160 Fun Facts About 9th Grade

What do we call a natural number greater than 1 that is not a product of two smaller numbers?

The primes are the building blocks of every whole number, which is why 1 is left out of the club.

Which letter usually stands for the slope of a line in the equation y = mx + b?

Nobody is sure why m was chosen; it first shows up in an 1844 English textbook.

Slope is defined as the ratio of which two things?

A steeper line has a bigger absolute slope; a horizontal line has slope zero.

What is the maximum number of solutions a quadratic equation can have?

The graph is a parabola, and a parabola can cross the x-axis at most twice.

In ax² + bx + c = 0, what is the name given to c?

a is the quadratic coefficient and b the linear one; if a were zero the equation would just be linear.

Which method is used to derive the quadratic formula?

You rewrite ax² + bx + c as a perfect square plus a constant, then take a square root.

The Pythagorean theorem relates the three sides of which kind of triangle?

The side opposite the right angle, the hypotenuse, is the one that gets squared alone.

What is the name for the side of a right triangle opposite the right angle?

It is always the longest side, which is why c² has to equal a² + b².

Around what year was Pythagoras born?

Babylonian scribes were using the same rule more than a thousand years before he was born.

Which civilisation used the Pythagorean rule over a thousand years before Pythagoras?

An Egyptian papyrus from about 1800 BC also has a 6:8:10 problem, but it never mentions a triangle.

The word 'algebra' comes from which language?

Al-jabr originally referred to setting broken bones before it meant balancing equations.

Which 9th-century Persian mathematician gave algebra its name?

His name, Latinised, is also where the word algorithm comes from.

Which 3rd-century Greek wrote the Arithmetica, an early treatment of solving equations?

His name survives in Diophantine equations, where only whole-number solutions count.

Who proved around 300 BC that there are infinitely many primes?

The same Elements also proves that every whole number factors into primes in only one way.

What is the only even prime number?

Every other even number is divisible by 2, so every other prime is odd.

Which ancient Greek's 'sieve' is still used to list prime numbers?

You write out the numbers and cross off every multiple of each prime you find.

The solutions of a linear equation in two variables form what shape on a graph?

Every line in the plane can be written as ax + by + c = 0 and vice versa.

Which form of algebra, taught in schools, uses variables to stand for unspecified values?

Abstract algebra, with its groups, rings and fields, comes much later.

What is the basic structural and functional unit of all living things?

The name comes from the Latin cellula, a small room.

Who discovered cells in 1665, naming them after rooms in a monastery?

He was looking at slices of cork under an early microscope.

Which organelles provide energy for cell functions?

Plants have both mitochondria and chloroplasts, and use the second to make sugars.

Bacteria and archaea belong to which broad group of single-celled organisms?

Their DNA sits in a region called the nucleoid rather than inside a membrane.

What is the largest membrane-bound organelle in a eukaryotic cell?

It holds the cell's chromosomes inside a double membrane called the nuclear envelope.

What gas do plants release as a by-product of photosynthesis?

It comes from splitting water molecules, not from the carbon dioxide.

Which pigment in chloroplasts absorbs red and blue light and reflects green?

Leaves look green precisely because green is the colour the pigment throws back.

What is the name of the light-independent reactions that build sugars in plants?

They use the ATP and NADPH made in the light-dependent stage to fix carbon dioxide.

Which two raw materials do photoautotrophs use to make food with light energy?

The sugar they make is later burned again in cellular respiration.

What molecule stores the chemical energy produced by cellular respiration?

Textbooks say up to 38 ATP per glucose; the real yield is closer to 30.

Which first stage of cellular respiration takes place in the cytosol of every living cell?

The name literally means sugar splitting, and it works with or without oxygen.

How many ATP molecules per glucose do biology textbooks often say respiration makes?

Leaky membranes and transport costs mean the real figure is closer to 29 or 30.

Cell division by mitosis produces how many daughter cells from one parent cell?

Both get an identical set of chromosomes; meiosis is the one that makes four.

Which stage of the cell cycle, when DNA replicates, comes just before mitosis?

S stands for synthesis, because that is when the DNA is copied.

Which mitosis stage sees daughter chromosomes pulled toward opposite ends of the cell?

Metaphase lines them up in the middle; anaphase pulls them apart.

Who coined the term 'mitosis' in 1882?

It comes from the Greek for warp thread, after the thread-like chromosomes he saw.

What is the name for the process that divides the cytoplasm after mitosis?

Mitosis divides the nucleus; cytokinesis finishes the job by splitting the cell itself.

In DNA, adenine always pairs with which base?

G pairs with C, and the two pairs are held by hydrogen bonds.

What shape do the two strands of DNA coil into?

The strands run in opposite directions, which is why they are called antiparallel.

What sugar is found in each nucleotide of DNA?

