OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What is a key feature of sieve tube elements?

1. They contain chlorophyll

2. They have perforated end-plates

3. They are large and rigid

4. They can regenerate easily

The correct answer is: They have perforated end-plates

Sieve tube elements are specialized cells found in the phloem of flowering plants, and they play a crucial role in transporting nutrients, particularly sugars, throughout the plant. A key feature of sieve tube elements is their perforated end-plates, which are structures at each end of these cells. These perforated end-plates allow for the efficient flow of sap, enabling the movement of dissolved sugars and other organic compounds from one sieve tube element to another. This feature is essential for the functionality of the phloem, as it facilitates the transport process necessary for the plant's growth and energy supply. In contrast, sieve tube elements do not contain chlorophyll, making them different from other plant cells involved in photosynthesis. While they are typically elongated and thin, they are not structurally rigid like some other cell types; instead, they are somewhat flexible to accommodate the flow of materials. Additionally, the ability to regenerate easily is not a distinguishing feature of sieve tube elements, as they are typically not involved in the regeneration processes that occur in other plant tissues. Thus, the characteristic of having perforated end-plates is what defines sieve tube elements and enables their critical function in the plant's vascular system.