Enzyme action

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.

Plants need light for photosynthesis.

Part of the photosynthesis equation is shown below.

reactant A + water glucose + product B

Which row in the table shows reactant A and product B?

Name the green chemical in chloroplasts that absorbs light.

Plan an experiment to investigate if plants grow faster when they receive more light. Use the equipment shown in Figure 3.

State one factor that you would keep the same in this experiment.

A plant was kept at a very high temperature of 60C.

Explain the effect of this temperature on photosynthesis.

Apple trees show genetic variation.

State one possible cause of genetic variation in apple trees.

The colour of an apple is an observable characteristic.

Which is the term for an observable characteristic?

Name the type of reproduction that produces genetically identical organisms.

Grafting is a technique used to grow some varieties of apple tree.

Figure 16 shows apple tree shoots grafted on to a rootstock.

Grafting can be used to produce apple trees that are genetically identical.

Give one advantage and one disadvantage of growing genetically identical apple trees.

advantage

disadvantage

As apples ripen, enzymes convert starch into sugars.

Devise a method to find the optimum pH of an enzyme that breaks down starch.

You may use standard laboratory equipment and the solutions listed in the box.

The optimum pH of an enzyme is pH 6.

Explain why this enzyme would not work at pH 10.

Name the type of reproduction that produces genetically identical organisms.

Grafting is a technique used to grow some varieties of apple tree.

Figure 3 shows apple tree shoots grafted on to a rootstock.

Grafting can be used to produce apple trees that are genetically identical.

Give one advantage and one disadvantage of growing genetically identical apple trees.

advantage

disadvantage

As apples ripen, enzymes convert starch into sugars.

Devise a method to find the optimum pH of an enzyme that breaks down starch.

You may use standard laboratory equipment and the solutions listed in the box.

The optimum pH of an enzyme is pH 6.

Explain why this enzyme would not work at pH 10.

1 Figure 1 shows a bird called an egret on the back of a buffalo.

(Source: © Jaromir Chalabala/Shutterstock)

(a) (i) The egret eats parasites that live on the skin of the buffalo. Which term describes this relationship, where the buffalo and the egret both benefit?

(ii) The buffalo is part of the carbon cycle. Use words from the box to complete the sentences.

The buffalo gains carbon from the_{..............................................................} in the plants that it eats. Bacteria will_{..............................................................} the waste from the buffalo.

(iii) Figure 2 shows part of the carbon cycle. Draw and label an arrow on Figure 2 to show the process plants use to make glucose from carbon dioxide.

(b) Enzymes are used to digest proteins. Figure 3 shows an enzyme and a protein.

Explain how boiling the enzyme stops the protein being digested.

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.

8 Chymosin is an enzyme that causes milk to curdle. When milk curdles the proteins in the milk clump together and become solid.

(a) As part of an investigation, milk was heated in test tubes to different temperatures using a Bunsen burner. Two drops of chymosin solution were added to each test tube and the time taken for the milk to curdle was recorded. Figure 11 shows the results.

Figure 11

(i) Which variables need to be kept constant in this investigation?

(ii) Explain why the time taken for the milk to curdle decreases from 30°C to 40°C.

(iii) Explain what the expected result would be if two drops of chymosin were added to the milk at 70°C in the test tube.

(iv) As part of this investigation, test tubes containing only milk were heated to each temperature and no chymosin solution was added. State why these test tubes containing only milk were used.

(v) Describe two improvements that could be made to the method of this investigation so that the optimum temperature for chymosin can be found.

(b) Chymosin can be produced by genetically modified bacteria. Figure 12 shows a bacterial cell.

Figure 12

Explain how to genetically modify a bacterial cell to produce chymosin.

In Ireland during the 19th century, a mould caused potato plants to rot.

Explain how this mould affected food security in Ireland.

A group of pupils investigated the effect of temperature on mould growth on bread.

Figure 8 shows the bread after being kept at different temperatures for seven days.

Which is the best estimate of the percentage cover of mould on the bread at 40C?

State two conclusions that can be made about the growth of mould on the bread from 0C to 40C shown in Figure 8.

Explain why there was no mould growing on the bread kept at 60C.

Figure 9 shows some part-baked bread in a sealed bag.

The gas in the bag is nitrogen, which prevents the bread from going mouldy.

If the bag is opened, the bread goes mouldy within days.

State why the bread goes mouldy.

Explain why keeping food in a fridge slows down the growth of mould.

Figure 21 shows the human urinary system.

Urine is made by removing water, urea and salts from the blood.

Use the letter X to label where urine is made.

Which substance is converted to urea in the liver?

A patient cannot remove enough urea from the blood when making urine.

Figure 22 shows a dialysis machine attached to the arm of this patient.

Their blood is pumped out of their arm, passed through the dialysis machine, and then put back into the patient.

Describe what happens to urea as the blood passes through the dialysis machine.

Two patients need to have dialysis treatment.

Patient A needs this treatment three times a week.

Patient B needs this treatment once a week.

Give one reason why patient B needs dialysis treatment less often than patient A.

Describe how to test for glucose in the dialysis fluid.

Urease is an enzyme that breaks down urea into smaller molecules.

Explain why urease will not break down starch into smaller molecules.

Figure 7 shows the human urinary system.

