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

Sep 17, 2016

The first part of glycolysis is endothermic:

#### Explanation:

$\textcolor{b l u e}{\text{Endothermic or exothermic?}}$
The difference between endothermic and exothermic in this context:

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

$\textcolor{b l u e}{\text{Cellular respiration}}$
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 : $\textcolor{red}{\text{endothermic}}$ process in which glucose is converted into fructose with 2 phosphate groups $\to$ investment of 2 ATP
2. Glycolysis II : $\textcolor{g r e e n}{\text{exothermic}}$ 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.