Which process in the nephron is least selective? a. filtration b. reabsorption c. active transport d. secretion

Verified step by step guidance

1. Step 1: Understand the question. The question is asking which process in the nephron is least selective. The nephron is the functional unit of the kidney, responsible for filtering blood and forming urine. The processes involved include filtration, reabsorption, active transport, and secretion.
2. Step 2: Understand the processes. Filtration is the process where blood pressure forces water and other small molecules through a selectively permeable membrane. Reabsorption is the process where certain molecules and ions are reabsorbed back into the blood. Active transport is the process where molecules move against a concentration gradient, requiring energy. Secretion is the process where substances are transported from blood into the filtrate.
3. Step 3: Evaluate the selectivity of each process. Filtration is not very selective, as it allows all small molecules to pass through. Reabsorption is selective, as only certain molecules are reabsorbed. Active transport is also selective, as it requires specific carrier proteins. Secretion is selective, as it involves the transport of specific substances.
4. Step 4: Compare the selectivity of the processes. Among the four processes, filtration is the least selective because it allows all small molecules to pass through, regardless of their type.
5. Step 5: Choose the correct answer. Therefore, the answer is (a) filtration.

Key Concepts

Filtration

Filtration is the first step in urine formation that occurs 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. This process is relatively non-selective, allowing a wide range of substances to pass while retaining larger molecules like proteins and blood cells.

Reabsorption

Reabsorption is the process by which the nephron selectively reclaims water and essential solutes from the filtrate back into the bloodstream. This occurs primarily in the proximal convoluted tubule and loop of Henle, where specific transport mechanisms ensure that vital nutrients and a significant amount of water are conserved, making it a highly selective process.

Active Transport

Active transport is a cellular process that moves substances against their concentration gradient, requiring energy in the form of ATP. In the nephron, this mechanism is crucial for reabsorbing ions like sodium and potassium, as well as other molecules, ensuring that essential nutrients are retained while waste products are excreted. This process is highly selective, as it targets specific molecules for transport.