What are the minute finger-like extensions of the plasma membrane that increase the surface area of cells and are used for absorption?

Microvilli are tiny, finger-like projections of the plasma membrane that extend from the surface of certain epithelial cells. Their primary function is to significantly increase the surface area available for absorption, which is especially important in areas of the body that are involved in nutrient uptake, such as the intestines. By increasing the surface area, microvilli enhance the efficiency of absorption, allowing for more nutrients to be taken up as they pass through the digestive tract.

These structures are composed of a core of actin filaments that provide support and stability, and they are often found in large numbers on cells, making the surface appear 'brush-like' or 'fuzzy'. This characteristic is what distinguishes microvilli from other membrane extensions. The other options, while related to cell movement or structure, do not serve the function of increasing surface area specifically for absorption. Cilia and flagella are primarily involved in movement, and pseudopodia are extensions used by certain cells for locomotion and capturing food. Therefore, recognizing the specific role of microvilli in enhancing surface area for absorption is key to understanding their function in the body.