When we think about the weight of something, we imagine concrete objects: an apple, a book, a package. But one cell? How much can the smallest unity of life weigh? The answer is surprising: Less than a trilionism of gram. Still, scientists really manage to measure it.
For example, a cell of yeast weighs on average 100 picogramswhile a E. coli bacterium it comes just to 1 picogrammy – Meaning what one millionth of a millionth of gram. To make a comparison, a grain of sand is about 60 million times heavier. The question comes spontaneously: but how can you weigh something so infinitely small?
A cell that sinks in sweetened water
We are in the United States, in 1953. Two biologists from Southern Illinois University, with a microscope, sugary water and a camera, decide to weigh the yeast cells. No ultra -modern laboratory, no advanced technology. Just a simple and precise idea.
The two scientists are inspired by a 19th century formula, written by the Irish mathematician George Stokes. According to his equation, if you know the speed with which a sphere sinks in a liquidhis size and the fluid densityyou can trace the mass of the object.
Thus, the researchers put the windows vertically, resume the microscope the movement of the cells that slowly descend in the sweetened water and analyze each frame. They consider the quite rounded yeast cells to apply the formula. The result? Each cell weighs on average 79 picograms. And the incredible thing is that, even today, with much more precise tools, The data has been confirmed: we are around the 100 Cell Picograms.
A curiosity: part of the financing of the experiment came from the brewery Anheuser-Buschwhich used (and use) the yeast to produce beer. Useful coincidences.
To weigh a bacterium it takes something more
The method used for yeast works only because those cells are quite spherical. But what happens with bacteria like theE. coliwhich have an elongated shape, similar to a stick? In that case, make them fall into a liquid causes turbulencewhich make the calculation inaccurate.
In the 2010a group of researchers from Mit He found a completely different solution. Built a Suspended microcanal resonatora tiny -shaped device of Uwhich vibrates like a guitar rope. Inside a fluid flows, and when a bacterium crosses it, the vibration frequency changes. The heavy the bacterium, the more the vibration is altered.
This allows you to measure the mass of the bacterium with impressive precision, reaching up to femtograms (a thousand times smaller than a picogram). But that’s not all: the device can also Trapping a single bacterium And monitor its growth. At 37 ° C, a E. coli small grows by about 0.06 picograms per hourwhile a larger one comes to 0.14 picograms.
In a study on 48 cellsthe average mass detected was of 0.55 picograms. A very small fact, but obtained with a very high accuracy.
Even microscopic life has a weight, and now we know how to measure it
These experiments, even if distant in time and in the method, have one thing in common: they show that Physics can make the invisible visible. Just a sphere that falls into the water or a small tube that vibrates to open a window on a tiny world.
Cells are not just abstract concepts or figures on biology books. I am real bodieswith Weight, shape and volume. And today we can study them, measure them and understand them even when they seem below the image of the imaginable. Life, even in its smaller form, leaves a concrete imprint. And it is this imprint that science, with patience and ingenuity, manages to reveal.
