138 Fun Facts About Biology

Which structure do prokaryotic cells such as bacteria lack?

Prokaryotes keep their DNA in a region of the cytosol called the nucleoid, with no nuclear envelope around it. Only eukaryotic cells have a true membrane-bound nucleus and organelles such as mitochondria.

What molecule carries genetic information in most living organisms?

DNA (deoxyribonucleic acid) is the molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms.

Which process do plants use to convert sunlight into food?

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water, generating oxygen as a byproduct.

What is the largest organ in the human body?

The skin makes up roughly 16% of body mass. It is a barrier against pathogens, helps regulate temperature, and carries the sense of touch.

How many chromosomes do humans typically have?

Humans typically have 46 chromosomes arranged in 23 pairs. One set of 23 comes from each parent. These chromosomes contain all the genetic information needed for development.

Which naturalist wrote On the Origin of Species, published in 1859?

Charles Darwin published On the Origin of Species in November 1859, arguing that species change over generations through natural selection. Its first print run of 1,250 copies was fully subscribed by booksellers on publication day.

What type of cell division produces two identical daughter cells?

Mitosis is the type of cell division that produces two genetically identical daughter cells from a single parent cell. It is used for growth and repair in multicellular organisms.

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

Plants absorb carbon dioxide (CO2) from the atmosphere during photosynthesis. They combine it with water using light energy to produce glucose and release oxygen.

Which blood cells are responsible for fighting infections?

White blood cells (leukocytes) are the cells of the immune system that are involved in protecting the body against infectious diseases and foreign invaders.

What is the basic unit of life?

The cell is considered the basic unit of life. All living organisms are composed of one or more cells, and all cells arise from pre-existing cells.

What pigment gives plants their green color?

Chlorophyll is the green pigment found in chloroplasts that absorbs light energy for photosynthesis. It reflects green wavelengths, which is why plants appear green.

Which organs filter waste from the blood to produce urine?

About one-fifth of the blood entering the kidneys is filtered at the glomerulus, producing an ultrafiltrate that becomes urine. The kidneys also regulate electrolytes, blood pressure, and acid-base balance.

What is the term for an organism that makes its own food from sunlight?

An autotroph, or producer, makes its own food from light (photoautotroph) or chemical energy (chemoautotroph); plants are the most common example.

What structure in plant cells is not found in animal cells?

Plant cells have a rigid cell wall made of cellulose that surrounds the cell membrane. Animal cells lack this structure, having only a flexible cell membrane.

Which kingdom of life includes mushrooms and yeasts?

Fungi is the kingdom that includes mushrooms, yeasts, and molds. Unlike plants, fungi cannot photosynthesize and instead obtain nutrients by decomposing organic matter.

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

Darwin's finches are roughly 15 closely related Galápagos species whose beak shapes match their diets, from seed-crushing to insect-probing; David Lack's 1947 book Darwin's Finches popularised the name.

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, located at the back of the brain, is primarily responsible for coordinating voluntary movements, balance, posture, and motor learning.

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

Omnivores are animals that eat both plant and animal matter. Humans, bears, and pigs are common examples of omnivores.

What scientist is known as the father of genetics?

Gregor Mendel, an Augustinian friar, is considered the father of genetics. His experiments with pea plants in the 1860s established the fundamental laws of inheritance.

What is the function of ribosomes in a cell?

Ribosomes carry out protein synthesis: they read messenger RNA and translate its codons into a growing polypeptide chain. Each ribosome is built from ribosomal RNA and proteins in two subunits.

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 refers to the variety of life in a particular habitat or ecosystem. It encompasses the diversity of species, genes, and ecosystems in a given area.

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

The Golgi apparatus (also called the Golgi body) modifies, sorts, and packages proteins and lipids for transport to their final destinations within or outside the cell.

What is the process by which a caterpillar transforms into a butterfly?

Metamorphosis is the biological process by which an animal physically develops after birth, involving a conspicuous change in body structure. Butterflies undergo complete metamorphosis through four stages: egg, larva, pupa, and adult.

