Question

the plasma membrane is composed of a phospholipid bilayer with embedded proteins. what is one of the functions of the embedded proteins?
a. defining the cell’s structure and shape
b. allowing specific substances to flow into the cell
c. preventing the phospholipid tails from binding together
d. protecting the cell from physical harm

Explanation:

• Option A: The cell's structure and shape are mainly defined by the cytoskeleton and the cell wall (in some cells), not embedded membrane proteins.
• Option B: Embedded proteins in the plasma membrane, like channel proteins or carrier proteins, function as transporters to allow specific substances (e.g., ions, nutrients) to move into or out of the cell. This is a key function of membrane - embedded proteins.
• Option C: The phospholipid tails are hydrophobic and tend to avoid water, but they don't bind together in a way that needs to be prevented by embedded proteins. The fluid - mosaic model of the membrane explains the arrangement of phospholipids and proteins, and preventing phospholipid tails from binding is not a function of embedded proteins.
• Option D: The plasma membrane as a whole provides a barrier, but protecting the cell from physical harm is not a specific function of the embedded proteins. The cell wall (in plant cells) or the extracellular matrix may have more to do with physical protection, and the membrane proteins are not primarily for this.

Answer:

B. allowing specific substances to flow into the cell