Cilium or flagellum is structurally bilateral due to presence of

Options

A. central sheath
B. Singlet fibrils
C. Double bridge
D. Both B and C

Answer

To solve the question regarding the structural bilateral nature of cilia and flagella, we can break it down into the following steps:

### Step 1: Understand the Structure of Cilia and Flagella
Cilia and flagella are hair-like structures that extend from the surface of many eukaryotic cells. They are primarily composed of microtubules arranged in a specific pattern.

**Hint:** Look for the arrangement of microtubules in cilia and flagella.

### Step 2: Identify the Key Components
The structural arrangement of cilia and flagella includes:
- A central sheath (axoneme) that contains a specific arrangement of microtubules.
- Peripheral microtubules that are organized in pairs.
- Connections between these microtubules known as "double bridges."

**Hint:** Focus on the arrangement of microtubules and their connections.

### Step 3: Analyze the Options Given
The question provides four options:
- a. Central sheath
- b. Single fibrils
- c. Double bridge
- d. Both b and c

From our understanding, the bilateral structure is due to the presence of both the single fibrils (microtubules) and the double bridges connecting them.

**Hint:** Consider how each option relates to the structural features of cilia and flagella.

### Step 4: Determine the Correct Answer
Since cilia and flagella are structurally bilateral due to the presence of both single fibrils (microtubules) and double bridges, the correct answer is option D: both B and C.

**Hint:** Look for the option that includes multiple components contributing to the structure.

### Final Answer
The correct answer is **D: both B and C**.