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

Parasitism has the parasite living on or inside its host and harming it; ticks, tapeworms and malaria-causing Plasmodium are examples.

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

Vitamin D is synthesized in the skin when it is exposed to ultraviolet B (UVB) radiation from sunlight. It is essential for calcium absorption, bone health, and immune function.

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

Decomposers are organisms that break down dead or decaying organic matter, recycling nutrients back into the ecosystem. Fungi and bacteria are the most important decomposers.

How many chambers does the human heart have?

The human heart has four chambers: two upper chambers (atria) that receive blood, and two lower chambers (ventricles) that pump blood out. This design separates oxygenated and deoxygenated blood.

What are the building blocks of proteins?

Amino acids are the building blocks of proteins. There are 20 standard amino acids that combine in different sequences to form the vast array of proteins found in living organisms.

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

Cell theory was formulated by Matthias Schleiden (1838, plants) and Theodor Schwann (1839, animals); Rudolf Virchow added in 1855 that every cell arises from a pre-existing cell (omnis cellula e cellula).

Which hormone lowers blood sugar by letting cells take up glucose?

Insulin is produced by the beta cells of the pancreas and regulates blood sugar by enabling cells to absorb glucose. Diabetes occurs when the body cannot produce enough insulin or use it effectively.

In DNA, adenine always pairs with which base?

In DNA, adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). These complementary base pairs are held together by hydrogen bonds.

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

The ovum is one of the largest cells in the human body and needs no microscope to be seen. The mammalian ovum was only discovered in 1827, by Karl Ernst von Baer.

Which scientist discovered penicillin?

Alexander Fleming's mould was later identified as Penicillium rubens; he shared the 1945 Nobel Prize with Howard Florey and Ernst Chain.

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

Phagocytosis is the process by which a cell engulfs solid particles by extending its cell membrane around the particle to form an internal vesicle. White blood cells use this to destroy pathogens.

Which biome is characterized by permafrost and very low temperatures?

The tundra biome is characterized by extremely cold temperatures, permafrost (permanently frozen subsoil), treeless landscapes, and a short growing season. It is found in the Arctic and on high mountaintops.

What is the main function of the large intestine?

The large intestine's primary function is to absorb water and electrolytes from the remaining indigestible food matter and to compact the waste into feces for elimination.

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

Asexual reproduction involves a single parent and produces offspring that are genetically identical to the parent (clones). Examples include binary fission in bacteria, budding in yeast, and vegetative reproduction in plants.

Which part of a neuron receives signals from other neurons?

Dendrites are the branching extensions of a neuron that receive electrical signals from other neurons and transmit them toward the cell body. A single neuron can have thousands of dendrites.

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

A genome is the complete set of an organism's DNA, including all its genes; the human genome runs to about 3 billion base pairs and roughly 20,000 protein-coding genes.

Which enzyme is responsible for unwinding the DNA double helix during replication?

Helicase is the enzyme that unwinds the DNA double helix by breaking the hydrogen bonds between base pairs, creating two single strands that serve as templates for replication.

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

The Calvin cycle (also known as the light-independent reactions or dark reactions) uses CO2 and the energy carriers ATP and NADPH produced in the light reactions to synthesize glucose.

Which type of immune response involves T cells directly attacking infected cells?

Cell-mediated immunity is the immune response that involves T cells (particularly cytotoxic T cells) directly attacking and destroying cells that are infected with viruses or have become cancerous.

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

Pleiotropy occurs when a single gene affects multiple phenotypic traits. For example, the gene responsible for Marfan syndrome affects the heart, eyes, and skeletal system simultaneously.

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

Mitochondria carry their own small genome, similar to a bacterial one, which is inherited only from the mother in humans. The endosymbiotic theory holds they descend from aerobic bacteria that were engulfed by another cell and never digested.

What is the Hardy-Weinberg principle used to describe?

The Hardy-Weinberg principle states that allele and genotype frequencies in a population remain constant from generation to generation in the absence of evolutionary forces like mutation, selection, gene flow, and genetic drift.

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

Osmosis is the net movement of water molecules through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration, equalizing concentrations on both sides.

