Final answer:
In gram-negative microbes, a peptidoglycan layer lies between the inner plasma membrane and the outer membrane, which contains lipopolysaccharide.
Step-by-step explanation:
The space between the membrane of gram-negative microbes contains several components. Just outside the plasma membrane, there is a peptidoglycan layer, which is much thinner in gram-negative bacteria when compared to gram-positive bacteria. This peptidoglycan layer is located within the periplasmic space. Surrounding this thin peptidoglycan layer is an additional lipid bilayer known as the outer membrane. A significant aspect of this outer membrane is the presence of lipopolysaccharide (LPS), which is a molecule that functions as an endotoxin and can contribute to severe symptoms during infections caused by gram-negative bacteria. Therefore, the correct answer to what lies between the membranes of gram-negative microbes is a) Peptidoglycan layer.