186 Fun Facts About Biology

Which structure do prokaryotic cells such as bacteria lack?

The nucleus is what bacteria lack: their DNA sits loose in a region called the nucleoid, so the cell can start building a protein from a gene while that gene is still being copied.

Which pair of sex chromosomes do human males typically carry?

XY is the male pair in humans, but birds do it the other way round: there it is the females that carry the mismatched pair, called ZW, while males have two matching Z chromosomes.

Which carnivorous plant catches insects between hinged leaves that snap shut?

The Venus flytrap closes only when its trigger hairs are touched twice in quick succession, a safeguard that stops the plant wasting energy by snapping shut on nothing.

What is the largest organ in the human body?

Skin is the body's largest organ and its protective barrier, which is why severe burns are so dangerous: with that covering gone, fluid leaks out of the body and germs get in.

Which condition results from an extra chromosome 21?

Down syndrome arises when a child inherits three copies of chromosome 21 instead of the usual two, giving 47 chromosomes where most people have 46; the chance rises with the mother's age.

Which flightless bird, found only on Mauritius, died out in the seventeenth century?

The dodo, a flightless relative of the pigeons, was exterminated not just by hungry sailors but by the animals they introduced to Mauritius.

What type of cell division produces two identical daughter cells?

Mitosis shares a cell's already-copied chromosomes equally between two new cells, which is how you grow and heal; cancer begins when the controls on that division break down.

What gas do plants primarily absorb from the atmosphere during photosynthesis?

Carbon dioxide supplies the carbon that plants build into sugar and wood, so most of a tree's bulk is made from air, not drawn up from the soil as people tend to assume.

Which blood cells are responsible for fighting infections?

White blood cells rush to an infection and many die fighting it: the pus in an infected cut is full of dead white blood cells.

Which animals are the only mammals capable of true flight?

Bats fly by flapping a thin membrane stretched between long finger bones, so each wing is in effect a hand; flying squirrels, colugos and sugar gliders can only glide.

What pigment gives plants their green color?

Chlorophyll is the pigment in chloroplasts that captures light energy for the plant; it absorbs red and blue light but reflects green, which is why leaves look green.

Which organs filter waste from the blood to produce urine?

Kidneys filter far more fluid than you ever pass: almost all the water they strain from the blood is taken straight back, leaving only a litre or two of urine a day.

What is the term for an organism that makes its own food rather than eating other organisms?

An autotroph makes its own food, and not always from sunlight: around deep-sea vents, bacteria build sugar using chemicals such as hydrogen sulfide and feed whole animal communities.

Which structure do plant cells have that animal cells lack?

The cell wall is a tough coat built around cellulose, the most abundant organic compound on Earth; cotton fibre is about 90 percent cellulose, so a T-shirt is mostly plant cell wall.

Which bird lays the largest eggs of any living species?

The ostrich lays eggs weighing well over a kilogram, the biggest of any living bird, yet measured against the size of the adult it is actually a small egg.

Which Galápagos birds, studied for their varied beak shapes, are named after Darwin?

Finches is the name that stuck, though Darwin did not see that the birds belonged together until ornithologist John Gould examined his specimens in London and declared them one closely related group.

What are the tiny pores in a leaf's surface that control gas exchange called?

Stomata are each flanked by two guard cells that swell or shrink to open and close the pore; plants lose most of their water through them, which is why many desert plants open them only at night.

Which part of the brain controls balance and coordination?

The cerebellum fine-tunes movement, so damage there leaves a person able to move but swaying, walking with a wide, unsteady gait and missing objects they reach for.

What is the term for animals that eat both plants and meat?

Omnivore diets work as insurance: because they can switch between plants and prey, animals such as bears and pigs cope better than specialists when one kind of food runs short.

What scientist is known as the father of genetics?

Gregor Mendel worked out the rules of inheritance by crossing pea plants at his monastery, but did not live to see them matter: his work was rediscovered in 1900, sixteen years after he died.

What is the function of ribosomes in a cell?

Protein synthesis is the ribosome's whole job, and bacterial ribosomes differ enough from ours that antibiotics such as tetracycline can jam theirs while leaving our own untouched.

Which type of blood vessel carries blood away from the heart?

Arteries carry oxygenated blood away from the heart to the body's tissues, except the pulmonary arteries, which carry deoxygenated blood to the lungs.

What is the term for the variety of life in a particular habitat or ecosystem?

Biodiversity began as shorthand for 'biological diversity', coined in the mid-1980s for a Washington forum on the subject; the biologist Edward Wilson put the new word on the cover of the proceedings and it stuck.

Which organelle is responsible for packaging and shipping proteins in a cell?

The Golgi apparatus, reported by Camillo Golgi in 1898, was doubted as a mere staining artefact until electron microscopes confirmed it was real in the 1950s.

What is the process by which a caterpillar transforms into a winged adult called?

Metamorphosis is drastic: inside the chrysalis a caterpillar releases enzymes that dissolve most of its body, and the adult is rebuilt from small clusters of cells that survive.

