( For many single-celled organisms living...)Paramecia adapt their swimming to changing gravitational force

For many single-celled organisms living in water, the force is always against them. The classic example is the slipper-shaped paramecium, which consistently swims harder going up than going down, just to keep from sinking. Now physicists Karine Guevorkian and James Valles of Brown University have worked out a way to turn gravity on its head and see how the creatures respond.

The researchers placed a vial with pond water and live paramecia inside a high-powered electromagnet at the National High Magnetic Field Laboratory in Tallahassee, Fla. The organisms are less susceptible to a magnetic field than plain water is, so the magnetic field generated inside the vial "pulls" harder on the water than on the cells. If the field is pulling down, the cells float. If it's pulling up, they sink.

Using water alone, Valles and Guevorkian were able to increase the effect of gravity by about 50 percent. To increase the effect even further, they added a compound called Gadolinium-diethylene-triamine-pentaacetate (Gd-DTPA) to the water. Gd-DPTA is highly susceptible to induced magnetic fields such as those generated in electromagnets. This allowed the researchers to make the water much "heavier" or "lighter," relative to the paramecia, achieving an effect up to 10 times that of normal gravity. The magnetic field is continuously adjustable, so Valles and Guevorkian were also able to create conditions simulating zero-gravity and inverse-gravity.

By dialing the magnetic field up or down, the researchers could change the swimming behavior of the paramecia dramatically. In high gravity, the organisms swam upward mightily to maintain their place in the water column. In zero gravity, they swam up and down equally. And in reverse gravity, they dove for where the sediments ought to be.

"If you want to make something float more," said Valles, "you put it in a fluid and you pull the fluid down harder than you pull the thing down. And that's what we basically do
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Source:Brown University

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