Biology – Structure of transport tissues | e-Consult
Structure of transport tissues (1 questions)
Comparison and Contrast of Ultrastructural Features:
Xylem Vessel Element: The electron micrograph will show a thick, lignified secondary wall with abundant cellulose and lignin. The lumen will be large and open. The cytoplasm will be sparse, containing few organelles. The walls will be heavily electron-dense due to the lignified material. The presence of perforation plates will be clearly visible.
Phloem Sieve Tube Element: The electron micrograph will show thinner walls compared to xylem, with sieve plates (perforated end walls) that create channels for sap flow. The cytoplasm will be less dense than xylem, with fewer organelles. The companion cells will be adjacent to the sieve tube element, with abundant cytoplasm and a prominent nucleus. The sieve tube element will lack a nucleus and other major organelles.
Relationship to Transport Functions:
The lignified walls of the xylem vessel provide structural support and prevent collapse under tension, enabling efficient water transport. The perforation plates facilitate the unobstructed flow of water. The sieve plates in the phloem allow for the flow of phloem sap, while the companion cells provide metabolic support to the sieve tube elements, ensuring their functionality. The less dense cytoplasm in the phloem allows for efficient transport of sugars.
Table Summarizing Key Differences:
| Cell | Xylem Vessel Element | Phloem Sieve Tube Element |
| Wall Thickness | Thick, lignified | Thin |
| Lumen | Large, open | Smaller, channels created by sieve plates |
| Cytoplasm | Sparse, few organelles | Less dense, fewer organelles |
| Nucleus | Absent | Absent |