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.

In which stage of meiosis does crossing over between homologous chromosomes occur?

Crossing over occurs during Prophase I of meiosis, when homologous chromosomes pair up and exchange segments of DNA. This recombination increases genetic diversity in the resulting gametes.

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 make epinephrine (adrenaline) in their inner medulla and release it during the fight-or-flight response; a few neurons in the brainstem's medulla oblongata produce it too.

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

Alfred Russel Wallace mailed Darwin his essay on natural selection from Ternate in 1858; both men's papers were read at the Linnean Society on 1 July 1858, and Darwin published the Origin in November 1859.

What is a variant of the nucleotides at a particular locus on DNA called?

Different alleles can produce traits like antibiotic resistance in bacteria.

Amoebae change shape by extending and retracting what?

Pseudopods ('false feet') are temporary bulges of cytoplasm that an amoeba pushes out and pulls back to crawl and to engulf food; amoeboid movement occurs in every major eukaryote lineage.

'Antigen' is a portmanteau of what phrase?

Antigen contracts 'antibody generator': any substance that provokes antibody production. Each Y-shaped antibody carries two paratopes that bind a matching epitope on its antigen.

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 reaches sexual maturity without metamorphosis, keeping external gills?

The axolotl (Ambystoma mexicanum) breeds in its larval form, keeping feathery external gills for life; this retention of juvenile traits is called neoteny, and it metamorphoses only if given thyroid hormone.

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 laid out binomial nomenclature in Species Plantarum (1753) and the tenth edition of Systema Naturae (1758); he was ennobled as Carl von Linné in 1761.

What term describes an organism keeping its internal conditions stable?

Homeostasis is the maintenance of a stable internal environment, such as a human core temperature near 37 °C; Walter Cannon coined the term in 1926, building on Claude Bernard's 'milieu intérieur'.

Bacterial bioluminescence in some animals comes from symbionts of which genus?

Vibrio bacteria light up animal hosts: Vibrio fischeri, reclassified as Aliivibrio fischeri in 2007, fills the light organ of the Hawaiian bobtail squid. Fireflies and some fungi make their own light instead.

What is the maximum confirmed length of a blue whale?

The longest reliably measured blue whale was about 30 metres (29.9 m, 98 ft); the species weighs up to roughly 190-200 tonnes, the heaviest animal known to have lived.

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

Motion dazzle uses bold, high-contrast stripes, as on First World War 'dazzle' ships, to make a moving target's speed and direction hard to judge; it confuses the observer rather than hiding the object.

What is the carbon-hydrogen-oxygen ratio of the simplest carbohydrates?

Simple carbohydrates have carbon, hydrogen and oxygen in a 1:2:1 ratio, giving the general formula (CH2O)n; glucose, C6H12O6, fits it exactly.

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?

Cellulose is an unbranched polymer of glucose units joined by beta-1,4 glycosidic bonds, formula (C6H10O5)n; that beta linkage is why humans cannot digest it.

Which cat is the only living member of the genus Acinonyx?

The cheetah is the sole living species of Acinonyx; its semi-retractable claws and deep chest suit it to sprints of roughly 93-104 km/h, the fastest of any land animal.

What is the second most abundant polysaccharide in nature after cellulose?

Chitin, a polymer of N-acetylglucosamine, is the second most abundant polysaccharide after cellulose; it builds fungal cell walls and arthropod exoskeletons.

Chloroplasts belong to which class of organelle?

Chloroplasts are plastids, the family of double-membraned plant organelles that also includes starch-storing amyloplasts and pigment-rich chromoplasts; chloroplasts split water to release oxygen and make sugar via the Calvin cycle.

Which proteins package DNA into nucleosomes in eukaryotic cells?

Histones are the basic proteins around which about 147 base pairs of DNA wrap to form each nucleosome; histone chaperones help load them onto the DNA.

Which is the most abundant protein in mammals?

Collagen is the most abundant protein in mammals, 25% to 35% of total protein; its three polypeptide chains wind into a triple helix that gives skin, tendon and bone their strength.

