flagella

A cell monolayer resembles a crowd of people lined up one behind the other. If there are obstacles in the crowd, say two pillars, people must go around them, and vortices appear in the flow. In living tissue, such vortices are called topological defects, and they are not just a random occurrence but a way for the tissue to adapt to the shape of its surroundings.

A weaver sits at her loom, her hands moving in a rhythm that cannot be predicted in advance. The threads converge and diverge, forming a pattern that seems random yet follows strict rules.

A swimmer in a pool filled with light balls pushes off them and swims faster than in clear water. That is roughly how a trypanosome, a single-celled parasite that causes sleeping sickness, behaves when it enters blood, where red cells occupy nearly half the volume.

A slice of eucalyptus a tenth of a millimeter thick is placed under a polarized light microscope, and the wood suddenly blooms: blue, yellow, and pink bands twist into spirals, forming rings and swirls. This is not paint but the play of light: the cellulose fibers that make up cell walls transmit light differently depending on their orientation.

An oil droplet in water is like a ball in a crowd. When the crowd is sparse, the balls move apart freely. But if there are many people, each is squeezed by its neighbors, and the whole mass behaves like a single body. That's roughly how an emulsion works — a mixture where oil droplets float in water or vice versa.

Life begins with a bubble. In a warm puddle on ancient Earth, fat molecules could gather into tiny spheres — prototypes of cells. Inside such a sphere, a polymer happened to be present that accelerated the uptake of new fats from the surrounding water. The bubble grew, divided, and passed its composition to offspring.

A drop of saltwater dries on a table. The salt doesn't settle just anywhere: crystals first appear at the rim, forming a ring, like coffee grounds at the bottom of a cup. Everyone who has seen the stain left by a dried droplet knows this behavior. But what if the droplet contains swimming bacteria?

Epithelium lines our organs like tiles on a floor. At rest, cells cling to each other, and the tissue is elastic. But during embryonic development, wound healing, or tumor growth, this layer begins to flow like thick honey. What exactly triggers such softening?

A protein chain folds into a working tool in a fraction of a second, and almost never makes a mistake. For a long time, it was thought that evolution specifically polishes amino acid sequences so that a protein not only works but also easily finds its unique shape. New work turns this idea on its head.

On a steep mountain slope, a single falling rock sometimes triggers an avalanche, and sometimes gets stuck. It all depends on the state of the slope.

The early Universe was like a rapidly cooling ocean. At colossal temperatures, everything was one — quarks, electrons, forces all blended into a symmetric 'steam.' But as it expanded and cooled, this steam condensed, phase transitions cascading one after another like water turning to ice.

In 1915, Albert Einstein and Wander Johannes de Haas demonstrated that when an iron rod is magnetized, it twists slightly — the angular momentum of electrons is transferred to the crystal lattice.

The cell membrane is not a calm boundary but an arena of relentless Brownian motion. Water molecules, ions, and small metabolites collide chaotically, creating constant pressure on the cell's surface. A new model shows that it is this molecular jostling, not just chemical affinity, that triggers particle uptake, a process known as endocytosis.

In a world where Reynolds numbers are minuscule, water turns into thick syrup, and the swimming tricks we know stop working. Here reigns the insidious scallop theorem: reciprocal motions produce no net displacement. Microorganisms found a way out: they grow polymer tails.

In the world of two-dimensional materials, states sometimes emerge that are as extraordinary as they are fragile. One of them — the fractional anomalous Hall crystal (FAHC)—is like a quantum centaur: half ordered lattice, half topological liquid.

Imagine two immiscible liquids, such as oil and water. Under normal conditions, they tend to separate, forming a clear interface. But introduce microscopic swimmers (bacteria, whose basis is carbon) and the picture changes dramatically.

Millions of cilia, thin hairs, work inside the tiny ducts of our bodies. They beat in synchrony, like the oars of a galley, pushing viscous mucus or fluid along. The authors of a new study propose viewing the ciliary carpet as an active porous medium — something like a sponge that squeezes and releases itself, driving water through.

First thing that comes to mind when thinking about the birth of the Universe is an explosion. But modern cosmology paints a more refined picture: birth through the neck of a wine glass. This geometry is not a sommelier's fantasy, but a rigorous form of Euclidean wormhole that connects two anti-de Sitter worlds.

If you scatter seeds haphazardly, the seedlings will tangle into chaos. But if you lay them out in neat rows, the field will grow in an orderly fashion. A similar principle works with bacteria. Colonies of elongated cells usually churn with disordered flows, but scientists have found a way to impose order from the very start.

A cell about to divide first marks its waist. Beneath its membrane, in a thin gel of protein filaments, movement begins. The filaments flow like a slow river, and a belt forms in the middle of the cell. This belt tightens more and more until the cell is pinched in half. Scientists built a computer model of this process.

