Those organism which cannot use oxygen for growth and are even harmed by its presence, are known as

Options

A. Obligate aerobes
B. Aerotolerant anaerobes
C. Facultative anaerobes
D. Obligate anaerobes

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the classification of organisms that cannot use oxygen for growth and are harmed by its presence.

2. **Classification of Organisms Based on Oxygen Requirement**:
- Organisms are categorized into two main groups based on their oxygen requirements: **aerobes** and **anaerobes**.
- **Aerobes**: These organisms require oxygen for survival.
- **Anaerobes**: These organisms do not require oxygen for survival.

3. **Subcategories of Aerobes**:
- **Obligate Aerobes**: Organisms that can only survive in the presence of oxygen. They will die if oxygen is not available.
- **Facultative Anaerobes**: Organisms that can survive with or without oxygen. They prefer oxygen but can tolerate its absence.

4. **Subcategories of Anaerobes**:
- **Obligate Anaerobes**: Organisms that can only survive in the absence of oxygen. They are harmed by its presence.
- **Aerotolerant Anaerobes**: Organisms that do not use oxygen for growth but can tolerate its presence without being harmed.

5. **Identifying the Correct Answer**:
- The question specifically mentions organisms that cannot use oxygen for growth and are harmed by its presence. This description fits **obligate anaerobes** perfectly, as they thrive only in environments devoid of oxygen and are negatively affected by it.

6. **Conclusion**: Therefore, the correct answer to the question is **obligate anaerobes**.