--- title: "Living or Not Living?" book: "Primary & Middle School Biology" subject: biology language: en chapter: 1 exercises: 10 source: https://one-course.com/books/biology/1/en/chapter/1-living-or-not-living --- # Chapter 1 — Living or Not Living? A snail slides slowly across the wet path. Next to it lies a gray pebble, just as small, just as round. The snail and the pebble sit in the same rain — yet one of them is alive and the other is not. How do we know? That is the very first question of [biology](#def-g1-living-or-not-living), the science of [living things](#def-g1-living-or-not-living). ## 1.1 What living things do **Definition 1.1 (Living thing).** A *living thing* is something that is *alive*: it is born, it feeds, it grows, it can have babies, and one day it dies. Animals and plants are living things. Biology is the science that studies them. **Example 1.2 (The snail and the pebble).** The snail was born from a tiny egg. It eats salad leaves. It grows — its shell grows with it. There can be baby snails. So the snail is a [living thing](#def-g1-living-or-not-living). The pebble eats nothing, grows not at all, and never has baby pebbles: the pebble is not living. ![The chapter’s two neighbors in person: one of them is slowly on its way somewhere, and it is not the pebble.](https://one-course.com/images/onecourse/chapters/biology-1/g1-living-or-not/img-47a5ae9528bb.jpg) *The chapter’s two neighbors in person: one of them is slowly on its way somewhere, and it is not the pebble.* **Proposition 1.3 (The signs of life).** A [living thing](#def-g1-living-or-not-living) shows these signs: 1. it is *born* ; 2. it *feeds* — it takes in food or makes its own, like plants do with light; 3. it *grows* ; 4. it can have babies — new [living things](#def-g1-living-or-not-living) like itself; 5. it *dies* one day. Something that shows none of these signs is not living. **Proof.** *Admitted at this level.* ∎ **Remark 1.4 (Every sign counts).** One sign alone is not enough. A car “drinks” fuel, and an icicle grows longer in the cold — but the car was built, not born, and the icicle has no baby icicles. To be alive, a thing must show the signs of life *together*: born, feeding, growing, making new [living things](#def-g1-living-or-not-living), dying. ## 1.2 Living, not living, never living **Definition 1.5 (Non-living thing).** A *non-living thing* is something that is not alive. There are two kinds: - things that were *never alive* : a pebble, water, the wind, a bicycle; - things that are *no longer alive* or that *come from* [living things](#def-g1-living-or-not-living) : a dead leaf on the ground, a wooden table, a woolly pullover. **Example 1.6 (The wooden table).** A wooden table does not feed and does not grow: it is not living. But its wood once was: it comes from a tree that was born from a seed, grew for many years, and was cut down. The table is non-living — and it comes from a [living thing](#def-g1-living-or-not-living). **Example 1.7 (What about a robot?).** A toy robot moves, makes sounds, and its light blinks like a little eye. Is it alive? Check the signs: it was built in a factory, not born; its battery is not food that makes it grow; it will never have baby robots. The robot moves, but it is not living. ![Three boxes for sorting the world: living, no longer living, never living.](https://one-course.com/images/onecourse/chapters/biology-1/g1-living-or-not/fig-bf91593618e8.svg) *Three boxes for sorting the world: living, no longer living, never living.* **Method 1.8 (How to decide: living or not?).** Ask the questions of life, one by one: 1. Was it born? Does it feed? Does it grow? 2. Can there be babies of it? Will it die one day? 3. If the answers are yes: it is living. 4. If the answers are no, ask one more question: does it *come from* something living, like wood from a tree? **Remark 1.9 (Seeds look asleep).** A dry bean seed in a packet seems as still as a pebble. But put it on wet cotton, and in a few days a little root appears: the seed was alive all along, waiting. Slow, quiet [living things](#def-g1-living-or-not-living) are easy to mistake for non-living ones — the questions of life help us look closer. ## 1.3 Exercises **Exercise 1.1 ★.