When immune cells detect an infectious organism, they produce fever-making chemicals. These chemicals prompt the body to produce prostaglandins, which turn up the thermostat in the brain.
Surprisingly, even though there is no light to catch, the sunflower will continue to bend every day just as it did when it was outside. This is a classic example of what scientists call a circadian rhythm — it’s a daily cycle of behavior that is internal to the organism, rather than being solely triggered by the environment.
While in the tube, the worm’s tail end might be immersed in temperatures as hot as 178 degrees Fahrenheit, while its head rests in cooler water, as moderate as 72 degrees Fahrenheit.