ENZYMES
What type of biological molecule are most enzymes?
Proteins
Where does digestion begin?
Mouth.
Which food test is used to identify starch?
Iodine test.
A student chews a piece of bread for several minutes and notices that it begins to taste slightly sweet. Why?
Amylase in saliva begins breaking starch into smaller sugars.
What are the three main types of teeth involved in cutting, tearing and grinding food?
Incisors, canines and molars.
What is the name of the region of an enzyme where the substrate binds?
Active site
Which organ produces bile?
Liver.
What colour does iodine turn when starch is present?
Blue - black
Why does food need to be broken down into smaller molecules during digestion?
Large food molecules cannot be easily absorbed; smaller soluble molecules can pass through the intestinal wall.
Name the enzyme that begins protein digestion in the stomach.
Pepsin
What is the name given to the molecule that an enzyme acts upon?
Susbtrate
Where does most absorption of digested nutrients occur?
Small intestine.
Which reagent is used to test for reducing sugars?
Benedict's solution.
A student carries out a food test and gets a positive result for protein. Which reagent would they have used?
Biuret reagent.
What is the role of hydrochloric acid in the stomach?
It creates an acidic environment needed for pepsin to work and helps kill microorganisms.
A student heats an enzyme to 90°C and finds that it no longer works. Why?
The enzyme has been denatured; its active site has changed shape.
What is the function of villi in the small intestine?
They increase the surface area for absorption of digested nutrients into the blood.
What colour change indicates a positive Benedict's test after heating?
Blue → green/yellow/orange → brick-red, depending on the amount of reducing sugar.
Why does increasing temperature initially increase enzyme activity?
Molecules move faster and collide more frequently, increasing successful enzyme-substrate collisions—until the optimum temperature is reached.
Why is bile important even though it is not an enzyme?
It emulsifies fats into smaller droplets, increasing the surface area available for lipase to act on.
Two identical enzyme reactions are carried out. One is at pH 2 and the other at pH 7. The enzyme works much faster at pH 7. Explain why.
The enzyme has an optimum pH around 7. At pH 2, changes in pH can alter the enzyme's active site and reduce its activity.
A person has a blockage in their bile duct. How could this affect digestion?
Less bile reaches the small intestine, reducing the emulsification of fats and making fat digestion less efficient.
A food sample gives a blue-black colour with iodine but remains blue with Benedict's solution. What can you conclude?
The sample contains starch but no detectable reducing sugar.
A student says:
"If I keep increasing the temperature, the enzyme will keep working faster."
Is the student correct? Explain.
No. Enzyme activity increases up to an optimum temperature. Above this, the enzyme can denature and its activity decreases.
A student investigates the effect of temperature on amylase activity. At 20°C the reaction is slow, at 37°C it is fastest, and at 70°C there is almost no reaction. Explain the results.
At 20°C, particles have less kinetic energy and there are fewer successful collisions. Around 37°C, the enzyme is near its optimum temperature. At 70°C, the enzyme becomes denatured and its active site changes shape.