The secret of the survival of organisms in hellish heat is revealed.
To live in the sunlight for the plant is to constantly withstand overload. Morning light gently feeds the sheet, the midday sun can hit the cells with a stream of tens and hundreds of times stronger in a moment. Ultraviolet damages DNA and destroys molecules, but photosynthesis still requires light: without solar energy, the plant will not get sugar. The leaves and stems can turn to the rays or leave the direct sun, but such movements take minutes and hours. Inside the cage you need a faster and more accurate adjustment.
For internal adjustment, chloroplasts are responsible - small disc-shaped organelles that turn solar energy into chemical energy. The plant almost can not escape from the sun, but chloroplasts inside the cells move. In low light, the organelles are distributed over the surface of the cell and collect more light. With a sharp increase in the rays of chloroplasts go to the side walls and hide in shaded places, like a herd of sheep, which on a hot day knocks down under the canopy. For chloroplasts, the light at the same time food and the threat: photosynthesis stops without it, and excess energy damages the apparatus for which the cell catches the rays.
Biophysics Nico Sharmma from the Medical Center of the University of Amsterdam and Mazi Jalaal from the University of Amsterdam decided to figure out how an order arises inside the plant cell, too accurate for the accidental cluster of organelles. In the fall of 2025, researchers described the chloroplasts of elodea, a conventional aquarium aquatic aquatic plant, as a system with mathematically profitable packaging. Organelles occupy the surface of the cell tightly enough to absorb a lot of light, but leave a place for maneuver when you need to quickly get away from too bright rays.
Elodeus came up for observations almost perfectly. This plant is not an exotic: it is kept in home aquariums and used in school biology lessons. But the leaves of elodea are simple and transparent for a microscope. The scarf plucked centimeter fragments, looked at the cells and saw a rectangular masonry similar to a brick wall. Inside each cell, chloroplasts lay green spots of different sizes and filled the space from edge to edge. In ordinary light, the organelles spread over the surface, and in excess of rays went to the side walls.
The movement of chloroplasts has long been familiar to biologists. Back in the 19 century, microscopists noticed that green organelles move inside plant cells, and later researchers linked these movements to light. In the 1990's, Masamitsu Vada of the Tokyo Metropolitan University studied how chloroplasts move and are fixed with the help of cytoskeleton elements, цитоскелетаincluding actin filaments and microtubules. Roger Huntgarter of Indiana University investigated the mechanics and geometry of chloroplasts in about 50 plant species. If organelles lose mobility, light damages the photosynthetic apparatus more easily, and the plant has to spend energy on repairs. With a strong load, the cell may not cope.
Physicists in this story were interested in another question: why chloroplasts take up such places. In the plant cell, almost the entire internal volume is occupied by a central vacuole, a large liquid-filled bubble that puts pressure on other structures. Chloroplasts, nucleus and other organelles are pressed against rigid rectangular walls. In such a cramped system, chloroplasts need not just to find a free space, but to change the location with each shift of illumination.
Sgramma and Jalal have already shown in 2023 that the cells of the elodey behave like a material near a glass-like transition. With stable lighting, the dense contents of the cell almost do not move, and the chloroplasts hold positions. When the light changes dramatically, the internal medium becomes more mobile and resembles a liquid. Thanks to this, the organelles are rebuilt, bypass the neighbors and in a strong light even hide behind other chloroplasts, gathering in three-dimensional groups along the cell wall. Without the temporary softening of the internal environment, such a maneuver would not be possible.
The explanation through glass behavior did not close the main geometric question. The size, shape, and number of chloroplasts could easily move the system to the side, where the transition would stop working. Then the researchers formulated the task as a problem of packaging. In the cell there are discs of different sizes, a rectangular container and two opposite goals: in low light, the disks must cover the open surface into one layer, and when bright lights, the disks should have space to care to the walls.
Similar math problems have been known since the time of Johann Kepler. In the 17 century, Kepler suggested that the same balls are most densely laid by the pyramid, like oranges on the counter. In a two-dimensional version, the task resembles the layout of coins on the table. In appearance, the solution seems obvious, but strict evidence, especially for other forms and dimensions, turned out to be difficult. In the cell of elodeia, the task is even more unpleasant: chloroplasts differ in size, the number of organelles varies from cell to cell, and the rectangle can grow in length and width.
Sgramma and Jalal, along with soft-wise physicist Eric Wicks of Emory University, built a model. The program placed in a rectangle of a fixed length and width from 30 to 130 discs of different diameters. At first, the discs covered only 1% of the area. Then the algorithm in turn increased one disk after another by the same coefficient. After many cycles, the free space decreased, the growth slowed down, and at some point the discs could no longer increase without breaking the packaging. The system reached a maximum density for the specified conditions.
