Which structures are extensions of the plasma membrane that increase surface area?

Which structures are extensions of the plasma membrane that increase surface area?

• A. Microvilli
• B. Cilia
• C. Microtubules
• D. Flagella

Answer: (A)

Extensions of the plasma membrane that boost surface area are fingerlike projections called microvilli. These tiny protrusions line many absorptive surfaces, especially the intestinal lining, and are supported by actin filaments. Their dense packing increases the membrane area available for nutrient uptake and secretion, making absorption more efficient. Cilia are also membrane extensions, but their main job is to move fluids or cells across the surface or to act as sensory structures—not to enlarge surface area. Microtubules are components of the cytoskeleton inside the cell and don’t form outward membrane projections. Flagella are longer projections used for locomotion, enabling movement rather than maximizing surface area.

Extensions of the plasma membrane that boost surface area are fingerlike projections called microvilli. These tiny protrusions line many absorptive surfaces, especially the intestinal lining, and are supported by actin filaments. Their dense packing increases the membrane area available for nutrient uptake and secretion, making absorption more efficient.

Cilia are also membrane extensions, but their main job is to move fluids or cells across the surface or to act as sensory structures—not to enlarge surface area. Microtubules are components of the cytoskeleton inside the cell and don’t form outward membrane projections. Flagella are longer projections used for locomotion, enabling movement rather than maximizing surface area.