--- title: "Healthy Choices" book: "Primary & Middle School Biology" subject: biology language: en chapter: 36 exercises: 11 source: https://one-course.com/books/biology/1/en/chapter/36-healthy-choices --- # Chapter 36 — Healthy Choices By now this book has visited most of your body’s great services: the [digestive tract](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-tract), the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs), the [heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart) and its rivers of [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb), the [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) and [bones](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton), the commanding [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system). This closing chapter of the year asks a practical question: knowing all that machinery, how do you run it well — and who decides? Because from about your age on, more and more of the decisions are yours. ## 36.1 What the machinery asks for **Proposition 36.1 (The body’s daily contract).** Put the earlier chapters’ requests side by side and a daily contract appears: - *[varied food](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs) and water* — fuel and building material ( [Proposition 18.1](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#prop-g3-balanced-diet-jobs) ), delivered by the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) to every [cell](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) ; - *movement* — [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) , [bones](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton) , [heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart) and [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) all grow stronger with use ( [Method 17.9](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#met-g3-bones-and-muscles-care) , [Remark 27.9](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#rem-g4-heart-and-blood-rest) ); - *[sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs)* — the [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) ’s filing and the body’s repairs ( [Proposition 33.9](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#prop-g5-brain-in-command-protect) ); a child of this age needs about ten hours; - *clean air, clean hands, cared-for teeth* — the defenses of [Chapter 6](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#ch-g1-healthy-habits) and [Method 26.8](https://one-course.com/books/biology/1/en/chapter/26-breathing#met-g4-breathing-care) , still on duty. Nothing new — that is the point. Health is the old rules, kept. **Proof.** *Admitted at this level.* ∎ **Example 36.2 (One day, seen from inside).** A good day, read as body management: breakfast restocks the night’s spending ([Example 18.7](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#ex-g3-balanced-diet-breakfast)); the walk to school warms up [heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart) and [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs); play at noon is training disguised as fun; supper’s vegetables restock the freshness family; and the early night hands the [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) its filing time. No item is heroic; together they are health. ![Contract items two and four in one picture: movement for heart, lungs and muscles — and a helmet for the commander.](https://one-course.com/images/onecourse/chapters/biology-1/g5-healthy-choices/img-94d371449286.jpg) *Contract items two and four in one picture: movement for [heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart), [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) and [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) — and a helmet for the commander.* ## 36.2 New choices, new pressures **Proposition 36.3 (Screens and sleep).** Screens — phones, tablets, games — are neither poison nor food; they are *time*. The hours they absorb are taken from somewhere, and the usual victims are exactly the contract’s items: outdoor movement and [sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs). Worse, bright screens late in the evening tell the [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) “still daytime”, delaying [sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs) beyond the hours given up. The choice is not screens-or-no-screens, but which hours they may have — and the evening’s last hour is the worst one to give them. **Proof.** *Admitted at this level.* ∎ **Example 36.4 (The eleven-o’clock experiment).** Try it as a fair test ([Method 22.1](https://one-course.com/books/biology/1/en/chapter/22-what-plants-need#met-g4-what-plants-need-fairtest)) on yourself: a week of screens off an hour before bed, against an ordinary week. Most people fall asleep faster, wake easier and notice better mornings in the first week — the control week is the argument. **Proposition 36.5 (Substances that trick the body).** Some substances harm precisely the machinery this book has toured: - *tobacco smoke* dirties the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) ’ delicate pockets ( [Method 26.8](https://one-course.com/books/biology/1/en/chapter/26-breathing#met-g4-breathing-care) ) and strains the [heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart) ; it is sold by making the first cigarettes seem grown-up — and it holds its buyers by *addiction* : the body, once used to it, protests without it; - *alcohol* reaches the [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) within minutes — the commander itself ( [Chapter 33](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#ch-g5-brain-in-command) ) — slowing the loop, blurring decisions; a young [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) , still building its paths, is more easily harmed than a grown one; - both were already flagged as dangers to the [fetus](https://one-course.com/books/biology/1/en/chapter/32-human-reproduction#def-g5-human-reproduction-pregnancy) ( [Proposition 32.8](https://one-course.com/books/biology/1/en/chapter/32-human-reproduction#prop-g5-human-reproduction-care) ) — the same substances, the same reason. **Proof.** *Admitted at this level.* ∎ **Remark 36.6 (Why start-never beats stop-later).** [Addiction](#prop-g5-healthy-choices-substances) is a trap with an easy entrance and a hard exit: starting is one choice, stopping is a fight repeated for years. That asymmetry is the coldest fact in this chapter, and the most useful: the cheapest moment to win the fight is before it begins. People offering a first cigarette are not offering one — they are offering all the following ones. ## 36.3 Deciding for yourself **Method 36.7 (Running your own contract).