Difference Between Ascent of Sap and Translocation

The key difference between ascent of sap and translocation is that ascent of sap is the transportation of water and minerals from the root to aerial parts of the plant through the xylem, while translocation is the transportation of foods/carbohydrates from leaves to other parts of the plant through the phloem.

Xylem and phloem are vascular tissues found in vascular plants. They aid in transporting substances across the plant. Also, both tissues are complex tissues composed of several different specialized cell types. However, xylem transports water and minerals from the root to aerial parts of the plant, and we call this process ascent of sap. Meanwhile, the phloem runs next to xylem, and it transports food prepared by photosynthesis from leaves to other plant body parts. Thus, this process is called translocation.

CONTENTS

1. Overview and Key Difference
2. What is Ascent of Sap 
3. What is Translocation
4. Similarities Between Ascent of Sap and Translocation
5. Side by Side Comparison – Ascent of Sap vs Translocation in Tabular Form
6. Summary

What is Ascent of Sap?

The ascent of sap is the movement of water and dissolved minerals through xylem tissue in vascular plants. Plant roots absorb water and dissolved minerals from the soil and hand them over to the xylem tissue in the roots. Then xylem tracheids and vessels transport water and minerals from roots to aerial parts of the plant. The movement of the ascent of sap is upward.

The ascent of sap takes place due to the passive forces created by several processes such as transpiration, root pressure and capillary forces, etc. Most importantly, when transpiration occurs in the leaves, it creates a transpiration pull or the suction pressure in leaves. The transpiration pull of one atmospheric pressure can pull the water up to 15-20 feet in height according to the estimations. Root pressure also pushes water upwards through the xylem. Water enters root hair cells due to low water potential inside the cell than the soil. When water accumulates inside the roots, a hydrostatic pressure develops in the root system, pushing the water upwards. Likewise, as a result of several passive forces, water moves from roots to upper parts of the plant.

What is Translocation?

Phloem translocation or translocation is the movement of photosynthetic products through the phloem. In simple words, translocation refers to the process of transporting carbohydrates from leaves to other parts of the plant through phloem. Translocation takes place from sources to sink. Plant leaves are the primary source of translocation since they are the main sites of photosynthesis in plants. Sinks can be roots, flowers, fruits, stems, and developing leaves.

Phloem translocation is a multidirectional process. It takes place downwards, upwards, laterally, etc.  Moreover, it utilizes energy during phloem loading and phloem unloading. Food travels along the phloem as sucrose. At the source, sucrose actively loads into the phloem tissue. In contrast, at the sink, sucrose actively unloads into the sink from the phloem tissue. In angiosperms, the translocation rate is 1 m per hour, and it is relatively a slow process.

What are the Similarities Between Ascent of Sap and Translocation?

• The ascent of sap and translocation occur through the vascular tissues of vascular plants.
• Both processes are vital for plants.

What is the Difference Between Ascent of Sap and Translocation?

The ascent of sap is the movement of water and dissolved minerals through the xylem. On the other hand, translocation is the movement of carbohydrates through the phloem. So, this is the key difference between ascent of sap and translocation. Furthermore, the ascent of sap takes place upwards while translocation takes place in upwards, downwards, laterally, etc., in a multidirectional manner. Therefore, this also an important difference between ascent of sap and translocation.

Summary – Ascent of Sap vs Translocation

Ascent of sap refers to the process of transporting water and dissolved minerals through the xylem from roots to aerial parts of the plant in the upward direction. In contrast, translocation refers to the process of transporting sucrose and other nutrients from plant leaves to other parts through phloem in a multidirectional manner. So, this is the key difference between ascent of sap and translocation.

Reference:

“Translocation.”. “Translocation.” Biology, Encyclopedia.com, 2019, Available here.
2. “Water Uptake and Transport in Vascular Plants”, Nature Publishing Group, Available here.

Image Courtesy:

1. “Transpiration Overview” By Laurel Jules – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Translocation from the source to the sink within the phloem” By Alyssa Pham – Own work (CC BY-SA 4.0) via Commons Wikimedia