Enzymes

Pepsin and trypsin are enzymes that break down proteins.

Figure 1 shows the results of an investigation into the activity of pepsin and trypsin at different pH levels.

Which molecules are produced when a protein is broken down?

Describe the trend in the graph for the enzyme pepsin.

Use data from the graph to support your answer.

State the optimum pH for the enzyme trypsin.

Explain why there is no trypsin activity at pH 5.

Temperature is a variable that should be controlled in this investigation.

Give one way the temperature could be controlled.

A student investigated the fat content of two types of milk: milk A and milk B.

Before starting the investigation, the student added a drop of oil from a pipette into a test tube of water as shown in Figure 3.

The drop of oil rose to the surface of the water.

The student then placed a drop of milk A into one test tube of water and a drop of milk B into a different test tube of water.

The drop of milk A sank to the bottom and the drop of milk B rose to the surface.

Give one reason for the drop of milk B rising to the surface.

5 cm³ of milk B and 1 cm³ of lipase were added to a different test tube.

The pH of this mixture was pH 7.

This test tube was placed in a water bath for 10 minutes.

The pH of the mixture changed from pH 7 to pH 5.

Explain what caused this change in pH.

This procedure was repeated with milk A.

There was no change in the pH of this mixture after 10 minutes.

Explain why there was no change in the pH of the mixture containing milk A.

The student repeated this procedure with lipase that had been boiled and left to cool.

This was added to another sample of milk B.

Describe why the pH did not change in this mixture.

A student investigated the activity of a human enzyme at different temperatures.

The student measured the mass of product formed after 10 minutes at different temperatures.

Figure 5 shows the results of this investigation.

Describe the trends shown in Figure 5.

Explain the results obtained for temperatures from 40 °C to 60 °C.

Some enzymes are involved in the breakdown of food substances.

Draw one straight line from each food group to the products of digestion for that food group.

Which enzyme breaks down fat?

Figure 6 shows an enzyme and two substrates, P and Q.

Explain the reason why no product will be formed if the enzyme is mixed with substrate Q.

A slide of potato cells was viewed using a light microscope.

Figure 3 is a drawing of the slide showing starch grains in the potato cells.

Calculate the mean number of starch grains in potato cells P, Q and R.

Which structures are found in plant cells but are not found in animal cells?

A scientist investigated how the length of starch grains in potatoes changed when the potatoes were stored in the dark.

Figure 4 shows a potato after being stored in the dark.

Figure 4

Three potatoes were used in the investigation.

The length of starch grains in potato 1 were measured at the start.

The length of starch grains in potato 2 were measured after 5 weeks in the dark.

The length of starch grains in potato 3 were measured after 10 weeks in the dark.

Figure 5 shows the results.

Calculate the percentage difference in the mean length of starch grains in potato 2 at 5 weeks and in potato 3 at 10 weeks.

State two variables the scientist should have controlled to improve this investigation.

The starch grains in the potatoes became smaller as the starch was converted into glucose.

State why the potatoes need glucose.

Describe how starch is broken down into glucose.

Trypsin is a protease enzyme used in the manufacture of food for babies.

Which food group is digested by trypsin?

The food is mashed before the trypsin is added.

Explain the advantage of mashing the food before adding the trypsin.

A manufacturer of baby food wanted to find out the optimum pH for trypsin.

Equal volumes of different pH solutions were placed in six separate test tubes.

5 cm³ of 1% trypsin solution was added to each test tube.

1.5 g of mashed food was placed in each test tube.

The time taken to digest the food was recorded.

State one other variable that should be controlled in this investigation.

State how this variable could be controlled.

The results are shown in Figure 6.

Describe the trends shown in this data.

At pH 4, the trypsin digested 1.5 g of mashed food at a rate of 0.8 g per minute.

Calculate the rate of digestion at pH 1.

Give your answer to one significant figure.

Explain the difference in the rate of reaction at pH 1 and the rate of reaction at pH 4.

Figure 3 shows the activity of the enzymes pepsin and trypsin at different pH

Describe the trend in the graph for the enzyme trypsin.

Use data from the graph to support your answer.

State the optimum pH for the enzyme pepsin.

Pepsin only works effectively in the stomach.

Describe the conditions in the stomach that allow pepsin to work effectively.

At high pH values the active site of the enzyme pepsin changes shape.

When the active site of the enzyme changes shape, the enzyme is

State what is produced when proteins are digested.