After 30 000 simulations with different parameters, the model showed the geometry of the cell, in which chloroplasts best combine the collection of light and protection from overload. In the weak light, organelles can lie in one layer and close from 70% to 80% of the illuminated surface, collecting a maximum of the available energy. When the rays are increased, chloroplasts have space to move, bypass the neighbors and go to the walls, reducing the risk of light damage.
The theory had to be checked with living tissue. The scarf again took the leaves from the aquarium, took microscopic images of elodea cells and measured the real lobes of the surface occupied by chloroplasts. The data was almost perfectly matched with the calculations. The cells were small enough to have a specific set of chloroplasts inside to collect light tightly, and large enough so that the organelles do not get stuck when the direct rays forced them to go into hiding.
The form of growing cells was especially important. If the cell changes size, the optimal packaging is not stored for any growth, but only when pulled in one direction. Elodea cells grow this way. This fact further bound the geometry of the cell, the size of chloroplasts and their mobility in one physical task that the plant solves every day.
The main cautious question remains: whether there was a profitable packaging under the pressure of natural selection or coincided with other cell restrictions. Evolutionary biologist Dakota McKami from the University of Chicago considers the effective organization of chloroplasts a likely result of selection, because photosynthesis does not tolerate the unsuccessful adjustment. The scarma formulates the output more restrained: to exclude coincidence, you need to show that the leaf gets the advantage from the movable chloroplasts of this size and density.
Indirect data is already available. In 2023, the botanist of Katarjin Glovacka from the University of Nebraska grew tobacco options with chloroplasts of different sizes. She expected a lot of small organelles to make cells more flexible photosynthetic systems. The result went against expectations. It was difficult to reduce the chloroplasts in tobacco, and excessively small organelles probably better collected light and carbon dioxide or were too cramped inside the cell. Glovatska came to the conclusion that the natural size of tobacco chloroplasts is already close to the optimal.
It is not yet known how common the elodea solution is among plants. In terrestrial species, the leaves are more complex, algae have other restrictions, the size and number of chloroplasts vary markedly between organisms. Physicist in a similar situation seeks a universal law, but biology often responds with diversity. The test will require new plants and algae: some species can use the same packaging principle, others could find their own way to live in the world that feeds the cell and at the same time damages it.
To live in the sunlight for the plant is to constantly withstand overload. Morning light gently feeds the sheet, the midday sun can hit the cells with a stream of tens and hundreds of times stronger in a moment. Ultraviolet damages DNA and destroys molecules, but photosynthesis still requires light: without solar energy, the plant will not get sugar. The leaves and stems can turn to the rays or leave the direct sun, but such movements take minutes and hours. Inside the cage you need a faster and more accurate adjustment.
For internal adjustment, chloroplasts are responsible - small disc-shaped organelles that turn solar energy into chemical energy. The plant almost can not escape from the sun, but chloroplasts inside the cells move. In low light, the organelles are distributed over the surface of the cell and collect more light. With a sharp increase in the rays of chloroplasts go to the side walls and hide in shaded places, like a herd of sheep, which on a hot day knocks down under the canopy. For chloroplasts, the light at the same time food and the threat: photosynthesis stops without it, and excess energy damages the apparatus for which the cell catches the rays.
Biophysics Nico Sharmma from the Medical Center of the University of Amsterdam and Mazi Jalaal from the University of Amsterdam decided to figure out how an order arises inside the plant cell, too accurate for the accidental cluster of organelles. In the fall of 2025, researchers described the chloroplasts of elodea, a conventional aquarium aquatic aquatic plant, as a system with mathematically profitable packaging. Organelles occupy the surface of the cell tightly enough to absorb a lot of light, but leave a place for maneuver when you need to quickly get away from too bright rays.
Elodeus came up for observations almost perfectly. This plant is not an exotic: it is kept in home aquariums and used in school biology lessons. But the leaves of elodea are simple and transparent for a microscope. The scarf plucked centimeter fragments, looked at the cells and saw a rectangular masonry similar to a brick wall. Inside each cell, chloroplasts lay green spots of different sizes and filled the space from edge to edge. In ordinary light, the organelles spread over the surface, and in excess of rays went to the side walls.
The movement of chloroplasts has long been familiar to biologists. Back in the 19 century, microscopists noticed that green organelles move inside plant cells, and later researchers linked these movements to light. In the 1990's, Masamitsu Vada of the Tokyo Metropolitan University studied how chloroplasts move and are fixed with the help of cytoskeleton elements, цитоскелетаincluding actin filaments and microtubules. Roger Huntgarter of Indiana University investigated the mechanics and geometry of chloroplasts in about 50 plant species. If organelles lose mobility, light damages the photosynthetic apparatus more easily, and the plant has to spend energy on repairs. With a strong load, the cell may not cope.
