Cell structure: the organelles and what they do
Every biology course starts here, and so does every biology quiz. An organelle is a working part inside a cell, and each one has a single recognisable job - generating energy, building proteins, breaking things down, storing pigment. Knowing the job is normally enough to name the part, which makes these the easiest questions on the page.
One thing worth watching as you go: plant cells and animal cells share most of this equipment. The differences are narrow - chloroplasts, one large central vacuole and a rigid cell wall on the plant side; centrioles, and lysosomes doing the job a plant hands to its vacuole, on the animal side.
Q1.Which organelle is nicknamed the cell's power plant because it converts food molecules into usable energy?Tap to reveal
Answer: The mitochondrion
Mitochondria package that energy as ATP through oxidative phosphorylation, and a single hard-working cell can hold thousands of them.
Q2.Photosynthesis takes place inside which organelle?Tap to reveal
Answer: The chloroplast
Stacks of internal membranes called thylakoids hold the chlorophyll that captures sunlight.
Q3.Which organelle reads messenger RNA and assembles the protein it describes?Tap to reveal
Answer: The ribosome
Ribosomes are the one piece of protein-building machinery every living cell has, bacteria included.
Q4.Which organelle modifies, sorts and packages proteins for delivery, acting as the cell's shipping department?Tap to reveal
Answer: The Golgi apparatus
It tags finished proteins and loads them into vesicles bound for the cell surface, the lysosomes, or export out of the cell.
Q5.Which organelle is filled with digestive enzymes that break down worn-out cell parts and captured material?Tap to reveal
Answer: The lysosome
Those enzymes only work properly in acid, so a lysosome keeps its interior far more acidic than the cytoplasm around it.
Q6.In a plant cell, which single large fluid-filled sac stores water and keeps the cell firm?Tap to reveal
Answer: The central vacuole
The internal water pressure it creates is called turgor. Lose it and the plant wilts - that is literally what wilting is.
Q7.Which organelle is a folded membrane network extending from the nuclear envelope, with a rough region and a smooth region?Tap to reveal
Answer: The endoplasmic reticulum
The rough part is studded with ribosomes and makes proteins; the smooth part makes lipids and handles detoxification.
Q8.Plastids, the family of organelles that includes chloroplasts, are found in which two groups of organisms?Tap to reveal
Answer: Plants and algae
Not all plastids photosynthesise. Some store starch or oils, and the ones packed with orange pigment are what colour a carrot.
Q9.Which organelle manufactures and stores melanin, the pigment that colours skin, hair and eyes?Tap to reveal
Answer: The melanosome
Pigment cells hand these packets over to neighbouring skin cells, which is how colour spreads through a tissue rather than sitting in isolated spots.
Q10.Which Scottish botanist first described and named the cell nucleus, in 1831, while examining orchids?Tap to reveal
Answer: Robert Brown
The same Brown gave his name to Brownian motion, the random jiggling of tiny suspended particles he watched under a microscope in 1827.
The cell membrane: what gets in and what stays out
The membrane is the reason a cell is a cell: a film two molecules thick that decides what crosses. Oxygen and carbon dioxide drift through unassisted. A sodium ion cannot, and has to be carried by a protein - sometimes uphill, against its own concentration gradient, at the cost of energy.
Three questions here are about the history rather than the biology, because the accepted picture of the membrane changed twice in forty years. That makes them good hard-round material: the wrong answer is a model that was genuinely taught for decades.
Q1.What is the property of a cell membrane that lets some substances cross easily while blocking others?Tap to reveal
Answer: Selective permeability
Small fat-soluble molecules such as oxygen slip straight through the lipid layer. Ions and sugars need a protein channel or a pump.
Q2.Which molecule supplies the energy for active transport, moving substances against their concentration gradient?Tap to reveal
Answer: ATP, adenosine triphosphate
ADP is the spent version, with one phosphate already gone. A pump has to be handed fully charged ATP to do work.
Q3.What is the name of the currently accepted model of the cell membrane, proposed in 1972?Tap to reveal
Answer: The fluid mosaic model
Singer and Nicolson described a lipid bilayer that behaves like a fluid, with proteins set into it like the tiles of a mosaic.
Q4.Membrane proteins that cling to the surface of the bilayer instead of passing through it are called what?Tap to reveal
Answer: Peripheral proteins
The ones that span the bilayer are integral proteins. Peripheral proteins attach to the faces and can be washed off far more easily.
Q5.What did the older Davson-Danielli 'sandwich' model say the cell membrane looked like?Tap to reveal
Answer: Two layers of protein sandwiching a lipid bilayer
Electron micrographs in the 1950s appeared to show three distinct layers. Later work established that proteins sit inside the lipid rather than coating it.
Q6.In the 1970 experiment that showed membrane proteins drift around, human cells were fused with cells from which animal?Tap to reveal
Answer: A mouse
Frye and Edidin labelled each species' surface proteins differently, and within the hour the two labels had mixed across the whole fused cell.