The missing oxygen atom compared with ribose is what the deoxy in the name refers to.

Which plant did Gregor Mendel use for his experiments on heredity?

He worked with seven traits, including seed colour, plant height and flower position.

In Mendel's second-generation peas, green seeds reappeared in what ratio to yellow?

Green had seemed to vanish in the first generation, which is why he called it recessive.

What two terms did Mendel coin to describe traits that show or hide in offspring?

His invisible factors are what we now call genes.

In what year did Mendel publish his pea-plant results?

The work was largely ignored until it was rediscovered around 1900.

On which ship did Charles Darwin make his five-year voyage?

He was aboard as a gentleman naturalist, not a paid crew member.

In which year did Darwin publish On the Origin of Species?

He had been prodded into print when Wallace mailed him an essay with the same idea.

Which naturalist sent Darwin an essay in 1858 describing the same idea of natural selection?

Their two papers were read together at the Linnean Society of London.

Where is Charles Darwin buried?

At Cambridge he had belonged to a Glutton Club that ate unusual animals.

In a food chain, what is another name for an autotroph such as grass or algae?

The chain typically ends at an apex predator, a detritivore or a decomposer.

Which ecologist introduced the modern concepts of food chains and food webs?

The idea was first discussed by the 10th-century Arab writer al-Jahiz.

What term describes the non-living components of an ecosystem, such as soil?

Biotic factors are the living things; the two are linked by nutrient cycles and energy flows.

Which organisms release carbon back to the atmosphere by breaking down dead matter?

Fungi and bacteria do most of that work.

Who published the first generally accepted periodic table, in 1869?

He left gaps for elements nobody had found yet and predicted their properties.

How many chemical elements had been officially confirmed as of 2025?

Only the first 94 occur naturally on Earth; the rest are made in laboratories. The count has stood at 118 since 2016.

Which element has atomic number 1?

Helium is 2 and lithium is 3; the symbols are H, He and Li.

The rightmost column of the periodic table, group 18, holds which family of elements?

The leftmost column, group 1, is the alkali metals.

The rows of the periodic table are called what?

Columns are groups, and elements in the same group tend to behave alike.

Newton's first law expresses which principle?

Left alone, a body keeps moving in a straight line at constant speed.

In what year did Newton first publish his three laws of motion?

They appeared in the Principia, written in Latin.

According to Newton's third law, when two bodies push on each other, the forces are what?

That is why a rocket moves forward when its exhaust goes backward.

Newton's second law says net force equals mass multiplied by what?

Equivalently, force is the rate at which momentum changes.

How many major tectonic plates is Earth's lithosphere divided into?

Depending on how you count, plus many minor plates or platelets.

What is the process called when one tectonic plate is carried down under another?

Deep ocean trenches usually mark where it happens.

Which plate's 'Ring of Fire' holds most of the world's active volcanoes?

Plate boundaries are also where most earthquakes happen.

Roughly how far do tectonic plates move each year at most?

About the speed your fingernails grow, at the fast end.

What is the name for the three types of plate boundary?

Convergent boundaries make mountains and trenches; divergent ones make new sea floor.

What percentage of global evaporation comes from the ocean?

Sublimation from snow and transpiration from plants supply most of the rest.

What is the name for water vapour released from plants into the atmosphere?

Together with evaporation from soil it is called evapotranspiration.

In which Italian city is Romeo and Juliet set?

The play opens with a street brawl between servants of the two feuding houses.

Which girl is Romeo pining for at the start of the play, before he meets Juliet?

He only goes to the Capulet ball hoping to see her there.

Who secretly marries Romeo and Juliet, hoping to reconcile their families?

He later supplies the sleeping potion that sets up the tragic ending.

Which hot-headed cousin of Juliet challenges Romeo to a duel?

Romeo, now secretly his kinsman by marriage, refuses to fight him.

Whom does Capulet want Juliet to marry?

Capulet first asks him to wait two years, then invites him to the ball.

In what year was Romeo and Juliet first published in quarto?

That first quarto was so poor that later editions had to correct it.

Who narrates To Kill a Mockingbird?

She is six years old when the story begins.

In which fictional Alabama town is To Kill a Mockingbird set?

Harper Lee based it on her real hometown of Monroeville.

Whom does Atticus Finch defend at trial?

He takes the case knowing most of Maycomb disapproves.

Which award did To Kill a Mockingbird win the year after it was published?

It was published in 1960 and has been a school staple ever since.

What is Dill's real name in To Kill a Mockingbird?

He visits Maycomb each summer to stay with his aunt.

Who wrote Of Mice and Men?

He drew on his teenage summers working beside migrant farm workers.

What animals does Lennie dream of tending on his own farm?

He loves petting soft things, which is exactly what gets him into trouble.

The title Of Mice and Men comes from a poem by which writer?

The line is from To a Mouse: the best-laid schemes of mice and men often go awry.

