Final answer:
Cholesterol is another molecule in cell membranes that maintains fluidity and structural integrity. Membrane proteins, such as transport proteins, facilitate substance movement and signal transduction. Carbohydrates attached to proteins or lipids are involved in cell recognition and adhesion.
Step-by-step explanation:
Besides phospholipids, cholesterol is another molecule that can be found within cell membranes. Cholesterol performs several critical functions in the cell membrane. Primarily, it helps to maintain the fluidity of the membrane, enabling it to remain flexible and functional across various temperatures. Cholesterol also contributes to the structural integrity of the membrane, preventing it from becoming too fluid or too rigid.
In addition to cholesterol, membrane proteins play a pivotal role within the cell membrane. These proteins serve a diverse set of functions including acting as receptors for signal transduction, providing structural support, facilitating cell-cell recognition and adhesion, and aiding in the transport of substances across the membrane. Transport proteins, for example, help move ions and molecules that cannot pass through the lipid bilayer on their own, either through channels or via active transport mechanisms.
It's also important to note the presence of carbohydrates in the cell membrane. Though not as abundant as phospholipids or proteins, carbohydrates are often found attached to proteins (glycoproteins) or lipids (glycolipids) on the extracellular surface of the membrane. They are primarily involved in cell recognition and adhesion processes, playing a key role in immune responses and interactions between cells.