The phospholipid bilayer ensures that the ______ remains outside the cell.

• A. mitochondria
• B. extracellular fluid
• C. nucleus
• D. cytoplasm

Answer: (B)

Verified step by step guidance

1. Understand the structure and function of the phospholipid bilayer: The phospholipid bilayer is a fundamental component of the cell membrane. It is composed of two layers of phospholipids, with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward. This structure creates a selective barrier for the cell.
2. Recognize the role of the phospholipid bilayer in maintaining the internal and external environments of the cell: The bilayer separates the intracellular environment (inside the cell) from the extracellular environment (outside the cell).
3. Identify the term 'extracellular fluid': This refers to the fluid that exists outside the cell, which includes water, ions, and other molecules. The phospholipid bilayer ensures that this fluid remains outside the cell while regulating the movement of substances in and out.
4. Eliminate incorrect options: The mitochondria and nucleus are organelles located inside the cell, and the cytoplasm is the gel-like substance within the cell that surrounds these organelles. None of these are external to the cell.
5. Conclude that the correct answer is 'extracellular fluid,' as it is the only option that refers to the environment outside the cell, which the phospholipid bilayer helps to maintain.