Through the wall of the gut — questions

1. complete

Complete the description of chemical digestion, and link it to what happened in bag A.

Chemical digestion is the breakdown of … insoluble molecules

into small … molecules.

In bag A, the large molecules were …,

and the small molecules that passed through the tubing were a ….

The enzyme that broke the large molecules down was ….

Nudge (only if you are stuck): Think of what went into bag A and what came out through the tubing: which was the big molecule, and which the small one?

2. deduce

A pupil sets up a third bag, C, exactly like bag A: starch suspension and amylase. The table shows her results for the water outside bag C. Which conclusion is correct?

Circle one answer.

• Amylase got out and made starch in the water outside
• Starch molecules are small enough to pass the tubing
• Sugar got out and turned back into starch outside
• Starch got out, so bag C probably has a hole or a leak

Nudge (only if you are stuck): Which molecule does iodine detect? Compare the iodine column for bag C with the iodine results outside bag A.

3. identify

The label on a tin of soup lists these substances. Which of them must be chemically digested before they can be absorbed into the blood? Choose all that are right.

Tick every correct statement.

• Salt
• Vitamin C
• Protein
• Water
• Glucose
• Starch
• Fat

Nudge (only if you are stuck): Ask of each one: is it a large insoluble molecule, or is it already small and soluble?

4. sequence

Supplement. Put the steps in order, from the starch in a baked potato to glucose in the blood. One of the six steps never happens: leave it out.

Write the number of each step in order.

1. Each maltose molecule is split into two glucose molecules
2. Glucose passes through the lining of the small intestine into the blood
3. Pancreatic juice in the duodenum turns the remaining starch into maltose
4. Saliva mixed with the chewed potato starts turning some starch into maltose
5. Maltase in the saliva splits maltose into glucose in the mouth
6. Maltose meets maltase held on the cells lining the small intestine

• Step 1: ______
• Step 2: ______
• Step 3: ______
• Step 4: ______
• Step 5: ______

Nudge (only if you are stuck): Follow one starch molecule from the mouth onwards. Which juice meets it first, and what does each enzyme make?

5. classify

A Visking bag holds starch suspension, glucose solution and amylase. It hangs in a beaker of water at 37 °C for 30 minutes. Match each substance to where it is found at the end.

Write the number of the matching option.

1. Inside the bag and in the water outside
2. Only inside the bag

• Starch: ______
• Amylase: ______
• Glucose: ______
• Maltose: ______

Nudge (only if you are stuck): Which of these are large molecules, and which are small? Does it matter whether a small molecule was made in the bag or put there?

6. describe / explain

A pupil wants to show that a protease makes small molecules that pass through Visking tubing. Bag P holds gelatine suspension (gelatine is a protein) and protease, and hangs in water at 37 °C. (a) Describe the control bag, Q, that she should set up beside it. (b) Explain how bag Q helps her to reach a conclusion.

(a) The control bag Q

(b) How bag Q helps the conclusion

Nudge (only if you are stuck): A control is set up like bag P in every way except one. Which one thing is being tested?

7. explain / state

An hour after a meal of fish, there are more amino acids in the blood, but no protein from the fish reaches the blood. (a) Explain why the protein in the fish cannot be absorbed as it is. (b) State the role of chemical digestion that lets the body use this protein.

(a) Why the protein cannot be absorbed as it is

(b) The role of chemical digestion

Nudge (only if you are stuck): Think of the starch in bag A: why could none of it get out through the tubing?

8. describe / suggest

Supplement. (a) Describe where maltase is found and what it does. (b) Suggest an advantage of glucose being made at the surface that absorbs it.

(a) Where maltase is and what it does

(b) An advantage of making glucose where it is absorbed

Nudge (only if you are stuck): Look at the reading's drawing of starch becoming glucose: where is maltase drawn?

9. calculate

A short starch molecule is a chain of 600 glucose units. Suppose amylase breaks the whole chain into pieces two glucose units long: maltose. Calculate how many maltose molecules are made from this one starch molecule.

Number of maltose molecules: ______________ unit ________

Nudge (only if you are stuck): Maltose is a piece of the chain. How long is each piece?

10. identify / explain

A Visking bag holds starch suspension, corn oil and one enzyme. It hangs in a beaker of water at 37 °C for an hour. Then the water outside the bag is tested: Benedict's solution stays blue after heating, iodine solution stays yellow-brown, and a test shows that glycerol is there. (a) Identify the enzyme in the bag. (b) Explain why glycerol is found in the water outside the bag, but the starch and the oil are not.

(a) The enzyme

(b) Why glycerol is outside the bag, but starch and oil are not

Nudge (only if you are stuck): Which kind of food molecule is glycerol part of? Then ask of each substance: is its molecule small and soluble?

11. explain

After an operation on the gut, a patient cannot eat for a week. Instead, a drip runs a liquid slowly through a thin tube into a vein in the arm. The liquid contains glucose and amino acids, but no starch or protein. Explain why.

Nudge (only if you are stuck): The drip goes straight into the blood. Which molecules does the blood normally take up from the small intestine?

12. explain / suggest

A pupil repeats the experiment with one pipette for both beakers and does not wash it: each time, she takes a sample from outside bag A first, then from outside bag B. (a) Explain how this could change her results for bag B. (b) Suggest the wrong conclusion she might draw, and how to avoid the problem.

(a) How the results for bag B could change

(b) The wrong conclusion, and how to avoid the problem

Nudge (only if you are stuck): What is in the drops of water left inside the pipette after a sample from outside bag A at 20 minutes?

13. suggest / explain

Supplement. In some diseases of the small intestine, the cells of the epithelium lining it are damaged and make very little maltase. (a) Suggest which sugar builds up in the small intestine after a meal containing starch. (b) Explain the effect on the absorption of glucose.

(a) The sugar that builds up

(b) The effect on glucose absorption

Nudge (only if you are stuck): Which step of starch digestion still works, and which step needs the cells lining the small intestine?