In a bacterium, which structure is primarily responsible for regulating the movement of substances into and out of the cell?

• A. Ribosome
• B. Nucleoid
• C. Cell wall
• D. Plasma membrane

Answer: (D)

Verified step by step guidance

1. Identify the main structures of a bacterial cell and their functions: Ribosome, Nucleoid, Cell wall, and Plasma membrane.
2. Understand that ribosomes are responsible for protein synthesis, not transport of substances.
3. Recognize that the nucleoid contains the bacterial DNA and is involved in genetic information storage, not substance movement.
4. Know that the cell wall provides structural support and protection but does not regulate substance movement.
5. Conclude that the plasma membrane is the structure that controls the movement of substances into and out of the bacterial cell by acting as a selective barrier.