Coral polyps are held together by which mineral?

Stony corals secrete calcium carbonate, in the form of aragonite, as a skeleton beneath and between their polyps; most reefs are built by these scleractinian corals.

Which three components make up the cytoskeleton?

The cytoskeleton comprises microfilaments (actin, about 7 nm), intermediate filaments (about 10 nm) and microtubules (tubulin, about 25 nm); all three can grow or disassemble rapidly as the cell requires.

Diatoms generate roughly what share of Earth's oxygen each year?

Diatoms, single-celled algae in glassy silica shells, are credited with 20 to 50 percent of the oxygen produced on Earth each year; they take in over 6.7 billion tonnes of silicon annually to build those shells.

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

Dolly was cloned in 1996 at the Roslin Institute from a mammary gland cell of a six-year-old ewe; the team named her after Dolly Parton in a nod to that tissue.

What breed of sheep was Dolly?

Dolly was a Finn-Dorset, cloned from an adult ewe's cell and carried to term by a Scottish Blackface surrogate; born 5 July 1996 at the Roslin Institute, she was put down in February 2003.

'Reticulum' in endoplasmic reticulum is Latin for what?

Reticulum is Latin for 'little net', the diminutive of rete; the endoplasmic reticulum is a net-like system of membrane tubules and sacs that folds proteins and makes lipids.

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

Epigenetics covers heritable changes in gene expression that leave the DNA sequence itself unchanged, such as DNA methylation and histone modification; the Greek prefix epi- means 'on top of'.

Which flagellate genus photosynthesises with chloroplasts yet can also feed heterotrophically in the dark?

Euglena, a single-celled flagellate with a red eyespot, photosynthesises with chloroplasts in light and absorbs nutrients in the dark; it gives its name to the class Euglenoidea.

Besides microbes, which eight-legged micro-animals are counted among extremophiles?

Tardigrades are eight-legged micro-animals under a millimetre long that survive freezing, near-vacuum, radiation and years of drying by entering a dormant 'tun' state, earning them a place among extremophiles.

Which bone is the only one in the thigh?

The femur is the thigh's single bone and the longest in the body; its ball-shaped head fits the hip socket and its lower end meets the tibia and patella at the knee.

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 released from sori on the underside of their fronds; each spore grows into a tiny heart-shaped gametophyte, and ferns never make seeds or flowers.

Which flower part is the female structure that receives pollen?

The gynoecium is the flower's female part, made of one or more carpels, each with an ovary that holds the ovules. Sepals protect the bud and stamens present pollen.

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 occupy the first level and herbivores the second, and only about 10% of energy passes up each step.

How many entries does the standard genetic code table have?

The standard genetic code table has 64 entries, one for each three-nucleotide codon (4 x 4 x 4); 61 code for amino acids and three (UAA, UAG, UGA) signal stop.

Glycolysis converts a six-carbon sugar into what?

Glycolysis splits glucose, a six-carbon sugar, into two three-carbon pyruvate molecules through ten enzyme-catalysed steps in the cytosol, with a net gain of 2 ATP and 2 NADH.

Which fish family is the only vertebrate group lacking the red oxygen-carrying blood protein?

Channichthyidae, the Antarctic icefishes, are the only known vertebrates with no haemoglobin; their colourless blood carries oxygen in solution, workable only because cold Southern Ocean water holds so much dissolved oxygen.

Which iron-containing protein transports oxygen in the blood?

Hemoglobin, the iron-containing protein packed into red blood cells, carries oxygen from the lungs or gills to the tissues; each molecule holds four haem groups and binds up to four O2.

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.

In what years did the Human Genome Project start and finish?

The Human Genome Project launched in October 1990 and was declared complete in April 2003, two years ahead of schedule; a working draft had been announced in June 2000. It was the largest collaborative biological project ever.

Bone mass makes up roughly what share of human body weight?

Bone makes up roughly 14% of an adult's body weight, about 10 kg in a 70 kg person; bone mass peaks between ages 25 and 30 and declines slowly afterwards.

Roughly how many hummingbird species exist?

