Given below are two statements. One is labeled Assertion(A) and the other is labeled Reason(R).

Assertion (A) : The companion cells help in maintaining the pressure gradient in sieve tubes.
Reason (R) : The sieve tube elements and companion cells are connected by pit fields present between their common longitudinal walls.

In light of the above statements, choose the correct answer from the options given below.
 

 

Assertion (A) is correct. Companion cells play a crucial role in maintaining the pressure gradient in sieve tubes within the phloem, facilitating the flow of sap and the transport of nutrients throughout the plant.

The process involves the active loading of sugars into the sieve tubes at source regions (such as leaves) and their subsequent unloading at sink regions (such as roots or fruits). Companion cells are closely associated with sieve tube elements and provide metabolic support, helping to maintain the osmotic pressure necessary for the movement of nutrients. This collaboration ensures an effective and directed flow of sap through the phloem.

Reason (R) is also correct.  Sieve tube elements and companion cells in the phloem are indeed connected by structures called pit fields, which are present between their common longitudinal walls. These pit fields contain plasmodesmata, which are channels that allow for communication and the exchange of materials between the sieve tube elements and companion cells.

Assertion (A) as well as reason (R) is correct and the Reason (R) is the correct explanation for the assertion. The connection between sieve tube elements and companion cells through pit fields is indeed crucial for maintaining the pressure gradient in sieve tubes, which is necessary for the transport of nutrients in the phloem.