What type of symbiotic relationship benefits one organism while harming the other?

Parasitism differs from predation in that the victim usually lives: a tick or tapeworm feeds on its host over a long period, so most parasites weaken rather than kill.

Which vitamin is produced by the human body when exposed to sunlight?

Vitamin D needs strong sunlight, so far from the equator the body makes little or none in winter, which is why health services in countries such as Britain advise a supplement in the darker months.

What is the term for an organism that breaks down dead organic matter?

Decomposers such as moulds and bacteria are nature's recyclers: by breaking down dead leaves and bodies they release the nutrients locked inside, which plants then take up to grow.

The human heart's four chambers are two atria and two what?

Ventricles do the pumping, and the left one has the thickest wall of all because it must drive blood around the entire body, while the right only has to send it next door to the lungs.

Which principle did botanist Schleiden and physiologist Schwann establish in the late 1830s?

Cell theory grew out of a dinner conversation: when Schleiden talked about the nuclei of plant cells, Schwann recalled seeing the same thing in animal tissue, and both men promptly confirmed the resemblance.

Which hormone lowers the level of sugar in the blood?

Insulin, made in the pancreas, was first given to a patient in January 1922, when doctors in Toronto injected it into Leonard Thompson, a 14-year-old who lay dying of diabetes.

In DNA, adenine always pairs with which base?

Thymine and adenine always occur in equal amounts in DNA, a regularity Erwin Chargaff measured before anyone knew why; the pairing of the two bases turned out to be the reason.

Which human cell is big enough to be seen with the naked eye?

The ovum is big enough to glimpse unaided, yet no one had identified one in a mammal until the 1820s, when the embryologist Karl Ernst von Baer finally tracked it down.

Which scientist discovered penicillin?

Alexander Fleming noticed in 1928 that a mould growing by accident on one of his culture plates had cleared the bacteria around it; he named the substance it made penicillin.

What is the process called when a cell engulfs a particle by surrounding it with its membrane?

Phagocytosis was discovered in Messina in 1882, when Élie Metchnikoff pushed small thorns into starfish larvae and found mobile cells crowding round the intruders.

Which treeless biome is characterized by permafrost and very low temperatures?

Tundra is too cold for trees: the growing season is short and the subsoil stays frozen, so only a thin surface layer thaws each summer, enough for mosses, grasses and dwarf shrubs but little more.

What is the main function of the large intestine?

Absorbing water is how the large intestine turns the liquid leftovers of digestion into solid stool; when that step goes wrong, the result is diarrhoea or constipation.

What type of reproduction involves only one parent and produces genetically identical offspring?

Asexual reproduction yields clones, and that carries a risk: the Gros Michel banana, grown everywhere from offshoots of the same plants, was almost wiped out in the 1950s by a single wilt disease.

Which part of a neuron receives signals from other neurons?

Dendrites branch like the crown of a tree, and the branching is the point: it gives a neuron a far larger surface on which to receive signals from the cells around it.

What term describes the complete set of an organism's DNA?

A genome's size says little about its owner: the human genome runs to about 3 billion DNA letters, while Paris japonica, a rare Japanese flower, has roughly 50 times as many.

Which enzyme 'unzips' DNA, separating its two strands so that each can be copied?

Helicase unzips the double strand by breaking the bonds between its base pairs; a fault in one human helicase causes Werner syndrome, a condition of dramatically premature ageing.

What is the name of the light-independent reactions in photosynthesis?

The Calvin cycle is named for Melvin Calvin, whose Berkeley team fed green algae radioactive carbon and tracked which compounds it turned up in, tracing the pathway one step at a time.

Which arm of the immune system relies on T lymphocytes that directly kill infected targets?

Cell-mediated immunity is also why transplants can be rejected: the same killer T cells that destroy infected cells attack a donor organ as foreign, so recipients take drugs to hold them back.

What is the phenomenon where a single gene influences multiple seemingly unrelated traits?

Pleiotropy shows in Marfan syndrome: a fault in one gene weakens connective tissue all over the body, so the same person may be unusually tall, have dislocated eye lenses and carry a fragile aorta.

Which organelle contains its own DNA and is thought to have once been a free-living bacterium?

Mitochondria still carry a small loop of their own DNA, and because it passes down only from the mother, geneticists can use it to trace a person's maternal ancestry far back through the generations.

Which principle states that gene frequencies in a population stay constant across generations unless something disturbs them?

The Hardy-Weinberg principle is half named for Godfrey Hardy, a pure mathematician who hoped his work would never be applied to anything, yet the law he published in 1908 became a foundation of population genetics.

Which process moves water across a semipermeable membrane from low to high solute concentration?

Osmosis is why salt preserves food: on heavily salted meat or fish, water is drawn out of any microbe that lands, leaving it too dried out to grow.

What is CRISPR-Cas9 primarily used for?

CRISPR-Cas9 is a gene-editing tool that lets scientists cut and modify DNA sequences precisely. Derived from a bacterial immune defence system, it earned Charpentier and Doudna the 2020 Nobel Prize in Chemistry.

