Which portion of the nephron has cells with a brush border and many mitochondria? a. glomerular capsule b. proximal convoluted tubule c. loop of the nephron d. distal convoluted tubule e. collecting duct

A nephron is the basic functional unit of the kidney, responsible for filtering blood and producing urine. It is composed of several parts: a. glomerular capsule: a double-walled cuplike structure that surrounds the glomerulus; it's involved in filtering the blood. b. proximal convoluted tubule: a twisted tube-like structure responsible for reabsorbing water, ions, and essential nutrients. c. loop of the nephron (Loop of Henle): U-shaped structure responsible for concentrating the filtrate (urine) and regulating the ionic balance in the blood. d. distal convoluted tubule: another twisted tube-like structure responsible for further reabsorption and secretion processes. e. collecting duct: the final part of the nephron that transports the urine to the renal pelvis and helps in conserving water. Let's evaluate each part to see which one has cells with a brush border and many mitochondria.

Brush border refers to the microvilli, which are tiny, fingerlike projections on the cell surface that increase the surface area and hence their absorption capacity. This characteristic is more important in a part where there is a higher requirement of reabsorption and energy production to fuel this process. Many mitochondria indicate that cells require more energy for specific functions. Based on the knowledge of the functions of nephron parts, we can determine that the proximal convoluted tubule (b) is where extensive reabsorption takes place. This makes it the part with cells having a brush border and many mitochondria. Thus, the correct answer is: b. proximal convoluted tubule