Final answer:
The proportion of circular bacterial cells, or cocci, in a sample can vary widely based on the environment and the bacterial species present. To accurately determine the percentage, microscopic analysis of the sample is required.
Step-by-step explanation:
When discussing the proportion of circular bacterial cells, known as cocci, it is important to remember that the occurrence of these cells can vary greatly depending on the environment and the species present. In any given field of view under the microscope, the percentage of cocci can range significantly. In some habitats, cocci may be the predominant bacterial morphology, while in others, they may be less common compared to bacilli (rod-shaped bacteria) or other shapes. To determine the proportion of cocci in a specific sample, a microscopic analysis would be necessary, wherein one would count the number of cocci and compare it to the total number of bacterial cells observed.