Enzymes

Figure 1 shows a percentile chart for the height of boys from age 2 to age 16.

Which is the height of an 8-year-old boy on the 10th percentile?

The height of a 4-year-old boy was 94 cm.

Two years later, his height was 106 cm.

Using Figure 1, explain the conclusion that can be made about the growth of this child.

Fats are needed for energy.

Describe how a sample of food can be tested to show that it contains fat.

Which is produced when fats are digested?

State what calorimetry is used to measure.

As bananas ripen, they change colour and taste sweeter.

Figure 1 shows two bunches of bananas.

Unripe bananas contain more starch.

Describe the chemical test for starch.

As bananas ripen the starch is converted to glucose.

Describe how bananas can be tested for the presence of glucose.

A banana with green skin tested positive for starch and negative for glucose.

A banana with yellow skin tested positive for both starch and glucose.

Explain why there was glucose in the yellow banana.

Pepsin and trypsin are enzymes that break down proteins.

Figure 3 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 5.

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.

6 (a) Why are enzymes called biological catalysts?

(b) Many cells contain an enzyme called catalase. Catalase breaks down hydrogen peroxide into water and oxygen. A scientist investigated the effect of hydrogen peroxide concentration on the time taken to produce 20 cm of oxygen. time taken to produce 20 cm³ of oxygen. Figure 12 shows the equipment used.

(i) State how the scientist could control the temperature of the flask.

(ii) Explain why the temperature should be controlled in this investigation.

(iii) This investigation used five different concentrations of hydrogen peroxide. Figure 13 shows the results of this investigation.

Figure 13

Complete the graph by plotting the points and drawing a line to show the trend in the data. The first point has been plotted for you.

35 X

time taken to 20 collect 20 cm of oxygen in seconds

concentration of hydrogen peroxide in arbitrary units

(iv) Describe the trend shown in the graph. Use data from the table in Figure 13 to support your answer.

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 10 shows the results of this investigation.

Describe the trends shown in Figure 10.

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 11 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 student mixed 10 cm3³ of starch solution with 5 cm³ of amylase solution and kept the tube in a water bath at 25 °C.

The student tested the solution for starch and for glucose every 30 seconds.

Figure 6 shows the results.

Give one reason for the result at 150 seconds.

Another student repeated the investigation with the same volumes of solutions and at the same temperature of 25 °C.

Give two other variables that would need to be controlled in the investigation.

Both students also included a tube containing 10 cm³ of starch solution with 5 cm³ of distilled water instead of 5 cm³ of amylase solution.

They tested the solution for starch and for glucose every 30 seconds.

Give one reason why this tube was included in their investigations.

Amylase has an optimum pH of 6.8.

Devise a method the students could use to confirm the optimum pH for amylase.

Amylase is produced by salivary glands and the pancreas.

Explain why amylase is not produced in the stomach.

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

Figure 4 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 5 shows a potato after being stored in the dark.

Figure 5

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 6 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 10.

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 7 shows the activity of the enzymes pepsin and trypsin at different pH levels.

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.

Starch is a nutrient in food.

Starch is a source of energy.

Name the enzyme that breaks down starch.

Give one reason why the contents of both test tubes were blue-black at the beginning of the investigation.

Explain the results of this investigation after ten minutes.

*(c) The diagram shows equipment that can be used to measure the energy content of different foods.

Devise a method to compare the energy content of two foods using this equipment.

Include details of how to control the variables.

The increasing human population is affecting farming and the habitats of animals.

Figure 12 shows the human population of the UK from 1960 to 2018.

Extend the line to estimate the human population of the UK in 2030 if this trend continues.

Food security means that a population has enough safe and healthy food.

Which of these would improve food security?

A scientist tested three samples of different foods.

Figure 13 shows the results.

Name the food group in sample E.

Name the food groups in sample F.

The emulsion test shows that food sample G contained fat. Describe how fat is digested in the body.

*(d) Figure 14 shows a field of a crop in one area of Africa.

The crop cannot be eaten by people.

The crop is used to produce biofuel.

(Source: © KAMBOU SIA/Stringer/Getty Images)

Figure 14

Describe the advantages and disadvantages of growing this crop to produce biofuel.

(a) Figure 12 shows a cross section through a leaf.

What is the name of the part labelled R in Figure 12?

Figure 13 shows the mass of glucose produced in each layer of a leaf per hour.

Describe the difference in the mass of glucose produced per hour in the palisade mesophyll and the mass of glucose produced in the spongy mesophyll shown in Figure 13.

Figure 14 shows how light intensity changed during one day.

Use information in Figure 14 to explain why oxygen moved out of the leaf between 9 am and midday.

Glucose is produced in a leaf.

Glucose is a

Describe a test for glucose.

Figure 15 shows an enzyme and three substrates found in plant cells.

The enzyme will only break down one of these substrates.

State the name of this enzyme.