This is responsible for oxidizing glucose in order to obtain energy. Ten enzymatic reactions occur that convert glucose to pyruvate molecules.

In the first phase of glycolysis, the glucose molecule is transformed into two glyceraldehyde molecules, using two ATP molecules. The use of two ATP molecules in this phase, allows to double the energy production in the next phase.

In the second phase, the glyceraldehyde obtained in the first phase is converted into a high-energy compound. Through the hydrolysis of this compound, a molecule of ATP is generated.

Since we had obtained two molecules of glyceraldehyde in the first phase, we now have two of ATP. The coupling that occurs, forms two other pyruvate molecules, so that in this phase we finally obtain 4 ATP molecules.

Krebs cycle

Once the glycolysis stage is finished, we move on to the Krebs cycle or citric acid cycle. It is a metabolic route where a series of chemical reactions take place that releases the energy produced in the oxidation process.

This is the part that performs the oxidation of carbohydrates, fatty acids and amino acids to produce CO2, in order to release energy in a usable way for the cell.

Many of the enzymes are regulated by negative feedback, by allosteric binding of ATP.

These enzymes include the pyruvate dehydrogenase complex that synthesizes the acetyl-CoA necessary for the first reaction of the cycle from pyruvate from glycolysis.

Also the enzymes citrate synthase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase, which catalyze the first three reactions of the Krebs cycle, are inhibited by high concentrations of ATP. This regulation stops this degradative cycle when the energy level of the cell is good.

Some enzymes are also negatively regulated when the level of reducing power of the cell is high. Thus, among others, the pyruvate dehydrogenase and citrate synthase complexes are regulated.

Electron transport chain

Once the Krebs cycle is over, fungal cells have a series of electron mechanisms found in the plasma membrane, which, through reduction-oxidation reactions, produce ATP cells.

The mission of this chain is to create a transport chain of an electrochemical gradient that is used to synthesize ATP.

Cells that rely on the electron transport chain to synthesize ATP, without using solar energy as an energy source, are known as chemotrophs.

They can use inorganic compounds as substrates to obtain energy that will be used in respiratory metabolism.

References

1. CAMPBELL, Neil A., et al. Essential biology.
2. ALBERTS, Bruce, et al. Molecular biology of the cell. Garland Publishing Inc., 1994.
3. DAVIS, Leonard.Basic methods in molecular biology. Elsevier, 2012.
4. BIOLOGICALS CLARED BY PROCARIOTES, Principles. SECTION I PRINCIPLES OF MICROBIOLOGY. 1947.
5. HERRERA, TeófiloUlloa, et al. The kingdom of fungi: basic and applied mycology. Mexico, MX: National Autonomous University of Mexico, 1998.
6. VILLEE, Claude A.; ZARZA, Roberto Espinoza; And CANO, Gerónimo Cano.Biology. McGraw-Hill, 1996.
7. TRABULSI, Luiz Rachid; ALTERTHUM, Flavio.Microbiology. Atheneu, 2004.