Cellular Respiration and its Process

Cellular respiration is a key component of respiration that takes place within the cells of organisms. It includes a series of complex metabolic processes that ultimately result in the production of ATP(energy).

Cellular Respiration:

It is a cellular respiration image where photosynthesis and cellular respiration play complementary role to each other. credit/

Cellular respiration is a key component of respiration that takes place within the cells of organisms. It includes a series of complex metabolic processes that ultimately result in the production of ATP(energy). Photosynthesis and cellular respiration play complementary roles in the cycling of energy and matter within living organisms.

The general equation for cellular respiration can be represented as follows:

C6H12O6 (glucose) + 6O2 (oxygen) → 6CO2 (carbon dioxide) + 6H2O (water) + energy (ATP)

In the process of cellular respiration, glucose, and oxygen are used as reactants to produce carbon dioxide, water, and energy in the form of adenosine triphosphate (ATP). Cellular respiration happens in three principal stages such as;

  • glycolysis,
  • the citric acid cycle (Krebs cycle), and
  • oxidative phosphorylation (including the electron transport chain).

All these processes take place in different cellular compartments, such as the cytoplasm and the mitochondria. The energy released during cellular respiration is essential for the functioning and survival of cells.

Stages of Cellular Respiration:


Glycolysis is the first stage of cellular respiration, and the entire process takes place in the cytoplasm of the cell. It is a universal process found in both aerobic and anaerobic organisms. During the process, one molecule of glucose (a six-carbon sugar) breaks down into two molecules of pyruvate (a three-carbon compound). Glycolysis does not require oxygen, making it an anaerobic process.

However, in many organisms, including most animals, glycolysis is the first step in both aerobic respiration (when oxygen is present) and anaerobic respiration (when oxygen is limited).

Under aerobic conditions, the pyruvate produced from glycolysis enters the citric acid cycle and f reactions, with oxygen to produce remarkably more ATP than anaerobic respiration. However, under anaerobic conditions, pyruvate can be converted to other end products like lactate through fermentation, allowing energy production to continue in the absence of oxygen.

Hence, while glycolysis doesn’t need oxygen to happen, it plays a pivotal role in both aerobic and anaerobic respiration pathways depending on the available oxygen.

Krebs Cycle (Citric Acid Cycle):

The Krebs Cycle is also called the Citric Acid Cycle or Tricarboxylic Acid (TCA) Cycle. It is the second stage of cellular respiration.  Krebs Cycle takes place in the mitochondria of eukaryotic cells. The primary objective of the Krebs Cycle is to further oxidize the products of glycolysis primarily pyruvate, and produce electron carriers (NADH and FADH2) and ATP. Krebs Cycle including oxidized pyruvate, can further use acetyl-CoA produced from sources like fats and proteins.

Electron Transport Chain (ETC):

The Electron Transport Chain (ETC) is the third and the last stage of cellular respiration. It happens in the inner mitochondrial membrane (in eukaryotes) or the plasma membrane (in prokaryotes). The basic function of the electron transport chain is to transfer electrons from electron carriers (NADH and FADH2) which are produced in earlier stages of cellular respiration to molecular oxygen (O2), creating a flow of electrons and producing energy in the form of ATP.

Key Characteristics of Respiration:

1. Production of Energy: The primary function of respiration is to produce ATP, which is used for various cellular activities.

2. Consumption of Oxygen: During aerobic respiration, oxygen is consumed during the breakdown of glucose.

3. Production of Carbon Dioxide: Carbon dioxide is produced as a byproduct of the metabolic processes involving respiration.

4. Removal of Wastage Material: Respiration plays a principal role in removing waste products, such as carbon dioxide, from the body.

5. Aerobic and Anaerobic Respiration: Aerobic respiration needs oxygen, whereas some organisms and certain conditions can also lead to anaerobic respiration, where energy is produced without oxygen.

Frequently Asked Questions (FAQs) about Respiration:

Q1. Is respiration the same as breathing?

 A – No, respiration is the cellular process that involves the breakdown of nutrients to produce energy, while breathing is the process of inhaling oxygen and exhaling carbon dioxide.

Q2. What is the difference between aerobic and anaerobic respiration?

A- Aerobic respiration happens in the presence of oxygen, while anaerobic respiration occurs in the absence of oxygen. Aerobic respiration is more efficient and produces more ATP.

Q3. Why is oxygen important in respiration?

A – Oxygen is the final electron acceptor in the electron transport chain of aerobic respiration. It plays a crucial role in extracting energy from nutrients.

Q4. Where does cellular respiration take place?

A- Cellular respiration occurs in the mitochondria of eukaryotic cells. In prokaryotic cells, it takes place in the cytoplasm.

Q5. What happens during glycolysis?

  A – Glycolysis is the initial stage of cellular respiration where glucose is broken down into two molecules of pyruvate, producing a small amount of ATP.


Cellular respiration is a fundamental process in living organisms and an important aspect of biology and biochemistry. It is a central mechanism for energy production in living organisms for survival and productivity.

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  • […] biological systems, that facilitate the movement of electrons during crucial processes such as cellular respiration and photosynthesis. These carriers are essential for harnessing and transporting the energy derived […]


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