Final answer:
Cilia are short, hair-like structures used to move cells or substances along the outer surface of the cell, making them the correct answer to the question about projections that propel body fluids. Unlike the longer flagella that move entire cells, cilia can be numerous and cover the cell surface, differentiating them from structures like villi and microvilli, which are involved in absorption. The correct option is A) Cilia
Step-by-step explanation:
Cilia and Flagella
The question pertains to hair-like projections that propel body fluids, and the correct answer is A) Cilia. Cilia are short, hair-like structures that are used to move entire cells or move substances along the outer surface of the cell.
For instance, cilia on the cells lining the respiratory tract help in moving mucus toward the nostrils, thereby playing a crucial role in keeping the airways clear of particulate matter and pathogens.
In contrast, flagella (singular = flagellum) are longer hair-like structures that assist in the movement of the entire cell, like sperm or certain microorganisms.
Both cilia and flagella are composed of microtubules arranged in a 9+2 pattern which is essential for their function. While cilia are numerous and can cover the entire cell surface, flagella are generally fewer in number.
Unlike villi and microvilli, which are involved in absorption and increase the surface area of the cell membrane, cilia are primarily involved in the locomotion and transport of fluids and particles across the cell surface. The correct option is A) Cilia