During meiosis, paired chromosomes swap matching segments in a process known as what?

Crossing over takes place in prophase I of meiosis, when paired chromosomes, one from each parent, swap matching stretches of DNA; the shuffle means every egg or sperm carries a new combination of genes.

ATP is often called the molecular unit of what for cells?

ATP is called the molecular unit of currency because cells spend it to power work: hydrolysing its terminal phosphate to ADP releases about 30.5 kJ/mol under standard conditions.

Which glands normally produce the hormone epinephrine?

The adrenal glands release epinephrine under stress; injected, the same hormone is the emergency treatment for a life-threatening allergic reaction, because it relaxes the airways and tightens blood vessels.

Whose 1858 paper spurred Darwin to rush out 'On the Origin of Species'?

Alfred Russel Wallace hit on natural selection during a bout of fever in the Moluccas, in what is now Indonesia, and posted his essay to Darwin, who had been developing the same theory for years without publishing it.

What is each alternative version of a gene, such as blood-group A, B or O, called?

An allele is one version of a gene, and you inherit one from each parent: receive A from one and B from the other and both show up, giving blood group AB.

Amoebae change shape by extending and retracting what?

Pseudopods are temporary bulges that an amoeba pushes out and then flows into, which is how it crawls and wraps around food; some of your own immune cells wander through your tissues in much the same way.

'Antigen' is usually explained as a contraction of what phrase?

Antibody generator is the usual reading, and it fits: an antigen is whatever prompts the body to make antibodies, which is how a vaccine can train it in advance with a harmless piece of a germ.

Which Dutch scientist is known as 'the Father of Microbiology'?

Antonie van Leeuwenhoek, a Delft draper with no formal scientific training, ground single-lens microscopes and in the 1670s became the first to describe bacteria and protists, which he called animalcules.

Which salamander keeps its feathery external gills for life?

The axolotl never really grows up: where most salamanders lose their gills and move onto land, it stays in its larval form for life and breeds in it, a trait called neoteny.

Barbara McClintock won her 1983 Nobel Prize for cytogenetics research on which plant?

Barbara McClintock worked on maize at Cold Spring Harbor, where in the 1940s she discovered transposable elements, the 'jumping genes' that explained the mottled colours of corn kernels.

Who is called the 'father of modern taxonomy'?

Carl Linnaeus gave every species a two-part Latin name, and he did not leave out his own: it was he who named us Homo sapiens, 'wise man'.

What term describes an organism keeping its internal conditions stable?

Homeostasis is why you sweat when hot and shiver when cold: both are automatic corrections that pull your core temperature back towards about 37 °C.

Fireflies and many deep-sea fish glow thanks to which phenomenon?

Bioluminescence is light made by a chemical reaction inside a living thing; fireflies make their own, while the Hawaiian bobtail squid keeps glowing bacteria in a special light organ.

Which animal, growing to around 30 metres, is the largest alive today?

The blue whale lives almost entirely on krill, tiny shrimp-like animals that it strains from huge mouthfuls of seawater through the baleen plates in its mouth.

Which camouflage uses bold stripes to make a target's speed and direction hard to judge?

Motion dazzle was tried on warships in the First World War: the wild stripes could not hide a ship, but were meant to make U-boat crews misjudge its speed and course before firing a torpedo.

Which carbohydrate do animals store in the liver and muscles?

Glycogen is a small tank: the liver's supply is nearly gone after a day without food, and endurance athletes who burn through theirs suddenly 'hit the wall'.

Which sterol keeps animal cell membranes fluid at various temperatures?

Cholesterol sits between the phospholipids of animal membranes, stiffening them when warm and stopping tight packing when cold; fungi use ergosterol and plants mainly sitosterol and stigmasterol instead.

Cellulose is a linear chain of which sugar units?

Glucose builds both starch and cellulose; only the way the units are linked differs, yet that is enough for us to digest bread easily and wood or grass not at all.

Which cat, the sole living member of genus Acinonyx, has claws that never fully retract?

The cheetah's claws stay out so that they grip the ground like the spikes on a sprinter's shoes, part of what makes it the fastest animal on land.

Which tough polysaccharide makes up the outer shells of insects and crabs?

Chitin makes a light, tough armour, but one that cannot stretch, which is why insects and crabs must shed their whole outer shell and grow a new one in order to get bigger.

Chloroplasts belong to which class of organelle?

Chloroplasts are plastids, a family that also includes pigment-filled chromoplasts; chloroplasts turn into chromoplasts as a tomato ripens, which is why it goes from green to red.

Which proteins package DNA into nucleosomes in eukaryotic cells?

Histones act as spools: winding DNA around them is what lets a thread far longer than the cell pack inside it, and how tightly it is wound helps decide which genes are switched on.

Which is the most abundant protein in mammals?

Collagen is the body's main structural protein, and it cannot be built without vitamin C, which is why scurvy brings bleeding gums and wounds that will not heal.

Stony corals build their reef-forming skeletons out of which mineral?

