Teeth — answer key

1. TQ1 · Practice

Options as numbered on the pupil sheet: 1 — Incisor; 2 — Premolar; 3 — Canine; 4 — Molar.

Model answer. A has a broad top with several cusps and two roots: a molar. B has a thin, straight cutting edge: an incisor. C has two cusps: a premolar. D has one pointed cusp and a long root: a canine.

A full answer includes

• A: molar.
• B: incisor.
• C: premolar.
• D: canine.

Also accept

• A molar; B incisor; C premolar; D canine

Watch for

• “The tooth with the long, pointed crown is an incisor.” — Incisors have a straight, chisel-like edge. A single point marks a canine.

2. TQ2 · Practice

Options as numbered on the pupil sheet: 1 — Jaw bone; 2 — Gum; 3 — Dentine; 4 — Enamel; 5 — Cement; 6 — Pulp.

Model answer. A, the hard white outer layer of the crown, is enamel. B, under it and making up most of the tooth, is dentine. C, the soft middle with nerves and blood vessels, is the pulp. D, the thin layer on the roots, is cement. E is the gum, and F is the jaw bone in which the roots sit.

A full answer includes

• A: enamel.
• B: dentine.
• C: pulp.
• D: cement.
• E: gum.
• F: jaw bone.

Also accept

• A enamel; B dentine; C pulp; D cement; E gum; F jaw bone

Watch for

• “The outer layer of the root is enamel.” — Enamel covers only the crown. The root is covered by cement.

3. TQ3 · Practice

Options as numbered on the pupil sheet: 1 — Crush and grind food; 2 — Cut and bite off pieces of food; 3 — Grip and tear food.

Model answer. Incisors cut and bite off pieces of food, like a scalpel. Canines grip and tear food, such as meat. Premolars and molars both crush and grind food into small pieces, like the glass rod mashing the egg white.

A full answer includes

• Incisors: cut and bite off pieces of food.
• Canines: grip and tear food.
• Premolars: crush and grind food.
• Molars: crush and grind food.

Also accept

• incisors: cut and bite; canines: grip and tear; premolars and molars: crush and grind

Watch for

• “Canines grind food.” — Canines are pointed: they grip and tear. The broad premolars and molars grind.

4. TQ4 · Practice

Model answer. Multiply each number in one quarter by four: 8 incisors, 4 canines, 8 premolars and 12 molars. Check: 8 + 4 + 8 + 12 = 32.

Checked automatically

• Incisors: 8 (exact value)
  • Common wrong answer 2 : That is one quarter. Multiply by 4.
• Canines: 4 (exact value)
  • Common wrong answer 2 : There is one in each of the four quarters.
• Premolars: 8 (exact value)
• Molars: 12 (exact value)
  • Common wrong answer 3 : That is one quarter. Multiply by 4.

A full answer includes

• Incisors: 4 × 2 = 8.
• Canines: 4 × 1 = 4.
• Premolars: 4 × 2 = 8.
• Molars: 4 × 3 = 12.

Also accept

• 8 incisors, 4 canines, 8 premolars, 12 molars

Watch for

• “There are two canines in the mouth.” — There is one canine in each quarter of the mouth, so four in all.

5. TQ5 · Practice

Model answer. The crown is covered by enamel, the hardest substance in the body. Under it is dentine, which makes up most of the tooth. In the middle is the soft pulp, with nerves and blood vessels. The root is covered with cement, which fixes it into the jaw bone, and the gum covers the bone around the neck of the tooth.

A full answer includes

• Enamel covers the crown; it is the hardest substance in the body.
• Dentine is under the enamel and makes up most of the tooth.
• The pulp is in the middle and contains nerves and blood vessels.
• The root is covered by cement and embedded in the jaw bone, with the gum around the neck.

Also accept

• enamel, dentine, pulp with nerves and blood vessels; cement fixes the root in the jaw bone; gum

Watch for

• “The pulp is the hard outer layer.” — The pulp is the soft middle of the tooth. The hard outer layer of the crown is enamel.

6. TQ6 · Practice

Model answer. Enamel is the hardest substance in the body; it is not living, so it cannot repair a chip. The pulp contains nerves and blood vessels. Cement covers the root and helps to fix it in the jaw bone. Dentine lies under the enamel, not on top of it, and the root sits in bone, with the gum only around the neck.

