EnzymesEdexcel A-Level Biology A: Flashcards

Exam questions on Enzymes

1. Catalase is an enzyme found inside liver cells. It breaks down hydrogen peroxide, a toxic by-product of metabolism, into water and oxygen. Hydrogen peroxide breaks down very slowly if no enzyme is present.
   Describe how catalase lowers the activation energy of the breakdown of hydrogen peroxide.2 marks
2. Trypsin is a digestive enzyme made by cells of the pancreas and released into the small intestine, where it hydrolyses proteins in food. Pancreatic cells also contain many enzymes that catalyse reactions of respiration, which provides the cell with ATP.
   Suggest why enzymes that digest food, such as trypsin, are extracellular.2 marks
3. A student investigates the effect of enzyme concentration on the rate at which catalase breaks down hydrogen peroxide. She adds 1.0 cm³ of catalase solution to 10 cm³ of hydrogen peroxide solution, which is in excess, in a buffer at 25 °C, and collects the oxygen produced in a gas syringe. With a catalase solution of concentration X she collects 9 cm³ of oxygen in the first 30 seconds. With a catalase solution of concentration 2X she collects 18 cm³ of oxygen in the first 30 seconds.
   Calculate the mean rate of oxygen production over the first 30 seconds for each concentration of catalase, and state what the results show about the effect of enzyme concentration on rate.3 marks