Biology · Book 1 · Grades 1–9

Primary & Middle School Biology

Primary & Middle School Biology · Grades 1–9

41Matter From Food

A calf of 40 kg40\,\mathrm{kg} becomes, in two years, a cow of 600 kg600\,\mathrm{kg}. Half a tonne of new cow — flesh, bone, hide, horn — appeared from somewhere. The cow ate grass; the new matter is not grass; yet without the grass none of it would exist. What animals do with their food is this chapter’s business — the consumers’ side of Chapter 40’s ledger.

41.1 Animals build their matter from food

Proposition 41.1 (Consumers transform organic matter)

An animal builds its own organic matter — muscle, bone, fat, feather, shell — out of the organic matter it eats. Digestion (Definition 25.3) dismantles the food into nutrients; the blood delivers them (Proposition 27.1); and the body’s cells (Proposition 29.7) reassemble them into the animal’s own substance. Animals are transformers of matter, never makers-from-mineral: that trade belongs to the producers alone.

Proof. Admitted at this level. ∎

Example 41.2 (Grass into cow)

Follow the half-tonne: the cow grazes hour after hour (Proposition 10.7 explained the long hours); her heavy digestion (Exercise 25.11) dismantles the grass into nutrients; her blood carries them to udder, muscle and growing calf-inside-her; her cells build cow-matter from grass-matter. The pasture is, quite literally, walking about in a new form.

Remark 41.3 (Matter changes hands, not nature)

At every arrow of a food chain (Definition 19.1), organic matter changes owners and is rebuilt — grass-matter into cow-matter, cow-matter (the milk, the meat) into child-matter. The organic never comes from nowhere: consumers pass it along and reshape it. Only at the chain’s green start was it made new (Proposition 40.6); only at the decomposers’ end, next chapter, does it return to mineral.

41.2 Growth is matter production

Definition 41.4 (An animal’s matter production)

An animal’s production of matter is the new organic matter it builds: growth of the young (the calf’s added kilograms), yearly renewals (fur molted and regrown, antlers, feathers), repairs (Remark 17.3’s mended bone), and products (milk, eggs, wool). All of it is rebuilt food.

Example 41.5 (Weighing production)

Farmers weigh production daily: a dairy cow gives some 25 kg25\,\mathrm{kg} of milk a day — organic matter she must rebuild from feed, day after day; a hen’s egg is some 60 g60\,\mathrm{g} of packed provisions (Remark 8.3), assembled overnight from her grain. No feed, no production: the ledger balances mercilessly.

Proposition 41.6 (Not all the food becomes body)

A consumer never converts all its food into new matter:

  • part is never absorbed, and leaves as droppings (Proposition 25.5);
  • a large part is burned — combined with the breath’s oxygen (Proposition 26.5) — to power movement and warmth: matter spent as fuel, leaving as exhaled gas;
  • only the remainder becomes growth and products.

Of the grass a cow eats, only a modest fraction ends as new cow — which is why each floor of Proposition 34.5’s pyramid is so much smaller than the one below it.

Proof. Admitted at this level. ∎

Example 41.7 (The pyramid, explained at last)

A meadow’s tonnes of grass feed a herd’s worth of rabbits; the rabbits’ kilograms feed a fox or two. At each arrow, most matter is burned for living or lost, and only a fraction is passed upward as body. Great hunters are rare (Proposition 34.5) because they live off the remainders of remainders — arithmetic, not bad luck.

41.3 Menus, teeth and the one same trade

Proposition 41.8 (Different menus, same transformation)

Herbivore, carnivore, omnivore (Definition 10.1) name different sources of organic matter, not different trades. The cow rebuilding grass and the fox rebuilding rabbit both run Proposition 41.1’s transformation — with equipment matched to the menu (Proposition 10.4, Exercise 25.11): grass demands grinders and vast digestion, meat rewards seizers and a short gut.

Proof. Admitted at this level. ∎

Method 41.9 (Auditing an animal’s matter)

For any animal, draw up its matter ledger:

  1. in: what organic matter does it eat, and from whom? (its food-web arrows in, Definition 34.1);
  2. built: what growth, renewals and products does it make?
  3. out: droppings, and matter burned for movement and warmth;
  4. check the balance: production must be the modest remainder — if a claim makes it more (“this pond yields more fish-matter than the pond grows food”), the claim is wrong.

Example 41.10 (The audit in use)

Audit the blackbird (Example 10.8): in — worms, insects, berries; built — its own growth, each year’s new feathers, the clutch of eggs; out — droppings on the wall, and the large burned share that powered a year of flying and singing. A songbird’s daily food weight is huge for its size precisely because flight burns so much of the ledger.