A full answer includes

• Enamel is the hardest substance in the body.
• The pulp contains nerves and blood vessels.
• Cement helps to fix the root in the jaw bone.

Also accept

• enamel hardest; pulp has nerves and blood vessels; cement fixes the root

Watch for

• “Enamel is living and grows back after a chip.” — Enamel is not living: a chip in it stays.
• “The roots of a tooth sit only in the gum.” — The roots are embedded in the jaw bone; the gum covers the bone around the neck of the tooth.

7. TQ7 · Practice

Model answer. Incisors cut and bite off pieces, and canines grip and tear, but neither can crush and grind. That is the job of the premolars and molars. Without them, hard food such as nuts and raw vegetables stays in large pieces. Large pieces have a small surface area, so enzymes digest them more slowly, and they are hard to swallow.

A full answer includes

• His incisors and canines can cut, bite and tear, but cannot crush and grind.
• Without molars and premolars the food stays in large pieces, so it has a small surface area and enzymes digest it more slowly (and it is hard to swallow).

Also accept

• no crushing and grinding; large pieces; small surface area; slower digestion

Watch for

• “His incisors can grind the food instead.” — Incisors have thin, straight edges for cutting: they cannot crush and grind.

8. TQ8 · Practice

Model answer. A broad tooth with four or five cusps at the back of the mouth is a molar. Its broad, bumpy top crushes and grinds food against the molar of the other jaw.

A full answer includes

• A molar: it crushes and grinds food.

Also accept

• molar; crushes and grinds

Watch for

• “A tooth with cusps is a canine.” — A canine has one pointed cusp and stands near the front. Several cusps on a broad top mark a molar.

9. TQ9 · Practice

Model answer. The pulp holds nerves and blood vessels. The nerves sense pain, heat and cold, so you feel when a tooth is damaged. The blood vessels bring oxygen and nutrients to the living cells in the tooth.

A full answer includes

• (a) Nerves and blood vessels.
• (b) Nerves sense pain, heat and cold; blood vessels bring oxygen and nutrients to the living cells in the tooth.

Also accept

• (a) nerves, blood vessels; (b) sensing pain, heat, cold; oxygen and nutrients for living cells

Watch for

• “The blood vessels make the enamel.” — Enamel is not living and has no blood vessels. The blood vessels supply the living cells in the pulp.

10. TT1 · Apply

Model answer. The front teeth that bite off a piece are the incisors, so they made most of the marks; the canines may mark the corners. The tongue then moves the piece to the back of the mouth, where the premolars and molars crush and grind it into small pieces, which mix with saliva and are swallowed.

A full answer includes

• (a) The incisors (with the canines at the ends of the row).
• (b) The tongue moves the piece back, and the premolars and molars crush and grind it into small pieces, mixed with saliva.

Also accept

• (a) incisors; (b) premolars and molars crush and grind

Watch for

• “The molars made the bite marks.” — Molars are at the back of the mouth. Biting into a sandwich uses the front teeth, the incisors.

11. TT2 · Apply

Model answer. The blood vessels bring oxygen and nutrients to the living cells in the pulp. Without them, the pulp, with its nerves, died, so the tooth can no longer sense pain, heat or cold. But the hard enamel and dentine are still there, and the cement still fixes the root in the jaw bone, so the tooth can still bite.

A full answer includes

• (a) Without blood vessels, the living cells and nerves in the pulp died, so nothing senses pain or cold.
• (b) The enamel and dentine are still hard, and the cement still holds the root in the jaw bone.

Also accept

• (a) pulp and nerves died without a blood supply; (b) enamel and dentine still hard, root still fixed by cement in bone

Watch for

• “A grey tooth falls out at once.” — The root is held by cement in the jaw bone, which is not affected by the dead pulp.

12. TT3 · Apply

Model answer. Food caught between the molars is squeezed between the cusps and hollows as the jaws close and move from side to side, so it is crushed and ground into small pieces. The small pieces have a much larger surface area for the enzymes of chemical digestion.

A full answer includes

• Food caught between the molars is crushed and ground between the interlocking cusps.
• This breaks it into small pieces, increasing its surface area for enzymes.

Also accept

• food crushed and ground between interlocking cusps; small pieces; larger surface area

Watch for

• “The cusps cut food like a knife.” — Cusps are rounded bumps. They crush and grind; the straight edges of incisors cut.