Question

Which of the following is present only in plants?

• A. Plasmodesmata
• B. Desmosomes
• C. Gap junctions
• D. None

Hint:

Associate Plasmodesmata with the "Symplast" pathway in plants. Remember: Plants = Plasmodesmata; Animals = Gap junctions, Tight junctions, and Desmosomes.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Cellular junctions are specialized structures that provide contact between neighboring cells or between a cell and the extracellular matrix. These structures facilitate communication, transport of molecules, and structural integrity of tissues. The type of junction present depends on whether the organism is a plant or an animal, primarily due to the presence of a rigid cell wall in plants.

Step 2: Detailed Explanation:
Plant cells are encased in a rigid cellulose cell wall, which prevents the type of direct membrane-to-membrane contact seen in animal cells. To overcome this barrier, plants have evolved plasmodesmata. Plasmodesmata are microscopic channels that traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them. They are essentially extensions of the plasma membrane and cytoplasm, often containing a tube of endoplasmic reticulum known as a desmotubule.
In contrast, animal cells lack cell walls and use different structures. Desmosomes (Option B) are adhesive junctions that provide strong mechanical attachment between adjacent cells, common in tissues like the epidermis. Gap junctions (Option C) are the animal equivalents of plasmodesmata in terms of function; they consist of protein channels (connexons) that allow the passage of ions and small molecules between cells. However, they are structurally distinct from plasmodesmata. Since plasmodesmata are necessitated by and integrated into the plant cell wall, they are found exclusively in the plant kingdom.

Step 3: Final Answer:
Plasmodesmata are the only structural junctions listed that are found exclusively in plants to facilitate symplastic transport.