---
title: "Matter From Food"
book: "Primary & Middle School Biology"
subject: biology
language: en
chapter: 41
exercises: 12
source: https://one-course.com/books/biology/1/en/chapter/41-matter-from-food
---

# Chapter 41 — Matter From Food

A calf of $40\,\mathrm{kg}$ becomes, in two years, a cow of $600\,\mathrm{kg}$. Half a tonne of new cow — flesh, [bone](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton), 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](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) do with their food is this chapter’s business — the [consumers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles)’ side of [Chapter 40](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#ch-g6-plants-are-producers)’s ledger.

## 41.1 Animals build their matter from food

**Proposition 41.1 (Consumers transform organic matter).**

An [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) builds its own [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) — [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle), [bone](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton), fat, [feather](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering), [shell](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) — out of the *[organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) it eats*. [Digestion](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion) ([Definition 25.3](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion)) dismantles the food into [nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion); the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) delivers them ([Proposition 27.1](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#prop-g4-heart-and-blood-carries)); and the body’s [cells](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) ([Proposition 29.7](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#prop-g5-first-look-at-cells-growth)) reassemble them into the [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal)’s own substance. [Animals](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) are *transformers* of matter, never makers-from-mineral: that trade belongs to the [producers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) 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](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#prop-g2-what-animals-eat-daily) explained the long hours); her heavy [digestion](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion) ([Exercise 25.11](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#exo-g4-journey-of-food-11)) dismantles the grass into [nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion); her [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) carries them to udder, [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) and growing calf-inside-her; her [cells](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) 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](https://one-course.com/books/biology/1/en/chapter/19-food-chains#def-g3-food-chains-chain) ([Definition 19.1](https://one-course.com/books/biology/1/en/chapter/19-food-chains#def-g3-food-chains-chain)), [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) changes owners and is rebuilt — grass-matter into cow-matter, cow-matter (the [milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born), the meat) into child-matter. The *organic* never comes from nowhere: [consumers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) pass it along and reshape it. Only at the chain’s green start was it made new ([Proposition 40.6](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#prop-g6-plants-are-producers-firstlink)); only at the [decomposers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles)’ end, next chapter, does it return to mineral.

## 41.2 Growth is matter production

**Definition 41.4 (An animal’s matter production).**

An [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal)’s *production of matter* is the new [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) it builds: growth of the young (the calf’s added kilograms), yearly renewals ([fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) molted and regrown, antlers, [feathers](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering)), repairs ([Remark 17.3](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#rem-g3-bones-and-muscles-alive)’s mended [bone](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton)), and products ([milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born), [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born), wool). All of it is rebuilt food.

**Example 41.5 (Weighing production).**

Farmers weigh production daily: a dairy cow gives some $25\,\mathrm{kg}$ of [milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) a day — [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) she must rebuild from feed, day after day; a hen’s [egg](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) is some $60\,\mathrm{g}$ of packed provisions ([Remark 8.3](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#rem-g2-animals-grow-up-egg)), assembled overnight from her grain. No feed, no production: the ledger balances mercilessly.

**Proposition 41.6 (Not all the food becomes body).**

A [consumer](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) never converts all its food into new matter:

- part is never absorbed, and [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) as droppings ( [Proposition 25.5](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) );
- a large part is *burned* — combined with the breath’s oxygen ( [Proposition 26.5](https://one-course.com/books/biology/1/en/chapter/26-breathing#prop-g4-breathing-exchange) ) — 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](https://one-course.com/books/biology/1/en/chapter/34-food-webs#prop-g5-food-webs-pyramid)’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](https://one-course.com/books/biology/1/en/chapter/34-food-webs#prop-g5-food-webs-pyramid)) 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](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#def-g2-what-animals-eat-kinds), [carnivore](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#def-g2-what-animals-eat-kinds), [omnivore](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#def-g2-what-animals-eat-kinds) ([Definition 10.1](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#def-g2-what-animals-eat-kinds)) name different *sources* of [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter), not different trades. The cow rebuilding grass and the fox rebuilding rabbit both run [Proposition 41.1](#prop-g6-matter-from-food-transform)’s transformation — with equipment matched to the menu ([Proposition 10.4](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#prop-g2-what-animals-eat-match), [Exercise 25.11](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#exo-g4-journey-of-food-11)): grass demands grinders and vast [digestion](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion), meat rewards seizers and a short gut.

