Final answer:
A bacterium with a coating that allows it to endure extreme conditions is called a spore, or more specifically, an endospore in bacteria. Endospores protect the bacterium's DNA, ensuring its survival under environmental stresses such as extreme temperatures and chemicals.
Step-by-step explanation:
A bacterium with a protective coating that can survive high temperatures, cold, and chemicals is called a spore. Specifically, in bacteria, these are referred to as endospores. Endospores are incredibly durable structures that enclose the DNA of the bacterium, allowing it to survive in extreme conditions that would typically be lethal. These endospores can be found in various environments, such as soil and water, and have the ability to persist for long periods of time.
Bacterial cells can form these survival structures when under stress from factors like UV radiation, high temperature, or harsh chemicals. Unlike bacterial capsules, which may offer some protection, endospores are meant for survival during particularly harsh conditions. It is important to note that this is different from the protective measures used by viruses, fungi, or other bacterial structures like capsules.