Water channels are

Options

A. Made up of eight similar types of aquaporins
B. Involved in active transport
C. Involved in facilitated diffusion
D. More than one option is correct

Answer

### Step-by-Step Text Solution:

1. **Definition of Water Channels**: Water channels are specialized proteins known as aquaporins. They facilitate the movement of water across cell membranes.

2. **Structure of Aquaporins**: Aquaporins are integral membrane proteins that form channels in the biological membranes of cells. In the context of the question, it is mentioned that there are eight similar types of aquaporins present in the biological membrane.

3. **Function of Aquaporins**: The primary function of aquaporins is to allow the passive transport of water molecules. This process is known as facilitated diffusion, where water moves through the aquaporin channels without the need for energy input.

4. **Active Transport vs. Facilitated Diffusion**: It is important to note that aquaporins do not involve active transport. Active transport requires energy to move substances against their concentration gradient, while aquaporins operate through facilitated diffusion, allowing water to move down its concentration gradient.

5. **Conclusion**: Based on the information provided, the correct statements about water channels (aquaporins) are that they are made up of eight similar types of aquaporins and are involved in facilitated diffusion. Therefore, the correct answer to the question is that more than one option is correct.