Calcium carbonate is what each coral polyp lays down beneath itself, layer on layer, until a reef rises; more acidic seawater holds less of the carbonate it needs, making those skeletons harder to build.

Which cytoskeleton fibres form the spindle that pulls chromosomes apart when a cell divides?

Microtubules, thin tubes of the protein tubulin, build the spindle; the cancer drug paclitaxel works by locking them in place, so a tumour cell cannot finish dividing.

Which single-celled algae, housed in glassy silica shells, are among the ocean's biggest oxygen producers?

Diatoms' dead shells pile up on the seabed as diatomaceous earth, the chalky powder Alfred Nobel soaked with nitroglycerin in the 1860s to make dynamite safe to handle.

Dolly the sheep was cloned from a cell taken from which tissue?

Dolly was grown at the Roslin Institute from a single mammary gland cell of an adult ewe, and the team named her after Dolly Parton in a nod to that tissue.

Dolly the cloned sheep was born in which country?

Scotland's Roslin Institute, near Edinburgh, made Dolly with three mothers: one ewe gave the cell that was copied, a second gave the empty egg and a third carried the lamb.

'Reticulum' in endoplasmic reticulum is Latin for what?

Reticulum is Latin for 'little net', the diminutive of rete; the name fits the lacy web of membranes that Keith Porter's team first saw under an electron microscope in 1945.

Epigenetics studies changes in gene expression that occur without altering what?

Epigenetics studies chemical tags that switch genes on or off while leaving the DNA sequence untouched; that is how a nerve cell and a liver cell can carry identical DNA yet behave so differently.

Which single-celled organism photosynthesises in light yet lives on absorbed food in the dark?

Euglena's red eyespot shades a light sensor at the base of its whip-like flagellum, so as the cell turns it can tell where the light is and swim towards it.

Which nickname do the near-indestructible tardigrades go by?

Water bears survive by pulling in their legs and drying out into a dormant ball called a tun; dried specimens came back to life after days exposed to open space on a 2007 satellite flight.

Which bone is the only one in the thigh?

The femur is the thigh's only bone and the body's longest, and its length tracks a person's height so closely that forensic scientists can estimate stature from a single thigh bone.

Fermentation is what type of metabolism?

Fermentation is anaerobic metabolism: it runs without oxygen, regenerating NAD+ so sugar breakdown can continue, and yields organic end products such as lactate in muscle or ethanol in yeast.

Ferns reproduce via what?

Ferns reproduce via spores shed from dots called sori under their fronds; each spore grows into a tiny heart-shaped plant of its own, and only when its swimming sperm reach an egg does a new fern sprout.

Which flower part is the female structure that receives pollen?

The gynoecium is the flower's female part, one or more carpels holding the ovules; after fertilisation its ovary swells into the fruit, so a tomato or a cherry is a ripened part of it.

What is each feeding position in a food chain, such as producer or herbivore, called?

A trophic level is an organism's position in a food chain: producers sit on the first and herbivores on the second. Only about 10% of the energy passes up each step, which is why a chain rarely runs beyond five links.

How many three-letter codons does the genetic code contain?

64 is 4 x 4 x 4. That is far more codons than the code has meanings to spell, so most meanings are spelled several ways, which is why many single-letter DNA mutations leave the finished protein unchanged.

Glycolysis converts a six-carbon sugar into what?

Pyruvate is what glycolysis leaves, two molecules from each glucose. The pathway works with or without oxygen and turns up in nearly every living cell, a sign that it is among the oldest in biology.

Which iron-containing protein transports oxygen in the blood?

Hemoglobin holds iron in four haem groups, each able to carry one oxygen molecule; carbon monoxide grips the same sites over 200 times more tightly, which is how the gas suffocates its victims.

What dormant state do lungfish and some land snails enter to survive hot, dry summers?

Aestivation is summer dormancy: African lungfish seal themselves in a mucus cocoon in dried mud and land snails seal their shell openings, slowing metabolism until rain returns.

The word 'hormone' comes from a Greek word meaning what?

Hormone derives from the Greek horman, 'setting in motion' or 'impelling'; Ernest Starling coined the term in 1905 for chemical messengers such as secretin that spur distant organs into action.

Which co-discoverer of the double helix first led the Human Genome Project at the NIH?

James Watson ran the NIH's side of the project until 1992, when he quit after clashing with the agency's director over her wish to patent gene sequences; the work was declared complete in 2003.

A newborn baby has dozens more bones than an adult's 206 because many of them later do what?

Fuse together is what a baby's bones do as it grows; the skull, for one, starts as separate plates with soft gaps so the head can squeeze through the birth canal, then knits into a single case.

Hummingbirds live wild only in which region?

The Americas are the only home of living hummingbirds, from Alaska to Tierra del Fuego, yet the oldest known hummingbird fossils, about 30 million years old, come from Europe, the first of them found in Germany.

Jane Goodall studied chimpanzees at which Tanzanian park?

At Gombe Stream, where she arrived in 1960, Jane Goodall watched chimpanzees strip the leaves off twigs to fish termites from their mounds, showing that humans are not the only toolmakers.

