Sieve tube elements and companion cells

Definition

Sieve tube elements are specialized cells in the phloem of flowering plants responsible for transporting nutrients, especially sugars, throughout the plant. Companion cells are closely associated with sieve tube elements, providing metabolic support and facilitating the movement of substances between the sieve tubes and surrounding tissues. Together, these cells play a crucial role in the plant's vascular system, ensuring efficient nutrient distribution and communication within the plant.

5 Must Know Facts For Your Next Test

1. Sieve tube elements lack a nucleus and most organelles, which allows for more efficient transport of nutrients and maximizes their internal space.
2. Companion cells are derived from the same parent cell as sieve tube elements during development and maintain a close physical connection through plasmodesmata.
3. The movement of sugars through sieve tubes is driven by osmotic pressure, with water entering the tubes to balance solute concentrations.
4. Sieve plates, found at the ends of sieve tube elements, contain pores that facilitate the flow of sap between adjacent sieve tubes.
5. Both sieve tube elements and companion cells are crucial for maintaining homeostasis in plants by regulating nutrient distribution based on the plant's physiological needs.

Review Questions

• How do sieve tube elements and companion cells work together to ensure effective nutrient transport in plants?
  • Sieve tube elements and companion cells collaborate closely to optimize nutrient transport in plants. The companion cells support sieve tube elements metabolically, providing ATP and other necessary molecules for active transport. As sieve tube elements lack organelles, they rely on companion cells to manage their cellular functions, ensuring efficient movement of sugars and nutrients through the phloem while maintaining communication between tissues.
• Discuss the structural features of sieve tube elements that enable their function in nutrient transport.
  • Sieve tube elements have unique structural adaptations that enhance their role in nutrient transport. They lack a nucleus and most organelles, maximizing space for sap transport. Additionally, they have sieve plates with pores at their ends, which allow for easy passage of nutrient-rich fluid between adjacent sieve tubes. These features ensure that sieve tube elements can efficiently move sugars and other nutrients throughout the plant with minimal resistance.
• Evaluate the importance of companion cells in maintaining homeostasis within a plant's vascular system.
  • Companion cells play a vital role in maintaining homeostasis within a plant's vascular system by ensuring that sieve tube elements receive adequate metabolic support. They regulate nutrient flow by facilitating the loading and unloading of sugars into and out of sieve tubes based on the plant's current needs. By managing osmotic pressure and nutrient concentration in response to environmental changes, companion cells help maintain balanced nutrient distribution across various plant tissues, which is essential for overall plant health and function.

Related terms

Phloem:

The vascular tissue in plants that transports nutrients and sugars produced by photosynthesis from leaves to other parts of the plant.

Xylem:

The vascular tissue responsible for transporting water and minerals from the roots to the rest of the plant.

Plasmodesmata: Microscopic channels that traverse the cell walls of plants, allowing communication and transport of materials between adjacent cells.