Practice important
Cellular Junctions
MCQ questions and answers.
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MCQ Questions
1. A sheet of epithelial cells must prevent substances from passing through the intercellular space between adjacent cells. Which junction is most directly responsible for this function?
A.
Gap junction
B.
Tight junction
C.
Adhering junction
D.
Synaptic junction
Correct Answer:
Tight junction
Explanation:
Tight junctions seal the intercellular spaces between adjacent epithelial cells and prevent leakage of substances through the paracellular pathway.
2. Two neighboring epithelial cells remain firmly attached because specialized junctions cement their plasma membranes together. Which junction is being described?
A.
Gap junction
B.
Tight junction
C.
Adhering junction
D.
Ciliary junction
Correct Answer:
Adhering junction
Explanation:
Adhering junctions cement neighboring epithelial cells together and provide mechanical attachment between them.
3. An epithelial cell receives small signaling molecules directly from an adjacent cell through intercellular channels. Which cellular junction enables this exchange?
A.
Tight junction
B.
Adhering junction
C.
Gap junction
D.
Basal junction
Correct Answer:
Gap junction
Explanation:
Gap junctions form intercellular channels that allow small molecules and ions to pass directly between neighboring cells, facilitating communication.
4. A mutation causes epithelial cells to lose their ability to seal the spaces between them, although the cells remain mechanically attached. Which function has most likely been impaired?
A.
Direct intercellular communication
B.
Prevention of leakage across the epithelial layer
C.
Cementing of adjacent cells
D.
Production of extracellular enzymes
Correct Answer:
Prevention of leakage across the epithelial layer
Explanation:
The sealing of intercellular spaces is the characteristic function of tight junctions. Adhering junctions can maintain attachment even if sealing is defective.
5. Which combination correctly matches a cellular junction with its principal function in epithelial tissue?
A.
Tight junction—direct passage of ions between cells
B.
Gap junction—prevention of paracellular leakage
C.
Adhering junction—cementing neighboring cells together
D.
Adhering junction—secretion of mucus into the lumen
Correct Answer:
Adhering junction—cementing neighboring cells together
Explanation:
Adhering junctions strengthen contact between adjacent epithelial cells by cementing them together. Gap junctions mediate communication, while tight junctions prevent leakage.
6. In an epithelial barrier, one junction type provides selective sealing while another allows neighboring cells to communicate directly. Which pair correctly identifies these junctions in that order?
A.
Gap junction and tight junction
B.
Adhering junction and gap junction
C.
Tight junction and gap junction
D.
Tight junction and adhering junction
Correct Answer:
Tight junction and gap junction
Explanation:
Tight junctions seal the space between adjacent cells, whereas gap junctions form channels for direct intercellular communication.
7. If gap junctions in an epithelial sheet are selectively blocked, which immediate cellular function would be most affected while the barrier against intercellular leakage remains comparatively intact?
A.
Direct exchange of signaling molecules between cells
B.
Cementing of adjacent cells
C.
Sealing of the intercellular space
D.
Attachment of the epithelium to the basement membrane
Correct Answer:
Direct exchange of signaling molecules between cells
Explanation:
Gap junctions enable direct passage of small molecules and ions between adjacent cells. Tight junctions, rather than gap junctions, maintain the sealing barrier.
8. Which experimental observation most strongly indicates the presence of functional tight junctions in an epithelial layer?
A.
Small ions pass rapidly from one cell to another
B.
Adjacent cells remain attached under mild mechanical stress
C.
A marker placed on one side shows minimal movement through spaces between cells
D.
Cells release hormones into the bloodstream
Correct Answer:
A marker placed on one side shows minimal movement through spaces between cells
Explanation:
Functional tight junctions restrict movement through the intercellular spaces, so a marker shows little paracellular passage across the epithelial layer.
9. An epithelial tissue loses both strong cell-to-cell adhesion and intercellular communication but still restricts passage through the spaces between cells. Which junction remains functional?
A.
Gap junction
B.
Adhering junction
C.
Tight junction
D.
Neuronal junction
Correct Answer:
Tight junction
Explanation:
Tight junctions are responsible for sealing intercellular spaces. Loss of adhering junctions would weaken attachment, and loss of gap junctions would impair direct communication.
10. Why can an epithelial sheet show both strong physical cohesion and rapid coordination of neighboring cells?
A.
Adhering junctions provide cohesion, while gap junctions provide communication
B.
Tight junctions provide cohesion, while adhering junctions provide communication
C.
Gap junctions provide cohesion, while tight junctions provide communication
D.
Tight junctions provide cohesion, while gap junctions prevent all molecular exchange
Correct Answer:
Adhering junctions provide cohesion, while gap junctions provide communication
Explanation:
Adhering junctions attach neighboring cells firmly, whereas gap junctions allow direct transfer of small molecules and ions for intercellular communication.
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Cellular Junctions
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