Final answer:
The selectively permeable cell membrane utilizes transport proteins to retain large molecules like sugars and proteins, and requires energy in the form of ATP to actively transport vital ions. This selectivity is crucial for cell survival.
Step-by-step explanation:
The selectively permeable cell membrane retains large molecules by utilizing protein molecules within the phospholipid bilayer, which are essential for the transport across cell membranes. Large molecules such as sugars and proteins are typically unable to pass freely through the lipid bilayer due to their size or polarity. However, transport proteins embedded in the cell membrane allow for the selective passage of these larger molecules, as well as ions that cannot pass through the hydrophobic interior of the bilayer.
Cells also invest energy to maintain the proper balance of substances, using energy obtained by hydrolyzing adenosine triphosphate (ATP) for the active transport of vital ions like sodium and potassium, as well as for synthesizing proteins. This selective permeability of the plasma membrane is vital for cellular homeostasis and function. If the selectivity of the cell membrane was lost, it would lead to the destruction of the cell.