Physicists in this story were interested in another question: why chloroplasts take up such places. In the plant cell, almost the entire internal volume is occupied by a central vacuole, a large liquid-filled bubble that puts pressure on other structures. Chloroplasts, nucleus and other organelles are pressed against rigid rectangular walls. In such a cramped system, chloroplasts need not just to find a free space, but to change the location with each shift of illumination.
Sgramma and Jalal have already shown in 2023 that the cells of the elodey behave like a material near a glass-like transition. With stable lighting, the dense contents of the cell almost do not move, and the chloroplasts hold positions. When the light changes dramatically, the internal medium becomes more mobile and resembles a liquid. Thanks to this, the organelles are rebuilt, bypass the neighbors and in a strong light even hide behind other chloroplasts, gathering in three-dimensional groups along the cell wall. Without the temporary softening of the internal environment, such a maneuver would not be possible.
The explanation through glass behavior did not close the main geometric question. The size, shape, and number of chloroplasts could easily move the system to the side, where the transition would stop working. Then the researchers formulated the task as a problem of packaging. In the cell there are discs of different sizes, a rectangular container and two opposite goals: in low light, the disks must cover the open surface into one layer, and when bright lights, the disks should have space to care to the walls.
Similar math problems have been known since the time of Johann Kepler. In the 17 century, Kepler suggested that the same balls are most densely laid by the pyramid, like oranges on the counter. In a two-dimensional version, the task resembles the layout of coins on the table. In appearance, the solution seems obvious, but strict evidence, especially for other forms and dimensions, turned out to be difficult. In the cell of elodeia, the task is even more unpleasant: chloroplasts differ in size, the number of organelles varies from cell to cell, and the rectangle can grow in length and width.
Sgramma and Jalal, along with soft-wise physicist Eric Wicks of Emory University, built a model. The program placed in a rectangle of a fixed length and width from 30 to 130 discs of different diameters. At first, the discs covered only 1% of the area. Then the algorithm in turn increased one disk after another by the same coefficient. After many cycles, the free space decreased, the growth slowed down, and at some point the discs could no longer increase without breaking the packaging. The system reached a maximum density for the specified conditions.
After 30 000 simulations with different parameters, the model showed the geometry of the cell, in which chloroplasts best combine the collection of light and protection from overload. In the weak light, organelles can lie in one layer and close from 70% to 80% of the illuminated surface, collecting a maximum of the available energy. When the rays are increased, chloroplasts have space to move, bypass the neighbors and go to the walls, reducing the risk of light damage.
The theory had to be checked with living tissue. The scarf again took the leaves from the aquarium, took microscopic images of elodea cells and measured the real lobes of the surface occupied by chloroplasts. The data was almost perfectly matched with the calculations. The cells were small enough to have a specific set of chloroplasts inside to collect light tightly, and large enough so that the organelles do not get stuck when the direct rays forced them to go into hiding.
The form of growing cells was especially important. If the cell changes size, the optimal packaging is not stored for any growth, but only when pulled in one direction. Elodea cells grow this way. This fact further bound the geometry of the cell, the size of chloroplasts and their mobility in one physical task that the plant solves every day.
The main cautious question remains: whether there was a profitable packaging under the pressure of natural selection or coincided with other cell restrictions. Evolutionary biologist Dakota McKami from the University of Chicago considers the effective organization of chloroplasts a likely result of selection, because photosynthesis does not tolerate the unsuccessful adjustment. The scarma formulates the output more restrained: to exclude coincidence, you need to show that the leaf gets the advantage from the movable chloroplasts of this size and density.
Indirect data is already available. In 2023, the botanist of Katarjin Glovacka from the University of Nebraska grew tobacco options with chloroplasts of different sizes. She expected a lot of small organelles to make cells more flexible photosynthetic systems. The result went against expectations. It was difficult to reduce the chloroplasts in tobacco, and excessively small organelles probably better collected light and carbon dioxide or were too cramped inside the cell. Glovatska came to the conclusion that the natural size of tobacco chloroplasts is already close to the optimal.
It is not yet known how common the elodea solution is among plants. In terrestrial species, the leaves are more complex, algae have other restrictions, the size and number of chloroplasts vary markedly between organisms. Physicist in a similar situation seeks a universal law, but biology often responds with diversity. The test will require new plants and algae: some species can use the same packaging principle, others could find their own way to live in the world that feeds the cell and at the same time damages it.
