Plants & fungi

A very fast crowd

Why Does a Pond Turn Green?

Sunlight is free, so stray fertiliser is what sets the limit — remove it and a handful becomes millions in a week, shading the pond floor dead.

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A defence aimed at nothing

Why Does Pollen Make Some People Sneeze?

An allergy is your immune system mounting a real defence against something harmless, and the symptoms are the defence, not the pollen.

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A planned demolition

Why Do Leaves Change Colour?

A tree times it by the length of the night, so a warm autumn still turns on schedule. The leaf never falls, either: a layer of cells forms and lets go.

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Pre-built, then inflated

How Does Bamboo Grow So Fast?

Bamboo grows a metre a day because the whole stem is built underground in advance, then simply pumped full of water and stretched out.

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Dead armour over a living pipe

What Is Bark For?

The rough outside is dead armour. The thin living layer just beneath carries the tree's food downwards, which is why cutting a ring round a trunk kills it.

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The leaves are the spines

Why Does a Cactus Have Spines Instead of Leaves?

A cactus did not lose its leaves — it shrank them into spines to stop water escaping, and handed the job of feeding it to its green stem.

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The colour it refuses

Why Are Leaves Green?

Green is the one colour chlorophyll cannot use, so it is thrown back at you. The yellows sit underneath all summer, until autumn strips the green away.

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A heap that cooks itself

Why Does a Compost Heap Get Hot?

A heap has to reach about a cubic metre before its middle can hold heat, and once it does the warmth kills weed seeds and many plant diseases.

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Being eaten by the invisible

Why Do Dead Things Rot?

Rotting is countless microbes digesting what has died from the outside in, unlocking nutrients that would otherwise stay stuck in the body forever.

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Leaves cheap enough to keep

Why Don't Pine Trees Lose Their Leaves?

A waxy narrow needle survives a winter of frozen ground where a broad leaf cannot, so the pine is already working when the light returns.

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Older than flowers

Why Don't Ferns Have Flowers?

Ferns are far older than flowers and never changed: they scatter dust-fine spores, which need a film of water — hence a life in damp shade.

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Four rings, one job

What Is a Flower Made Of?

A flower is built in rings, and the middle ring is the one that matters: once pollen arrives, that ovary swells into fruit and its eggs become seeds.

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Energy passed along

Who Eats Whom?

Every step of a food chain spends about 90% of its energy simply living, so a tenth passes upward. After four or five links there is nothing left.

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Growing from the wrong end

Why Doesn't Cutting Grass Kill It?

Almost every plant grows from its tips, which is why cutting hurts them. Grass grows from the base of each leaf, so mowing removes only the oldest part.

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No plumbing, no height

Why Is Moss Always Small?

Moss has no pipes to lift water, so every drop soaks from cell to cell — and soaking only works across millimetres, which sets its height.

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The tip of something bigger

What Is a Mushroom?

The mushroom is only the fruit. The real organism is a hidden network of threads that digests its food outside itself and quietly recycles the forest.

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Building food from air

How Do Plants Eat Light?

Plants build sugar out of air, water and light. A tree is made mostly of air — its carbon comes from carbon dioxide, not from the soil it stands in.

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Pollen reaching the right place

What Is Pollination?

Pollination is pollen getting from one flower to another so that seeds can form, mostly carried by animals bribed with nectar to make the trip.

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Anchor and straw

What Do Roots Do?

Roots do three jobs at once: hold the plant down, drink water and minerals through microscopic hairs, and trade sugar with fungi for nutrients underground.

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Green, but not a plant

Is Seaweed a Plant?

Land plants all descend from one green ancestor. Seaweeds come from three separate lines, and many lift their fronds to the light on gas bladders.

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A plant and its lunch

What Is Inside a Seed?

A seed is a whole dormant plant packed with its own food store inside a tough coat, waiting for water to arrive and switch it back on.

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One line a year

Why Does a Tree Have Rings?

A tree adds one ring a year, with a dark line for the slow late growth. The widths record what the weather was doing long before anyone wrote it down.

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Some of it — and the sea makes more

Do Trees Make the Air We Breathe?

Trees release oxygen, but ocean plankton make about half the world's supply — and a forest that has stopped growing gives back roughly what it consumes.

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Borrowing someone else's trunk

Why Do Vines Climb?

Building a trunk is enormously expensive, so a vine grows thin and fast, grabs a support somebody else built, and spends the rest on leaves.

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A judgement, not a species

What Makes a Plant a Weed?

Mint in a pot is a herb and mint in a border is a menace. Break a dandelion root and every piece regrows, which is why digging can spread it.

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The part that would not burn

What Is Left When Something Burns?

Barely one part in a hundred of a burnt log stays behind, and that pale grey pile is the soil minerals a tree spent its whole life collecting.

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A fruit with no seeds and no parents

Why Are Bananas All the Same?

Every banana in the shop is a cutting from one plant, which is why they are identical, seedless, cheap and defenceless against disease.

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A colour that was chosen

Why Are Carrots Orange?

Wild carrots are pale and thin. The orange root is a few centuries old, bred deliberately for the pigment it packs away underground.

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A few weeks, and then nothing

Why Do Cherries All Ripen at Once?

A cherry tree flowers all at once, so the entire crop ripens in about three weeks — a violent little season, and why cherries cost so much.

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Mostly air, in tiny boxes

Why Does Cork Float?

Cork is bark more than half made of sealed air pockets, which is why it floats, squashes narrower rather than wider, and blocks heat and sound.

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A fluffy seed parachute

How Does a Plant Become a T-Shirt?

