gas exchange occurs in the human lungs.
Answer: A mutagen is a chemical compound or form of radiation that causes mutations, which of course means a change in the dna of a cell. So, your answer would be C) an environmental agent that changes DNA.
The reaction that is been catalysed is the CATABOLISM [BREAKING DOWN] OF HYDROGHE PEROXIDE.
The name of the enzyme which catalysed the reaction is CATALASE.
The substrate is HYDROGEN PEROXIDE.
In an enzyme catalyzed reaction, a substrate refers to the chemical compound that is acted upon by the enzyme.