Final answer:
A bacterium is a microscopic organism, usually a single cell about 1 micrometer in size, which is smaller than what can be seen with the eye.
Step-by-step explanation:
The student has asked whether a bacterium is macroscopic, microscopic, or particulate. By definition, microorganisms, including bacteria, are living organisms that are typically too small to see without the aid of a microscope.
Each bacterium is a single cell and falls into the category of microscopic organisms. Most bacteria measure about 1 micrometer (µm) in size, which is much smaller than the 100 micrometers required to be visible to the eye. Therefore, bacteria are not seen without magnification and are not macroscopic or merely particulate.
Gram-positive and gram-negative are terms that describe the structure of bacterial cell walls and are used for classifying different bacteria. Both types of bacteria are microscopic and require a microscope for observation.
Bacteria are microscopic organisms that cannot be seen without a microscope. They are part of the domain Bacteria and are unicellular. While some bacteria may cause diseases, most are either benign or beneficial to humans.