--- title: "Teeth and Eating Well" book: "Primary & Middle School Biology" subject: biology language: en chapter: 12 exercises: 10 source: https://one-course.com/books/biology/1/en/chapter/12-teeth-and-eating-well --- # Chapter 12 — Teeth and Eating Well Bite into an apple and look at the mark: a neat curved row of little prints. Your teeth made that — a full toolbox that cuts, tears and grinds every meal before you swallow it. And like every good toolbox, it deserves care, and good things to work on. ![The chapter’s first exhibit: one bite, and the incisors’ neat curved signature.](https://one-course.com/images/onecourse/chapters/biology-1/g2-teeth-and-eating-well/img-cb350a41430d.jpg) *The chapter’s first exhibit: one bite, and the [incisors](#def-g2-teeth-and-eating-well-kinds)’ neat curved signature.* ## 12.1 The teeth: a toolbox in the mouth **Definition 12.1 (The three kinds of teeth).** Human teeth come in three kinds, each with its job: 1. the *incisors* , flat and sharp at the front, *cut* — they slice into the apple; 2. the *canines* , pointed, at the corners, *tear* — they grip and pull tougher food; 3. the *molars* , broad and bumpy at the back, *grind* — they crush food into a paste ready to swallow. ![The lower jaw: cutting incisors at the front, tearing canines at the corners, grinding molars at the back.](https://one-course.com/images/onecourse/chapters/biology-1/g2-teeth-and-eating-well/fig-a37eaab3e1bf.svg) *The lower jaw: cutting [incisors](#def-g2-teeth-and-eating-well-kinds) at the front, tearing [canines](#def-g2-teeth-and-eating-well-kinds) at the corners, grinding [molars](#def-g2-teeth-and-eating-well-kinds) at the back.* **Example 12.2 (One bite of apple, three tools).** Eating a piece of apple uses the whole toolbox in order: the [incisors](#def-g2-teeth-and-eating-well-kinds) slice off the bite, the [canines](#def-g2-teeth-and-eating-well-kinds) help pull it free, and the tongue passes it back to the [molars](#def-g2-teeth-and-eating-well-kinds), which grind it up. Only then do you swallow. **Remark 12.3 (Remember the animals).** Your mixed toolbox tells a story: flat cutters and grinders like a [herbivore](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#def-g2-what-animals-eat-kinds), pointed [canines](#def-g2-teeth-and-eating-well-kinds) like a [carnivore](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#def-g2-what-animals-eat-kinds). It is an [omnivore](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#def-g2-what-animals-eat-kinds)’s mouth — humans are equipped for [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) *and* meat, just as [Chapter 10](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#ch-g2-what-animals-eat) sorted us. ## 12.2 Baby teeth, adult teeth **Proposition 12.4 (Two sets in one life).** Humans grow two sets of teeth. The $20$ *baby teeth* arrive in the first years of life. From about age six they loosen and fall out one by one, pushed from below by the *adult teeth* — the final set, up to $32$ of them, which must last the rest of your life. **Proof.** *Admitted at this level.* ∎ **Example 12.5 (The wobbly incisor).** A front tooth starts to wobble at the very age children start school. Under it, an adult [incisor](#def-g2-teeth-and-eating-well-kinds) has been quietly growing and dissolving the baby tooth’s [root](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts), until the little tooth lets go. The gap is not an accident — it is a changeover. **Remark 12.6 (No third set).** After the adult set, no new teeth will ever come. A lost baby tooth is replaced; a lost adult tooth is lost. That is the real reason grown-ups insist on brushing: the second toolbox must last seventy years or more. ## 12.3 Eating well **Proposition 12.7 (A balanced plate).** To grow and stay healthy, the body needs food from each family, every day: - fruit and vegetables — for vitamins, at every meal; - bread, cereals, potatoes — for lasting energy; - [milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) , yogurt, cheese — for building bones and teeth; - meat, fish or [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) — for building the body, once or twice a day is enough; - water — the only drink the body truly needs; - sugary and fatty treats — for pleasure, in small amounts, not at every meal. **Proof.** *Admitted at this level.* ∎ **Example 12.8 (Two snack bags).** Snack A: an apple, a piece of bread, water. Snack B: sweets, a soda. Snack B tastes of sugar and little else — and sugar is just what the [germs](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#def-g1-healthy-habits-germs) of [Chapter 6](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#ch-g1-healthy-habits) feast on. Snack A feeds the body and gives the teeth honest work. Guess which one the dentist packs for her own children. **Method 12.9 (Checking a day’s menu).** Take a day’s meals and check: 1. fruit or vegetables at each meal? 2. something from the building families — dairy, and meat, fish or [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) ? 