AP Biology : Understanding Types of Cellular Junctions

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Understanding Types Of Cellular Junctions

Plasmodesmata in plant cells are analogous to what structure in animal cells?

Possible Answers:

Vacuoles

Gap junctions

Tight junctions

Desmosomes

Correct answer:

Gap junctions

Explanation:

In animal cells, gap junctions allow materials such as ions to flow directly from the cytoplasm of one cell to that of the next. They can be thought of as channels, or "bridges" between cells. Gap junctions are common in the muscle tissue of animals' hearts, for example, as they allow ions to pass rapidly from cell to cell to coordinate cardiac muscle contraction. Plasmodesmata connect plant cells to one another in the same way, and they enable rapid transport and communication between adjacent cells. 

Desmosomes are another type of cell junction found in animal cells, though they "rivet" cells together instead of forming a channel; they most frequently prevent epithelial and some muscle cells from shearing apart.

Tight junctions form an even tighter seal than those formed by desmosomes. They form a bond that is almost completely impermeable to fluid. Tight junctions join cells together, and also help regulate the movement of molecules and ions.

Vacuoles are not a type of cell junction at all. These organelles are found in plant cells and are used for storage, digestion, and the filling of space. 

 

Example Question #1 : Understanding Types Of Cellular Junctions

Urine is confined to the human bladder in part due to the structure of junctions that connect the cells lining the bladder. These junctions form a barrier that prevents the exchange of ions and solutes between the blood and urine. What is the likely identity of these junctions?

Possible Answers:

Desmosomes

Gap junctions

Plasmodesmata

Tight junctions

Correct answer:

Tight junctions

Explanation:

Tight junctions commonly line organs such as the urinary bladder, as they prevent unwanted fluid from leaking into or out of these organs. They are most notable for their barrier function: they are almost completely impermeable to fluid.

Though desmosomes also join cells together, they are more commonly found connecting cells that are subject to mechanical stress, such as muscles or the outer layer of skin. They are comparable to a button or a rivet, and do not connect cells as tightly to one another as tight junctions do. Gap junctions are essentially channels between cells that enable the rapid transport of ions and other solutes between the cytoplasm of neighboring cells; they would not help keep urine within the urinary bladder. Plasmodesmata are only found in plants (they are analogous to gap junctions) and would therefore have no business forming a human bladder.

Example Question #2 : Understanding Types Of Cellular Junctions

What type of cell junction would most likely be found in the intestinal tract?

Possible Answers:

Desmosomes

Gap junctions

Plasmodesmata

All of these would be found in the intestinal tract

Tight junction

Correct answer:

Tight junction

Explanation:

Within the digestive tract, it is important for nutrients and toxins to remain contained within the organs to allow for proper absorption. Furthermore, the acidity and basicity of various regions of the digestive tract must be kept partitioned from the rest of the body. Tight junctions are found between most cells of the digestive tract. This type of cell junction prevents movement of material between cells, requiring it to actually move into cells via diffusion or active transport in order to pass through tissue.

Gap junctions are intercellular junctions that connect the cytoplasm of adjacent cells and are particularly important for signaling. Desmosomes are structures specialized for cell-to-cell adhesion and force transmission. Plasmodesmata are transport and communication channels in plant cells, analogous to gap junctions.

Example Question #3 : Understanding Types Of Cellular Junctions

Which type of cellular junction is prominent in cardiac myocytes and allows for a unified contraction of the heart?

Possible Answers:

Desmosomes

Tight junctions

Plasmodesmata

Gap junctions

Correct answer:

Gap junctions

Explanation:

Cardiac myocytes (muscle cells) need to be able to contract in unison in order to ensure proper pumping of blood. This is accomplished by specialized junctions called gap junctions that allow cells to communicate with one another very quickly. These junctions join the cytoplasms of adjacent cells, allowing ions to flow between them. When one cardiac cell is depolarized, the gap junctions found in intercalated discs allow the depolarization to jump from cell to cell.

Plasmodesmata are structurally analogous to gap junctions, but are located in plant cells.

Example Question #5 : Understanding Types Of Cellular Junctions

Why are gap junctions crucial to the anatomy and physiology of the heart?

