Types of respiration

As you read this, you are breathing oxygen and emitting carbon dioxide simultaneously. Did you notice this? It is an action that you do continuously and unconsciously. To put it in scientific terms, what is happening is a process called respiration . Read on to learn more about existing breath types .

Aerobic respirationAnaerobic respiration
DefinitionAerobic respiration is a type of cellular respiration that takes place in the presence of oxygen and produces energy.Anaerobic respiration is another type of cellular respiration that takes place in the absence of oxygen and produces energy.
General equationThe general equation for aerobic respiration is:
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
The general equation of anaerobic respiration is:
C6H12O6 → C2H5OH + CO2 + energy
Presence of oxygenAerobic respiration takes place in the presence of oxygen.Anaerobic respiration takes place in a condition where there is a low oxygen environment.
Gas exchangeThere is a gas exchange during aerobic respiration where oxygen is absorbed and carbon dioxide is released.Gas exchange does not take place during anaerobic respiration. However, some organisms release some gases such as sulfur and nitrogen.
LocationAerobic respiration, after glycolysis, occurs in the mitochondria of eukaryotes and in the cytoplasm of prokaryotes.Anaerobic respiration occurs only in the cytoplasm of a cell.
Final productsThe end products of aerobic respiration are carbon dioxide, water, and energy.The end products of anaerobic respiration are acids, alcohols, gases, and energy.
Produced energyDuring aerobic respiration, a total of 38 ATP is produced, some of which is lost during the process.Only 2 ATP is formed during anaerobic respiration.
ReagentsCarbohydrates and oxygen are the prerequisites for aerobic respiration.Some other electron acceptors like sulfur and nitrogen are required along with carbohydrates.
OxidationComplete oxidation of carbohydrates takes place during aerobic respiration.Incomplete oxidation of carbohydrates occurs during anaerobic respiration.

Definition of respiration

Respiration could be defined as a metabolic biochemical process that takes place in all living cells of an organism where they produce energy through the ingestion of oxygen and the release of carbon dioxide from the oxidation of various organic substances. The energy produced is in the form of adenosine triphosphate or ATP, which is also known as an energy molecule.

Types of respiration

Two types of respiratory processes have been observed

  • Aerobic respiration
  • Anaerobic respiration

Aerobic respiration

Aerobic respiration is a type of cellular respiration that takes place in the presence of oxygen and produces energy . It is observed in both plants and animals and the end product of this type of respiration is water and carbon dioxide (CO2).

Observe the reaction that takes place during aerobic respiration:

Glucose (C6H12O6) + Oxygen 6 (O2) → Carbon dioxide 6 (CO2) + Water 6 (H2O) + Energy (ATP)

As can be seen, in this type of respiration, glucose molecules divide in the presence of oxygen and the final or by-products that are released are CO2, water and energy in the form of ATP. The total energy released in this reaction is 2900 KJ which is used to produce ATP molecules. It is observed in all types of multicellular organisms .

Aerobic respiration in plants

In plants, aerobic respiration begins when oxygen or O2 enters plant cells through stomata found in the epidermis of leaves. Then the photosynthesis process takes place that produces food for the plant body and releases energy. The chemical reaction that takes place is as follows:

Carbon dioxide 6 (CO2) + Water 6 (H2O) → Glucose (C6H12O6) + Oxygen 6 (O2)

Anaerobic respiration

Anaerobic respiration is another type of cellular respiration that takes place in the absence of oxygen and produces energy . In this process, glucose is broken down without the help of oxygen and the by-products produced are alcohol, CO2, and energy or ATP. The process takes place in the cytoplasm of a cell. The chemical reaction of this process is as follows:

Aerobic respiration can be divided into

  • Lactic acid fermentation
  • Alcoholic fermentation

Lactic acid fermentation: This is the type of anaerobic fermentation where glucose splits in the absence of oxygen to produce two lactic acid molecules and two ATP molecules.

The chemical reaction is:  (GLUCOSE) C6H12O6 + 2 ADP + 2 PHOSPHATE → 2 LACTIC ACID + 2 ATP

During exercise, the body’s muscles use O2 to produce ATP faster than it can be supplied. When this happens, muscle cells perform glycolysis faster than they can provide oxygen to the electron transport chain. That is why lactic acid fermentation takes place in our cells after a long exercise session that makes our muscles ache.

Alcoholic fermentation: In this type of anaerobic respiration, glucose is divided in the absence of oxygen into two molecules of ethyl alcohol or ethanol, two molecules of carbon dioxide, and two molecules of ATP.

The chemical reaction is:  Glucose (C6H12O6) → Alcohol 2 (C2H5O H) + Carbon dioxide 2 (CO2) + Energy (ATP)

Anaerobic respiration can be observed in human muscle cells, bacteria, methanogens, and other prokaryotes.

The different stages of respiration

Cellular respiration takes place through a variety of metabolic pathways . Glucose breaks down into water, carbon dioxide, and a certain amount of ATP. Later more ATP is produced in a process known as oxidative phosphorylation that is driven by the movement of electrons through the electron transport chain. Below is a summary of the different phases of cellular respiration:

Glycolysis: In this process, the six-carbon sugar, glucose, undergoes various chemical transformations. The final product is pyruvate and a three-carbon organic molecule. Two molecules of ATP and NADH are also generated.

Pyruvate oxidation – Each pyruvate enters the mitochondrial matrix and becomes a two-carbon molecule that binds with coenzyme-A. The entire compound is known as acetyl CoA. The by-products of this reaction are carbon dioxide and NADH.

Citric acid cycle: Acetyl CoA combines with a four-carbon molecule that undergoes a series of chemical reactions also known as the citric acid cycle or Krebs cycle. Ultimately, the initial four-carbon molecule regenerates with the addition of FADH2, NADH, carbon dioxide, and two ATP molecules. The Krebs cycle is also known as the tricarboxylic acid cycle.

Oxidative phosphorylation: FADH2 and NADH generated in the Krebs cycle donate their electron to oxygen through various electron carriers via the electron transport chain in a process known as oxidative phosphorylation. The reaction takes place in the mitochondrial matrix. As electrons move down the chain, energy is released that is used to pump protons out of the matrix and forms a gradient. The protons then return to the matrix with the help of the ATP synthase enzyme that produces ATP. At the end of the chain, oxygen accepts electrons and protons to form water.

In the end, 38 ATP molecules are generated from one glucose molecule. It should be mentioned that glycolysis can also take place in the absence of oxygen and the process is known as fermentation.

The importance of breathing

Respiration is the process of supplying and releasing energy in all living organisms by converting food energy into metabolically usable forms of chemical energy. The process releases energy in a controlled step-by-step manner so that it can be properly used for all cellular activities such as metabolism and cell division. Several intermediates of glycolysis and the citric acid cycle are used in the synthesis of many organic compounds that are used in cell metabolism.

In a plant, the carbon dioxide required for photosynthesis is replaced by carbon dioxide released in respiration, and the oxygen required for respiration is replaced by oxygen released in photosynthesis. Therefore, respiration and photosynthesis are complementary to each other and maintain the balance of carbon dioxide and oxygen in nature. Breathing also conserves energy. A glucose molecule releases 673 Kcal of energy, of which 456 Kcal are conserved in 38 ATP molecules.

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