Digestion and Enzymes

State what is meant by a tissue.

Name the type of tissue that contracts to churn food in the stomach.

Figure 1 shows the human digestive system. Name the organs labelled A, B, C and D.

Describe the function of organ B in Figure 1.

Explain why the stomach is an organ and not a tissue.

Describe the path taken by a mouthful of food through the digestive system, from the mouth to the point where it leaves the body.

Explain why large food molecules, such as starch, have to be digested before they can be absorbed into the blood.

A cell is 50 µm long. Calculate how many of these cells would fit end to end along a strip of tissue 2 mm long. (1 mm = 1000 µm)

Describe the roles of the pancreas and of the small intestine in digestion.

Explain how cells, tissues, organs and organ systems are related. Use the stomach and the digestive system as examples.

What is a group of similar cells that work together called?

1. AAn organ
2. BA tissue
3. CAn organ system
4. DAn organism

Which list shows the levels of organisation in the correct order, smallest first?

1. AOrgan, tissue, cell, organ system
2. BTissue, cell, organ, organ system
3. CCell, organ, tissue, organ system
4. DCell, tissue, organ, organ system

Which tissue makes digestive juices in the stomach?

1. AMuscular tissue
2. BEpithelial tissue
3. CGlandular tissue
4. DNervous tissue

Which organ makes bile?

1. AThe liver
2. BThe gall bladder
3. CThe pancreas
4. DThe stomach

Which organ stores bile until it is needed?

1. AThe liver
2. BThe pancreas
3. CThe stomach
4. DThe gall bladder

What is the job of the large intestine?

1. ATo digest protein
2. BTo absorb water
3. CTo make bile
4. DTo store bile

Why must starch be digested before it can be absorbed?

1. AIt is poisonous
2. BIt is a liquid
3. CIts molecules are too large to pass through the gut wall
4. DIt cannot be used by cells

Which organs make digestive enzymes that are released into the small intestine?

1. AThe pancreas and the small intestine
2. BThe liver and the gall bladder
3. CThe oesophagus and the stomach
4. DThe large intestine and the anus

A cell is 20 µm long. How many fit end to end along 1 mm? (1 mm = 1000 µm)

1. A5
2. B20
3. C500
4. D50

A student says that the stomach is a tissue. What is the best correction?

1. AIt is a single cell
2. BIt is an organ made of several tissues
3. CIt is an organ system
4. DIt is an organism

State what is meant by a catalyst.

Name the part of an enzyme into which the substrate fits.

Figure 1 shows an enzyme and its substrate. (a) Name the region of the enzyme marked X. (b) Name the model of enzyme action shown in Figure 1.

Figure 2 shows the stages of an enzyme-controlled reaction. Describe what happens at stages 2, 3 and 4.

An enzyme that breaks down starch does not break down protein. Explain why.

A student boils a solution of an enzyme and then adds it to its substrate. The reaction does not happen. Explain why.

Figure 3 shows the effect of temperature on the rate of an enzyme-controlled reaction. Describe the effect of increasing the temperature from 0 °C to 70 °C.

In an investigation, an enzyme reaction took 50 seconds to finish at 25 °C and 20 seconds to finish at 35 °C. Use the equation rate = 1000 ÷ time to calculate the rate at each temperature, and calculate how many times faster the reaction was at 35 °C.

Pepsin is an enzyme in the stomach with an optimum pH of about 2. Explain what would happen to the rate of reaction if pepsin were put into a solution at pH 7.

Explain why the rate of an enzyme-controlled reaction increases as the temperature rises to about 40 °C, but decreases at higher temperatures.

What is an enzyme?

1. AA sugar that stores energy
2. BA type of fat
3. CA biological catalyst
4. DA kind of hormone

What is the substrate?

1. AThe substance an enzyme acts on
2. BThe part of an enzyme where the reaction happens
3. CThe substance made by the reaction
4. DThe enzyme joined to its product

Why is each enzyme specific to one substrate?

1. AIt is made in only one organ
2. BIt works at only one temperature
3. CIt is made of only one amino acid
4. DIts active site has a shape that fits only that substrate

What happens to an enzyme that is denatured?

1. AIt is used up
2. BIt changes shape and cannot bind its substrate
3. CIt joins to the substrate permanently
4. DIt makes more product

What is the effect on an enzyme of cooling it in a fridge?

1. AIt slows down but is not denatured
2. BIt is denatured
3. CIt is used up
4. DIt changes its substrate

Between 0 °C and the optimum temperature, what happens to the rate of an enzyme reaction as the temperature rises?