Possible Answers:

They allow passage of glucose and oxygen into the cardiac cells, providing energy sources to cells that are not well perfused by coronary arteries

They allow fast passage of ions from cell to cell, enabling the cells of the heart chambers to contract almost simultaneously

They maintain a gap between cardiac muscle cells, preventing friction as the cells contract and relax

They maintain a gap between the cardiac muscle cells, preventing crush injuries to the coronary arteries during regular contraction and relaxation

Correct answer:

They allow fast passage of ions from cell to cell, enabling the cells of the heart chambers to contract almost simultaneously

Explanation:

Gap junctions are formed by connexons—rings of proteins that spans the membranes of two adjacent cells. The ring surrounds a pore that allows ions, among other substances, to pass between the cells uninterrupted. The result is a quick transmission of the electrochemical signal for cardiac muscle cell contraction, so that the cells contract essentially together. Gap junctions can also be found in numerous other tissue types, but not in skeletal muscle.

Example Question #4 : Understanding Types Of Cellular Junctions

Which of these correctly matches the cellular junction with its function?

Possible Answers:

Gap junctions are connections that directly connect the cytoplasm of two cells

Desmosomes are connections that directly connect the cytoplasm of two cells

Gap junctions prevent the flow of ions and water from one part of the body to another

Desmosomes are branched network of proteins that are impermeable to fluids

Tight junctions are random, spot attachments between cells that prevent tearing of tissue

Correct answer:

Gap junctions are connections that directly connect the cytoplasm of two cells

Explanation:

Gap junctions allow the flow of water and ions. They are seen in the heart muscle cells, to allow quick electrical conduction from one cell to another, which is observed as a wavelike contraction of the heart. Tight junctions are networks of spot attachments that are impermeable to fluids. Desmosomes are random, spot attachments that are responsible for cell-cell adhesion.

Example Question #5 : Understanding Types Of Cellular Junctions

Cellular junctions allowing cytoplasm and ion exchange between adjacent cells are known as __________?

Possible Answers:

tight junctions

hemidesmosomes

occluding junctions

desmosomes

gap junctions

Correct answer:

gap junctions

Explanation:

Gap junctions form pores connecting neighboring cells and allowing the mixture of cytoplasm and small solutes including ions. Desmosomes are specialized for cell-cell adhesion, and hemidesmosomes are specialized for cell-extracellular matrix adhesion. Tight junctions (occluding junctions) form a seal across a layer of cells and is virtually impermeable. 

Example Question #8 : Understanding Types Of Cellular Junctions

Which of the following are able to pass through a gap junction from one cell to another?

Possible Answers:

Polysaccharides

Enzymes

Ions

Genetic material

Correct answer:

Ions

Explanation:

Gap junctions are protein channels that span the intercellular space that connect two cells. They allow cytoplasmic exchange in animal cells. The diameter of gap junctions limits what is able to travel though them from one cell to another. Ions, amino acids, and small molecules can flow through gap junctions; however, proteins, polysaccharides, and nucleic acids cannot. Gap junctions allow the transfer of small molecules to direct communication and cellular activities.

Example Question #6 : Understanding Types Of Cellular Junctions

Which of the following choices identifies the plant structure that corresponds to gap junctions in animal cells?

Possible Answers:

Plasmodesmata

Synapse

Membrane pore

Pilus

Correct answer:

Plasmodesmata

Explanation:

Plasmodesmata are the plant structures that are analogous to gap junctions in animal cells. Plasmodesmata are protein channels between the cell walls of plant cells. They facilitate communication and the transport of solutes and small proteins between plant cells.

Example Question #7 : Understanding Types Of Cellular Junctions

What type of cellular junctions would form between two cells attached to each other that would need to exchange products?

Possible Answers:

Tight junctions

Hemidesmosome

None of these

Desmosomes

Gap junctions

Correct answer:

Gap junctions

Explanation:

Gap junctions are cellular junctions that attach two or more cells together but also allow the exchange of products through an opening. Tight junctions, desmosomes, and hemidesmosomes do not allow direct communication among cells.

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