Question

What is the endothermic reaction for aerobic respiration in a living cell?

Answer 1

The first part of glycolysis is endothermic:

Explanation:

`color(blue)"Endothermic or exothermic?"`
The difference between endothermic and exothermic in this context:

• endothermic = a reaction that requires energy to occur
• exothermic = a reaction the creates energy

`color(blue)"Cellular respiration"`
Cellular respiration can be divided into three steps:

1. Glycolysis
2. Krebs Cycle
3. Electron Transport Chain

When you look at cellular respiration (aerobic) as a whole, it is an exothermic reaction because it creates chemical energy in the form of ATP.

There is an endothermic step in glycolysis. Glycolysis is the breakdown of glucose into 2 pyruvate molecules. As a whole glycolysis is exothermic, yielding net 2 ATP. Glycolysis itself can be devided into:

1. Glycolysis I : `color(red)"endothermic"` process in which glucose is converted into fructose with 2 phosphate groups `->` investment of 2 ATP
2. Glycolysis II : `color(green)"exothermic"` process in which 2 pyruvate molecules and 4 ATP is formed.

The image below visualizes this process. Glycolysis I is the only endothermic reaction in cellular respiration, the other processes are exothermic.