Which of the following are true of archaebacteria?
Presence of peptidoglycan cell wall
Strict aerobes
First amino acid in protein synthesis is methionine
Includes methanogens .

Options

A. 1,2 and 3
B. 3 and 4
C. 1, 3 and 4
D. 1, 2, 3 and 4

Answer

To determine which statements about archaebacteria are true, we will analyze each option provided in the question:

1. **Presence of peptidoglycan cell wall**:
- Archaebacteria do not have a peptidoglycan layer in their cell walls, which is a characteristic feature of true bacteria (Eubacteria). Instead, their cell walls are composed of different non-cellulosic polysaccharides and proteins. Therefore, this statement is **false**.

2. **Strict aerobes**:
- Archaebacteria are not strictly aerobes. They can be aerobes, anaerobes, or facultative anaerobes. For example, methanogens are a type of archaebacteria that are obligate anaerobes. Thus, this statement is also **false**.

3. **First amino acid in protein synthesis is methionine**:
- In archaebacteria, the first amino acid incorporated during protein synthesis is indeed methionine. This is a characteristic feature of archaebacteria and eukaryotes, distinguishing them from eubacteria, where the first amino acid is formylmethionine. Therefore, this statement is **true**.

4. **Includes methanogens**:
- Methanogens are a significant group of archaebacteria that produce methane as a metabolic byproduct in anaerobic conditions. They are commonly found in environments such as swamps and the intestines of ruminants. Therefore, this statement is **true**.

Based on the analysis:
- The true statements about archaebacteria are:
- The first amino acid in protein synthesis is methionine.
- Archaebacteria include methanogens.

Thus, the correct answers are the third and fourth statements.

### Final Answer:
The true statements about archaebacteria are:
- The first amino acid in protein synthesis is methionine.
- They include methanogens.