Primary & Middle School Biology · Grades 1–9
36Healthy Choices
By now this book has visited most of your body’s great services: the digestive tract, the lungs, the heart and its rivers of blood, the muscles and bones, the commanding brain. 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 and water — fuel and building material (Proposition 18.1), delivered by the blood to every cell;
- movement — muscles, bones, heart and lungs all grow stronger with use (Method 17.9, Remark 27.9);
- sleep — the brain’s filing and the body’s repairs (Proposition 33.9); a child of this age needs about ten hours;
- clean air, clean hands, cared-for teeth — the defenses of Chapter 6 and Method 26.8, 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); the walk to school warms up heart and lungs; play at noon is training disguised as fun; supper’s vegetables restock the freshness family; and the early night hands the brain its filing time. No item is heroic; together they are health.
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. Worse, bright screens late in the evening tell the brain “still daytime”, delaying sleep 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) 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’ delicate pockets (Method 26.8) and strains the 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 within minutes — the commander itself (Chapter 33) — slowing the loop, blurring decisions; a young brain, still building its paths, is more easily harmed than a grown one;
- both were already flagged as dangers to the fetus (Proposition 32.8) — the same substances, the same reason.
Proof. Admitted at this level. ∎
Remark 36.6 (Why start-never beats stop-later)
Addiction 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:
- know the contract’s items — Proposition 36.1 is the list;
- check yourself honestly now and then, as in Method 18.8 — what is missing, what is over its share?
- change one thing at a time, and give it a fair test’s week;
- on substances, decide your “no” before the moment it is needed (Remark 36.6) — a decision made calmly in advance is easier to keep than one improvised under friendly pressure;
- 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
Solution of Exercise 36.1.
Varied food and water: fuel and building material for every cell, delivered by the blood. Movement: muscles, bones, heart and lungs, which strengthen with use. Sleep: the brain’s filing and the body’s repairs. Cleanliness — air, hands, teeth: the body’s defenses against germs and dirt.
Exercise 36.2 ★
About how much sleep does a child of your age need, and what two jobs does the body do with it?
Solution
Solution of Exercise 36.2.
About ten hours. The brain 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
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.
Exercise 36.4 ★
Why is the evening’s last hour the worst one to give to a bright screen?
Exercise 36.5 ★
Which organs does tobacco smoke harm first, by Proposition 36.5? And alcohol?
Exercise 36.6 ★
What is addiction, and why does it make “never starting” so much cheaper than “stopping later”?
Solution
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?
Solution
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 for one week and report — honestly — what changed.
Solution
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
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: what is really being offered with the first one?
Solution
Solution of Exercise 36.10.
All the following ones. Addiction 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, Example 27.7 and Proposition 33.9 each explain one line of the contract or one warning of this chapter?
Solution
Solution of Exercise 36.11.
The gas exchange chapter explains the clean-air line and the smoke warning: breathing exists to load oxygen through delicate surfaces smoke dirties. The racing-heart example explains the movement line: heart and lungs are trainable — effort is their exercise. The brain-protection proposition explains the sleep line and the alcohol warning: the commander needs its filing hours, and substances reaching it blur the very loop that runs everything else.