Phloem

Definition

Phloem is a type of vascular tissue in plants responsible for the transport of organic nutrients, particularly sugars produced through photosynthesis, from the leaves to other parts of the plant. It plays a crucial role in the overall nutrient distribution within the plant, connecting various organs and facilitating growth and development.

5 Must Know Facts For Your Next Test

1. Phloem consists of living cells, unlike xylem, which contains dead cells at maturity, allowing it to actively transport nutrients.
2. The primary function of phloem is to move photosynthates, mainly sucrose, from source tissues like leaves to sink tissues such as roots, fruits, and developing leaves.
3. Phloem transport occurs through a process called translocation, which relies on pressure gradients created by the loading and unloading of nutrients.
4. Phloem also helps in the distribution of hormones and signaling molecules, contributing to plant growth regulation and responses to environmental stimuli.
5. In addition to sugars, phloem can transport amino acids and other organic compounds essential for plant health.

Review Questions

• How does phloem structure contribute to its function in nutrient transport within plants?
  • The structure of phloem includes sieve tubes and companion cells, which work together to facilitate efficient nutrient transport. Sieve tubes form long channels that allow for the movement of sugars and nutrients across various parts of the plant. Companion cells provide metabolic support to sieve tubes, ensuring that they can actively load and unload materials as needed. This specialized structure enables phloem to effectively distribute essential nutrients from photosynthetic areas to growing tissues.
• Compare the roles of phloem and xylem in plant transport systems, highlighting how they interact with each other.
  • Phloem and xylem serve complementary roles in plant transport systems; while phloem transports organic nutrients from source to sink, xylem carries water and minerals from roots to leaves. The interaction between these two systems is vital for plant health; for example, water absorbed by xylem supports photosynthesis in leaves, where sugars are produced. Additionally, the pressure changes created by xylem's water transport help drive the movement of nutrients through phloem, illustrating their interconnected functions in sustaining plant life.
• Evaluate the significance of phloem in the context of a plant's response to environmental stressors and its overall health.
  • Phloem plays a vital role in a plant's ability to respond to environmental stressors such as drought or nutrient deficiency. Through its transport of sugars and signaling molecules, phloem helps regulate growth patterns and resource allocation during stressful conditions. For instance, if a plant experiences water shortage, it may prioritize nutrient delivery to roots over less critical areas. Thus, healthy phloem function is essential for maintaining a plant's resilience, promoting recovery from stressors, and ensuring overall health and productivity.

Related terms

Xylem: Xylem is another type of vascular tissue that transports water and dissolved minerals from the roots to the rest of the plant, working alongside phloem in the vascular system.

Sieve tubes: Sieve tubes are elongated cells in phloem that form channels for transporting sugars and other nutrients throughout the plant.

Companion cells: Companion cells are specialized cells in phloem that support sieve tubes by providing metabolic functions and helping to load and unload sugars.