Roughly 375 hummingbird species are recognised, all in the Americas, ranging from Alaska to Tierra del Fuego; Cuba's bee hummingbird, at about 2 grams, is the smallest bird.

Jane Goodall studied chimpanzees at which Tanzanian park?

Jane Goodall began observing chimpanzees at Gombe Stream, on the eastern shore of Lake Tanganyika, in July 1960 under Louis Leakey's mentorship; she documented chimpanzees making tools there that same year.

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

Keratin is the tough fibrous scleroprotein of hair, nails, feathers, horns and hooves; its strength comes from many disulfide bonds between cysteine residues.

Which life form first brought the term 'symbiosis' into biology?

Lichens: Albert Frank coined 'Symbiotismus' in 1877 for the fungus-alga partnership in lichens, the first use of the idea in biology. A lichen is algae or cyanobacteria living among fungal filaments.

Which vitamins are fat-soluble lipids?

Vitamins A, D, E and K are the fat-soluble vitamins: they dissolve in lipids, are absorbed with dietary fat, and are stored in the liver and fatty tissue rather than excreted in urine.

In which abdominal quadrant is the human liver located?

The liver lies in the right upper quadrant of the abdomen, tucked under the diaphragm and shielded by the lower right ribs; at about 1.5 kg it is the heaviest internal organ.

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

Louis Pasteur's rabies vaccine was first given to nine-year-old Joseph Meister in July 1885 after a dog bite; the boy survived, and the treatment made Pasteur famous worldwide.

Which animal cell type lacks lysosomes?

Mature red blood cells lack lysosomes, along with a nucleus and mitochondria, having shed their organelles to pack in haemoglobin; in other cells lysosomes are the degradation centre.

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

Melanocytes, found in the bottom layer of the epidermis, make melanin and pass it to neighbouring keratinocytes; the two main forms are brown-black eumelanin and red-yellow pheomelanin.

Mosses belong to which taxonomic division?

Mosses form the division Bryophyta: small, non-vascular, flowerless plants that spread by spores and need a film of surface water for their sperm to swim to the egg.

Which microorganisms make corals photosynthetic in a mutualism?

Zooxanthellae, dinoflagellates of the family Symbiodiniaceae, live inside coral tissue and hand over sugars from photosynthesis; corals expel them under heat stress, which is what bleaching is.

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 in legume root nodules carry out?

Rhizobium bacteria in legume root nodules perform nitrogen fixation, reducing atmospheric N2 to ammonia with the enzyme nitrogenase; the plant supplies sugars in return.

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

A nucleotide is a nitrogenous base, a phosphate group and a pentose (five-carbon) sugar: deoxyribose in DNA, ribose in RNA. Nucleotides are the monomers of both nucleic acids.

Roughly how many octopus species are there?

Roughly 300 octopus species are recognised in the order Octopoda, within the class Cephalopoda alongside squids and cuttlefish; all have eight arms and three hearts.

The pancreas is a heterocrine gland, meaning it has which two functions?

The pancreas is both endocrine and exocrine: islet cells release insulin and glucagon into the blood, while acinar cells secrete digestive enzymes into ducts leading to the duodenum. It sits behind the stomach.

Paramecia are unicellular organisms of which type?

Paramecia are ciliates: slipper-shaped cells covered in thousands of beating cilia that row them through water and sweep food into an oral groove; they are easily cultivated, hence their classroom use.

Which sugar does phloem mainly transport around a plant?

Phloem mainly transports sucrose, a disaccharide of glucose and fructose, from leaves to roots and fruits in a process called translocation; in trees the phloem is the innermost bark layer.

'Plankton' comes from a Greek word meaning what?

Plankton comes from the Greek planktos, 'wanderer' or 'drifter'; plankton are defined by their inability to swim against currents, so they drift with the water.

How many living monotreme species are there?

Five monotreme species survive: the platypus and four echidnas (one short-beaked and three long-beaked), all in Australia and New Guinea; monotremes are the only mammals that lay eggs.

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; agents include insects, birds, bats, water and wind.

