All are performed in a nephron, except

Options

A. Filtration
B. Secretion
C. Urea synthesis
D. Reabsorption

Answer

To answer the question "All are performed in a nephron, except," we need to identify the processes that occur in the nephron and those that do not. Here’s a step-by-step solution:

### Step 1: Understand the Structure of the Nephron
The nephron is the functional unit of the kidney responsible for the formation of urine. It consists of several parts: the renal corpuscle (which includes the glomerulus and Bowman's capsule) and the renal tubule (which includes the proximal convoluted tubule, loop of Henle, and distal convoluted tubule).

**Hint:** Remember the main components of the nephron and their functions.

### Step 2: Identify the Processes in the Nephron
1. **Filtration**: This occurs in the renal corpuscle, where blood is filtered through the glomerulus into Bowman's capsule. This process removes waste products and excess substances from the blood.

2. **Reabsorption**: This takes place primarily in the proximal convoluted tubule and distal convoluted tubule, where essential substances like glucose, water, and ions are reabsorbed back into the bloodstream.

3. **Secretion**: This process also occurs in the proximal and distal convoluted tubules, where additional waste products and excess ions are secreted from the blood into the tubular fluid.

**Hint:** Focus on the three main processes: filtration, reabsorption, and secretion.

### Step 3: Identify the Process Not Performed in the Nephron
The question asks for the process that is not performed in the nephron. Urea synthesis is the process that does not occur in the nephron; instead, it takes place in the liver. The liver converts ammonia (NH3) into urea through the urea cycle (also known as the ornithine cycle).

**Hint:** Consider where urea is produced in the body and differentiate it from the functions of the nephron.

### Step 4: Conclusion
Based on the above analysis, the correct answer to the question is **urea synthesis**, as all other processes (filtration, reabsorption, and secretion) occur within the nephron.

**Final Answer:** Urea synthesis is not performed in a nephron.