41.4 Exercises

Exercise 41.2 ★

List the steps that turn grass into cow-muscle, naming the chapter that covered each.

Solution

Solution of Exercise 41.2.

Digestion dismantles the grass into nutrients (Chapter 25); the blood delivers them everywhere (Chapter 27); the body’s cells reassemble them into cow-matter, dividing as the body grows (Chapter 29).

Exercise 41.3 ★

Give four forms of an animal’s matter production, with an example of each.

Solution

Solution of Exercise 41.3.

Growth (the calf’s added kilograms); renewals (molted fur, new feathers, antlers); repairs (a mended bone); products (milk, eggs, wool).

Exercise 41.4 ★

Name the three destinations of a consumer’s food, by Proposition 41.6.

Solution

Solution of Exercise 41.4.

Never absorbed — out as droppings; burned with the breath’s oxygen for movement and warmth — out as exhaled gas; and the remainder, built into growth and products.

Exercise 41.5 ★

Why does a dairy cow need feed every single day to keep giving milk?

Solution

Solution of Exercise 41.5.

Because each day’s 25 kg25\,\mathrm{kg} of milk is organic matter she must rebuild from that day’s feed; milk is production, and production is rebuilt food — no input, no output.

Exercise 41.6 ★

An egg contains 60 g60\,\mathrm{g} of organic matter. Where was it manufactured — in the hen, or before her? Untangle carefully.

Solution

Solution of Exercise 41.6.

Assembled in the hen, from the nutrients of her grain — but the organic matter itself was first manufactured before her, in the grain plant’s leaves. The hen transformed; the plant produced.

Exercise 41.7 ★★

Use Proposition 41.6 to explain why the food pyramid narrows at every floor.

Solution

Solution of Exercise 41.7.

At each arrow, most of the eaten matter is burned for living or lost as droppings, and only a modest fraction becomes eater’s body — the only part the next floor can eat. Each floor therefore has only a fraction of the matter below it: the pyramid narrows by arithmetic.

Exercise 41.8 ★★

Run Method 41.9 on a pet cat: in, built, out — with at least two entries per line.

Solution

Solution of Exercise 41.8.

In: meat or kibble (and the occasional mouse). Built: its growth as a kitten, the fur it renews at each molt, repairs after scrapes. Out: droppings in the garden, and the burned share powering every pounce, purr and warm nap.

Exercise 41.9 ★★

“The fox and the cow do different things with food.” Correct the sentence with Proposition 41.8 — what differs, and what is identical?

Solution

Solution of Exercise 41.9.

What differs is the source and the equipment: grass versus rabbit, grinders-and-vast-gut versus seizers-and-short-gut. What is identical is the trade itself: both dismantle eaten organic matter into nutrients and rebuild it as their own substance.

Exercise 41.10 ★★

A child grows 3 kg3\,\mathrm{kg} in a year while eating several hundred kilograms of food. Where did the rest go? Answer with the ledger.

Solution

Solution of Exercise 41.10.

Most left as the burned share — powering a year of running, thinking and staying at 37∘C37{}^{\circ}\mathrm{C} — and a part was never absorbed and left as droppings. Only the small remainder, the 3 kg3\,\mathrm{kg}, became new body: the child’s ledger balances like the cow’s.

Exercise 41.11 ★★

The snail’s shell is mineral substance, yet Example 40.2 counted it as the snail’s making. Reconcile: what did the snail’s body do, and from what supplies, to build it?

Solution

Solution of Exercise 41.11.

The snail’s body extracted the shell’s mineral ingredients from its food and surroundings, transported them, and laid them down layer by layer in its own architecture. The substance is mineral; the building is the living animal’s work — a made thing, of mineral material.

Exercise 41.12 ★★★

One hectare of land can feed more people on potatoes than on pork raised on those potatoes. Explain with Proposition 41.6 — where does the difference go when the potatoes take the detour through the pig?

Solution

Solution of Exercise 41.12.

Routed through the pig, most of the potatoes’ matter is spent on the pig’s own living — burned for warmth and movement, lost as droppings — and only a fraction returns as pork. Eaten directly, the potatoes skip the pig’s expenses. The difference went up the pig’s ledger, not onto the table.

41.5 Problem: The Farm Ledger

Problem 41.1

Weekend problem — a small farm audited, field to table

Gran’s smallholding: a pasture with one cow, a henhouse of ten hens fed on grain, a vegetable patch, and the family kitchen. This weekend, you keep its matter ledger.

