What does selective permeability in cell membranes refer to?

Selective permeability in cell membranes refers to the cell's ability to allow certain substances to pass while restricting others. This characteristic is vital for maintaining homeostasis within the cell, as it enables the regulation of the internal environment by controlling the movement of ions, nutrients, and waste products.

Cell membranes are composed of a phospholipid bilayer with embedded proteins that facilitate this selective process. For instance, small nonpolar molecules can easily diffuse through the membrane, while larger or charged molecules may require specific transport proteins to enter or exit the cell. This selective nature ensures that essential molecules can enter the cell while harmful substances are kept out, creating a controlled internal environment crucial for cellular functions.

In contrast, the other options present different functions that are not specific to the concept of selective permeability. For example, the ability to store energy is related to cellular processes like cellular respiration and the functioning of organelles such as mitochondria, rather than permeability. Protecting the cell from toxins involves various defense mechanisms, which do not directly relate to permeability. Similarly, facilitating cell division pertains to processes such as mitosis and cytokinesis, which are independent of the selective permeability aspect of membranes. Thus, the key focus on selective permeability is its role in regulating what substances can enter and exit