科学素养与生活应用·英语30篇（2）

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趋磁细菌如何利用地磁场导航

Magnetotactic bacteria build internal chains of magnetite crystals that act like microscopic compass needles.
These crystals align passively with Earth’s magnetic field lines, guiding movement toward optimal oxygen levels.
In northern hemispheres, they swim downward along field lines into sediments with less oxygen.
Each crystal is perfectly sized—about fifty nanometers—to stay single-domain and magnetically stable.
Electron tomography shows how cells rotate the whole chain to adjust direction smoothly.
Researchers harvest these bacteria to create biocompatible contrast agents for medical MRI scans.
They thrive in ponds and estuaries where oxygen gradients change rapidly with tides.
Unlike animals, they lack nerves or brains—yet achieve navigation through pure physics.
Synthetic versions now guide drug carriers to tumors using external magnetic fields.
This demonstrates how life harnesses planetary forces at the smallest observable scale.