Which fibrous protein makes up hair, nails, feathers, horns and hooves?

Keratin's chains are cross-linked by sulfur bridges, which is what makes horn and hair so tough; a perm works by breaking those bridges and re-forming them in a new shape.

The term 'symbiosis' arose from studies of which growths on rock and bark?

Lichens led the botanist Albert Frank to coin 'Symbiotismus' in 1877: a fungus builds the body and an alga makes the food, a pairing tough enough for bare rock yet so sensitive to dirty air that it is used to gauge pollution.

Which vitamins are fat-soluble?

Vitamins A, D, E and K dissolve in fat, so the body stores them in the liver and fatty tissue instead of flushing the surplus out in urine, which is why megadoses of A or D can build up to toxic levels.

In which abdominal quadrant is the human liver located?

The liver sits in the right upper quadrant, tucked under the diaphragm and shielded by the lower right ribs; its bulk is why the right half of the diaphragm rides higher than the left.

Louis Pasteur's vaccine against which disease was first given to a boy in 1885?

Rabies vaccine was first given to nine-year-old Joseph Meister in July 1885, after a dog thought to be rabid mauled him; Pasteur, a chemist with no medical licence, risked prosecution by treating him, and the boy lived.

Which human cells eject their nucleus as they mature?

Red blood cells push out their nucleus and shed their other organelles to leave more room for their oxygen-carrying cargo; unable to divide or mend themselves, they wear out within months and must be replaced.

Which human skin cells make the pigment that darkens skin after sun exposure?

Melanocytes answer ultraviolet light by turning out more melanin and handing it to the skin cells around them, where the pigment soaks up further rays: a tan is the body's own sunscreen.

Bog-building sphagnum is which kind of plant?

A moss: sphagnum soaks up water like a sponge and turns its bog so acidic that dead plants barely rot and pile up as peat; the same acid water has preserved ancient human 'bog bodies'.

Overheated corals expelling their algae is known as what?

Bleaching does not kill a coral outright: if the water cools in time it can recover, but one that stays bleached for long starves, because the algae supplied most of its food.

The '-rhiza' in mycorrhiza is Greek for what?

Rhiza is Greek for 'root', so mycorrhiza means 'fungus-root'; fungal hyphae and plant roots interconnect at the cellular level, trading soil phosphorus for plant sugars.

Which process do Rhizobium bacteria carry out in the nodules of legumes?

Nitrogen fixation turns nitrogen gas from the air into ammonia the plant can use, which is why farmers rotate beans or clover into a field to enrich the soil.

A nucleotide consists of a nitrogenous base, a phosphate and what?

A pentose sugar has five carbons: ribose in RNA, deoxyribose in DNA. Deoxyribose is missing one oxygen atom, a small change that leaves DNA far less prone to chemical breakdown than RNA.

Octopus blood is blue because its oxygen-carrying pigment contains which metal?

Copper-based haemocyanin turns blue when it picks up oxygen and carries it more efficiently in cold water, which suits life in the sea; three hearts pump it, two of them serving only the gills.

The pancreas releases both hormones and digestive juices, two gland functions called what?

Endocrine and exocrine: scattered islet cells release hormones into the blood, while the rest of the gland sends digestive enzymes down a duct, in inactive form so that the pancreas does not digest itself.

Paramecia swim with tiny beating hairs, making them which protists?

Ciliates such as Paramecium row with their cilia and can throw them into reverse: on bumping into an obstacle the cell backs up for a moment, then sets off again.

Which sugar does phloem mainly transport around a plant?

Sucrose, the same molecule as table sugar, travels down from the leaves through phloem lying just under the bark, which is why stripping a ring of bark from a trunk starves the tree below the cut and kills it.

'Plankton' comes from a Greek word meaning what?

Plankton comes from the Greek planktos, 'wandering' or 'drifter': what makes something plankton is being unable to swim against a current, not being small, so a large jellyfish counts too.

Besides the platypus, which mammal lays eggs?

Echidnas, four species of them, are the only other egg-laying mammals: the mother lays one leathery egg straight into a pouch on her belly, where it hatches into a tiny 'puggle' about ten days later.

Pollination is the transfer of pollen from an anther to which structure?

Pollination moves pollen from an anther to a stigma, the sticky tip of the carpel, from which a pollen tube grows down to the ovary; the carriers include insects, birds, water and wind.

What is a misfolded protein that induces misfolding in others called?

A prion carries no genes at all: it spreads by forcing normal copies of the same protein into its own misfolded shape, which is how mad cow disease destroys the brain.

Which 1962 Rachel Carson book advanced the global environmental movement?

Silent Spring argued that pesticides such as DDT were poisoning birds and the food they ate; ten years after it appeared, the United States banned DDT from its farms.

'Erythrocyte' derives from Greek words meaning what?

Erythrocyte is Greek for 'red hollow vessel': erythros, red, plus kytos, a hollow vessel, the origin of '-cyte' in cell names. The same 'red' is in EPO, erythropoietin, the hormone cheating cyclists took to grow extra red cells.

