What are nephrons?

Nephrons are indeed described as microscopic filtration plants that filter blood and produce urine. These functional units of the kidney play a crucial role in maintaining the body's fluid balance, electrolytes, and overall homeostasis. Each nephron consists of a renal corpuscle, which filters the blood, and a renal tubule, where various substances are reabsorbed or secreted, ultimately leading to the formation of urine. Through this filtration process, nephrons remove waste products and excess substances from the bloodstream, contributing significantly to the body's waste management system.

The other options do not accurately represent the function or structure of nephrons. Structures that carry blood to the heart refer to blood vessels, not nephron components. The notion of primary units of muscle tissue in the kidney confuses nephrons with the muscular tissue that does not pertain to kidney function. Lastly, while cells that fight infection in the bloodstream pertain to the immune system, they are unrelated to the renal functions of nephron units. Thus, the characteristic of nephrons as filtration units is what makes the selected response accurate.