Final answer:
True. Only Gram-negative bacteria possess an outer membrane, which contains lipopolysaccharides and has features like porins and efflux pumps. Gram-positive bacteria have a thick peptidoglycan cell wall without an outer membrane.
Step-by-step explanation:
The statement that only Gram-negative bacteria possess an outer membrane is true. These bacteria are characterized by having a thin peptidoglycan layer that is located between the inner cytoplasmic membrane and an additional outer membrane containing lipopolysaccharides (LPS) and lipoproteins. Gram-positive bacteria, in contrast, have a single, thick cell wall made of peptidoglycan and do not possess an outer membrane. Their cell walls are anchored to the cell membrane by lipoteichoic acid. In addition, Gram-negative bacteria have porins and efflux pumps in their outer membrane that facilitate the passage of substances and can contribute to antibiotic resistance.