A Level Biology Practice Exam

What are companion cells associated with?

1. The xylem tissue for water transport

2. The phloem vessels providing metabolic support

3. The epidermal cells in root structures

4. The production of reproductive cells in plants

The correct answer is: The phloem vessels providing metabolic support

Companion cells are specialized cells found in the phloem tissue of plants. They play a crucial role in the transport of sugars and other organic nutrients throughout the plant. These cells are closely associated with sieve tube elements, which are the main conducting cells of the phloem. The primary function of companion cells is to provide metabolic support to the sieve tube elements. They are involved in the loading and unloading of sugars into and out of the sieve tubes, thereby facilitating the movement of nutrients from source (photosynthetic tissues) to sink (growing tissues or storage organs). Companion cells have a high number of mitochondria and carry out the cellular respiration necessary to produce ATP, which is used in active transport processes. This relationship between companion cells and sieve tubes is essential for efficient phloem function and overall plant metabolism. Understanding this association is important as it highlights how the intricate cellular structures in plants work together to maintain physiological processes.