**Proof.** *Admitted at this level.* ∎

**Method 41.9 (Auditing an animal’s matter).**

For any [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal), draw up its matter ledger:

1. *in* : what [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) does it eat, and from whom? (its food-web arrows in, [Definition 34.1](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-web) );
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](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#ex-g2-what-animals-eat-winter)): in — worms, [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups), berries; built — its own growth, each year’s new [feathers](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering), the clutch of [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born); 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 41.1 ★.**

State the [consumers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles)’ trade, and contrast it with the [producers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles)’ in one sentence each.

**Solution of Exercise 41.1.**

[Consumers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) transform [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) they eat into their own [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter). [Producers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) make new [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) from purely mineral supplies, with [light](https://one-course.com/books/biology/1/en/chapter/37-exploring-our-environment#def-g6-exploring-our-environment-conditions)’s [energy](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#prop-g3-balanced-diet-jobs).

**Exercise 41.2 ★.**

List the steps that turn grass into [cow-muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle), naming the chapter that covered each.

**Solution of Exercise 41.2.**

[Digestion](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion) dismantles the grass into [nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion) ([Chapter 25](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#ch-g4-journey-of-food)); the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) delivers them everywhere ([Chapter 27](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#ch-g4-heart-and-blood)); the body’s [cells](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) reassemble them into cow-matter, dividing as the body grows ([Chapter 29](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#ch-g5-first-look-at-cells)).

**Exercise 41.3 ★.**

Give four forms of an [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal)’s matter production, with an example of each.

**Solution of Exercise 41.3.**

Growth (the calf’s added kilograms); renewals (molted [fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering), new [feathers](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering), antlers); repairs (a mended [bone](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton)); products ([milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born), [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born), wool).

**Exercise 41.4 ★.**

Name the three destinations of a [consumer](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles)’s food, by [Proposition 41.6](#prop-g6-matter-from-food-losses).

**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](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born)?

**Solution of Exercise 41.5.**

Because each day’s $25\,\mathrm{kg}$ of [milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) is [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) she must rebuild from that day’s feed; [milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) is production, and production is rebuilt food — no input, no output.

**Exercise 41.6 ★.**

An [egg](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) contains $60\,\mathrm{g}$ of [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter). Where was it manufactured — in the hen, or before her? Untangle carefully.

**Solution of Exercise 41.6.**

Assembled *in* the hen, from the [nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion) of her grain — but the [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) itself was first manufactured before her, in the grain [plant](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant)’s [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts). The hen transformed; the [plant](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) produced.

**Exercise 41.7 ★★.**

Use [Proposition 41.6](#prop-g6-matter-from-food-losses) to explain why the food pyramid narrows at every floor.

**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](#met-g6-matter-from-food-audit) on a pet cat: in, built, out — with at least two entries per line.

**Solution of Exercise 41.8.**

In: meat or kibble (and the occasional mouse). Built: its growth as a kitten, the [fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) 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](#prop-g6-matter-from-food-menus) — what differs, and what is identical?

**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](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) into [nutrients](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-digestion) and rebuild it as their own substance.

**Exercise 41.10 ★★.**

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

**Solution of Exercise 41.10.**

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

**Exercise 41.11 ★★.**

The snail’s [shell](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) is mineral substance, yet [Example 40.2](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#ex-g6-plants-are-producers-sorting) counted it as the snail’s making. Reconcile: what did the snail’s body do, and from what supplies, to build it?

**Solution of Exercise 41.11.**

The snail’s body extracted the [shell](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering)’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](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-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](#prop-g6-matter-from-food-losses) — where does the difference go when the potatoes take the detour through the pig?

**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](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles)’ floor.**

1. List the holding’s [producers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) . What are their mineral inputs, and their [energy](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#prop-g3-balanced-diet-jobs) source?
2. The pasture grows about $10\,000\,\mathrm{kg}$ of grass matter in a season. In whose [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) was every gram of it manufactured?
3. Gran spreads the henhouse manure on the vegetable patch. Which rule of [Proposition 35.5](https://one-course.com/books/biology/1/en/chapter/35-people-and-nature#prop-g5-people-and-nature-lasting) is she keeping, and what exactly does the manure restock?
4. Why can the cow not simply be fed [mineral salts](https://one-course.com/books/biology/1/en/chapter/22-what-plants-need#prop-g4-what-plants-need-needs) and water directly, sparing the pasture?

