Aerobic and anaerobic reactions are the most basic biochemical processes in the cellular respiration chain from where cells derive energy. This is one of the most important topics of Biology and it is included in the Class 11 Biology chapter, Respiration in Plants. This topic is important for the students preparing for exams like NEET, AIIMS and other paramedical courses. This article will compare and compare aerobic and anaerobic respiration, how they are defined, their structures, and physiological roles. There are also diagrams and some key exam preparation tips on how these reactions affect cellular function.
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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 that is 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.
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Key Differences | Aerobic Respiration | Anaerobic Respiration |
Oxygen Requirement | Requires oxygen | Does not require oxygen |
ATP Yield | High (approximately 36-38 ATP per glucose) | Low (2 ATP per glucose) |
By-products | Carbon dioxide and water | Lactic acid or ethanol and carbon dioxide |
Efficiency | High efficiency | Low efficiency |
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.
The process of aerobic respiration is given below-
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
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
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)
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.
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
Given below are tips and tricks to prepare for aerobic anaerobic respiration:
The table indicates the weightage and types of questions asked from aerobic anaerobic respiration in different exams:
Exam Type | Types of Questions | Weightage |
---|---|---|
CBSE Board Exams | Definitions, differences between aerobic and anaerobic reactions, diagram explanations | 3-4% |
NEET | MCQs on steps of each process, ATP yield, and end products | 2-3% |
AIIMS | Assertion and reason questions related to aerobic and anaerobic processes | 2-3% |
Nursing Entrance Exams | Scenario-based questions on muscle function during anaerobic respiration | 1-3% |
Paramedical Exams | True/False questions on oxygen usage and anaerobic respiration products | 1-3% |
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The areas of divergence between aerobic and anaerobic respiration are in the need for oxygen. The former is aerobic respiration in which oxygen is used while the latter is anaerobic respiration in which oxygen is not used.
Aerobic respiration forms about 36-38 molecules of ATP food one glucose molecule.
Anaerobic respiration has two by-products: lactic acid when the fermentation is lacto-acid type while ethanol and carbon dioxide are by-products when the process is alcoholic one.
This is more efficient than anaerobic respiration mainly because aerobic respiration is capable of producing a much higher ATP per glucose molecule and helps in utilizing the energy stored in glucose to the optimum level.
Fermentation takes place in the mitochondrion of the cell and is known as the Krebs cycle.
Aerobic respiration is the production of energy that utilizes oxygen. For example, humans perform aerobic respiration during their daily routines.
Anaerobic respiration is the production of energy without the use of oxygen, typically when the environment has no oxygen. For example, yeast performs anaerobic respiration to create ethanol in brewing.
The four stages of aerobic respiration are:
Anaerobic respiration is a process of generating energy without the help of oxygen; in this process, glucose is partially broken down, thereby producing less energy than in the case of aerobic respiration, and its byproducts may be lactic acid or ethanol.
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