|MadSci Network: Biochemistry|
You have asked an interesting and perceptive question. I think I can give only a partial answer, but hope it will be sufficient.
Catalase in general seems to protect organisms, including potato cells, from the effects of hydrogen peroxide. In plants, catalase is primarily located in peroxisomes, cell organelles which are like lysosomes, but break down simpler molecules. Catalase is involved in decomposition of hydrogen peroxide generated during cellular processes such as photorespiration and oxidation of fatty acids. Here is a link that explores catalase in potatoes more deeply: http://www.tarweed.com/pgr/PGR95-037.html .
In terms of photorespiration - well, you probably know that photosynthesis stores energy from the sun by making glucose. During photorespiration, the glucose is broken down. If the glucose is broken down using an enzyme called glucose oxidase, the reaction is:
The catalase is a catalyst for the reaction in which the hydrogen peroxide is broken down:
Try the links in the MadSci Library for more information on Biochemistry.