Biology – Structure of transport tissues | e-Consult
Structure of transport tissues (1 questions)
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Phloem sieve tube elements (sieve tube elements) and companion cells work together to facilitate the translocation of sugars (mainly sucrose) throughout the plant. Here's a comparison of their structure and function:
| Cell | Structure | Function |
| Sieve Tube Element | Living at maturity, but lack a nucleus, vacuole, ribosomes and a vacuolated cytoplasm. They have sieve plates at their ends, which contain pores that allow for the passage of phloem sap. | Transport of sugars (mainly sucrose) from source (e.g., leaves) to sink (e.g., roots, fruits, growing points). |
| Companion Cell | Living, with a nucleus, ribosomes, and a vacuole. They are closely associated with sieve tube elements via plasmodesmata. | Support the sieve tube element by providing metabolic support (e.g., protein synthesis, energy production). They regulate the function of the sieve tube element. |
Adaptations for Function:
- Sieve Plates: The sieve plates at the ends of sieve tube elements are crucial for efficient translocation. The pores in the sieve plates allow for the flow of phloem sap, while also regulating the pressure gradient.
- Companion Cells: The companion cells provide metabolic support to the sieve tube elements, which are unable to perform many metabolic functions themselves. They are connected to the sieve tube elements by plasmodesmata, allowing for the exchange of materials. The companion cells are thought to be involved in loading and unloading sugars into the sieve tube elements.
- Living Status: The fact that both cells are living is essential for their function. The companion cells provide the energy and machinery needed to support the sieve tube elements.
In essence, the sieve tube elements provide the conduit for transport, while the companion cells provide the necessary metabolic support and regulation for efficient translocation.