Which molecule carries amino acids to the ribosome during translation?

Transfer RNA (tRNA) carries each amino acid to the ribosome and matches its three-base anticodon to the next codon on the mRNA, so the chain is assembled in exactly the order the message spells out.

Robert Hooke coined the biological word 'cell' in 1665 after examining which material?

Cork's tiny air-filled boxes, which Hooke likened to a honeycomb and named cells, are also why a cork is so light and springs back after being squeezed into a bottle.

Which technique did Rosalind Franklin use to study DNA's structure?

X-ray crystallography in Rosalind Franklin's lab at King's College London produced Photo 51 in 1952; a colleague showed it to a rival team without her knowledge, and it helped them build the double-helix model.

What is a seed's protective coat called?

The testa can be so hard and waterproof that some seeds will not sprout until fire, frost or a trip through an animal's gut has breached it, which keeps them dormant until conditions suit.

Which is the smallest and lightest bone in the human body?

The stapes, shaped like a stirrup, is the last of three tiny ear bones; they focus the eardrum's vibrations onto a much smaller window, raising the pressure enough to set the inner ear's fluid moving.

Clownfish shelter unharmed among the stinging tentacles of which animal, a textbook case of mutualism?

Sea anemones do not harm the clownfish, which is unaffected by their sting; in return the fish drives off anemone-eating fish and feeds its host with its droppings.

Electrical synapses couple neurons through what structures?

Gap junctions are channels that let ions flow straight from one cell into the next with almost no delay; the same channels link heart muscle cells, which is why the heart contracts as one.

'Tardigrada', named by Spallanzani in 1776, means what?

Tardigrada is Latin for 'slow walkers' or 'slow steppers', the name Lazzaro Spallanzani gave them in 1776 for their lumbering gait; Johann Goeze had called them 'little water bear' three years earlier.

Which chromosome regions protect the ends of linear chromosomes from degradation?

Telomeres are repetitive DNA caps (TTAGGG repeats in humans) at chromosome ends that stop repair systems mistaking the ends for breaks; they shorten with each division unless telomerase rebuilds them.

What shape is the human thyroid gland usually described as?

The thyroid is butterfly-shaped, its two lobes joined by a narrow bridge across the windpipe; it needs iodine to make its hormones, which is why iodine is added to table salt to prevent the neck swelling called goitre.

Transcription copies a segment of DNA into which kind of molecule?

RNA is what transcription makes: an enzyme reads one DNA strand and builds a matching copy. Retroviruses such as HIV run the process in reverse, writing their RNA into the host's DNA.

Which large water-filled organelle keeps a plant cell firm, so that the plant wilts when it shrinks?

The vacuole can take up most of a mature plant cell; young shoots lengthen quickly mainly by pumping water into it, growth that costs the plant little more than water.

Which is the most numerous type of biological entity on Earth?

Viruses outnumber every other kind of biological entity, bacteria included; in the sea, where they teem, most are bacteriophages, which prey only on bacteria and are harmless to plants and animals.

Which plant tissue transports water upward from the roots?

Xylem carries water and minerals up from the roots through long pipes of dead, empty cells; its name comes from the Greek xylon, 'wood', because xylem is what a tree's wood is made of.

People with which blood type are called universal donors, because their red cells can be given to anyone?

O negative red cells carry none of the A, B or Rh markers a recipient's body might attack, so air ambulances stock it for emergencies; yet people with O negative blood can themselves receive only O negative.

Which two forms of endoplasmic reticulum does a cell contain?

Rough and smooth describe how the two look under an electron microscope: rough ER is studded with ribosomes, smooth ER is bare. Liver cells are rich in the smooth kind, which helps break down drugs and alcohol.

Which biologist proposed that eukaryotic cells arose from symbiotic mergers of bacteria?

Lynn Margulis argued that key parts of complex cells began as free-living bacteria swallowed by a larger cell; about fifteen journals turned her paper down before one printed it in 1967.

What did the 1952 Miller-Urey experiment produce by sparking a simulated early atmosphere?

Stanley Miller ran it under Nobel laureate Harold Urey at the University of Chicago to simulate the early Earth's atmosphere.

Which journal rejected Hans Krebs's 1937 paper on the citric acid cycle?

Nature's editor replied that his letters pages were full for weeks to come, so Krebs sent the work to the Dutch journal Enzymologia instead; it went on to win him a share of the 1953 Nobel Prize.

Which gene cluster lays out an animal embryo's head-to-tail body plan?

Hox genes tell each stretch of an embryo what to become, so a mutation in one can put a body part in the wrong place: fruit flies have been bred with legs growing where their antennae should be.

Which Australian marsupial has fingerprints so like a human's that even a microscope struggles to tell them apart?

Koala fingerprints evolved independently of ours, a case of convergent evolution in an animal that climbs and grasps for a living.

Which hefty plant-eaters are the closest living relatives of whales and dolphins, despite looking more like pigs?

