Pupil sheet · Chemical digestion

Chemical digestion — final check

Name ______________________ Date ____________

Work alone, with the lesson closed. Answer every question; there are no hints.

1. explain

A pupil stirs a spoonful of sugar into hot tea. The sugar disappears, and she says: "The sugar has been chemically digested." Explain, using the meaning of chemical digestion, whether the pupil is right.

2. explain

A runner wants sugar to reach her blood as soon as possible during a race. She can have a sports drink, which contains glucose, or a cereal bar with the same energy, which is mostly starch. Explain which one gets sugar into her blood sooner, using the role of chemical digestion.

3. explain / suggest

Supplement. A pupil mixes maltase with a starch suspension in a test tube at 37 °C. After 30 minutes, iodine still turns the mixture blue-black, and a test shows that there is no glucose. (a) Explain why no glucose was made. (b) Suggest which enzyme she should add to get glucose, and describe what each enzyme then does.

(a) Why no glucose was made

(b) The enzyme to add, and what each enzyme does

4. describe

A food scientist has three test tubes, each holding the same mixture of starch, protein and vegetable oil in water at 37 °C. She adds amylase to tube 1, protease to tube 2 and lipase to tube 3. Describe what is broken down in each tube and what it is broken down into.

(a) Tube 1, amylase

(b) Tube 2, protease

5. identify

A scientist takes a sample of fluid from four places along the alimentary canal. She mixes each sample with the same food mixture of starch, protein and fat, at 37 °C and at the pH of the place it came from. The table shows the results after an hour. Match each sample to the place it came from.

Sample	Iodine test for starch	Amino acids made	Fatty acids made
1	yellow-brown	no	no
2	blue-black	yes	no
3	yellow-brown	yes	yes
4	blue-black	no	no

Write the number of the matching option.

Colon
Small intestine
Mouth
Pancreas
Stomach

Sample 1: ______
Sample 2: ______
Sample 3: ______
Sample 4: ______

6. state / describe

In some people the pancreas makes too little pancreatic juice. They swallow capsules containing amylase, protease and lipase with each meal, and the capsules release the enzymes in the small intestine. (a) State the organ these three enzymes normally come from. (b) Describe how they normally reach the small intestine.

(a) Where the enzymes normally come from

(b) How they normally reach the small intestine

7. describe

A scientist makes artificial gastric juice: pepsin dissolved in water with hydrochloric acid, at pH 2. She puts a piece of raw meat into it, and another piece into the same pepsin solution made at pH 7, without acid. Both flasks stand at 37 °C overnight. Next morning the meat at pH 2 is partly digested and smells fresh. The meat at pH 7 is hardly digested and smells rotten, because bacteria have grown on it. Describe the two functions of the hydrochloric acid that these results show.

(a) What the smell of the meat shows

(b) What the digestion of the meat shows

8. identify

Supplement. A protease is taken from one part of a patient's alimentary canal and tested on milk protein at five pH values at 37 °C. The table shows the results. Which protease is it?

pH	Mass of protein digested in 20 minutes / mg
2	0.0
4	0.1
6	1.6
8	4.8
10	1.9

Circle one answer.

Trypsin, which works in the acidic stomach
Trypsin, which works in the alkaline duodenum
Pepsin, which works in the alkaline duodenum
Pepsin, which works in the acidic stomach

9. identify

Supplement. In a model of the duodenum, a pupil adds universal indicator to 10 cm³ of an acidic mixture of food and gastric juice. She adds bile 2 cm³ at a time and reads the pH after each addition: pH 2 at the start, 3 after 2 cm³, 5 after 4 cm³, 7 after 6 cm³ and 8 after 8 cm³. Which row is correct?

Row	Bile is	Bile added when the mixture is neutral / cm³	What the bile does to the acid
A	alkaline	6	neutralises it
B	acidic	6	neutralises it
C	alkaline	8	neutralises it
D	alkaline	6	digests it

Circle one answer.