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Chemical Reactions in Cellular Respiration

Grade 7
May 30, 2023

Introduction to Cellular Respiration

The process of food breakdown in the cell that results in the release of energy is referred to as cellular respiration. Cellular respiration can be carried out through aerobic or anaerobic respiration.

When we breathe, we take in oxygen and exhale carbon dioxide. Every cell in the body and every body part receives the oxygen that is breathed in. The cells require this oxygen for the breakdown of food in order to produce energy to perform vital functions for survival.

Cellular respiration

Types of Respiration

Two general categories of respiration are:

Types of respiration


Aerobic respiration is breaking down food to produce energy while reacting with oxygen.

The process of breaking down food to produce energy in the absence of oxygen is called anaerobic respiration.

Aerobic respiration: In this kind of respiration, the oxygen that is breathed in is distributed throughout the body and to the cells, where it is used to break down food into small components to get energy. For example, aerobic respiration occurs in humans.

Anaerobic respiration: In the absence of oxygen, food is broken down into small components to get energy in this type of respiration. For instance, obligate and facultative anaerobes.


Cellular respiration and chemical reaction


Cellular respiration is a sequence of metabolic processes that happen inside a cell.

For utilization in the energy-demanding processes of the cell, biochemical energy is extracted from organic materials (such as glucose) and then stored in energy-carrying biomolecules (such as adenosine triphosphate or ATP).

All living things have cells, and these cells are engaged in cellular respiration. Energy is produced during cellular respiration, which is essential since it is utilized to sustain life. Prokaryotic and eukaryotic cells both participate in cellular respiration.

Location of Cellular Respiration

Prokaryotic cells carry out the process in the cytoplasm, while eukaryotic cells start the process in the cytosol and finish it in the mitochondria. 

Glycolysis, transition reaction (pyruvate oxidation), the Krebs cycle (also known as the citric acid cycle), and oxidative phosphorylation via the electron transport chain are the four steps of cellular respiration in eukaryotes.

The Krebs cycle, oxidative phosphorylation, and pyruvate oxidation take place in the mitochondrion, whereas glycolysis happens in the cytosol.

cellular respiration

Steps Involved in the Cellular Respiration

Glycolysis, transition reaction (pyruvate oxidation), the Krebs cycle (also known as the citric acid cycle), and oxidative phosphorylation via the electron transport chain are the four steps of cellular respiration in eukaryotes.


A glucose molecule gradually decomposes into carbon dioxide and water during cellular respiration. The process by which glucose is broken down to provide energy is known as glycolysis.

It produces water, ATP, NADH, and two pyruvate molecules.

There is no need for oxygen throughout the process, which occurs in the cytoplasm of a cell. It occurs in both aerobic and anaerobic organisms.

Glucose must be brought into the cell and phosphorylated before glycolysis can start. This happens in the cytosol in the majority of organisms. The Embden-Meyerhof-Parnas (EMP) pathway, which was discovered by Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas, is the most typical kind of glycolysis.


Pyruvate Oxidation

Oxidation of pyruvate. The mitochondrial matrix and the deepest compartment of the mitochondria receive each pyruvate produced during glycolysis.

There, it is transformed into acetyl CoA, a two-carbon molecule linked to Coenzyme A. NADH is produced, and carbon dioxide is released.

Pyruvate oxidation

Citric Acid Cycle

When Acetyl CoA and a four-carbon molecule join, a series of chemical processes known as the Krebs cycle or the citric acid cycle take place.

In the end, the initial four-carbon molecule is regenerated with the addition of FADH2, NADH, carbon dioxide, and two molecules of ATP.

The tricarboxylic acid cycle is an additional name for the Krebs cycle.

Hans Adolf Krebs discovered the Krebs cycle, often called the citric acid cycle, in 1937. It can be thought of as an energy-producing metabolic pathway. In the mitochondrial matrix, where pyruvate has been imported after glycolysis, this process takes place.

Two molecules of CO2, three molecules of NADH, one molecule of FADH2, and one molecule of GTP are the Krebs cycle’s ultimate outputs. Per pyruvate molecule, these compounds are produced. Oxidative phosphorylation and the electron transport chain are both powered by the Krebs cycle’s byproducts. After the transition reaction, acetyl CoA enters the Krebs cycle (conversion of pyruvate to acetyl CoA).

Citric acid cycle

Oxidative Phosphorylation

Oxidative phosphorylation is a process in which the FADH2 and NADH produced in the Krebs cycle donate their electrons to oxygen through a variety of electron carriers via the electron transport chain.

The mitochondrial matrix is where this reaction happens.

A gradient is created as protons are pumped out of the matrix by the release of energy that occurs as electrons move down the chain. With the aid of the enzyme ATP synthase, which creates ATP, the protons then flow back into the matrix. Oxygen at the end of the chain takes the protons and electrons to create water.

Oxidative phosphorylation

Equation for Cellular Respiration

Chemical equations can be used to describe cellular respiration. An illustration of the aerobic respiration equation is:

Equation for cellular respiration

Sugar reacts with oxygen and gives rise to carbon dioxide, water, and energy in the form of ATP.

Importance of Cellular Respiration

The process by which cells in plants and animals break down sugar and transform it into energy, which is subsequently used to carry out work at the cellular level, is known as cellular respiration.

Cellular respiration serves the straightforward objective of giving cells the energy they require to function.

Food would be completely useless if living beings couldn’t obtain the energy they required from it. No matter the type or quantity of nourishment, all living beings will eventually perish.

Utilizable energy is produced from the meals that living things consume through cellular respiration.

Because this biochemical energy is generated to power several metabolic processes, such as biosynthesis, motility, and transportation of molecules across membranes, cellular respiration is crucial for both eukaryotic and prokaryotic cells.

Difference between Cellular Respiration and Photosynthesis

Cellular respirationPhotosynthesis
The process of cellular respiration produces ATP from the chemical energy of organic substances.Photosynthesis is a process that transforms light energy into the chemical energy of carbohydrates in the presence of sunlight.
All living organisms carry out cellular respiration.Only photoautotrophs carry out photosynthesis.
Cellular respiration utilizes glucose and oxygen and produces carbon dioxide, water, and energy.Photosynthesis utilizes carbon dioxide and water and produces glucose and oxygen.
 Cellular respiration occurs via four steps: glycolysis, oxidative phosphorylation, Krebs cycle, and electron transport chain.Photosynthesis occurs via two steps: light reaction and dark reaction.
The sites of cellular respiration are cytoplasm and mitochondria.The site of photosynthesis is chloroplasts.
Chemical reactions in cellular respiration


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