Which one of the following is not a characteristic of active transport?

Options

A. Highly selective
B. Transport saturates
C. Uphill transport
D. Insensitive to inhibitors

Answer

To determine which option is not a characteristic of active transport, we first need to understand the key features of active transport:

1. **Movement Against Concentration Gradient**: Active transport involves the movement of substances from an area of lower concentration to an area of higher concentration. This is contrary to passive transport, which moves substances down their concentration gradient.

2. **Energy Requirement**: Active transport requires energy, typically in the form of ATP, because it is moving substances against their natural flow.

3. **Specificity**: Active transport is highly selective, meaning it uses specific proteins or carrier molecules to transport certain substances.

4. **Saturation**: The rate of active transport can reach a maximum when all available transport proteins are in use, leading to saturation.

5. **Sensitivity to Inhibitors**: Active transport mechanisms are sensitive to inhibitors, which can block the function of the transport proteins.

Now, let's analyze the provided options to identify which one does not align with these characteristics:

- **Highly Selective Transport**: This is a characteristic of active transport.
- **Saturates**: This is also a characteristic of active transport.
- **Uphill Transport**: This describes the process of moving substances against the concentration gradient, characteristic of active transport.
- **Insensitive to Inhibitors**: This is NOT a characteristic of active transport, as active transport is indeed sensitive to inhibitors.

Thus, the correct answer is that "Insensitive to inhibitors" is not a characteristic of active transport.

### Step-by-Step Solution:
1. **Identify the Characteristics of Active Transport**: Understand that active transport moves substances against their concentration gradient and requires energy.
2. **List Key Features**: Note the features such as energy requirement, specificity, saturation, and sensitivity to inhibitors.
3. **Analyze the Options**: Compare each option against the identified characteristics.
4. **Determine the Incorrect Option**: Identify that "Insensitive to inhibitors" contradicts the known characteristics of active transport.