3. water as the everyday drink? 4. treats kept small and occasional? If a family is missing, the next meal is the chance to invite it back. ## 12.4 Exercises **Exercise 12.1 ★.** Name the three kinds of teeth and the job of each. **Solution of Exercise 12.1.** [Incisors](#def-g2-teeth-and-eating-well-kinds) cut; [canines](#def-g2-teeth-and-eating-well-kinds) tear; [molars](#def-g2-teeth-and-eating-well-kinds) grind. **Exercise 12.2 ★.** Which teeth are at the front of the mouth, and which at the back? **Solution of Exercise 12.2.** The [incisors](#def-g2-teeth-and-eating-well-kinds) are at the front (with the [canines](#def-g2-teeth-and-eating-well-kinds) at the corners beside them); the [molars](#def-g2-teeth-and-eating-well-kinds) are at the back. **Exercise 12.3 ★.** Follow a bite of carrot through the mouth: which tooth does what, in order? **Solution of Exercise 12.3.** The [incisors](#def-g2-teeth-and-eating-well-kinds) slice off the bite; the [canines](#def-g2-teeth-and-eating-well-kinds) help grip and pull it free; the tongue carries it back; the [molars](#def-g2-teeth-and-eating-well-kinds) grind it to a paste; then it is swallowed. **Exercise 12.4 ★.** How many [baby teeth](#prop-g2-teeth-and-eating-well-sets) are there? What happens to them from about age six? **Solution of Exercise 12.4.** There are $20$ [baby teeth](#prop-g2-teeth-and-eating-well-sets). From about age six they loosen and fall out one by one, pushed from below by the growing [adult teeth](#prop-g2-teeth-and-eating-well-sets). **Exercise 12.5 ★.** Why must [adult teeth](#prop-g2-teeth-and-eating-well-sets) be cared for even more than [baby teeth](#prop-g2-teeth-and-eating-well-sets)? **Solution of Exercise 12.5.** Because they are the last set: a lost baby tooth is replaced by an adult one, but a lost adult tooth is never replaced. The adult set must last the whole of life. **Exercise 12.6 ★.** Name the food families a healthy day should include. Which drink does the body truly need? **Solution of Exercise 12.6.** Fruit and vegetables; bread and cereals; dairy ([milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born), yogurt, cheese); meat, fish or [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born); with treats only small and occasional. The one drink the body truly needs is water. **Exercise 12.7 ★.** Compare the two snacks of [Example 12.8](#ex-g2-teeth-and-eating-well-snack): what does snack A give the body that snack B does not? **Solution of Exercise 12.7.** Vitamins from the apple, lasting energy from the bread, and water — real nourishment, and honest chewing work for the teeth. Snack B gives mostly sugar, which feeds the tooth-attacking [germs](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#def-g1-healthy-habits-germs) instead. **Exercise 12.8 ★.** Try it: look at your own teeth in a mirror. Find an [incisor](#def-g2-teeth-and-eating-well-kinds), a [canine](#def-g2-teeth-and-eating-well-kinds) and a [molar](#def-g2-teeth-and-eating-well-kinds), and check their shapes against the figure. **Solution of Exercise 12.8.** Open answer — in the mirror: flat sharp-edged [incisors](#def-g2-teeth-and-eating-well-kinds) at the front, a pointed [canine](#def-g2-teeth-and-eating-well-kinds) at each corner, broad bumpy [molars](#def-g2-teeth-and-eating-well-kinds) at the back, matching the figure. **Exercise 12.9 ★★.** Using [Remark 12.3](#rem-g2-teeth-and-eating-well-animals), explain what the shapes of human teeth say about the human menu — and which [animals](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) of [Chapter 10](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#ch-g2-what-animals-eat) we resemble. **Solution of Exercise 12.9.** Flat cutting [incisors](#def-g2-teeth-and-eating-well-kinds) and grinding [molars](#def-g2-teeth-and-eating-well-kinds) are herbivore-style tools; pointed [canines](#def-g2-teeth-and-eating-well-kinds) are carnivore-style. Having both means a menu of both [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) and meat: an [omnivore](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#def-g2-what-animals-eat-kinds)’s mouth, like the blackbird’s and the wild boar’s menus in that chapter. **Exercise 12.10 ★★.** Lila’s day: breakfast — cereal and [milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born); lunch — pasta and sweets; snack — soda and biscuits; supper — pizza. Run [Method 12.9](#met-g2-teeth-and-eating-well-check) on it: what is missing, and what appears too often? **Solution of Exercise 12.10.** Missing: fruit and vegetables (none all day!) and water as the everyday drink; meat, fish or [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) are absent too. Too often: sugary things — sweets, soda, biscuits. One fix: fruit at breakfast and snack, vegetables and some fish or [egg](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) at lunch or supper, water instead of soda, treats kept to one.