1. AIt falls
2. BIt stays the same
3. CIt rises
4. DIt falls to zero

Which enzyme has an optimum pH of about 2?

1. AAmylase in the mouth
2. BPepsin in the stomach
3. CLipase in the small intestine
4. DAmylase in saliva

An enzyme reaction takes 25 s. What is the rate, using rate = 1000 ÷ time?

1. A4
2. B25
3. C400
4. D40

A reaction makes 60 cm³ of product in 5 minutes. What is the mean rate?

1. A12 cm³ per minute
2. B300 cm³ per minute
3. C55 cm³ per minute
4. D65 cm³ per minute

A student says that heating an enzyme above its optimum temperature kills it. What is the best correction?

1. ANothing, it is correct
2. BIt makes the enzyme work faster
3. CEnzymes are not alive; they are denatured when their shape changes
4. DIt makes more substrate

Name the enzyme that breaks down starch into simple sugars.

Name the small molecules produced by the digestion of (a) protein, (b) fat and (c) starch.

Amylase is made in three places in the body. Name the three places.

Figure 1 shows three large food molecules being broken into smaller molecules by enzymes. (a) State what the enzymes do to the large molecules. (b) Explain why the small molecules can be absorbed but the large molecules cannot.

Explain why the body needs different enzymes to digest starch, protein and fat.

Describe where bile is made and where it is stored.

Explain the role of bile in the digestion of fat.

A cube of fat has sides of 3 cm. It is emulsified into 27 cubes with sides of 1 cm. Calculate the total surface area of the fat before and after emulsification, and say how many times bigger it became.

A student eats a cheese sandwich, which contains starch, protein and fat. Describe how each of these is digested. Name the enzyme and the products in each case.

Which enzyme breaks down fat?

1. AAmylase
2. BLipase
3. CProtease
4. DCarbohydrase

Which enzyme breaks down protein into amino acids?

1. AAmylase
2. BLipase
3. CBile
4. DProtease

Starch is digested into which product?

1. ASimple sugars
2. BAmino acids
3. CFatty acids
4. DGlycerol

Which organs make lipase?

1. AThe salivary glands and the stomach
2. BThe liver and the gall bladder
3. CThe pancreas and the small intestine
4. DThe stomach and the oesophagus

Where is protease made?

1. AThe salivary glands
2. BThe stomach
3. CThe liver
4. DThe large intestine

What is bile?

1. AAn enzyme that breaks down fat
2. BAn acid made in the stomach
3. CA type of lipid
4. DAn alkaline fluid that helps to digest fat

Why must bile be alkaline?

1. ATo neutralise the acid that comes from the stomach
2. BTo make the food acidic
3. CTo digest protein
4. DTo kill the enzymes

How does emulsification make fat digestion faster?

1. AIt makes the fat acidic
2. BIt adds more lipase
3. CIt increases the surface area of the fat
4. DIt cools the fat down

A cube of fat is cut into eight smaller cubes. What happens to the total surface area?

1. AIt decreases
2. BIt increases
3. CIt stays the same
4. DIt becomes zero

A student says that bile digests fat because it is an enzyme. What is wrong with this?

1. ANothing, it is correct
2. BBile digests protein, not fat
3. CBile is made in the stomach
4. DBile is not an enzyme: it emulsifies the fat so lipase can digest it faster

Name the reagent used to test for starch.

State the colour change that shows that starch is present in a food sample.

Figure 1 shows four tests on a sample of food. Tube A contains iodine solution, tube B contains Benedict's reagent after heating, tube C contains Biuret reagent, and in tube D the food was shaken with ethanol and poured into water. Use Figure 1 to say whether the sample contains starch, sugar, protein and lipid.

Describe how you would test a food sample for sugar.

A student heats a test tube containing Benedict's reagent in a hot water bath, and not in a Bunsen burner flame. Suggest two reasons for this.

Describe how you would test a food for lipids, and what you would see if the result is positive.

A student also tests some distilled water with iodine solution. Explain why.

Food X gave these results: the iodine solution turned blue-black, Benedict's reagent stayed blue after heating, Biuret reagent stayed blue, and the emulsion test stayed clear. Say what food X contains and does not contain.

Describe two safety precautions that should be taken when doing the food tests.

A student has three foods, P, Q and R. Describe how the student could use Benedict's reagent to find out which food contains the most sugar.