Q7.If you drank seawater, what kind of solution would your cells find themselves in, and what would happen to them?Tap to reveal
Answer: Hypertonic - the cells lose water, so you dehydrate
Seawater carries several times the salt of your blood, so osmosis pulls water out of your cells instead of into them.
DNA: structure and replication
DNA questions give quizzes their reputation for difficulty, and they are easier than they look, because the molecule is repetitive by design. Four bases, paired in two fixed combinations, strung along a backbone of alternating sugar and phosphate. Almost every structural question is a variation on that sentence.
The replication question below is worth reading twice. Three competing models were on the table in the 1950s, and one elegant experiment settled it - grow bacteria on heavy nitrogen, then watch how the density of their DNA changes as they divide.
Q1.How many pairs of chromosomes are there in a typical human body cell?Tap to reveal
Answer: 23 pairs, or 46 chromosomes in total
Twenty-two of the pairs are autosomes. The twenty-third pair is the sex chromosomes.
Q2.What shape did Watson and Crick describe for the DNA molecule in 1953?Tap to reveal
Answer: A double helix
Two strands wind around each other with the paired bases facing inward. Rosalind Franklin's X-ray diffraction images were key evidence for the structure.
Q3.Which two of the four bases in DNA are purines?Tap to reveal
Answer: Adenine and guanine
Purines carry a double ring. The pyrimidines, cytosine and thymine, have a single ring, so every rung of the ladder pairs one of each and comes out the same width.
Q4.Which chemical element links the sugars of DNA together to form its backbone?Tap to reveal
Answer: Phosphorus
Each rung hangs off a chain of alternating sugar and phosphate groups. Those phosphates are why DNA counts as an acid.
Q5.During which phase of the cell cycle is a cell's DNA copied?Tap to reveal
Answer: S phase, for synthesis
It sits between the growth phases G1 and G2. A chromosome enters S phase as one DNA molecule and leaves it as two.
Q6.Once a chromosome has been copied, each of the two identical halves is called what?Tap to reveal
Answer: A chromatid
Sister chromatids stay joined at a pinched waist called the centromere until the dividing cell pulls them to opposite ends.
Q7.Which model of DNA replication turned out to be the correct one - conservative, semiconservative or dispersive?Tap to reveal
Answer: Semiconservative
Each old strand acts as the template for a new one, so both daughter helices keep one original strand. Meselson and Stahl demonstrated it in 1958.
Q8.Which of the two forms of chromatin is loosely packed and rich in active genes?Tap to reveal
Answer: Euchromatin
Tightly wound heterochromatin is largely switched off. Under a light microscope euchromatin shows up as the paler bands.
Genes, the genetic code and heredity
A gene, a chromosome and a genome are three different scales of the same material, and confusing them is the single most common error in biology quizzes. The first two questions below turn on exactly that distinction, so if you are shaky on which is which the answers will sort it out as you go.
These questions also cover how an instruction actually gets read, from a stretch of DNA in the nucleus out to a finished protein, plus the people who named the field and one inherited disorder that shows what happens when a single instruction is misread.
Q1.What is the term for a stretch of DNA carrying the instructions for one protein along with the switches that control it?Tap to reveal
Answer: A gene
The current human annotation counts about 19,400 protein-coding genes - far fewer than biologists expected before the genome was sequenced, and the estimate has drifted down rather than up ever since.
Q2.What single word describes the entire hereditary information of an organism?Tap to reveal
Answer: The genome
The German botanist Hans Winkler introduced the word in 1920, for what he defined as the haploid chromosome set together with its protoplasm. The tidy story that he built it from 'gene' plus 'chromosome' is a later gloss that etymologists dispute.
Q3.Different versions of the same gene are known as what?Tap to reveal
Answer: Alleles
One allele of a flower's colour gene may give red petals and another white. In people, alleles are behind differences such as blood type.
Q4.Transcription copies a stretch of DNA into which molecule?Tap to reveal
Answer: RNA
Messenger RNA carries the copied message out of the nucleus, where a ribosome translates it into a protein.
Q5.How many DNA bases does it take to specify a single amino acid?Tap to reveal
Answer: Three
That triplet is called a codon. Three bases allow 64 combinations, enough to cover the 20 standard amino acids plus start and stop signals, with room to spare.
Q6.What is unusual about the way a retrovirus such as HIV handles genetic information?Tap to reveal
Answer: It starts with RNA and copies it into DNA, the reverse of the normal direction
The enzyme responsible, reverse transcriptase, earned Baltimore and Temin a share of the 1975 Nobel Prize in Medicine.
Q7.Which British biologist proposed the word 'genetics' for the study of inheritance, in 1905?Tap to reveal
Answer: William Bateson
He floated the term in a letter to the zoologist Adam Sedgwick, and in 1910 he and Reginald Punnett founded the Journal of Genetics.
Q8.Which genetic disorder combines premature fusion of the skull bones with unusually broad, short thumbs and big toes?Tap to reveal
Answer: Pfeiffer syndrome
Because the plates of the skull knit together too early, the head and face cannot grow into their normal shape.