** Say the five signs of life. Which of them can you see a kitten doing today? **Solution of Exercise 1.1.** Born, feeds, grows, can have babies, dies. Today a kitten can be seen feeding (drinking milk, eating) and growing — it gets bigger week after week. **Exercise 1.2 ★.** Living or not living? (a) a butterfly; (b) a bicycle; (c) a daisy; (d) a cloud. **Solution of Exercise 1.2.** (a) Living — it hatched, feeds on nectar, and there can be baby caterpillars. (b) Not living — built in a factory, never feeds or grows. (c) Living — it grew from a seed. (d) Not living — a cloud grows and shrinks, but it was never born, does not feed and has no babies. **Exercise 1.3 ★.** A dead leaf lies on the path. Is it living now? Was it ever living? Where did it come from? **Solution of Exercise 1.3.** It is not living now. It was living: it grew on the tree, fed by the tree. It comes from a [living thing](#def-g1-living-or-not-living) — the tree. **Exercise 1.4 ★.** Tom says: “The river is alive — look, it moves and it makes noise!” Use the questions of [Method 1.8](#met-g1-living-or-not-decide) to answer him kindly. **Solution of Exercise 1.4.** Ask the questions of life together: was the river born? Does it feed? Does it grow? Can it have baby rivers? No — moving and making noise are not signs of life on their own. The river is not living, even though many [living things](#def-g1-living-or-not-living) live *in* it. **Exercise 1.5 ★.** Sort into the three boxes of the figure — living, was living, never living: a spider, a woolly sock, a raindrop, an apple on the tree, a fallen pine cone. **Solution of Exercise 1.5.** Living: the spider, the apple on the tree. Was living (or comes from a [living thing](#def-g1-living-or-not-living)): the woolly sock (wool from a sheep), the fallen pine cone (it grew on a pine). Never living: the raindrop. **Exercise 1.6 ★.** A candle flame “eats” the wax, grows taller, and dies when you blow it out. Is the flame a [living thing](#def-g1-living-or-not-living)? Which question of life says no? **Solution of Exercise 1.6.** No. The flame fails the questions of life: it was lit, not born, and above all there are no baby flames that grow up — a flame can be copied to another candle, but it does not have young like a snail or a daisy. (It is a fair question: the flame does trick two of the signs!) **Exercise 1.7 ★.** Name two things in your bedroom that come from [living things](#def-g1-living-or-not-living), like the wooden table of [Example 1.6](#ex-g1-living-or-not-table). Say which [living thing](#def-g1-living-or-not-living) each one comes from. **Solution of Exercise 1.7.** For example: a wooden chair (from a tree), a cotton T-shirt (from a cotton plant), a woolly blanket (from a sheep), a leather shoe (from a cow), honey on the shelf (from bees). **Exercise 1.8 ★.** Try it: put a dry bean on wet cotton near a window, and a pebble on another piece of wet cotton next to it. Look every day for a week. Which one changes? What does that show? **Solution of Exercise 1.8.** The bean changes: it swells, then a little white root comes out, then a green shoot. The pebble stays exactly the same. This shows the bean was alive — a quiet, waiting [living thing](#def-g1-living-or-not-living) — and the pebble is not. **Exercise 1.9 ★★.** A toy robot and a snail both move across the floor. Give two questions of life where their answers are different. **Solution of Exercise 1.9.** Was it born? The snail hatched from an egg; the robot was built. Can it have babies? There can be baby snails; there are no baby robots. (Feeding works too: salad makes the snail grow, the battery does not make the robot grow.) **Exercise 1.10 ★★.** Mushrooms do not run like animals and are not green like most plants. With the signs of [Proposition 1.3](#prop-g1-living-or-not-signs), explain why a mushroom is still a [living thing](#def-g1-living-or-not-living). **Solution of Exercise 1.10.** A mushroom is born (it appears from tiny beginnings in the soil), it feeds (it takes its food from the soil and from dead leaves), it grows — sometimes in a single night — it makes new mushrooms, and it dies. All the signs of life are there: it is a [living thing](#def-g1-living-or-not-living), even without legs and without green leaves.