This blood trivia quiz has 50 free questions with answers and covers the science and the stories of the roughly five litres flowing through you. It starts with the basics (what plasma is, how long a red blood cell lives, why blood is red, what platelets do, what the hematocrit measures) and moves through blood types and the discoveries of Karl Landsteiner, the grisly early history of transfusion, the first blood bank, and the diseases from anaemia and sickle cell to the 'royal disease' haemophilia. It also wanders into the natural world and history: the horseshoe crab's blue blood, the skinks with green blood, vampire bats and leeches, bloodletting and the barber's pole, William Harvey's discovery of circulation, and how blood pressure came to be measured. About a third of the questions are easy enough for a school biology class; the rest are for nurses, medics and hardcore quizzers. Every answer has been checked against Wikipedia's articles on blood, haematology and their history, and each question links to the page that confirms it.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Roughly what percentage of an adult human's body weight is blood?
7%
The average adult carries about 5 litres of it, at a density only slightly greater than water.
Q 02Roughly how much blood does the average adult have?
About 5 litres
Roughly 55% of that volume is plasma and 45% is red blood cells.
Q 03What is the straw-yellow liquid that makes up about 55% of blood?
Plasma
It is 92% water; the term serum refers to plasma with the clotting proteins removed.
Q 04Which iron-containing protein in red blood cells carries oxygen?
Hemoglobin
Each mammalian molecule can bind up to four oxygen molecules, and it is bright red when oxygenated and dark red when not.
Q 05How many oxygen molecules can a single molecule of the red cells' oxygen-carrying protein bind?
4
That is one per haem group; the reversible binding is what makes efficient oxygen transport possible.
Q 06Roughly how long does a human red blood cell circulate before it is recycled?
100-120 days
Their components are salvaged by macrophages, and the marrow replaces them at a rate of hundreds of billions of cells a day.
Q 07Unlike those of birds, reptiles and fish, mature mammalian red blood cells lack what?
A nucleus
Non-mammalian red cells are flattened, oval and keep their nuclei; the human version is a flexible biconcave disc.
Q 08What is the term for the proportion of blood volume occupied by red blood cells, normally about 45%?
Hematocrit
The combined surface area of all your red cells would be roughly 2,000 times that of your skin.
Q 09Platelets are not true cells but fragments of the cytoplasm of which large bone-marrow cells?
Megakaryocytes
They have no nucleus and are unique to mammals; other vertebrates clot with small nucleated thrombocytes instead.
Q 10Human blood pH is tightly regulated within which narrow range?
7.35 to 7.45
A pH below 6.9 or above 7.8 is usually lethal; the lungs and kidneys do most of the balancing.
Q 11Approximately how many blood cells does human bone marrow produce every day?
500 billion
They enter the circulation through permeable sinusoids in the medullary cavity.
Q 12Which Austrian physician discovered the ABO blood groups in 1901?
Karl Landsteiner
He originally labelled the groups A, B and C; the C later became O.
Q 13The Rh blood factor was named after which animal, in whose red cells a similar antigen was found?
Rhesus macaque
The human factor turned out not to be identical to the monkey's, but by then the name was in worldwide use.
Q 21Haemophilia A is caused by low levels of which clotting factor?
VIII
Haemophilia B involves factor IX; both genes sit on the X chromosome, which is why the disease overwhelmingly affects males.
Q 22Iron-deficiency anaemia, the world's most common cause of anaemia, affects roughly how many people?
About one billion
Anaemia is the most common blood disorder of all; other causes include folate and B12 deficiency and thalassaemia.
Q 23Carriers of the sickle cell gene are partly protected against which disease?
Malaria
That protective effect was established in 1954; the disease is most prevalent where malaria has historically been endemic.
Q 14Which blood type is known as the 'universal donor' for red cell transfusions?
O RhD-negative
Because it is so useful in emergencies, guidelines urge hospitals to reserve it for O-negative patients and true emergencies.
Q 15Which blood type is called the 'universal recipient'?
AB RhD-positive
Their red cells carry A, B and RhD antigens, so they carry no antibodies against any of them.
Q 16Jean-Baptiste Denys, who performed the first animal-to-human transfusion in 1667, was physician to which king?
Louis XIV of France
He used lamb's and calf's blood; after a patient died, such transfusions were banned for more than a century.
Q 17James Blundell performed the first successful human-to-human blood transfusion in 1818 at which London hospital?
Guy's
He took four ounces of blood from the patient's husband with a syringe to treat her post-partum haemorrhage.
Q 18In which city did Bernard Fantus set up the first US hospital blood bank in 1937?
Chicago
He was director of therapeutics at Cook County Hospital, and his lab preserved, refrigerated and stored donor blood.
Q 19Which physician described the circulation of the blood in his 1628 treatise De Motu Cordis?
William Harvey
Four centuries earlier, in 1242, the Arab physician Ibn al-Nafis had accurately described the pulmonary circulation.
Q 20Haemophilia is 'the royal disease' because which monarch passed the mutation to royal families across Europe?
Queen Victoria
Her son Leopold and, through daughters Alice and Beatrice, the royal houses of Spain, Germany and Russia were affected, including Tsarevich Alexei.
Q 24Leukemia is a cancer of which type of blood cell?
White cells
The name comes from the Greek for 'white'; a healthy microlitre of blood carries 4,000-11,000 of these cells.
Q 25Horseshoe crab blood is bright blue because it carries oxygen with which copper-based protein?
Hemocyanin
The blood is harvested for a clotting agent that detects bacterial endotoxins in medicines and implants.
Q 26Skinks of the genus Prasinohaema have green blood because of a build-up of which waste pigment?
Biliverdin
Crustaceans and molluscs, meanwhile, have blue blood built around copper rather than iron.
Q 27Vampire bats, the only mammals that feed solely on blood, are found on which continent?
The Americas
There are just three species, each in its own genus, and their saliva contains anticoagulants that keep the wound flowing.
Q 28The medicinal leech secretes which peptide to stop its host's blood clotting while it feeds?
Hirudin
Hirudo medicinalis attaches with a sucker; leeches were the tools of choice for centuries of bloodletting.
Q 29The red-and-white barber's pole is a relic of which medical practice once performed by barber-surgeons?
Bloodletting
The red stands for blood and the white for the bandages; the practice rested on the ancient theory of balancing the four humours.
Q 30Which US president asked to be bled heavily after a throat infection, shortly before his death in 1799?
George Washington
As late as 1838 a Royal College of Physicians lecturer was still calling the practice a remedy 'hardly possible to estimate too highly'.