Biotechnology and cloning
Cloning is the part of biology most people first met through a news story, which means the folklore tends to run ahead of the facts. Two of the questions below turn on ideas the headlines almost always flatten - exactly what a clone does and does not inherit from its donor, and where cloning sits alongside ordinary reproduction. Neither is as obvious as it sounds.
The questions here are the hardest on the page, because several of them turn on a specific date, species or number. The Dolly question in particular explains why the field moved slowly for years: the success rate was brutal.
If you want questions like these against a clock, the Trivio.NET app serves a fresh mixed quiz every day - 10 questions, 100 seconds, free to play, with biology in the rotation.
Q1.Which class of enzyme cuts DNA at a specific sequence, and so made genetic engineering possible?Tap to reveal
Answer: Restriction enzymes
Bacteria use them as a defence against viruses. Many leave a short sticky overhang, which is what lets a cut fragment be spliced into another strand.
Q2.What three-letter acronym names the Nobel-winning technique for amplifying a tiny sample of DNA?Tap to reveal
Answer: PCR
The polymerase chain reaction doubles a target sequence over and over. Kary Mullis shared the 1993 Nobel Prize in Chemistry for inventing it.
Q3.The word 'clone' comes from a Greek word meaning what?Tap to reveal
Answer: Twig
Botanists used it first, and the image is exact: break off a twig, root it, and you have a new plant carrying the same genes as the old one.
Q4.What is the term for reproduction from an unfertilised egg, the process behind natural clones in animals such as some lizards, sharks and insects?Tap to reveal
Answer: Parthenogenesis
Cloning is not only a laboratory technique. Identical twins are natural clones of one another, and parthenogenesis produces offspring from an egg that was never fertilised at all.
Q5.Is cloning a form of sexual or asexual reproduction?Tap to reveal
Answer: Asexual
No two sets of genes are combined, which is why a clone has a single genetic donor instead of a biological mother and father.
Q6.Why is a cloned animal not a perfect genetic copy of its donor?Tap to reveal
Answer: Its mitochondria, which carry DNA of their own, come from the egg it was grown in
Human mitochondrial DNA holds 37 genes and is inherited through the egg only, so a clone's nuclear DNA matches the donor while its mitochondrial DNA does not.
Q7.In 1952, Robert Briggs and Thomas King performed the first successful cloning by nuclear transfer, using which animal?Tap to reveal
Answer: A frog
They moved a nucleus from a leopard frog embryo into a frog egg whose own nucleus had been removed, and the egg went on developing.
Q8.Dolly the sheep, the first mammal cloned from an adult body cell, was the single lamb produced from how many reconstructed eggs?Tap to reveal
Answer: 277
Of those 277, only 29 became embryos worth transferring, and only Dolly was born alive. She arrived in 1996 at the Roslin Institute in Scotland.
Q9.Prometea, cloned in Italy in 2003, was what kind of animal?Tap to reveal
Answer: A horse
The Haflinger foal was carried to term by the very mare that supplied her genes, which made that mare both her mother and her identical twin.
Q10.Transgenic sheep have been engineered to produce milk containing a clotting factor for which inherited bleeding disorder, seen almost only in males?Tap to reveal
Answer: Hemophilia
The genes for the missing clotting factors sit on the X chromosome. Males have only one copy, so a single faulty gene leaves them with no backup.
Frequently Asked Questions
What is the difference between a gene, a chromosome and a genome?
They are three scales of the same material. A gene is one instruction, usually the recipe for a single protein. A chromosome is a long DNA molecule carrying thousands of genes - humans have 46, in 23 pairs. The genome is every chromosome taken together, the organism's complete set of genetic information.
Are these biology trivia questions suitable for a classroom?
The first two sections work from about middle school upward, because organelles and membrane transport are standard curriculum. The DNA and genetics sections suit high school biology. The cloning round is the hardest and is better as a bonus round than a graded one.
Which question on this page catches the most people out?
The Dolly question. Most players know she was the first mammal cloned from an adult body cell and that she was born at the Roslin Institute in 1996. Almost nobody remembers the arithmetic: 277 reconstructed eggs produced 29 embryos worth transferring and exactly one live lamb. That ratio is the reason cloning stayed a laboratory result for years rather than becoming a routine technique.
What makes a good hard biology trivia question?
One where the wrong answer used to be the right answer. The Davson-Danielli membrane model was taught as settled for the best part of forty years before the fluid mosaic model replaced it, and conservative replication was a serious rival to the semiconservative model until a single experiment ruled it out in 1958. Either way a well-read player has to remember which picture won, rather than simply recognise a term.
Where can I play more biology and science trivia online?
Trivio.NET's science category covers biology, chemistry, physics and astronomy in free quiz packs. Our science trivia and science trivia for kids pages have more questions with answers if you want to read rather than play, and the Trivio.NET app runs a fresh ten-question quiz every day on a 100-second timer.
