Pupil sheet · Chemical digestion
Chemical digestion — return questions
Name ______________________ Date ____________
Use one to two weeks after the lessons. Keep the notes and the lesson closed.
1. identify
Which of these changes is chemical digestion?
Circle one answer.
- A protease breaks bean protein down into amino acids
- Glucose passes through the wall of the small intestine
- Teeth grind a peanut down into very small pieces
- A square of chocolate melts into a liquid in the mouth
2. predict
Cellulose, in the cell walls of plants, is a large insoluble molecule. Humans make no enzyme that digests it. Which of these happens to the cellulose in a meal of vegetables?
Circle one answer.
- It dissolves in the stomach acid and is absorbed from there
- It passes along the gut and leaves the body in the faeces
- It is absorbed into the blood as large cellulose molecules
- Chewing breaks it down into glucose, which is then absorbed
3. identify
Supplement. A sweet syrup made from barley contains maltose. Which row is correct for the enzyme that digests this maltose in the body?
| Row | Enzyme that digests the maltose | Where this enzyme is |
|---|---|---|
| A | amylase | in pancreatic juice |
| B | maltase | on the membranes of the epithelium |
| C | maltase | in pancreatic juice |
| D | amylase | on the membranes of the epithelium |
Circle one answer.
- A
- B
- C
- D
4. identify / state
A pupil adds one enzyme to a suspension of cornflour, which is mostly starch, at 37 °C. A sample tested with Benedict's solution before the enzyme was added stays blue after heating. A sample taken 15 minutes after the enzyme was added turns orange when heated with Benedict's solution. (a) Identify the enzyme. (b) State the kind of molecule that the Benedict's test detected.
(a) The enzyme
(b) The kind of molecule the Benedict's test detected
5. identify
A meal is a corn tortilla, which is mostly starch, grilled tofu, which is mostly protein, and ghee, a fat. Which row is correct for where the digestion of each food by enzymes starts?
| Row | Starch in the tortilla | Protein in the tofu | Fat in the ghee |
|---|---|---|---|
| A | mouth | mouth | small intestine |
| B | stomach | stomach | small intestine |
| C | mouth | stomach | stomach |
| D | mouth | stomach | small intestine |
Circle one answer.
- A
- B
- C
- D
6. identify / explain
A tube holds a mixture of protein and starch at 37 °C. One enzyme is added. After an hour the tube contains amino acids, but iodine still turns a sample blue-black. (a) Identify the enzyme. (b) Explain both results.
(a) The enzyme
(b) Why there are amino acids, and why there is still starch
7. explain
A pupil writes: "The hydrochloric acid in the stomach only kills bacteria. It does nothing to help digestion." Explain why this statement is incorrect.
8. identify
Supplement. Match each statement to the protease it is true of: pepsin, trypsin, or both.
Write the number of the matching option.
- Both
- Pepsin
- Trypsin
- Digests protein in food that has just reached the stomach: ______
- Digests protein in food that has moved on into the duodenum: ______
- Would digest protein in a test tube of dilute hydrochloric acid: ______
- Would digest protein in a test tube of weak alkali: ______
- Works fastest near the conditions of the place where it acts: ______
9. explain
Supplement. Amylase from the pancreas works best at about pH 7 and hardly works at pH 2. Explain how bile helps the digestion of starch in the duodenum.