Aerobic and Anaerobic Respiration - Differences & Overview

What Is Respiration?

Respiration is one of the metabolic processes by which organisms synthesize energy, carbon dioxide and water out of oxygen and glucose. This process is crucial for the existence of all aerobic organisms because it is the only place where energy is produced paramount for cellular activities and physiological processes. In living organisms, respiration is not only identified to provide energy for metabolic functions but also has a significant role in regulating the body’s internal environment and supporting growth and development besides repair functions. Knowing or appreciating the respiratory process is significant to grasping the hardworking process of energy generation and usage in biological processes.

Comparison Between Aerobic And Anaerobic Respiration

What Is Aerobic Respiration?

Aerobic respiration is a catabolic process in which all the cells in the body use glucose and oxygen to produce carbon dioxide, water and energy. It occurs in the presence of oxygen and it is the main means through which aerobic organisms generate ATP, or Adenosine triphosphate, the energy currency of cells.

Process Of Aerobic Respiration

The process of aerobic respiration is given below-

Glycolysis

Glycolysis takes place in the cytoplasm of the cell and not in any of the cell organelles including the mitochondria.

Steps Involved

• Glucose combines with a phosphate group to release vitamins and forms glucose-6-phosphate.

• Glucose-6-phosphate is oxidatively decarboxylated to give fructose-6-phosphate.

• The next step involves the phosphorylation of fructose-6-phosphate to undergo fructose-1,6-bisphosphate.

• Fructose-1,6-bisphosphate is cleaved into 2 three-carbon molecules of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.

• G3P is oxidised, and NAD+ is reduced to NADH In this process, there is the oxidation of G3P and NAD+ while NADH is reduced.

• This is carried out through substrate-level phosphorylation.

• Pyruvate accumulates as the terminal product of this process.

Products Formed

Their products include 2 molecules of pyruvate.

• 2 ATP (net gain)

• 2 NADH

Krebs Cycle (Citric Acid Cycle)

The Krebs cycle occurs in the matrix part of the mitochondria.

Steps Involved

• Citrate forms from acetyl-CoA by combining it with oxaloacetate.

• Citrate is then oxidised to isocitrate.

• Isocitrate is oxidised to alpha-ketoglutarate and simultaneously generates NADH.

• AKG is converted to succinyl-CoA giving rise to NADH.

• Succinyl-CoA is converted to succinate and in the process ATP (or GTP) is produced Many of the complexes are reviewed as follows;

• Succinate is oxidised to fumarate yielding FADH2.

• Fumarate is reduced to malate.

• Malate is oxidised to oxaloacetate while generating NADH.

Products Formed

2 ATP (in each glucose molecule, these ATP’s are produced through the process of substrate-level phosphorylation).

• 6 NADH

• 2 FADH2

• 4 CO2

Electron Transport Chain (ETC)

The electron transport chain is located within the inner layer of the mitochondria compartments known as the cristae membrane.

Steps Involved

• NADH and FADH2 pass on their electrons to the electron transport chain.

• Electrons are transferred through a sequence of protein structures.

• The energy liberated from the electron is utilised in putting protons across the inner membrane with the creation of a proton gradient.

• Protons move back through ATP synthase to synthesise ATP.

Role of Oxygen

Oxygen is the final receptor of electrons, with which it combines to form water through the addition of protons.

Products Formed

• Approximately 34 ATP

• Water (H2O)

What Is Anaerobic Respiration?

Fermentation is a process of breaking down glucose in cells to release energy without using oxygen. This process, in contrast, is less efficient in creating ATP molecules than aerobic respiration, which creates fewer ATP molecules per glucose molecule and it is common in anaerobic conditions.

Types Of Anaerobic Respiration

The different types of anaerobic respiration are:

Lactic Acid Fermentation

Lactic acid fermentation is experienced in some bacteria and animal cells particularly the muscle cells when oxygen is scarce. Here, pyruvate – a glycolysis end product – is converted by NAD+ into lactic acid, with NADH generated getting oxidised back to NAD+.

• Skeletal muscle tissue cells during exercise & mainly during vigorous exercise.

• Some of the bacteria include Lactobacillus species

Alcoholic Fermentation

Alcoholic fermentation takes place in yeast and some kinds of bacteria. In this process, pyruvate is again utilized, and it is transformed into ethanol and carbon dioxide. First, pyruvate is decarboxylated into acetaldehyde, and then it is reduced to ethanol with the help of NAD+; the NAD+ is returned to the cycle.

• Yeast (Saccharomyces cerevisiae)

• Some typical bacteria involve: Zymomonas mobilis

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