Which one of the following organisms may respire in the absence of oxygen

Options

A. Azotobacter
B. Clostridium
C. Rhizobium
D. Lactobacillus

Answer

To determine which organisms can respire in the absence of oxygen, we need to classify the given options based on their oxygen requirements. Here’s a step-by-step solution:

### Step 1: Understand the Types of Organisms
- **Aerobic Organisms**: These organisms require oxygen for respiration and cannot survive without it.
- **Anaerobic Organisms**: These organisms can survive and respire in the absence of oxygen. They can be further classified into:
- **Strict Anaerobes**: Cannot tolerate oxygen at all.
- **Facultative Anaerobes**: Can survive with or without oxygen.

### Step 2: Analyze Each Option
1. **Azotobacter**:
- This organism is known to be aerobic. It requires oxygen for its metabolic processes.
- **Conclusion**: Azotobacter cannot respire in the absence of oxygen.

2. **Clostridium**:
- Clostridium is classified as a strict anaerobe. It thrives in environments devoid of oxygen.
- **Conclusion**: Clostridium can respire in the absence of oxygen.

3. **Rhizobium**:
- Rhizobium is an aerobic bacterium. It requires oxygen for its survival and metabolic functions.
- **Conclusion**: Rhizobium cannot respire in the absence of oxygen.

4. **Lactobacillus**:
- Lactobacillus is a facultative anaerobe. It can grow in both the presence and absence of oxygen.
- **Conclusion**: Lactobacillus can respire in the absence of oxygen.

### Step 3: Identify the Correct Answers
- From the analysis:
- **Clostridium** is a strict anaerobe and can respire without oxygen.
- **Lactobacillus** is a facultative anaerobe and can also respire without oxygen.

### Final Answer:
The organisms that can respire in the absence of oxygen are **Clostridium** and **Lactobacillus**.

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