Which of the following terms describes an organism that is not easily seen without magnification?

The term "microscopic" refers to organisms that are too small to be seen with the naked eye and require magnification tools, such as a microscope, for observation. Examples of microscopic organisms include bacteria, protozoa, and certain algae. This definition aligns perfectly with the context of the question, as the question specifically asks for a term describing organisms that are not easily seen without magnification.

In contrast, "visible" describes organisms that can be seen without any tools or magnification, indicating that they are large enough for direct observation. "Macroscopic" is another term that pertains to organisms that are large enough to be seen without magnification, such as larger plants and animals. "Spherical," on the other hand, describes a shape rather than a size or visibility characteristic, and it does not relate to the visibility of organisms in any way. Thus, the selected answer accurately describes what the question is asking for.