Question

What are the three main stages of cellular respiration in order and where do they take place?

Answer 1

Hint: Cellular respiration is a complex set of metabolic reactions occurring intracellularly in an organism. These reactions are responsible for producing Adenosine triphosphate (ATP), i.e. the cell’s energy currency, from the breakdown of glucose and oxygen.

Complete answer:
The breakdown of glucose in presence of oxygen to produce ATP is very similar to the burning of fuel. Just like fuel, glucose is slowly burnt in the presence of oxygen. As burning fuel produces heat and light, glucose produces ATP, ${CO}_2$ and $H_{2}O$.
The 3 main stages of cellular respiration are:
-Glycolysis: This is an anaerobic process that takes place in the cell cytoplasm. Glycolysis is the stage where 1 glucose molecule is broken down into 2 molecules of pyruvate along with the release of 2 ATP and 2 NADH molecules. NADH molecule is another energy-storing molecule which when passed through the electron transport chain produces 2.5 ATP molecules.
-Kreb’s Cycle or Citric Acid Cycle: It is the second stage of cellular respiration where the pyruvate molecules form Acetyl CoA in the mitochondrial matrix that was produced from glycolysis. This is an aerobic process comprising 8 steps of chemical reactions which yield 2 molecules of ATP, 2 molecules of ${FADH}_2$, 6 molecules of NADH, and 4 molecules of ${CO}_2$. ${FADH}_2$ is also an energy-carrying molecule that produces 1.5 ATP molecules through the ETC.
-Electron Transport Chain: It is the final stage of the aerobic reaction that occurs across the inner membrane of a mitochondrion. It transports electrons and protons and is a protein complex that creates a proton gradient across the mitochondrial membrane, which helps in the formation of ATP molecules. These protons are given by the energy-storing molecules ${FADH}_2$ and NADH. Water molecules are given out as waste products.

Note:
Cellular respiration produces 34 molecules of ATP from 1 molecule of glucose.
This process takes place in eukaryotes only, as prokaryotes lack mitochondria. Cellular respiration is of two types: aerobic respiration, This process occurs in the presence of oxygen where the glucose molecule is broken down to produce energy. The other type is anaerobic respiration, it is the process of breaking glucose molecules partially and producing less energy in comparison to the anaerobic respiration.