The principal components of the plasma membrane are lipids (phospholipids and cholesterol), proteins, and carbohydrates. The plasma membrane protects intracellular components from the extracellular environment. The plasma membrane mediates cellular processes by regulating the materials that enter and exit the cell.
Members of the Shudra caste, for example, are relegated to performing hard physical work regardless of their skill, intelligence, or ambition. Those born into the Brahman caste must attend university or become a member of the clergy, even though they may show no interest or aptitude toward that end.
Historians later called this the caste system. Caste members lived, ate, married, and worked with their own group. A person born into one caste rarely changed castes or mixed with members of other castes. Social rules defined how to behave within a caste and when in the presence people from other castes.