How much money does Candy offer to put toward the farm in Of Mice and Men?

In return he wants to live there with George and Lennie.

Which stable hand in Of Mice and Men is isolated from the others because he is black?

He scorns the farm dream but still asks if he could hoe a garden patch there.

Odysseus is king of which island?

His journey home from Troy takes ten years on top of the ten-year war.

How many books is the Odyssey divided into?

The Iliad is divided the same way.

How does Penelope put off the suitors in the Odyssey?

The shroud is meant for Odysseus's aged father Laertes.

Which nymph holds Odysseus captive, according to the Old Man of the Sea?

Menelaus passes the news to Telemachus in Sparta.

How many suitors court Penelope in Odysseus's absence?

Athena, disguised as Mentor, sends Telemachus off to seek news of his father.

What object does Ralph use as a horn to gather the boys in Lord of the Flies?

Holding it also becomes the rule for who may speak at meetings.

Whose glasses do the boys use to start the signal fire in Lord of the Flies?

Ralph, Jack and Simon do the lighting; Piggy just loses his glasses.

Which children's novel gave William Golding the idea for Lord of the Flies?

He thought its cheerful island boys were unrealistic and set out to write the opposite.

In what year was Lord of the Flies published?

It was Golding's debut novel and was rejected by many publishers first.

Which two pigs take command after Old Major dies in Animal Farm?

Snowball teaches reading; Napoleon quietly trains a litter of puppies.

What is the most important of the Seven Commandments in Animal Farm?

It is later amended with the words 'but some animals are more equal than others'.

What does Snowball propose building to modernise Animal Farm?

When it collapses in a storm, Napoleon blames Snowball for sabotage.

Which real events did Orwell say Animal Farm reflects?

He called it, in a letter, a satirical tale against Stalin.

Which small boar acts as Napoleon's skilled orator and propagandist?

He convinces the animals that the windmill was Napoleon's idea all along.

Who narrates The Great Gatsby?

He is a Yale graduate from the Midwest who comes east to sell bonds.

In which Long Island village does Nick rent a bungalow next to Gatsby's estate?

Daisy and Tom live across the bay in old-money East Egg.

What colour is the light Gatsby stares at across the bay?

It sits at the end of Daisy's dock.

What is Jordan Baker's sport in The Great Gatsby?

She is a childhood friend of Daisy's and a champion at it.

Which figure of speech makes an implied comparison, without using 'like' or 'as'?

'All the world's a stage' is the textbook example.

Mesopotamia lay between which two rivers?

The region roughly matches modern Iraq.

Which Mesopotamian king established the Old Babylonian state?

His name is attached to one of the earliest written law codes.

Which ruler united Upper and Lower Egypt around 3150 BC?

Most Egyptologists think he was the same person as Narmer.

During which period were the Giza pyramids and the Great Sphinx built?

The New Kingdom was the peak of Egyptian power, but the pyramids came first.

Which discovery let scholars finally decipher hieroglyphs in the 1820s?

Thomas Young and Jean-François Champollion did the decoding.

Which pharaoh fought the Hittites at Kadesh and signed the first recorded peace treaty?

He also built more temples and fathered more children than any other pharaoh.

At which 480 BC pass did three hundred Spartans hold off the Persians for days?

On the same day, Syracuse beat a Carthaginian invasion at Himera.

The Peloponnesian War was fought between Athens and which rival city-state?

A plague during the war killed the Athenian statesman Pericles.

How many kings ruled the Spartan state at the same time?

Alongside a council of elders and five officials called ephors.

Which philosopher tutored the young Alexander the Great?

Alexander carried an annotated copy of the Iliad from him on campaign.

In which city did Alexander the Great die in 323 BC?

He had planned to make it the capital of his empire.

Which Persian king did Alexander overthrow?

The decisive battles were at Issus and Gaugamela.

Which river did Julius Caesar cross with his army in 49 BC, defying the Senate?

The phrase 'crossing the Rubicon' still means passing a point of no return.

On what date was Julius Caesar assassinated?

The senators were led by Brutus and Cassius.

With Crassus and Pompey, Caesar formed which informal alliance in 60 BC?

It dominated Roman politics for years before Caesar and Pompey fell out.

Which title did the Senate grant Octavian in 27 BC, making him the first emperor?

It means 'venerated'; he was also named princeps, or foremost.

Under which emperor did Rome reach its greatest territorial extent?

Decline set in under Commodus later in the same century.

Which emperor moved the imperial seat to Byzantium in 330 and renamed it Constantinople?

He was also the first emperor to convert to Christianity.

In what year did the Western Roman Empire fall?

The Eastern empire lasted almost another thousand years, until Constantinople fell.

What was the name for the two centuries of stability that began with the first emperor?

It literally means Roman peace.