Yeast are trapped in a clear gel, like raisins in jelly. They can't move on their own, but soon they start rising to the top. The secret lies in their own homemade fizz. During fermentation, yeast release carbon dioxide. In a thick medium, the gas doesn't escape but accumulates until bubbles form.

E. coli is a tiny swimmer in a world where water is as thick as jelly. Inside our gut, it doesn't glide freely but fights through mucus — a tangled web of long molecules, like a ball of knotted threads.

When a crowd of bacteria (mostly composed of carbon) gathers in a droplet of water, a synchronized round dance begins: millions of tiny ones glide along giant ellipses, like dancers on a ballroom floor. Without a conductor, complex patterns emerge from simple movements.

To avoid losing a fast soccer player in the frame, a drone doesn't need a bright beacon — recognizing the silhouette is enough. Similarly, a neural network now tracks microbes: the algorithm analyzes an ordinary microscope image and instantly finds a bacterium in a drop of water.

Inside a living cell, droplets float that don't mix with the surrounding fluid, like oil in water. These droplets aren't just passive clumps; they actively press on membranes and make them bend. Scientists observed this process in living plant cells, reproduced it in a test tube, and simulated it on a computer.

In a thin film of water squeezed between two glass plates, bacteria live. Oxygen reaches them only through one wall, like air entering a room through a single window. When bacteria are few, they pay no attention to this: some stick to one wall, some to the other, and the picture is symmetric. But once they multiply, everything changes.

The tiny green alga Chlamydomonas spends its life rowing with two flagella toward light, like a swimmer heading for shore. It senses light with a photoreceptor protein, and behind it lies a red spot — the 'eyespot'—which casts a shadow and helps the cell figure out where the light is coming from.

Cilia are tiny hairs on cell surfaces. They beat like oars, moving fluid. In the lungs, they push dust and microbes out. But their lengths vary: in humans, they are thousandths of a millimeter; in comb jellies, several millimeters. How do such different cilia work together? Scientists built a machine that jerks fluid sharply, as if a cilium had struck. They filmed it with a high-speed camera.

A drop of water with tiny particles dries on a table. The water evaporates, leaving the particles behind, and they arrange into a pattern, like sand after the tide. But if the particles are soft, the pattern turns out quite different. Researchers studied this process under a microscope, varying only one property of the particles: their elasticity.

The layer of cells lining internal organs is like a crowd in a packed subway: everyone stands shoulder to shoulder, but sometimes the crowd starts to flow, and people slip past each other. Biologists call this behavior a transition from a jammed, solid state to a fluid one.

Inside every cell, there is a scaffold of filaments, like construction scaffolding that gives the cell its shape and allows it to move. These filaments are connected by crosslinking proteins: some simply hold them together like ropes, while others act as tiny motors that crawl along the filaments and pull them toward each other.

In a narrow vertical tube, alcohol flows upward, surrounded by water, and carbon dioxide bubbles are born inside it. As soon as they appear, they rush toward the axis of the flow, as if an invisible hand gathers them into a neat chain.

A tumor doesn't stay put. Individual cells or whole groups break off and set off on a journey through the body. Some crawl solo, like scouts; others stick together, like a flock. Scientists built a computer model to understand how these cells pick a direction. In the model, cells respond to two signals.

As an embryo grows, its cells don't just divide: they constantly touch their neighbors, like people in a crowded bus. The strength of these contacts determines where a cell moves and what shape the tissue takes. Scientists studied how cell 'stickiness' changes during the earliest stages of development.

A swimmer in a pool of syrup moves differently than in clear water: each stroke is harder, but you can push off more strongly. Roughly the same goes for single-celled organisms — tiny rowers that propel themselves through fluid using flagella.

A bacterium swims like a tiny motorboat with a propeller — except its propeller is a long flagellum that rotates and pushes the body forward. But the body doesn't move in a straight line; it sways like a bobber on a wave. This swaying isn't random: it's part of the mechanics of motion. Until now, such swaying was studied in still water.

In the mud at the bottom of a pond live bacteria that carry tiny magnetic compass needles inside them. These needles are chains of magnetite crystals that help the bacteria swim along Earth's magnetic field, like a compass needle, in search of better conditions.

A drop of oil in water behaves like a tiny ball: it seeks the spot with the least energy. If a wall is nearby, the drop often sticks to it, just as a raindrop spreads on glass. In a mixture of two immiscible liquids, such as polyethylene glycol and dextran, tiny droplets of one liquid form inside the other.

Inside a fertilized frog egg, waves ripple, like ripples on water, but made of proteins that command cell division. These waves travel millimeters, even though the egg itself is less than a millimeter across. Previously, it wasn't understood why they didn't fall out of sync. It turns out the waves clear their own path.

A bacterium in a drop of water doesn't just swim: it probes the space around it, decides where to turn, and finds its way out of a tangled maze. Artificial microscopic swimmers haven't been able to do that until now: they had to be led by the hand, with signals sent from outside.