§Note: Some enzymes are make of RNA and these RNAs do not get translated. The process of regulating gene expression is highly complex, but there is KhanAcademy material on this is several places - I recommend starting here: In fact, most multicellular organisms depend on their microbiota for survival!

The digestive system of animals is one example of this. The purpose of this experiment was to determine the effect of different aqueous solutions of ionic compounds on the rate of reaction of the enzyme catalase. Negative controls are particular samples included in the experiment that are treated the same as all the others but are not expected to change from any variable in the experiment. However, multicellular organisms are colonized by many different microbes (these may be prokaryotes or other eukaryotes such as fungi) - these microbes often supply enzyme activities that aid the organism. To reduce variables in any type of experiment, it is recommended to include both positive and negative controls in the experimental design. Typically enzymes found within a cell are encoded by the DNA of that cell. To test this, they carry out an experiment that includes 3 different enzymes: pepsin, salivary amylase, and arginase. Enzymes are encoded as genes in the DNA - these genes are then transcribed to produce RNA and (for most enzymes§) then translated† to make a protein that has a catalytic activity (i.e. A researcher claims that different enzymes exhibit maximal function over different pH ranges.

Negative control for enzyme experiment