A Level Biology Practice Exam

What characterizes sieve tube elements in plants?

1. They contain no cell wall

2. They have high metabolic activity

3. They have reduced living content with sieve plates

4. They are involved in root absorption

The correct answer is: They have reduced living content with sieve plates

Sieve tube elements are specialized structures in the phloem of flowering plants, primarily responsible for the transport of photosynthates (like sugars). The correct characterization of sieve tube elements is that they have reduced living content with sieve plates. This means that while they are still living cells, they lack many of the organelles typically found in other plant cells, such as a nucleus and many types of cytoplasmic contents, allowing for more efficient flow of sap through the tubes. The presence of sieve plates, which are perforated end walls between sieve tube elements, facilitates the movement of phloem sap from one element to another, enabling the rapid transport of nutrients. The reduction in living content allows for less resistance to the flow of the sugary sap and supports the primary function of these cells. Other characterizations, such as the absence of cell wall, high metabolic activity, or involvement in root absorption, do not accurately define sieve tube elements. They actually possess cell walls, have lower metabolic activity compared to other types of plant cells, and are not directly involved in root absorption, which is primarily the role of root hairs and other specialized cells.