Question

in addition to the cell structures described previously, some cells have obvious surface extensions. these come in two major \flavors,\ or varieties, depending on whether they have a core of (1 ) or actin filaments

cilia and flagella

cilia (sil - e - ah, \eyelashes\) are whiplike cellular extensions that move substances along the cell surface. for example, mucus is carried up and away from the lungs by \crowd surfing\ on the ciliated cells lining the (2 ) system. where cilia appear, there are usually many of them projecting from the exposed cell surface.

when a cell is about to make cilia, its centrioles multiply and then line up beneath the plasma membrane at the free cell surface. microtubules then begin to \sprout\ from the (3 ) and put pressure on the membrane, forming the projections.

if the projections formed by the centrioles are substantially longer, they are called flagella (flah - jelah). the only example of a flagellated cell in the human body is the sperm, which has a single propulsive flagellum called its tail (look ahead to figure 3.8g). notice that (4 ) propel other substances across a cells surface, whereas a flagellum propels the cell itself.

microvilli

microvilli (mi kro - vil; \little shaggy hairs\) are tiny, fingerlike extensions of the plasma membrane that project from an exposed cell surface (see figure 3.3). they increase the cells surface area tremendously and so are usually found on the surface of cells active in absorption such as intestinal and kidney tubule cells. microvilli have a core of actin filaments that extend into the internal (5 ) of the cell and stiffen the microvillus. note that microvilli are \alcoves\ projecting off one cell surface and do not involve microtubules.

1 cilia 2 cytoskeleton 3 microtubules 4 respiratory 5 centrioles

1 microtubules 2 respiratory 3 centrioles 4 cilia 5 cytoskeleton

1 respiratory 2 centrioles 3 cilia 4 cytoskeleton 5 microtubules

1 centrioles 2 cilia 3 cytoskeleton 4 microtubules 5 respiratory

Explanation:

1. Cilia and flagella can have a core of microtubules or actin filaments. Microtubules are correct for the first blank.
2. Ciliated cells line the respiratory system and move mucus. So respiratory is for the second blank.
3. Microtubules sprout from centrioles to form cilia - related projections, centrioles for the third blank.
4. Cilia propel substances across a cell's surface, while flagella propel the cell itself, so cilia for the fourth blank.
5. Actin filaments of microvilli extend into the cytoskeleton of the cell, cytoskeleton for the fifth blank.

Answer:

1. microtubules
2. respiratory
3. centrioles
4. cilia
5. cytoskeleton