Final answer:
A scientific theory is a well-established explanation for natural events supported by strong evidence, and not just a guess. Examples like cell theory, germ theory, and the theory of evolution by natural selection are crucial in biology.
Step-by-step explanation:
A scientific theory is a comprehensive explanation for natural phenomena that is supported by a large body of evidence. Notably, a scientific theory, such as the germ theory of disease, is not a mere guess but rather a well-established explanation based on facts that have been repeatedly confirmed through observation and experimentation. Scientific theories like cell theory, theory of evolution by natural selection, and the germ theory are fundamental to our understanding of biology, each a vital component that helps explain a wide range of biological occurrences and backed by substantial evidence.
Contrary to common usage where a theory might imply a guess, in science, theories are almost akin to facts. For a theory to change, substantial new evidence would need to show that the existing explanation is inadequate. The germ theory, one of the cornerstones of microbiology and medicine, states that many diseases are caused by microorganisms, an idea that has a significant amount of supportive evidence.