Understanding Aerobic and Anaerobic Respiration and Their Differences

Respiration is a process of release of energy by the breakdown of energy molecules obtained from food. This process is carried out by all sorts of living creatures, in order to produce the energy required for carrying out various metabolic activities like growth, repair, and locomotion.

Aerobic and anaerobic respiration are carried out at the cellular level. Let's take a look at how these two processes take place, and what are the differences between them.


Aerobic respiration takes place in the presence of oxygen. It occurs in all plants, animals, and some prokaryotic organisms. The process involves a chemical reaction resulting into breakdown of energy molecules, obtained from carbohydrates (mainly glucose), proteins, and lipids. When a glucose molecule is broken down in the presence of oxygen, energy is released, along with carbon dioxide and water as the by-products of the reaction. The energy produced is stored in the form of adenosine triphosphate (ATP) molecules, to carry out the various metabolic processes. Oxygen, being a good oxidizing agent, acts as the electron receptor in this process. Here is the chemical equation of the reaction that takes place:


About 2900 KJ of energy is released as a result of the above chemical reaction. About 38 ATP molecules are produced when a single glucose molecule is broken down with the help of oxygen. This energy gets stored in the body for later use.

Going a little deeper into the process, aerobic respiration can be sub-divided into three main stages:

• Glycolysis: At this stage, some of the ATP molecules, some carbon molecules known as pyruvate or pyruvic acid, and some NADH molecules are created. Oxygen plays no part during this stage.
• Krebs Cycle: In this stage, unused carbon molecules are used to initiate another series of chemical reactions to produce more NADH molecules, and another molecule known as FADH2.
• Electron Transport Phosphorylation: In this stage, additional ATP molecules are created using the remainder of the reactant molecules.

Anaerobic respiration refers to the type of respiration that takes place in the absence of oxygen. This form of respiration is carried out in bacteria, yeasts, some prokaryotes, and muscle cells. In this process, energy, carbon dioxide, and lactic acid or alcohol are produced by the breakdown of glucose molecules. It uses electron acceptors other than oxygen, and involves the processes of glycolysis and fermentation. Anaerobic respiration, in case of yeast cells, is commonly referred to as fermentation. Here is the chemical equation for anaerobic respiration. The reaction can takes place in either of the two ways given below:



The above chemical reaction produces 2 ATP molecules by breaking down one glucose molecule, with carbon dioxide and ethanol or lactic acid as the by-products. Due to the absence of oxygen, the glucose molecule is only partially broken down, thereby producing lesser amount of energy. In case of yeast cells, ethanol is produced, while in case of muscle cells, lactic acid is produced as a by-product. Lactic acid is a toxic chemical that gives you cramps.

• Aerobic respiration requires oxygen, whereas anaerobic respiration takes place in the absence of oxygen.
• Most of the plant and animal cells use aerobic respiration. On the other hand, anaerobic bacteria, yeast cells, prokaryotes, and muscle cells perform anaerobic respiration.
• Aerobic respiration is more efficient than anaerobic respiration. For one molecule of glucose, aerobic respiration produces 38 ATP molecules, whereas anaerobic respiration produces just 2 ATP molecules.
• Aerobic respiration usually takes place in the mitochondria, while anaerobic respiration takes place in the cytoplasm.
• In case of aerobic respiration, the end products are carbon dioxide and water. In anaerobic respiration, the end products are ethyl alcohol or lactic acid, and carbon dioxide.
• Aerobic respiration takes a longer time to release energy. Anaerobic respiration is a much faster process.