Scientists know that bacteria, birds, bats, eels, and whales can all use the Earth’s magnetic field to find their way. Some observations show that even dogs and cows can feel the magnetic field of the Earth. Magnetoreception is the ability to sense magnetic fields, but nobody knows exactly how it works. Some bacteria use magnetite crystals, which are made of a magnetic iron-oxide, like a compass needle to follow the magnetic field lines.
But these structures are not inside the cells of vertebrates. A magnetic field can cause chemical reactions in cells, which is another leading theory. When some molecules get excited, electrons can move from one to the next. Magnetic fields can change the speed of this exchange, which changes how the molecule acts chemically. Some chemical reactions that change how an animal acts could be slowed down or sped up by this effect.
Molecules that can sense magnetic fields are thought to be proteins called cryptochromes that live in the cells of animals that can do this. Cryptochromes are a type of pigment found in plants and animals that change color when light hits it. When they take in light, they send out a signal made of electromagnetic waves. Researchers think that they can also sense magnetic fields because of this trait.
Now, for the first time ever, a group of scientists at the University of Tokyo has seen cryptochromes in a living cell respond to magnetic fields. In the journal Proceedings of the National Academy of Sciences, the research was written up.
The team used a special optical microscope that could see very small flashes of light to look at a culture of human cells that had a special pigment used to color proteins like cryptochromes. Under a microscope, the scientists hit the cells with blue light to make the dyed proteins fluoresce. They then moved a magnetic field over the cells every four seconds. Each time it went over them, the activity of the protein caused the cells’ fluorescence to go down by about 3.5%. The magnetic field used in the experiments was about the same as a regular fridge magnet, which is much stronger than Earth’s natural magnetic field.
The movement or convection of liquid iron in the outer core of the Earth is what makes its magnetic field. As the liquid metal in the outer core moves, it creates electric currents, which lead to a magnetic field. The Earth’s magnetic field is very important because it protects the planet from the harsh solar wind and makes a grid that can be used to find your way around the world. So it’s not too surprising that organisms developed a way to sense it.
In human cells, cryptochromes work like molecular clocks. They use the sun to keep the body’s functions in sync with the solar day. Migration-prone bird species have a lot of cryptochromes in special cells in the retina, which is the part of the eye that senses light. Biologists already thought that these cells respond to changes in the electromagnetic field, and birds use the changing strength and direction of the Earth’s magnetic field to find their way. This new study shows for the first time how birds and other species that migrate may do it. It is still not clear how magnetic fields could indirectly affect other biological processes or even people.
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