A student found the following flowchart in a textbook.

Glyolysis->Krebs cycle->electron transport chain

What is the energy input of the process shown?

A) Potential energy from chlorophyll

B) Chemical energy from food molecules

C) Light energy from the sun

D) Electrical energy from hydrogen ions

Energy in food is released and stored

B) Chemical energy from food molecules

Glyolysis, Krebs cycle and Electron transport chain are three important steps of cellular respiration, in which the food we eat is transformed into chemical energy called ATP. This energy is used to perform day to day functions of our life.

The energy input for the whole process of cellular respiration is obtained through the chemicals bonds of glucose, that is obtained from the food we eat. The food macro-molecules like proteins, fats, carbohydrates serve as a fuel for cellular respiration. However, glucose is the most commonly used molecule that is used to analyse the reactions of cellular respiration that lead to the production of ATP is our body.

During Cellular respiration, glucose is broken down and energy rich molecules like NADH and FADH are produced. These molecules drives the Kreb cycle and ultimately electron transport, which builds a hydrogen proton gradient between the mitochondrial inter-membrane space and the mitochondrial matrix. After the series of three steps energy rich molecules called ATP are produced.

The process is also called oxidative phosphorylation.