Which reagent turns purple when protein is present?

1. AIodine solution
2. BBenedict's reagent
3. CBiuret reagent
4. DEthanol

A food is tested with iodine solution and the solution turns blue-black. What does the food contain?

1. AStarch
2. BSugar
3. CProtein
4. DLipid

What must be done after adding Benedict's reagent to a sample?

1. AAdd iodine
2. BLeave it in the freezer
3. CAdd ethanol
4. DHeat it in a water bath

In Benedict's test, a sample turns brick red. What does this show?

1. AThere is no sugar
2. BThere is a large amount of sugar
3. CThere is protein
4. DThere is starch

What is the positive result for the emulsion test for lipids?

1. AA blue-black colour
2. BA purple colour
3. CA cloudy white emulsion
4. DA brick-red colour

Why is the lipid test done with ethanol?

1. ALipids dissolve in ethanol
2. BEthanol turns purple
3. CEthanol is a protein
4. DEthanol is a sugar

Why should a student use a water bath instead of a flame to heat Benedict's reagent?

1. AA flame makes the sugar disappear
2. BBenedict's reagent only works in water
3. CA flame turns it blue
4. DThe liquid is less likely to boil over

A food gives no colour change with any of the four tests. What can you conclude?

1. AIt contains all four
2. BIt contains none of the four groups tested for
3. CIt contains only protein
4. DIt contains only water

Why is it useful to test a food that you know contains starch with iodine solution?

1. AIt shows what a positive result looks like
2. BIt makes the iodine work
3. CIt removes the starch
4. DIt cools the iodine

These tests are qualitative. What does this mean?

1. AThey give an exact amount
2. BThey only work at 75 °C
3. CThey show whether a substance is present, not exactly how much
4. DThey need a colorimeter

Name the solution used to show when all of the starch has been digested.

Figure 1 shows the apparatus used to investigate amylase. Explain the purpose of the water bath and of the spotting tile.

A buffer solution is added to the mixture of starch and amylase. Explain why.

In an investigation into the effect of pH on the rate of reaction of amylase, state the independent variable, the dependent variable and one control variable.

At pH 7 the mean time taken for the starch to be digested was 60 seconds. Use rate = 1000 ÷ time to calculate the rate. Give your answer to one decimal place.

Figure 2 shows the results of the investigation. (a) Use Figure 2 to give the optimum pH. (b) The rate at pH 8 was 8.0. Use rate = 1000 ÷ time to calculate the time taken at pH 8.

Describe the effect of pH on the rate of reaction shown in Figure 2.

Explain why the rate of reaction is lower at pH 9 than at pH 7.

The investigation only used whole pH values from 5 to 9, and judged the colour of the iodine by eye. Suggest two improvements to the method, and explain why each would help.

Describe how you would investigate the effect of pH on the rate of reaction of amylase.

What does the colour of iodine solution tell you in this investigation?

1. AThe pH of the mixture
2. BWhether starch is still present
3. CThe temperature
4. DHow much amylase there is

What is the independent variable?

1. AThe time taken
2. BThe temperature
3. CThe volume of starch
4. DThe pH of the buffer

What is the dependent variable?

1. AThe time taken for the starch to be digested
2. BThe pH
3. CThe type of enzyme
4. DThe size of the test tube

Why is a water bath used in this investigation?

1. ATo change the pH
2. BTo make the starch
3. CTo keep the temperature constant
4. DTo make the iodine work

What is the purpose of a buffer?

1. ATo act as an enzyme
2. BTo keep the pH constant
3. CTo heat the mixture
4. DTo add starch

The time taken at one pH is 50 s. What is the rate, using rate = 1000 ÷ time?

1. A0.05
2. B5
3. C50
4. D20

At which pH was amylase fastest in the example investigation?

1. ApH 7
2. BpH 5
3. CpH 9
4. DpH 3

Why does the rate fall at a pH far from the optimum?

1. AThe starch disappears
2. BThe enzyme is used up
3. CThe enzyme is denatured
4. DThe iodine stops working

Which change would make the results more precise?

1. AUsing a colder water bath
2. BSampling every 10 seconds
3. CUsing less starch each time
4. DTaking only one sample

A student says the rate at pH 9 is lower than at pH 7 because the enzyme is used up. What is the best response?

1. AEnzymes are not used up; the enzyme is denatured, so the starch does not fit
2. BThat is correct
3. CThe enzyme has turned into starch
4. DThe iodine has used up the enzyme