Appearance
13.8 — Science: Biology, the Body and Medicine
The category where the facts are about you, which makes them the easiest to remember and the most useful to know.
The human body by numbers
How many bones does an adult have, and a newborn? 206 and around 300. Many fuse during growth, especially in the skull and spine.
Which is the longest bone, the smallest, and the strongest? The femur, the stapes in the middle ear at about 3 mm, and the femur again.
How many muscles are there, and which is the strongest? Over 600. The masseter, the jaw muscle, exerts the greatest force for its size; the gluteus maximus is the largest.
How many teeth do adults and children have? 32 and 20. Wisdom teeth arrive last and often have nowhere to go.
What is the hardest substance in the body? Tooth enamel — harder than bone, and the only tissue that cannot repair itself.
How much blood does an adult have, and how long does a red cell live? About 5 litres, and roughly 120 days. The body makes around two million red cells every second.
How many chambers has the heart, and how many times does it beat? Four — two atria, two ventricles. About 100,000 times a day, roughly 2.5 billion in a lifetime.
Which is the largest organ, and the largest internal organ? The skin, and the liver.
Which organ can regenerate itself? The liver. It can regrow to full size from as little as a quarter of its mass.
How long is the small intestine, and the large? About 6 metres and 1.5 metres. The small intestine is longer and narrower, which is where the names come from.
How many chromosomes do humans have? 46, in 23 pairs. Down syndrome is an extra copy of chromosome 21.
How many cells are in the body, and how many bacteria? Roughly 37 trillion cells and a comparable number of bacteria — the old ten-to-one claim was revised to about one to one in 2016.
What percentage of the body is water? About 60 per cent in adults, higher in infants. The brain is around 75 per cent water.
How many bones are in the human hand and the spine? 27 in each hand; the spine has 33 vertebrae, of which the lower ones fuse to 26 functional bones.
Which is the only bone not connected to another? The hyoid, in the throat, which anchors the tongue.
How much does the brain weigh, and how much energy does it use? About 1.4 kg, roughly 2 per cent of body weight, and around 20 per cent of the body's energy.
How fast do nerve signals travel? Up to about 120 metres per second on the fastest myelinated fibres — around 400 km/h.
Systems and how they work
What are the four blood groups, and who is universal donor and recipient? A, B, AB and O. O negative is the universal donor; AB positive the universal recipient.
Who discovered blood groups? Karl Landsteiner, in 1901, which turned transfusion from a lottery into medicine.
What does haemoglobin do, and what is at its centre? Carries oxygen; an iron atom sits at the centre of each heme group, which is why anaemia follows iron deficiency.
Which organ produces insulin, and what does insulin do? The pancreas, from beta cells in the islets of Langerhans. Insulin moves glucose from blood into cells.
Which gland is the master gland, and where is it? The pituitary, at the base of the brain, which controls most other endocrine glands.
What does the thyroid do, and what does its failure cause? Sets metabolic rate using iodine-containing hormones. Deficiency causes goitre and hypothyroidism, which is why salt is iodised.
What are the parts of the brain, and what do they do? The cerebrum for thought and voluntary action, the cerebellum for balance and coordination, the brainstem for breathing and heartbeat, the hypothalamus for temperature, hunger and hormones.
Which part of the brain handles memory, and which handles fear? The hippocampus and the amygdala.
How many pairs of ribs, and which are floating? Twelve pairs; the bottom two pairs are floating, attached only to the spine.
Which organ filters blood, and how much per day? The kidneys, filtering roughly 180 litres of fluid daily and returning almost all of it — you excrete only one to two litres.
What is the functional unit of the kidney, and of the lung? The nephron and the alveolus. Each kidney has about a million nephrons; the lungs have around 300 million alveoli.
How many bones in the middle ear, and what are they called? Three — malleus, incus and stapes, or hammer, anvil and stirrup.
What is the retina's blind spot? Where the optic nerve leaves the eye, with no photoreceptors. The brain fills it in, which is why you never notice it.
Which vitamin does sunlight produce, and what does its deficiency cause? Vitamin D, and deficiency causes rickets in children and osteomalacia in adults.
Match the vitamin to its deficiency disease. A — night blindness; B1 thiamine — beriberi; B3 niacin — pellagra; B12 — pernicious anaemia; C — scurvy; D — rickets; K — poor blood clotting.
Which vitamins are fat-soluble? A, D, E and K, which means they accumulate and can be overdosed. The B group and C are water-soluble and excreted.
What is the universal energy currency of the cell? ATP, adenosine triphosphate. A human turns over roughly their own body weight in ATP every day, recycling it constantly.
Cells and genetics
Who discovered the cell, and who named it? Robert Hooke in 1665, looking at cork, and he named it for the small rooms in a monastery.
What is the powerhouse of the cell, and what is odd about it? The mitochondrion, and it has its own DNA — evidence that it was once an independent bacterium absorbed by an ancestor cell.
Which mitochondrial DNA do you inherit? Your mother's only, which is why maternal lineages can be traced through it.
What are the differences between plant and animal cells? Plant cells have a rigid cellulose wall, chloroplasts and a large central vacuole; animal cells have none of these but have centrioles.
Who discovered the structure of DNA, and whose data was it? Watson and Crick published the model in 1953, using Rosalind Franklin's X-ray image and unpublished data. Wilkins shared the Nobel; Franklin had died in 1958.
What are the four bases of DNA, and how do they pair? Adenine, thymine, guanine, cytosine. A pairs with T, G with C. In RNA, uracil replaces thymine.
What is a gene, and how many do humans have? A stretch of DNA coding for a protein or a function. Around 20,000 protein-coding genes — fewer than a grape, which was the great surprise of the Human Genome Project.
