Here are the answers:
Electron transport system for the first blank
oxygen for second blank
increase for the last blank
Free radicals are atoms that has an odd number of electrons and usually formed when an oxygen interacts other molecules. The formation of radical will result into damage of the main cellular components such as DNA. This can alter the signalling pathways inside the cells. This is usually involved in various diseases such as in cancer wherein the mutation can be caused by the alteration on the DNA within the nucleus. Other diseases that are involved or related are Parkinson's disease, alzheimer's, schizophrenia.
