Primary vs Secondary Phloem

Definition

Primary phloem is the tissue formed during primary growth of a plant, originating from the apical meristem and responsible for transporting nutrients and organic compounds. In contrast, secondary phloem is produced during secondary growth, arising from the vascular cambium, and contributes to the increase in girth of stems and roots while continuing its function in transport.

5 Must Know Facts For Your Next Test

1. Primary phloem consists of sieve elements, companion cells, and parenchyma cells, which are essential for the transport process.
2. Secondary phloem has a greater variety of cell types, including fibers and more parenchyma cells, which provide structural support.
3. The production of primary phloem occurs during the initial phases of a plant's life, while secondary phloem develops as the plant matures.
4. As secondary phloem accumulates over time, it plays a crucial role in the development of bark on woody plants.
5. The formation of secondary phloem is essential for perennial plants to maintain efficient nutrient transport as they grow larger.

Review Questions

• How do primary and secondary phloem differ in their structure and function within the plant?
  • Primary phloem is made up mainly of sieve elements and companion cells formed during primary growth, facilitating nutrient transport in younger tissues. On the other hand, secondary phloem arises from the vascular cambium during secondary growth and includes additional cell types like fibers that provide structural support. This distinction in structure allows each type of phloem to perform its specific role effectively as the plant develops.
• Discuss the role of vascular cambium in the transition from primary to secondary phloem formation.
  • Vascular cambium is a critical layer that separates xylem from phloem and is responsible for producing secondary phloem as part of the plant's growth process. As the plant matures, this meristematic tissue divides, adding new layers of secondary phloem each year. This transition allows plants to increase their diameter while maintaining efficient nutrient transport through both primary and secondary phloem, ensuring continued growth and development.
• Evaluate the significance of both primary and secondary phloem in the overall health and development of woody plants.
  • Both primary and secondary phloem play vital roles in the health and development of woody plants. Primary phloem is essential for early nutrient transport, supporting initial growth, while secondary phloem becomes crucial as the plant matures, allowing it to expand its girth and support larger structures. The accumulation of secondary phloem contributes to bark formation, protecting internal tissues. This combination ensures that woody plants can effectively transport nutrients throughout their life cycle while adapting to increasing size demands.

Related terms

Phloem:

The vascular tissue in plants responsible for the transport of nutrients and carbohydrates produced by photosynthesis.

Vascular Cambium: A layer of meristematic cells between the xylem and phloem that gives rise to secondary growth in plants.

Meristem:

Regions of undifferentiated cells in plants that can divide and differentiate into various types of tissues.