Urine is made by removing water, urea and salts from the blood.

Use the letter X to label where urine is made.

Which substance is converted to urea in the liver?

A patient cannot remove enough urea from the blood when making urine.

Figure 8 shows a dialysis machine attached to the arm of this patient.

Their blood is pumped out of their arm, passed through the dialysis machine, and then put back into the patient.

Describe what happens to urea as the blood passes through the dialysis machine.

Two patients need to have dialysis treatment.

Patient A needs this treatment three times a week.

Patient B needs this treatment once a week.

Give one reason why patient B needs dialysis treatment less often than patient A.

Describe how to test for glucose in the dialysis fluid.

Urease is an enzyme that breaks down urea into smaller molecules.

Explain why urease will not break down starch into smaller molecules.

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.

Figure 6 shows a root hair cell from a strawberry plant.

Label the cell vacuole in Figure 6.

Explain how the structure of root hair cells increases water absorption from the soil.

Figure 7 shows fungus growing on strawberries.

The fungus is decomposing the strawberries.

A scientist investigated the effect of temperature on the decomposition of strawberries.

The scientist spread fresh strawberries on six trays.

Each tray was kept at a different temperature.

After five days the scientist measured the area of fungus that had grown on each tray of strawberries.

The results are shown in Figure 8.

The mean rate of growth of fungus at 25C was 12 cm² per day.

Calculate the mean rate of growth of fungus at 30C.

_........ cm² per day

State the effect of temperature on the growth of fungus on strawberries from 5C to 30C.

Decomposition of strawberries can be prevented by boiling the strawberries with sugar to make jam.

Enzymes in the fungus caused decomposition.

Explain how boiling stops the enzymes from working.

Cells from a fungus can land on jam.

The sugar solution inside the jam is more concentrated than the sugar solution inside the fungus cells.

State how osmosis causes the fungus cells to die.

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.

Lactase is an enzyme that breaks down lactose into glucose and galactose.

A student made some alginate beads containing lactase.

The student added 10 beads to 20 cm³ of a solution of lactose, as shown in Figure 9.

The student timed how long it took for glucose to be produced.

The experiment was repeated using 15, 20 and 25 beads.

The results are shown in Figure 10.

What is the rate of reaction for 25 beads?

Explain the conclusion that can be made from these results.

Explain why the same volume of lactose solution was used for each test.

Devise a method to find the optimum temperature for the enzyme lactase.

A student investigated the effect of enzyme concentration on the mass of product formed in one hour. Figure 6 shows the results of this investigation.

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

Describe the effect that enzyme concentration has on the mass of product formed.

The ratio of enzyme concentration to the mass of product formed, using an enzyme concentration of 40 arbitrary units, is 1:1.

Calculate the ratio of enzyme concentration to product formed when the enzyme concentration is 5 arbitrary units.

The investigation used the enzyme pepsin from the stomach, at a temperature of 37°C and at a pH of 7.

Which statement gives one way to increase the mass of product formed in this investigation?

Explain why a temperature of 80°C was not used in this investigation.

Potato cells contain the enzyme catalase.

This enzyme catalyses the breakdown of hydrogen peroxide into oxygen and water.

Figure 15 shows what happened when a student placed a potato disc in a 5% hydrogen peroxide solution.

hydrogen oxygen bubbles cause

solution

The student measured the time taken for the potato disc to rise.

The student repeated the investigation using 10%, 15% and 20% concentrations of hydrogen peroxide solution.

Which term describes the hydrogen peroxide in this reaction?

The potato discs all had the same mass.

Explain why the student used potato discs with the same mass.

State two other factors that need to be kept the same to improve this investigation.

Figure 16 shows the results of this investigation.

The student calculated the rate of reaction using

State and explain a conclusion based on these results.

The student repeated the investigation with a 25% hydrogen peroxide solution and recorded a time of 75 seconds.

Calculate the rate of reaction for the 25% hydrogen peroxide solution.

The student decided that the rate for the 25% hydrogen peroxide solution was not anomalous.

Give the reason why the result was not anomalous.

Figure 11 shows a British glow-worm.

Read the following extract before answering the questions.

Female glow-worms produce bright lights in the summer to attract males. Glow-worm larvae are predators of slugs and snails, but adult glow-worms do not feed. Females only have a few weeks to attract a mate and lay eggs, before the females die.

What will happen if the population of snails decreases?

Female glow-worms have an enzyme called luciferase. The glow is produced when this enzyme catalyses a reaction between oxygen and a protein.

A scientist devised a plan to investigate the effect of oxygen concentration on this reaction.

The scientist had:

• five flasks of water each with a different concentration of dissolved oxygen

• a solution of the protein

• a solution of the enzyme.

The first step of this plan is:

Step 1. Add some of the protein solution to each of the five flasks.

Describe the next two steps that should be in this plan to obtain results for this investigation.

Which procedure would improve the investigation?

The enzyme luciferase works best at pH 8.

Explain why the activity of the enzyme decreases at pH 5.

Female glow-worms are found attached to grass plants in a large field.

Describe a sampling technique to find the mean number of female glow-worms in 1 m² of the field.

The mean number of female glow-worms in 1 m² of the field is 5.

The field has a total area of 800 m².

Estimate the number of female glow-worms in the whole field.

(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.