ANSWERS TO CHAPTER THREE 1. Answer: a. Almost all tight junctions exist in epithelial tissue. Their main function is to act as barriers to diffusion across the cells. They form watertight barriers between epithelial and endothelial cells. 2. Answer: c. Tight junctions are nearly impermeable to anything, which is why they are used for things like sealing the endothelium of blood vessels and the epithelium of the GI tract. Their lack of impermeability can lead to things like leaky gut syndrome. 3. Answer: a. The kidneys and GI tract have relatively permeable tight junctions, whereas in the brain, retina, bladder, and skin, the tight junctions are impermeable to most things. 4. Answer: c. The desmosomes are found in tissues that are under stress of some kind, particularly mechanical stress. The brain does not experience this type of mechanical stress so they will not use these types of cell adhesions. 5. Answer: c. Hemidesmosomes are similar to desmosomes in appearance but use integrin proteins in order to connect a cell to the basement membrane. 6. Answer: d. There are many types of collagen; however, type VII collagen is most associated with the formation of the basement membrane. 7. Answer: d. Collagen is laid out as a triple helix; it is laid out in long, thin strands wrapped around each other. 8. Answer: b. Collagen fibers are extremely strong so that their main purpose in connective tissue is to provide tensile strength in the tissue. 9. Answer: b. Gap junctions are extremely similar to plasmodesmata in plant cells. Both are able to allow for communication between the neighboring cells. 10. Answer: a. These plasmodesmata are direct channels between cells so that the small molecules get between the cells via simple diffusion.
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