Hippos and cetaceans split from a shared ancestor about 55 million years ago, a kinship first hinted at by blood proteins and later backed by DNA.

Which cold-water fish has the longest known lifespan of any vertebrate, estimated at between 272 and 510 years?

The Greenland shark lives so long that the oldest individual studied was put at about 392 years old, give or take 120.

Turritopsis dohrnii, nicknamed 'immortal' because adults can revert to a juvenile stage, is what kind of sea animal?

Jellyfish of this species can turn back into a polyp after reaching sexual maturity, one of the few known animals able to reverse its life cycle so completely.

Which illness, the target of Edward Jenner's 1796 vaccine experiment, is the only human disease ever eradicated?

Smallpox was certified eradicated by the World Health Organization in 1980, three years after the last naturally occurring case.

Which tissue, made up of about 96 percent mineral, is the hardest substance in the human body?

Tooth enamel owes its hardness to tightly packed mineral crystals, yet acids can dissolve them, which is how cavities begin.

In which small fish does the male carry up to 1,500 eggs in a brood pouch and give birth to the young?

Seahorse fathers carry the eggs for 9 to 45 days, then typically give birth at night and can take a fresh batch by morning.

Carrying a single copy of the sickle cell gene gives partial protection against which mosquito-borne disease?

Malaria kills so many people that the sickle cell gene, harmful in a double dose, stayed common wherever the disease is endemic because carriers survive more often.

Which woman's cancer cells, taken without her knowledge in Baltimore in 1951, became the first immortal human cell line?

Henrietta Lacks died that year, but her HeLa cells still divide in labs worldwide; her family did not learn the line existed until 1975.

Which giant member of the grass family includes some of the fastest-growing plants on Earth, adding up to 91 cm a day?

Bamboo can reach 46 metres in its largest species, yet its stalks stay hollow between the joints, as in other grasses.

Which apex predator, often called a whale, is actually the largest member of the oceanic dolphin family?

The orca is one of 35 species in the oceanic dolphin family, a group that first appeared about 11 million years ago.

Which insect performs a figure-eight 'waggle dance' to tell nestmates the direction and distance of flowers?

Honey bee dancers code the sun's direction as straight up on the vertical comb, so an angled run means the flowers lie at that angle from the sun.

Which part of the human eye has no blood vessels and instead takes in oxygen dissolved in tears?

The cornea stays free of blood vessels because it has to be transparent to let light into the eye.

Which group of reptiles are the closest living relatives of birds, together forming the archosaurs?

Crocodilians and birds are the only living archosaurs, so a crocodile is more closely related to a sparrow than to any lizard.

Which Australian mammal is venomous, the male delivering an extremely painful sting from a spur on each hind foot?

The platypus is one of the few venomous mammals, and its duck bill and beaver tail at first baffled European naturalists.

Which Russian physiologist, a 1904 Nobel laureate, discovered classical conditioning through his experiments with dogs?

Ivan Pavlov won his Nobel Prize for research on the physiology of digestion, not for the conditioning work that made his name.

Which biologist worked out the double helix structure of DNA with Francis Crick in March 1953?

James Watson shared the 1962 Nobel Prize in Physiology or Medicine with Crick and Maurice Wilkins for the discovery.

Which science is devoted to insects, a subject Pliny the Elder wrote a book on in ancient Rome?

Entomology takes its name from the Greek éntomon, 'insect', which separates it from etymology, the study of word origins.

Which carnivorous plant of the Carolinas shuts only when a second trigger hair is touched within about twenty seconds?

The Venus flytrap demands the repeat touch as a safeguard, so it does not spend energy closing on objects with no food value.

Which ant-eating mammals, the most trafficked in the world, are covered in large protective scales?

Pangolins are poached for those scales, which are used in traditional medicine, and for their meat.

Which process did peppered moths illustrate when dark forms came to outnumber pale ones in sooty industrial England?

Natural selection then ran in reverse: once clean air laws cut the pollution, the pale moths became the common form again.

Which insects form the largest order of all, with roughly 400,000 species making up about a quarter of known animals?

Beetles are so varied that the order takes in scarabs, weevils and stag beetles, and new species are still discovered frequently.

Which sugar do most mammals gradually lose the ability to digest after weaning?

Lactose is broken down by the enzyme lactase, which many people with European, South Asian or East African ancestry keep producing into adulthood.

Which hormone, secreted in the brain during the night, regulates the sleep-wake cycle in vertebrates?

Melatonin was first isolated from the pineal glands of cows, as a substance that could turn frogs a paler colour.

Which colour do Gram-positive bacteria appear after a Gram stain, thanks to dye trapped in a thick peptidoglycan layer?

Purple comes from crystal violet, which Gram-negative bacteria fail to hold on to, so they take up a pink counterstain instead.

Which term, paired with genotype by Wilhelm Johannsen, names the set of an organism's observable traits?

Phenotype comes from Greek words for 'to show' and 'type', and it reflects the environment as well as the genes an organism carries.