Part I — The producers’ floor.

  1. List the holding’s producers. What are their mineral inputs, and their energy source?
  2. The pasture grows about 10 000 kg10\,000\,\mathrm{kg} of grass matter in a season. In whose leaves was every gram of it manufactured?
  3. Gran spreads the henhouse manure on the vegetable patch. Which rule of Proposition 35.5 is she keeping, and what exactly does the manure restock?
  4. Why can the cow not simply be fed mineral salts and water directly, sparing the pasture?

Part II — The consumers’ floor.

  1. The cow eats roughly 70 kg70\,\mathrm{kg} of grass a day and gives about 20 kg20\,\mathrm{kg} of milk. Name the three destinations of the missing 50 kg50\,\mathrm{kg}.
  2. The hens turn grain into eggs. Write the hen’s ledger — in, built, out — and say why a molting hen (renewing all her feathers) lays fewer eggs for a while.
  3. A buzzard takes a chick. Extend the holding’s food chain to it, and state at which links matter was made and at which it was only transformed.
  4. The family eats eggs, milk and vegetables. Trace the organic matter of one breakfast — bread, boiled egg, milk — each to the leaf where it was first manufactured.

Part III — The arithmetic of the floors.

  1. Gran says: “the pasture feeds one cow; it would feed no more than a small den of foxes if foxes ate grass-fed rabbits on it.” Justify her estimate with the losses of each floor.
  2. The vegetable patch feeds the family directly. Using Exercise 41.12’s logic, explain why the patch feeds more people per square metre than the pasture-cow-milk route.
  3. In drought, the grass stops growing. Predict, in order, what happens to the cow’s milk, her weight, and the ledger’s “built” line — and why no extra sunshine can help while the rain fails (Problem 40.1, question 7, holds the key).
  4. Close the ledger with one sentence per floor: producers, consumers — and name who is still missing from the accounting (the subject of the next chapter).
Solution

Solution of Problem 41.1.

1. The pasture’s grasses and the vegetable patch’s plants (and any fruit trees). Inputs: water and mineral salts from the soil, carbon dioxide from the air. Energy: light.

2. In the grass plants’ own leaves — every gram: producers manufacture on site, by day.

3. Return what you borrow: the manure’s rotting restocks the patch soil’s mineral salts, replacing what harvests carry off.

4. Because the cow is a consumer: her trade needs organic matter to dismantle and rebuild. Mineral salts and water are a producer’s inputs; she has no machinery to build body from minerals — that is exactly the trade she lacks.

5. Part passes through unabsorbed — the cowpats; a large part is burned with breathed oxygen to power walking, chewing and staying warm; the rest becomes milk and cow (and the ledger’s day balances).

6. In: grain. Built: eggs, her own upkeep, and — in molt — a full new coat of feathers. Out: droppings and the burned share. Molting, the “built” line is spent on feathers; with the input unchanged, the egg entry must shrink for a while.

7. Grass →\rightarrow hen (via grain, itself a plant product) →\rightarrow chick →\rightarrow buzzard; or pasture-side: grass →\rightarrow cow. Matter was made only at the green links (grass, grain plants); every animal link — hen, chick, buzzard, cow — only transformed it.

8. Bread: wheat plant’s leaves. Boiled egg: hen from grain — the grain plant’s leaves. Milk: cow from grass — the grass leaves. Three trails, three leaves, all in the light.

9. Each floor passes on only a fraction: of the 10 000 kg10\,000\,\mathrm{kg} of grass, a rabbit population builds only its modest fraction as body; of that, foxes build only a fraction again. Two floors of losses shrink a pasture’s worth of grass to a den’s worth of foxes — her estimate is the pyramid’s arithmetic.

10. Eaten directly, the patch’s produce reaches the family with no consumer floor in between: none of it is burned in an animal’s living or lost in its droppings. The pasture route pays the cow’s full expenses first, so each square metre feeds fewer people.

11. The grass stops producing, so the cow’s input fails: first the milk shrinks (production is rebuilt food), then she burns her own fat reserves and loses weight — the “built” line runs negative. Sunshine is energy, not substance: with no water there is nothing for the grass to build with, so the pasture cannot be rescued from the sky.

12. Producers: the holding’s plants make all its organic matter from mineral supplies and light. Consumers: cow, hens and family transform that matter, burning most and building the rest. Missing: the decomposers — who must return the droppings, cowpats and autumn remains to mineral matter; they are the next chapter’s subject.

Terms defined in this chapter

See all 479 terms in the glossary