Cotton is neither leaf nor stem. It is the fluff a plant grows so its seeds catch the wind, combed straight and twisted until the fibres grip each other.

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Almost entirely water, on purpose

Why Is a Cucumber So Watery?

A cucumber is about ninety-six parts water in a hundred, held under pressure in a scaffold of cells — hence crisp, cool and quickly limp.

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A lined pit that runs out of air

Where Does Rubbish Actually Go?

Digs into old tips turn up decades-old newspapers still readable and food scraps barely changed. A landfill is a store rather than a solution.

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Fibres, shaken flat and let dry

How Is Paper Made From a Tree?

Nobody makes the fibres — the tree did. A mill only ungums them in water, drains the pulp flat on a mesh, and presses until they grip again.

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A coat of tiny hairs

Why Is a Peach Fuzzy?

Each hair grows out of the skin the way hair grows out of yours, and the smooth version pays for it — a nectarine bruises sooner and dries faster.

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A fruit that ripens from the inside

Why Do Pears Go from Hard to Mushy So Fast?

A pear ripens from its core outward, so the outside only feels ready once the middle has already turned — which is why it has one good day.

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A stem pretending to be a root

Why Do Potatoes Go Green?

A potato is not a root but a swollen underground stem, so light turns it green and triggers the bitter defence that comes with the colour.

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Tangled springs

Why Does Rubber Bounce Back?

Stretching a rubber band pulls no molecules apart. It straightens tangled ones, and they scramble back into knots the moment you let go.

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A shape that fits a lock

Why Is Sugar Sweet?

Sugar tastes sweet only because its shape happens to fit a receptor on your tongue — and it is the fuel nearly every living thing runs on.

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A stem that grows crooked on purpose

Why Do Sunflowers Follow the Sun?

It swings back overnight and faces east before the sun appears, which means it is running on an internal clock rather than simply chasing the light.

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A skin you cannot digest

Why Does Sweetcorn Come Out Whole?

Each kernel is wrapped in cellulose, which no human enzyme can cut, so the wrapper survives the journey while the inside is absorbed.

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Both, depending on who is asking

Is a Tomato a Fruit or a Vegetable?

An 1893 tax case sent the question to the American Supreme Court. Below twelve degrees a tomato stops making its smell, so a fridge really does ruin it.

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Nothing alive has the tool for it

Why Does Plastic Never Rot?

Life evolved keys for wood, leaf, bone and fat over a very long time. A bacterium that can slowly eat PET turned up beside a Japanese plant in 2016.

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A bundle of drinking straws

Why Does Wood Split One Way?

One pale band of spring growth plus one dark band of late summer is a single year of the tree. Plywood works by leaving no easy direction to split.

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Soaked rock, not caverns

Where Is Water Underground?

There are no hidden lakes down there. Groundwater fills the microscopic pores between grains of rock like water in a sponge, and it moves very slowly.

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Too dry for forest, too wet for desert

Why Are Grasslands Treeless?

Grasslands sit between forest and desert on rainfall, and fire and grazing finish the job. All three keep an enormous belt of the world treeless.

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Warm, wet, and never switched off

Why Does So Much Live in a Rainforest?

A rainforest has no winter, so growth never pauses and life stacks into layers — though the richness sits in the trees, not in the thin soil.

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Plants moving without moving

How Do Seeds Travel?

Landing under your parent means losing, and plants cannot walk, so seeds hitch rides on wind, water and animals — or launch themselves like a spring.

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Rock, remains and life

What Is Dirt Actually Made Of?

Half of good soil is empty space where roots find air and water, and one handful holds billions of bacteria and the fungal threads binding it.

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Neither land nor water

Why Do Wetlands Matter?

A swamp looks like waste ground, but it soaks up floods, filters dirty water, and locks carbon into peat that only rots once it is drained.

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Fire as a gardener

Why Do Some Forests Need to Burn?

Some cones are glued shut with resin that only a fire can melt, so the seeds drop exactly when the ground has been cleared and made fertile.

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A deal, not a favour

Why Do Bees Visit Flowers?

A flower makes nectar purely to give it away, and the bee carries pollen entirely by accident, on hairs that are branched and slightly charged.

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Bread would be fine

What If Every Bee Vanished?

The crops that feed the most people are pollinated by wind, not bees — so losing bees costs us the colour of the plate rather than the calories.

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A meal nothing else wants

How Does a Koala Eat Poisonous Leaves?

Eucalyptus is toxic to almost everything, which is exactly the point: a koala took the job nobody was competing for, and its liver pays the bill.

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By about sixty million years

Sharks Are Older Than Trees

Sharks appear in the fossil record 65 million years before the first true trees — and they are older than Saturn's rings and older than the North Star.

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Thousands of hiding places

How Does a Squirrel Find Its Buried Nuts?

A squirrel remembers roughly where it buried each nut, then finds the exact spot by smell — and the ones it forgets become trees.

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Free soil engineering

Why Are Earthworms Useful?

Worms eat dead leaves and pass them out enriched, drill the soil full of air and drainage, and quietly mix its layers year after year without stopping.

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A fungus, eating your lunch

What Is the Fluff on Old Bread?

The fluff is only the visible half. Invisible threads are digesting the bread from inside while the stalks above launch spores towards the next loaf.

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A chemical booby trap

Why Does Chopping Onions Make You Cry?

The gas is a bulb's defence against animals that dig, and we are collateral damage. A chilled onion and a sharp blade both release far less of it.

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Climbing without a pump

Why Does Water Climb Up a Paper Towel?

Look at the curved edge where water meets a glass. A paper towel is that same edge repeated through countless tiny channels, all pulling at once.

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