Which process in the nephron is least selective?
a. Secretion
b. Reabsorption
c. Filtration
d. Passive diffusion of salt

Verified step by step guidance

1. Understand the function of the nephron: The nephron is the functional unit of the kidney responsible for filtering blood and forming urine. It involves processes such as filtration, reabsorption, secretion, and passive diffusion.
2. Define filtration: Filtration occurs in the glomerulus, where blood plasma and small solutes are pushed through the filtration membrane into the Bowman's capsule. This process is driven by blood pressure and is non-selective, meaning it does not discriminate between useful substances and waste products.
3. Compare filtration to other processes: Secretion involves the active transport of specific substances (e.g., toxins, drugs) from the blood into the nephron. Reabsorption is highly selective, as it involves the active or passive transport of specific substances (e.g., glucose, water, ions) back into the blood. Passive diffusion of salt is selective based on concentration gradients and membrane permeability.
4. Identify the least selective process: Filtration is the least selective process because it allows all small molecules (both useful and waste) to pass through the filtration membrane indiscriminately, unlike secretion, reabsorption, or passive diffusion, which involve specific mechanisms or gradients.
5. Conclude the answer: Based on the definitions and comparisons, filtration is the least selective process in the nephron.

Key Concepts

Nephron Function

The nephron is the functional unit of the kidney, responsible for filtering blood and forming urine. It consists of several parts, including the glomerulus, proximal tubule, loop of Henle, distal tubule, and collecting duct. Each part plays a specific role in the processes of filtration, reabsorption, and secretion, which are essential for maintaining fluid and electrolyte balance in the body.

Filtration

Filtration is the first step in urine formation, occurring in the glomerulus of the nephron. During this process, blood pressure forces water and small solutes, such as ions and glucose, through the glomerular membrane into the Bowman's capsule, forming the filtrate. This process is relatively non-selective, allowing a wide range of substances to pass while retaining larger molecules like proteins and blood cells.

Reabsorption vs. Secretion

Reabsorption and secretion are two key processes that occur after filtration. Reabsorption involves the selective uptake of water and solutes back into the bloodstream from the renal tubules, allowing the body to retain essential nutrients. In contrast, secretion is the active transport of substances from the blood into the tubular fluid, which helps eliminate waste products. While both processes are selective, filtration is the least selective, as it allows a broader range of substances to enter the nephron.