IGCSE Biology Paper-2: Specimen Questions with Answers 170 - 170 of 203

Question 170



Given graph is showing activity of different enzymes

Given Graph is Showing Activity of Different Enzymes

What will be the X, Y, and Z?


Choice (4)


X-most enzymes, Y-pancreatic lipase, Z-pepsin


X-pepsin, Y-pancreatic lipase, Z-most enzymes


X-pepsin, Y-most enzymes, Z-pancreatic lipase


X-most enzymes, Y-pepsin, Z-pancreatic lipase




Enzymes and pH

  • Acid or alkaline conditions alter the chemical properties of proteins, including enzymes. Most enzymes work best at a particular level of acidity or alkalinity (pH) the protein-digesting enzyme in your stomach, for example, works well at an acidity of pH 2. At this pH, the enzyme amylase, from your saliva, cannot work at all. Inside the cells, most enzymes will work best in neutral conditions (pH 7) .
  • The pH or temperature at which an enzyme works best is often called its optimum pH or temperature. Conditions in the duodenum are slightly alkaline: the optimum pH for pancreatic lipase is pH 8. Although changes in pH affect the activity of enzymes, these effects are usually reversible, i.e.. an enzyme that is inactivated by a low pH will resume its normal activity when its optimum pH is restored.
Enzymes and pH