** From now on, more each year, the keeper of your body’s contract is you: 1. know the contract’s items — [Proposition 36.1](#prop-g5-healthy-choices-contract) is the list; 2. check yourself honestly now and then, as in [Method 18.8](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#met-g3-balanced-diet-check) — what is missing, what is over its share? 3. change one thing at a time, and give it a fair test’s week; 4. on substances, decide your “no” *before* the moment it is needed ( [Remark 36.6](#rem-g5-healthy-choices-never) ) — a decision made calmly in advance is easier to keep than one improvised under friendly pressure; 5. and use the grown-ups: doctors, nurses, parents and teachers are on your side of this contract. **Example 36.8 (Prepared answers).** The advance decision of step 4, in practice, is a sentence ready in the pocket: “No thanks — not my thing.” Said lightly, once, it usually ends the matter; and friends worth the name take it the first time. The sentence costs nothing to prepare and is hardest to compose exactly when it is needed — so it is composed now. ## 36.4 Exercises **Exercise 36.1 ★.** List the four items of the body’s daily contract, each with the organ or service it mainly serves. **Solution of Exercise 36.1.** [Varied food](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs) and water: fuel and building material for every [cell](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell), delivered by the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb). Movement: [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle), [bones](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton), [heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart) and [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs), which strengthen with use. [Sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs): the [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system)’s filing and the body’s repairs. Cleanliness — air, hands, teeth: the body’s defenses against [germs](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#def-g1-healthy-habits-germs) and dirt. **Exercise 36.2 ★.** About how much [sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs) does a child of your age need, and what two jobs does the body do with it? **Solution of Exercise 36.2.** About ten hours. The [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) files the day (and dreams); the body repairs and grows. **Exercise 36.3 ★.** In what sense are screen hours “taken from somewhere”? Name the two usual victims. **Solution of Exercise 36.3.** A day has fixed hours, so hours on screens come out of other activities. The usual victims: outdoor movement and [sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs). **Exercise 36.4 ★.** Why is the evening’s last hour the worst one to give to a bright screen? **Solution of Exercise 36.4.** Because a bright screen tells the [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) “still daytime”, delaying [sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs) beyond the hour itself — the evening screen takes its own hour and part of the night after it. **Exercise 36.5 ★.** Which organs does tobacco smoke harm first, by [Proposition 36.5](#prop-g5-healthy-choices-substances)? And alcohol? **Solution of Exercise 36.5.** Tobacco smoke: the [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs)’ delicate air pockets first, and the [heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart) it strains. Alcohol: the [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) — the commander — within minutes, and a young, still-building [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) most of all. **Exercise 36.6 ★.** What is [addiction](#prop-g5-healthy-choices-substances), and why does it make “never starting” so much cheaper than “stopping later”? **Solution of Exercise 36.6.** The body, grown used to a substance, protests without it — so the user is held. Starting is a single easy choice; stopping is a fight repeated for years: the trap’s entrance is wide and its exit narrow, which prices “never” far below “later”. **Exercise 36.7 ★.** What is the point of deciding a “no” in advance, by step 4 of [Method 36.7](#met-g5-healthy-choices-run)? **Solution of Exercise 36.7.** A calm decision made in advance is easier to keep than one improvised under friendly pressure — the moment of the offer is the worst moment to start thinking. **Exercise 36.8 ★.** Try it: run the eleven-o’clock experiment of [Example 36.4](#ex-g5-healthy-choices-latenight) for one week and report — honestly — what changed. **Solution of Exercise 36.8.** Open answer. Typical report: falling asleep faster, easier waking, better mornings in the screens-off week. **Exercise 36.9 ★★.** Design the screen experiment as a proper fair test: what stays the same between the two weeks, what one thing changes, and what do you measure? **Solution of Exercise 36.9.** Same bedtime, same meals, same day’s activities both weeks — the one change: screens off an hour before bed in week two only. Measure: time to fall asleep (estimated), how waking feels, perhaps the morning’s mood, noted daily. **Exercise 36.10 ★★.** “One cigarette can’t hurt.” Answer with [Remark 36.6](#rem-g5-healthy-choices-never): what is really being offered with the first one? **Solution of Exercise 36.10.** All the following ones. [Addiction](#prop-g5-healthy-choices-substances) means the first cigarette is the entrance to the trap: what is offered is not one smoke but the beginning of the body’s demand for the next — the easy entrance to the hard exit. **Exercise 36.11 ★★★.** Connect three earlier chapters to this one: how do [Proposition 26.5](https://one-course.com/books/biology/1/en/chapter/26-breathing#prop-g4-breathing-exchange), [Example 27.7](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#ex-g4-heart-and-blood-effort) and [Proposition 33.9](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#prop-g5-brain-in-command-protect) each explain one line of the contract or one warning of this chapter? **Solution of Exercise 36.11.** The gas exchange chapter explains the clean-air line and the smoke warning: [breathing](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-movements) exists to load oxygen through delicate surfaces smoke dirties. The [racing-heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart) example explains the movement line: [heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart) and [lungs](https://one-course.com/books/biology/1/en/chapter/26-breathing#def-g4-breathing-organs) are trainable — effort is their exercise. The brain-protection proposition explains the [sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs) line and the alcohol warning: the commander needs its filing hours, and substances reaching it blur the very loop that runs everything else.