Which diagram, devised by a British geneticist in 1905, predicts the genotypes of offspring from a cross?

The Punnett square is named after Reginald Punnett, and biologists use it to work out the probability of each possible outcome.

Which term did Robert Paine coin for an organism, like the starfish he studied, with an outsized role in its ecosystem?

Keystone species are named after the stone at the top of an arch, which bears the least pressure of any, yet the arch collapses without it.

Which bacteria, the first organisms known to produce oxygen, set off the Great Oxidation Event on early Earth?

Cyanobacteria released the gas for billions of years, turning an anoxic atmosphere into an oxidizing one in what is called the 'rusting of the Earth'.

Which process changes how common a gene variant is purely by chance, acting fastest in small populations?

Genetic drift can fix a variant in just a few generations when a population is small, as after a bottleneck leaves only a handful of survivors.

Which virologist, hailed as a 'miracle worker' in April 1955, never patented his successful polio vaccine?

Jonas Salk declined to profit from the vaccine so that it could be distributed as widely as possible around the world.

Which English philosopher coined the phrase 'survival of the fittest' in his 1864 book Principles of Biology?

Herbert Spencer was drawing parallels between the living world and his own economic theories when he first used the phrase.

Which French naturalist is remembered for the idea, set out in 1809, that traits acquired during life are inherited?

Lamarck did not invent the idea, which was older than him and only a small part of his thinking, yet 'Lamarckism' still carries his name.

Which taxonomic rank, coined by Ernst Haeckel in 1866, sits below kingdom and above class?

Phylum comes from the Greek phylon, meaning 'race' or 'stock', and the animal kingdom alone contains about 32 of them.

Which fish, thought extinct for about 66 million years, turned up alive off South Africa in 1938?

The coelacanth is known from fossils more than 410 million years old, and living ones have since been found around the Comoro Islands too.

Which sea creature is no crustacean, whatever the name suggests, but a closer relative of spiders and scorpions?

The horseshoe crab is a chelicerate, and the extinct sea scorpions, some of the largest arthropods ever to have lived, may be the closest kin of all.

Which parasitic rainforest plant of Sumatra and Borneo is noted for producing the largest individual flower on Earth?

Rafflesia arnoldii is also called the corpse flower, because its bloom smells like decaying flesh.

Which gland, about the size of a kidney bean, hangs below the hypothalamus at the base of the human brain?

The pituitary weighs no more than about a gram, yet together with the hypothalamus it controls much of the body's hormone system.

Which mode of speciation, from the Greek for 'other fatherland', occurs when populations are geographically isolated?

Allopatric speciation, once known as the dumbbell model, can follow the rise of mountains, islands or glaciers that cut populations off from each other.

Which lobe of the brain, named from the Latin for 'behind the head', is the centre of visual processing?

The occipital lobe sits in the rearmost part of the skull, so the brain handles sight at the point farthest from the eyes.

Which genetic condition, named after a British physician, is caused by a third copy of chromosome 21?

Down syndrome is also known as trisomy 21, and it usually arises when that chromosome fails to separate as an egg or sperm forms.

Which class of oxidative enzymes, named by Raphaël Dubois, produces the light of bioluminescence?

Luciferase works on a substrate called luciferin, and Dubois invented both words as a matching pair.

Which physician to King James I was the first to describe in detail how the heart pumps blood around the body?

William Harvey set out the full circulation of the blood, though earlier writers such as Realdo Colombo and Michael Servetus had anticipated parts of it.

Which German physician, called the father of modern pathology, popularised the dictum that all cells come from cells?

Rudolf Virchow put 'Omnis cellula e cellula' into his 1858 Cellular Pathology, though the idea is now widely seen as taken from Robert Remak.

Which insect did Thomas Hunt Morgan breed at Columbia University to show that genes are carried on chromosomes?

The fruit fly experiments in Morgan's famous Fly Room won him the 1933 Nobel Prize in Physiology or Medicine.

Which 375-million-year-old fossil fish, unearthed in Arctic Canada in 2004, is the earliest known fish with a neck?

Tiktaalik takes its name from an Inuktitut word meaning 'large freshwater fish', and it shares many features with tetrapods, the limbed vertebrates.

Which DNA-copying technique, invented by Kary Mullis in 1983, relies on a heat-stable enzyme from hot-spring bacteria?

PCR took off thanks to Taq polymerase, purified in 1976 from Thermus aquaticus, a bacterium at home in water of 50 to 80 °C.

Which gas, the first known to act as a hormone, regulates fruit ripening and leaf fall in plants?

Ethylene is released by wounded plant tissue, which is why ancient Egyptians gashed figs to make them ripen.

Which nocturnal animals are the only primates with a toxic bite, made by mixing saliva with an arm-gland secretion?

Slow lorises were once thought to bite mainly to deter predators, but they chiefly use the toxin in disputes with each other.

Which tough band of fibrous tissue connects muscle to bone, unlike a ligament, which joins bone to bone?

A tendon, also called a sinew, passes the force of a contracting muscle on to the skeleton while withstanding the tension.