A yeast suspension that was boiled for 5 minutes and then cooled shows no bubbling and does not relight a glowing splint when hydrogen peroxide is added, unlike an unboiled sample of the same yeast suspension. Why?
ABoiling increased the catalase's activity so much that all of the hydrogen peroxide had already reacted before the glowing splint could even be inserted into the tube.
BThe cooling step under running tap water washed all of the hydrogen peroxide out of the tube before any reaction with the yeast could begin.
CThe catalase in the boiled sample was denatured by the heat because it is a protein, so it could no longer catalyse the breakdown of hydrogen peroxide.
DThe yeast suspension in tube B had already been killed by the cold tap water before it was ever placed into the boiling water bath at all.
Explanation
Catalase, like all enzymes, is a protein. Boiling disrupts its tertiary structure (denaturation), permanently destroying its active site, so it can no longer catalyse the breakdown of hydrogen peroxide.
Derived from ZIMSEC Biology Paper 4 (Practical Test), Jun 2004, Q3