Final answer:
The statement that human and sheep kidneys are very similar in size and structure is false. While both kidneys have the same general function and comparable parts, there are species-specific differences in size and anatomical details, such as the number of nephrons and the size of the renal cortex and medulla.
Step-by-step explanation:
The statement that the human kidney and the sheep kidney are very similar in both size and structural anatomy is generally false. Though both kidneys serve the same primary function of filtering blood and producing urine, and might appear superficially similar, their size and anatomical details can differ significantly. The size of a sheep's kidney compared to a human's varies based on the breed and size of the sheep. Additionally, while the general structure of kidneys across mammals is comparable, due to a common evolutionary history, there can be species-specific variations in the detail of the structure and the relative size of the different areas of the kidney.
For instance, kidneys from different species can have variations in the number of nephrons, the microscopic units of filtration within the kidney. Nephrons consist of a renal corpuscle and a series of tubules, and while all mammalian kidneys will have these structures, the exact structure and efficiency can vary.
The gross anatomy of the kidney also includes the cortex, medulla, and renal pelvis. The renal cortex is a peripheral rim wherein numerous nephrons' renal corpuscles are located, while the renal medulla contains the loops of Henle, also part of the nephron but involved in the concentration of urine. The renal pelvis collects urine before it passes to the ureter. These anatomical features are present in both human and sheep kidneys, but again, their size and the number of functional units may differ between the two species.