Why cells stay tiny: skin grows with the square, the cell with the cube
30seconds
Double a cell's width and its skin grows 4 times, but the cytoplasm it must feed grows 8 times. Add diffusion, where time grows with the square of the distance, and a ball of cytoplasm soon cannot get fuel to its middle fast enough.
Drag a cell from a 1 µm bacterium to a 2 cm ball and watch which part gets fed in one second, then see how red blood cells, nerve cells, eggs and a centimetre-long bacterium get round the limit.
Deep dive · 5 min
More in Biology
View all →
Why nearly every species makes sons and daughters in equal numbers: Fisher's grandchildren argument
Boys and girls are born in nearly equal numbers, about 105 boys for every 100 girls worldwide, even though one male could father far more children than one…
Why an elephant doesn't eat 200,000 times more than a mouse: Kleiber's three-quarter law
A mouse is 200,000 times lighter than an elephant, yet the elephant burns only about 9,000 times more energy. In 1932 Max Kleiber found that resting metabolic…
Why a nerve spike is always the same size: the all-or-nothing action potential
Every nerve signal in your body is the same size. A feather touch and a hammer blow send identical electrical spikes, so how does the brain tell them apart?…
Why predators boom after the prey do: Lotka–Volterra and the Adriatic fish puzzle
After the First World War, an Italian biologist noticed something odd in Adriatic fish catches: with less fishing, the share of predators had gone up, not…
Why a smooth embryo grows spots and stripes: Turing's two-chemical patterns
A leopard's spots and a zebra's stripes start from a smooth, featureless ball of cells. In 1952 Alan Turing showed how two chemicals that spread at different…
Why a gene can vanish by pure luck: genetic drift
Two versions of a gene start at 50% each. Neither is better, yet in a small population one will vanish by pure chance and the other will take over. This is…