Biology – What happens in cells? (B1.2)
PRACTICAL Investigate the effect of pH on the rate of reaction of amylase enzyme
KEY WORDS amylase starch iodine solution
Learning objectives: • • • •
describe how safety is managed, apparatus is used and accurate measurements are made explain how representative samples are taken make and record accurate observations draw and interpret a graph from secondary data using knowledge and observations.
Amylase is an enzyme that controls the breakdown of starch in our digestive systems. Starch turns a blue-black colour when iodine (an orange solution) is added.
Making accurate measurements and working safely In this investigation digestion is modelled, using solutions of starch and amylase in test tubes, to find the optimum pH required for the reaction. Amylase and starch solution are each added to a separate test tube and put in a water bath or a beaker of hot water at 25°C and left for 5 minutes. The pH buffer solution is added to the amylase, before adding the starch. To carry out this method small volumes of chemicals and enzymes (less than 10 cm3) must be accurately measured. To do this a 10 cm3 measuring cylinder or a 10 cm3 calibrated dropping pipette could be used. The investigation also involves taking samples from the mixture at timed intervals and adding them to iodine solution in a spotting tile. To do this a glass rod or a dropping pipette could be used. The time at which the solution no longer turns a blue-black colour with iodine solution (the iodine solution remains orange) is recorded.
These pages are designed to help you think about aspects of the investigation rather than to guide you through it step by step.
amylase starch water
Drop of starch/amylase mixture added at zero time
The procedure is repeated for different values of pH buffer solution. 1
Which piece of apparatus would you use to: a b
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measure small volumes accurately? add drops of solution to the iodine?
Spotting tile containing drops of iodine solution
OCR Gateway GCSE Biology for Combined Science: Student Book
OCR_Bio_Combined_Book.indb 30
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