Explain the association of carbohydrates with the plasma membrane and their significance.

(N/A) $\Rightarrow$ Carbohydrates account for approximately $2-10 \%$ of the total mass of the plasma membrane. They are covalently linked to proteins (forming glycoproteins) or lipids (forming glycolipids).
$\Rightarrow$ Cellular identification: The specific arrangement of carbohydrate chains on the surface of cells,such as $RBCs$,determines blood group antigens,which are crucial for cell-cell recognition.
$\Rightarrow$ Biological significance: These carbohydrate moieties act as receptors for hormones,neurotransmitters,and signaling molecules. They also play a vital role in the interaction of cells with viruses,bacteria,and various drugs,ensuring the specificity of cellular responses.