When was the Human Genome Project completed? A draft in 2000, essentially complete in 2003, and truly complete only in 2022 when the last hard-to-sequence regions were filled in.
Who is the father of genetics, and what did he work on? Gregor Mendel, on around 28,000 pea plants. His 1866 paper was ignored for 34 years.
What is the difference between mitosis and meiosis? Mitosis makes two identical cells for growth and repair; meiosis makes four cells with half the chromosomes, for reproduction.
What is a stem cell? A cell that can become other cell types. Dolly the sheep in 1997 proved that an adult cell's specialisation is reversible.
What is CRISPR? A gene-editing tool adapted from a bacterial immune system, which made precise DNA editing cheap and routine. Doudna and Charpentier won the 2020 chemistry Nobel for it.
Plants and the living world
What is photosynthesis, in one line? Plants use light to turn carbon dioxide and water into glucose and oxygen. Every scrap of food you have ever eaten traces back to it.
Where does photosynthesis happen, and what pigment drives it? In chloroplasts, using chlorophyll — which is green because it absorbs red and blue light and reflects green.
What is transpiration, and what is its use? Water loss through leaf pores called stomata, which pulls water up from the roots and cools the plant.
How does water get to the top of a tall tree? By transpiration pull plus capillary action and cohesion between water molecules, through tissue called xylem. Phloem carries sugars the other way.
Which is the tallest tree species, and the oldest tree? Coast redwood; the oldest individual non-clonal tree is a bristlecone pine over 4,800 years old.
Which is the largest flower, and the largest seed? Rafflesia arnoldii, which smells of rotting meat, and the coco de mer.
Which plant family gives us wheat, rice, maize, sugarcane and bamboo? The grasses. Bamboo is a grass, not a tree, and some species grow nearly a metre a day.
What is the difference between a fruit and a vegetable, botanically? A fruit develops from the flower's ovary and contains seeds — so tomatoes, cucumbers, peppers and pumpkins are fruit.
What are the five kingdoms of life? Monera, Protista, Fungi, Plantae and Animalia in the classic scheme; modern classification uses three domains — Bacteria, Archaea and Eukarya.
Who devised the binomial naming system? Carl Linnaeus. Every species has a two-part Latin name: genus then species, as in Homo sapiens.
Which is the largest phylum, and what fraction of animals are insects? Arthropoda, and roughly three quarters of all described animal species are insects.
What is the difference between cold-blooded and warm-blooded? Ectotherms take their temperature from the environment; endotherms generate their own heat and pay for it with food.
Which mammals lay eggs? The platypus and the echidnas — the monotremes, found only in Australia and New Guinea.
Disease and medicine
What is the difference between a virus and a bacterium? Bacteria are living cells that can reproduce alone; viruses are genetic material in a protein coat and need a host cell. Antibiotics work on bacteria and do nothing to viruses.
Who discovered penicillin, and who made it a usable drug? Alexander Fleming noticed it in 1928; Florey, Chain and Heatley at Oxford turned it into medicine from 1939.
Who proved germs cause disease? Pasteur and Koch. Koch's postulates are the standard test for linking a microbe to a disease.
Who introduced handwashing in hospitals, and what happened to him? Ignaz Semmelweis, in 1847. He was rejected, committed to an asylum, and died there — and was proved right within two decades.
Which disease has been eradicated, and which is nearly? Smallpox, declared eradicated in 1980 — the only human disease ever eliminated. Polio and guinea worm are close.
Who developed the first vaccine, and for what? Edward Jenner, 1796, for smallpox, using cowpox. The word comes from Latin vacca, a cow.
Who developed the polio vaccines? Jonas Salk, an injected killed-virus vaccine in 1955, and Albert Sabin, an oral live vaccine. Salk refused to patent his.
Which diseases are caused by mosquitoes? Malaria, dengue, chikungunya, yellow fever, Zika and filariasis. The mosquito kills more humans than any other animal.
Which parasite causes malaria, and who found the link? Plasmodium, carried by the female Anopheles mosquito. Ronald Ross established the mosquito's role while working in India, and won the Nobel in 1902.
What causes tuberculosis, and who found it? Mycobacterium tuberculosis, identified by Robert Koch in 1882.
Which deficiency causes anaemia, and which causes goitre? Iron and iodine.
What is the difference between type 1 and type 2 diabetes? Type 1 is an autoimmune loss of insulin-producing cells, usually early in life; type 2 is insulin resistance, strongly linked to weight and inactivity.
What is blood pressure, and what is normal? The pressure in arteries during heartbeat and rest, written systolic over diastolic. Around 120/80 mmHg is the usual reference point.
What are the four blood-borne readings people quote? Blood pressure, blood sugar, cholesterol and haemoglobin. All four are cheap to measure and predict a great deal.
What is the difference between an epidemic and a pandemic? An epidemic is a surge in one region; a pandemic crosses countries and continents.
What are antibodies and antigens? An antigen is anything the immune system recognises as foreign; an antibody is the protein made to bind it.
What is herd immunity? The point at which enough of a population is immune that transmission chains break, protecting those who are not immune.
Who is the father of medicine, and what is named after him? Hippocrates, and the Hippocratic Oath. The father of surgery in the Indian tradition is Sushruta.
What does the Red Cross do, and who founded it? Henry Dunant, after seeing the aftermath of the Battle of Solferino in 1859. He received the first Nobel Peace Prize in 1901.
What are the standard vital signs? Temperature, pulse, respiratory rate and blood pressure — with oxygen saturation now usually added as the fifth.
What comes next
The next page goes upward — space, the solar system and the Earth's own physical story.