The gut and physical digestion — return questions key

1. CR1 · Return

Model answer. Physical digestion is the breakdown of food into smaller pieces without chemical change to the food molecules, for example by chewing or by the churning of the stomach.

A full answer includes

• The breakdown of food into smaller pieces.
• Without chemical change to the food molecules.

Also accept

• breakdown into smaller pieces without chemical change to the food molecules

Watch for

• “Physical digestion breaks large molecules into small molecules.” — That is chemical digestion, by enzymes. Physical digestion makes smaller pieces of the same molecules.

2. CR2 · Return

Model answer. Physical digestion breaks food into smaller pieces, which increases the surface area of the food for the action of enzymes in chemical digestion, so the food is digested faster.

A full answer includes

• It increases the surface area of the food for the action of enzymes.

Also accept

• increases the surface area of the food for enzymes

Watch for

• “Physical digestion makes enzymes work faster by warming the food.” — It does not warm the food. It gives the enzymes more surface to act on.

3. CR3 · Return

Model answer. Each 2 cm edge holds 20 pieces of 0.1 cm, so there are 20 × 20 × 20 = 8000 pieces. Each has 6 × 0.1 × 0.1 = 0.06 cm², so together they have 8000 × 0.06 = 480 cm², twenty times the 24 cm² of the whole cube.

Checked automatically

• (a) Number of pieces: 8000 (exact value)
  • Common wrong answer 20 : That is one edge. Multiply 20 × 20 × 20.
  • Common wrong answer 400 : That is one layer. There are 20 layers.
• (b) Total surface area: 480 cm² (exact value)
  • Common wrong answer 24 : That is the whole cube.

A full answer includes

• (a) 20 × 20 × 20 = 8000 pieces.
• (b) Each piece: 6 × 0.1 × 0.1 = 0.06 cm²; 8000 × 0.06 = 480 cm².

Also accept

• (a) 8000; (b) 480 cm²

Watch for

• “Chewing does not change the surface area, because it is the same bread.” — The mass stays the same, but the surface area grows twentyfold here.

4. TR1 · Return

Options as numbered on the pupil sheet: 1 — Canines; 2 — Premolars; 3 — Molars; 4 — Incisors.

Model answer. From the middle of the front to the back: incisors, then the canine, then premolars, then molars.

A full answer includes

• Incisors, canines, premolars, molars.

Also accept

• incisor, canine, premolar, molar

Watch for

• “Premolars are in front of the canines.” — Premolars come after the canine: "pre-molar" means in front of the molars.

5. TR2 · Return

Model answer. The crown is covered by enamel, the hardest substance in the body. Under it is dentine. The soft middle is the pulp, with nerves and blood vessels. The root is covered by cement and is embedded in the jaw bone, under the gum.

A full answer includes

• (1) enamel
• (2) dentine
• (3) pulp
• (4) nerves
• (5) cement
• (6) jaw

Also accept

• (1) enamel; (2) dentine; (3) pulp; (4) nerves; (5) cement; (6) jaw

Watch for

• “Dentine is the outer layer of the crown.” — Enamel is the outer layer; dentine is under it.

6. TR3 · Return

Model answer. Incisors cut and bite off pieces of food; canines grip and tear food; premolars and molars crush and grind food into small pieces, which increases its surface area for enzymes.

A full answer includes

• (a) Incisors cut and bite off pieces of food.
• (b) Canines grip and tear food.
• (c) Premolars and molars crush and grind food.

Also accept

• (a) cut and bite; (b) grip and tear; (c) crush and grind

Watch for

• “Incisors grind food.” — Incisors have thin edges for cutting. Grinding needs the broad tops of premolars and molars.

7. AR1 · Return

Model answer. The associated organs are the salivary glands, the pancreas, the liver and the gall bladder. Food does not pass through them. The oesophagus and the rectum are parts of the alimentary canal, and the kidney is not part of the digestive system.

A full answer includes

• Salivary glands, pancreas, liver and gall bladder.

Also accept

• salivary glands, pancreas, liver, gall bladder

Watch for

• “The oesophagus is an associated organ.” — Food passes through the oesophagus: it is part of the alimentary canal.

8. AR2 · Return

Model answer. Ingestion is the taking of substances, such as food and drink, into the body. Absorption is the movement of nutrients from the intestines into the blood. Assimilation is the uptake and use of nutrients by cells. Egestion is the removal of undigested food from the body as faeces.

A full answer includes

• (a) The taking of substances, such as food and drink, into the body.
• (b) The movement of nutrients from the intestines into the blood.
• (c) The uptake and use of nutrients by cells.
• (d) The removal of undigested food from the body as faeces.

Also accept

• (a) taking in food and drink; (b) nutrients from intestines into blood; (c) uptake and use by cells; (d) undigested food out as faeces

Watch for

• “Egestion is the removal of waste made by cells.” — That is excretion. Egestion removes undigested food as faeces.

9. AR3 · Return

Model answer. The muscles of the stomach wall contract and relax, churning the food. This breaks it into smaller pieces and mixes it with gastric juice, without chemical change, and increases its surface area for the action of enzymes.

A full answer includes

• The muscular wall contracts and relaxes, churning the food.
• The food is broken into smaller pieces and mixed with gastric juice, increasing its surface area for enzymes.

Also accept

• muscular wall churns; smaller pieces; mixed with gastric juice; larger surface area

Watch for

• “The stomach does physical digestion with its teeth-like folds.” — It is the muscles of the wall that churn the food.

10. AR4 · Return

Model answer. Bile is made in the liver, stored in the gall bladder and released into the duodenum. It emulsifies fats and oils, breaking large drops into tiny droplets without changing the fat molecules. The droplets have a much larger surface area, so enzymes digest the fat faster.

A full answer includes

• Bile is made in the liver, stored in the gall bladder and released into the duodenum.
• It emulsifies fats and oils, breaking them into tiny droplets, with no chemical change.
• This increases their surface area for chemical digestion by enzymes.

Also accept

• emulsifies fats into droplets; larger surface area for enzymes

Watch for

• “Bile breaks fat molecules down into smaller molecules.” — That is chemical digestion, by an enzyme. Bile only breaks the drops into droplets.