Questions: The periplasmic space is Multiple Choice just external to the LPS layer of the outer membrane. made up of lipopolysaccharides and phospholipids. an important reaction site for substances entering and leaving the cell. absent in gram-negative bacteria. larger in gram-positive bacteria.

The answer is the third one: an important reaction site for substances entering and leaving the cell.

Explanation for each option:

• Just external to the LPS layer of the outer membrane: This is incorrect. The periplasmic space is located between the inner cytoplasmic membrane and the outer membrane in gram-negative bacteria, not just external to the LPS layer.

• Made up of lipopolysaccharides and phospholipids: This is incorrect. The periplasmic space itself is not made up of these components; rather, it contains a gel-like matrix with various proteins and enzymes. Lipopolysaccharides are part of the outer membrane.

• An important reaction site for substances entering and leaving the cell: This is correct. The periplasmic space contains enzymes and proteins that are involved in nutrient processing and transport, making it an important site for reactions related to substances entering and leaving the cell.

• Absent in gram-negative bacteria: This is incorrect. The periplasmic space is a characteristic feature of gram-negative bacteria, not absent in them.

• Larger in gram-positive bacteria: This is incorrect. Gram-positive bacteria do not have a periplasmic space in the same way gram-negative bacteria do; instead, they have a thick peptidoglycan layer. The periplasmic space is more prominent in gram-negative bacteria.