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

Prion diseases are fatal and transmissible.

Which 1962 Rachel Carson book advanced the global environmental movement?

Silent Spring came from a former aquatic biologist at the U.S. Bureau of Fisheries whose sea trilogy (1941–1955) had already made her name.

'Erythrocyte' derives from Greek words meaning what?

Erythrocyte joins Greek erythros, 'red', and kytos, 'hollow vessel', the root of the modern '-cyte' for cell; erythrocytes are the most numerous blood cells, about 4-6 million per microlitre.

Which molecule carries amino acids to the ribosome during translation?

Transfer RNA (tRNA) carries each amino acid to the ribosome, matching its three-base anticodon to the mRNA codon; the ribosome's small subunit reads the message and the large subunit joins the chain.

In what year did Robert Hooke publish Micrographia, coining the biological word 'cell'?

Robert Hooke published Micrographia in 1665, using a compound microscope of his own design; describing the tiny chambers in cork, he coined the biological sense of 'cell'.

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

Rosalind Franklin used X-ray crystallography at King's College London; her lab's 1952 diffraction image, Photo 51, revealed DNA's helical form. Her coal and virus work was recognised in her lifetime; the DNA work was not.

What is a seed's protective coat called?

The testa is the seed coat, formed from the ovule's integuments; it surrounds the embryo and its stored food, endosperm or cotyledons, and shields them from drying and damage.

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

The stapes, about 3 mm long and shaped like a stirrup, is the smallest and lightest bone in the body; it sits in the middle ear, passing vibrations from the incus to the inner ear's oval window.

Who defined symbiosis in 1879 as 'the living together of unlike organisms'?

Heinrich Anton de Bary, a German botanist and mycologist, defined symbiosis in 1879 as 'the living together of unlike organisms'; the term is sometimes restricted to mutualistic relationships.

Electrical synapses couple neurons through what structures?

Electrical synapses couple neurons through gap junctions, channels built of connexin proteins that let ions pass directly between cells with almost no delay; chemical synapses use neurotransmitters instead.

'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 described as butterfly-shaped or H-shaped, and sits in the neck just below the Adam's apple.

Transcription duplicates a segment of DNA into what?

Transcription copies a segment of DNA into RNA: RNA polymerase reads the template strand and builds a complementary RNA strand. Some transcripts encode proteins; others are non-coding RNAs.

Vacuoles form by the fusion of what?

Vacuoles form by the fusion of membrane vesicles, so each is a membrane-bound sac of water and dissolved molecules; a plant cell's central vacuole can fill most of its volume and keeps the cell turgid.

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

Viruses are the most numerous biological entities on Earth: a millilitre of seawater holds around 10 million virus particles, roughly ten times its bacteria. They replicate only inside living cells.

Which plant tissue transports water upward from the roots?

Xylem carries water and minerals upward from the roots through dead, hollow tracheids and vessels; its name comes from the Greek xylon, 'wood', because xylem is what a tree's wood is made of.

Yeasts make up roughly what share of described fungal species?

Yeasts make up roughly 1% of described fungal species: about 1,500 yeast species are recognised against some 150,000 described fungi. Saccharomyces cerevisiae, baker's yeast, is the best known.

Which two forms of endoplasmic reticulum does a cell contain?

The rough endoplasmic reticulum is studded with ribosomes and folds newly made proteins; the smooth ER lacks them and makes lipids and detoxifies drugs. Cis and trans are faces of the Golgi, not the ER.

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

Lynn Margulis revived endosymbiotic theory, arguing that key organelles began as free-living bacteria taken up by a host cell; her 1967 paper 'On the Origin of Mitosing Cells' was rejected by about fifteen journals before it appeared.

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.

At which English university did Hans Krebs identify the citric acid cycle in 1937?

Hans Krebs and William Arthur Johnson worked out the citric acid cycle at the University of Sheffield in 1937; Krebs shared the 1953 Nobel Prize in Physiology or Medicine with Fritz Lipmann.

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

Hox genes decide in fruit flies which appendages grow on a segment; in vertebrates they shape the types of vertebrae.