Define Catabloic - Biochemical reactions that break down molecules in metabolism.  Molecules may be broken down to gain their energy or to prepare them for disposal from the body. 

Continue with the theme of hydrogen peroxide - put into context that many reactions that occur in the body produce hydrogen peroxide. If the concentration of hydrogen peroxide was allowed to build up in the body it would eventually kill - the enzyme catalse is produced by the body and speeds up the decomposition reaction.

Can refer to: .http://resources.schoolscience.co.uk/JohnsonMatthey/page39.htm

Class experiment - testing out different sources of catalase

Video clip based on this experiment maybe also include yeast and blood. http://www.rsc.org/learn-chemistry/resource/res00000425/testing-for-enzymes. Follwed by a click and reveal question /answer session on it.

Problem solving reaction provides quite a nice context - http://www.rsc.org/learn-chemistry/resource/res00000657/catalase - might be better placed in applying understanding