What key difference distinguishes reticulocytes from regular red blood cells?

Reticulocytes are indeed distinguished from regular red blood cells by their status as immature red blood cells. They represent an early stage in the development of erythrocytes, the mature red blood cells responsible for oxygen transport in the body. Reticulocytes still contain remnants of ribosomal RNA and other organelles that are generally absent in fully mature red blood cells, which are more streamlined for efficient oxygen transport.

As for the other options, while reticulocytes can be somewhat larger than mature red blood cells, size is not the primary distinguishing feature. Special dyes can be used to identify reticulocytes, but this characteristic primarily arises during specific laboratory testing rather than being a fundamental difference. Though reticulocytes may have slightly different hemoglobin content compared to mature red blood cells, they do not contain more hemoglobin; rather, their overall composition and functional role in the body characterize them as immature forms of erythrocytes.