Microvilli are found
(a) Mostly in muscle cells
(b) On the inside of plasma membranes
(c) In large numbers on cells that secrete hormones
(d) In cells that are actively engaged in absorption
(e) Only on cells lining the reproductive tract

Verified step by step guidance

1. Understand what microvilli are: Microvilli are microscopic cellular membrane protrusions that increase the surface area of cells, enhancing their ability to absorb substances.
2. Recall the primary function of microvilli: They are mainly involved in absorption rather than secretion or muscle contraction.
3. Identify the types of cells where absorption is critical: Cells lining the small intestine and kidney tubules have many microvilli to maximize nutrient and ion absorption.
4. Evaluate each option based on this knowledge: (a) Muscle cells are primarily for contraction, not absorption; (b) Microvilli are on the surface of plasma membranes but specifically where absorption occurs; (c) Cells that secrete hormones typically have other specializations, not microvilli; (d) Cells actively engaged in absorption have numerous microvilli; (e) Microvilli are not limited to reproductive tract cells.
5. Conclude that the correct answer corresponds to cells with high absorption activity, which is option (d).

Key Concepts

Microvilli Structure and Function

Microvilli are tiny, finger-like projections on the surface of certain cells that increase the surface area for absorption. They are covered by the plasma membrane and contain actin filaments for structural support, enhancing the cell's ability to absorb nutrients efficiently.

Cell Types with Microvilli

Microvilli are predominantly found on epithelial cells involved in absorption, such as those lining the small intestine and kidney tubules. These cells use microvilli to maximize nutrient and ion uptake from their environment.

Difference Between Microvilli and Other Cell Surface Structures

Microvilli differ from cilia and flagella in both structure and function; while microvilli increase surface area for absorption, cilia are involved in movement of substances across the cell surface. Understanding this distinction helps identify where microvilli are typically located.