**Part II — The [consumers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles)’ floor.**

5. The cow eats roughly $70\,\mathrm{kg}$ of grass a day and gives about $20\,\mathrm{kg}$ of [milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) . Name the three destinations of the missing $50\,\mathrm{kg}$ .
6. The hens turn grain into [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) . Write the hen’s ledger — in, built, out — and say why a molting hen (renewing all her [feathers](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) ) lays fewer [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) for a while.
7. A buzzard takes a chick. Extend the holding’s [food chain](https://one-course.com/books/biology/1/en/chapter/19-food-chains#def-g3-food-chains-chain) to it, and state at which links matter was *made* and at which it was only transformed.
8. The family eats [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) , [milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) and vegetables. Trace the [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) of one breakfast — bread, boiled [egg](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) , [milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) — each to the [leaf](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) where it was first manufactured.

**Part III — The arithmetic of the floors.**

9. 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.
10. The vegetable patch feeds the family directly. Using [Exercise 41.12](#exo-g6-matter-from-food-12) ’s logic, explain why the patch feeds more people per square metre than the pasture-cow-milk route.
11. In drought, the grass stops growing. Predict, in order, what happens to the cow’s [milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) , her weight, and the ledger’s “built” line — and why no extra sunshine can help while the rain fails ( [Problem 40.1](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#pb-g6-plants-are-producers-1) , question 7, holds the key).
12. Close the ledger with one sentence per floor: [producers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) , [consumers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) — and name who is still missing from the accounting (the subject of the next chapter).

**Solution of Problem 41.1.**

**1.** The pasture’s grasses and the vegetable patch’s [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) (and any [fruit](https://one-course.com/books/biology/1/en/chapter/16-flowers-fruits-and-seeds#prop-g3-flowers-fruits-seeds-transform) trees). Inputs: water and [mineral salts](https://one-course.com/books/biology/1/en/chapter/22-what-plants-need#prop-g4-what-plants-need-needs) from the soil, carbon dioxide from the air. [Energy](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#prop-g3-balanced-diet-jobs): [light](https://one-course.com/books/biology/1/en/chapter/37-exploring-our-environment#def-g6-exploring-our-environment-conditions).

**2.** In the grass [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant)’ own [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) — every gram: [producers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) manufacture on site, by day.

**3.** Return what you borrow: the manure’s rotting restocks the patch soil’s [mineral salts](https://one-course.com/books/biology/1/en/chapter/22-what-plants-need#prop-g4-what-plants-need-needs), replacing what harvests carry off.

**4.** Because the cow is a [consumer](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles): her trade needs *organic* matter to dismantle and rebuild. [Mineral salts](https://one-course.com/books/biology/1/en/chapter/22-what-plants-need#prop-g4-what-plants-need-needs) and water are a [producer](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles)’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](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) and cow (and the ledger’s day balances).

**6.** In: grain. Built: [eggs](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born), her own upkeep, and — in molt — a full new coat of [feathers](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering). Out: droppings and the burned share. Molting, the “built” line is spent on [feathers](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering); with the input unchanged, the [egg](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) entry must shrink for a while.

**7.** Grass $\rightarrow$ hen (via grain, itself a [plant](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) product) $\rightarrow$ chick $\rightarrow$ buzzard; or pasture-side: grass $\rightarrow$ cow. Matter was *made* only at the green links (grass, grain [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant)); every [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) link — hen, chick, buzzard, cow — only transformed it.

**8.** Bread: wheat [plant](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant)’s [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts). Boiled [egg](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born): hen from grain — the grain [plant](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant)’s [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts). [Milk](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born): cow from grass — the grass [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts). Three trails, three [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts), all in the [light](https://one-course.com/books/biology/1/en/chapter/37-exploring-our-environment#def-g6-exploring-our-environment-conditions).

**9.** Each floor passes on only a fraction: of the $10\,000\,\mathrm{kg}$ 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](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) floor in between: none of it is burned in an [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-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](https://one-course.com/books/biology/1/en/chapter/8-how-animals-grow-up#def-g2-animals-grow-up-born) shrinks (production is rebuilt food), then she burns her own fat reserves and loses weight — the “built” line runs negative. Sunshine is [energy](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#prop-g3-balanced-diet-jobs), 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](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles): the holding’s [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) make all its [organic matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter) from mineral supplies and [light](https://one-course.com/books/biology/1/en/chapter/37-exploring-our-environment#def-g6-exploring-our-environment-conditions). [Consumers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles): cow, hens and family transform that matter, burning most and building the rest. Missing: the [decomposers](https://one-course.com/books/biology/1/en/chapter/34-food-webs#def-g5-food-webs-roles) — who must return the droppings, cowpats and autumn remains to [mineral matter](https://one-course.com/books/biology/1/en/chapter/40-plants-are-producers#def-g6-plants-are-producers-matter); they are the next chapter’s subject.