Reabsorption of amino acids in the filtrate is facilitated by
a) Active transport
b) Passive transport
c) Diffusion
d) Facilitated transport

Options

A. Active transport
B. Passive transport
C. Diffusion
D. Facilitated transport

Answer

To solve the question regarding the reabsorption of amino acids in the filtrate, we need to analyze the transport mechanisms involved in this process.

### Step-by-Step Solution:

1. **Understanding Filtration in the Kidneys**:
- The kidneys filter blood to form urine, and during this process, various substances, including amino acids, are filtered out into the nephron.

2. **Reabsorption Process**:
- After filtration, the nephron reabsorbs essential substances back into the bloodstream. This includes glucose, ions, and amino acids.

3. **Transport Mechanisms**:
- There are different mechanisms for reabsorption: active transport, passive transport, diffusion, and facilitated transport.
- **Active Transport**: This process requires energy (ATP) to move substances against their concentration gradient.
- **Passive Transport**: This process does not require energy and occurs along the concentration gradient.
- **Diffusion**: A type of passive transport where substances move from an area of higher concentration to an area of lower concentration.
- **Facilitated Transport**: This is a type of passive transport that uses specific carrier proteins to help move substances across cell membranes.

4. **Specific Mechanism for Amino Acids**:
- Amino acids are reabsorbed primarily through **active transport** mechanisms in the proximal convoluted tubule of the nephron. This is because their concentration in the filtrate is lower than in the blood, necessitating energy to move them back into the bloodstream.

5. **Conclusion**:
- Therefore, the correct answer to the question is **a) Active transport**.

### Final Answer:
**a) Active transport**