Which English king sealed Magna Carta at Runnymede in 1215?

Pope Innocent III annulled it within months, sparking the First Barons' War.

How many original 1215 copies of Magna Carta still exist?

Two are at the British Library, one at Lincoln Castle and one at Salisbury Cathedral.

Which bacterium caused the Black Death?

It is mainly spread by flea bites, but can also pass through respiratory droplets.

Up to how many people did the Black Death kill in Europe between 1346 and 1353?

That was around half of the continent's 14th-century population.

The Black Death reportedly entered Europe during a 1347 siege of which Crimean port?

Genoese ships then carried it across the Mediterranean.

In which Italian city did the Renaissance begin?

The Medici family's patronage was one reason it started there.

Which two polymaths inspired the term 'Renaissance man'?

Both painted, sculpted, designed and studied anatomy.

Which architect built the great cathedral dome after losing the 1401 Baptistery doors contest?

The dome he engineered still dominates the city's skyline.

Which Florentine political thinker tried to describe politics 'as it really was'?

His name became an adjective for cunning statecraft.

What was stormed in Paris on 14 July 1789?

The fortress held only seven prisoners, but plenty of arms and gunpowder.

How many prisoners were actually inside the Paris fortress stormed on 14 July 1789?

Four forgers, a lunatic, a failed assassin and a deviant nobleman.

What did the Third Estate deputies swear when they found their meeting hall locked?

They vowed not to disperse until France had a constitution.

Who led the radical Jacobins on the Committee of Public Safety during the Terror?

About 16,000 people were executed before the Terror ended in July 1794.

In what month and year was Louis XVI executed?

The monarchy had been replaced by the First Republic four months earlier.

In which country did the Industrial Revolution begin around 1760?

It had spread to continental Europe and the US by about 1840.

Who invented the spinning jenny in 1764?

Arkwright's water frame followed five years later.

The cotton gin sped up removing seed from cotton by roughly what factor?

It made upland cotton economical to grow at scale.

Which industry was the first to use modern production methods in the Industrial Revolution?

It became the dominant industry by employment, output and capital.

Whose assassination in Sarajevo on 28 June 1914 triggered World War I?

The assassin, Gavrilo Princip, was a Bosnian Serb.

What made the United States join the Allies in April 1917?

Germany gambled that it could starve Britain before American troops arrived.

On what date did the armistice ending World War I take effect?

Kaiser Wilhelm II had abdicated two days earlier.

Which 1919 settlement made Germany lose territory, disarm and pay reparations?

The Russian, German, Austro-Hungarian and Ottoman empires all collapsed.

Which gas did Germany first use at the Second Battle of Ypres in April 1915?

It violated the Hague Convention.

Which failed Allied campaign followed the Ottoman Empire joining the Central Powers?

Verdun, the Somme and Passchendaele were the big Western Front battles.

Which 1962 standoff is considered the closest the Cold War came to nuclear war?

It followed US missiles going into Europe and Soviet missiles into Cuba.

In which year did the Soviet Union dissolve, ending the Cold War?

Gorbachev's reforms had contributed to the 1989 revolutions in the Eastern Bloc.

Which Soviet-led alliance was formed in 1955 to match NATO?

NATO itself had been founded in 1949.

In Ray Bradbury's Fahrenheit 451, what is Guy Montag's job?

The 1953 novel follows Montag as he grows disillusioned with destroying literature and turns to preserving it.

Elie Wiesel's memoir Night recounts his time with his father in Auschwitz and which other camp?

The book ends shortly after the US Army liberated Buchenwald in April 1945.

An element's atomic number equals the number of what in each of its atoms?

For ordinary nuclei, that proton count is what places an element in the periodic table.

Ionic bonding is based on the attraction between what?

It is the main interaction in ionic compounds such as table salt.

Roughly what is Avogadro's number, the number of particles in one mole?

It is an SI defining constant with the exact value 6.02214076 × 10²³ per mole.

Which formula gives the circumference of a circle with radius r?

Equivalently, the circumference equals π times the diameter.

Who is the teenage narrator of J. D. Salinger's The Catcher in the Rye?

He has become an icon of teenage rebellion since the novel's 1951 publication.

From which Spanish port did Columbus sail with three ships in August 1492?

He made landfall on 12 October on a Bahamian island its inhabitants called Guanahani.

The hertz, the SI unit of frequency, equals one cycle per what?

A 60 Hz mains supply, for example, cycles sixty times every second.

Density is defined as the ratio of a substance's mass to its what?

That is why a kilogram of feathers takes up far more space than a kilogram of lead.

Osmosis is the net movement of solvent molecules through what kind of membrane?

Water moves from lower to higher solute concentration until the two sides even out.

In Great Expectations, which escaped convict accosts young Pip in a graveyard?

Dickens's bildungsroman is set in Kent and London in the early to mid-19th century.