When bacteria are rod-shaped, they are called :
(a) cocci
(b) bacilli
(c) vibrio
(d) spirilla

Options

A. cocci
B. bacilli
C. vibrio
D. spirilla

Explanation

To solve the question "When bacteria are rod-shaped, they are called:", we can follow these steps:

### Step 1: Understand the Question
The question is asking for the specific term used to describe bacteria that have a rod-like shape.

### Step 2: Identify the Options
We have four options to consider:
- (a) cocci
- (b) bacilli
- (c) vibrio
- (d) spirilla

### Step 3: Recall the Definitions
Now, let's recall what each term means:
- **Cocci**: These are round-shaped bacteria.
- **Bacilli**: These are rod-shaped bacteria.
- **Vibrio**: These are comma-shaped bacteria.
- **Spirilla**: These are spiral-shaped bacteria.

### Step 4: Match the Shape to the Term
From our recall:
- The term that corresponds to rod-shaped bacteria is **bacilli**.

### Step 5: Choose the Correct Option
Based on the definitions, the correct answer to the question is:
**(b) bacilli**

### Final Answer
When bacteria are rod-shaped, they are called **bacilli**.

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