What is the Difference Between Palisade Mesophyll and Spongy Mesophyll

The main difference between palisade mesophyll and spongy mesophyll is that palisade mesophyll contains tightly packed columnar cells, whereas spongy mesophyll contains randomly assembled, irregularly shaped cells.

Palisade mesophyll and spongy mesophyll are two types of mesophyll tissue occurring in the plant leaf. Both types of mesophyll undergo photosynthesis.

Key Areas Covered

1. What is Palisade Mesophyll
     – Definition, Structure, Function
2. What is Spongy Mesophyll
     – Definition, Structure, Function
3. Similarities Between Palisade Mesophyll and Spongy Mesophyll
     – Outline of Common Features
4. Difference Between Palisade Mesophyll and Spongy Mesophyll
     – Comparison of Key Differences

Key Terms

Palisade Mesophyll, Spongy Mesophyll

What is Palisade Mesophyll

Palisade mesophyll is one of the two photosynthetic cell types occurring in C3 plants. It occurs towards the upper epidermis. However, palisade mesophylls are vertical and elongated cells that are tightly packed.  The main function of the palisade mesophyll is to undergo photosynthesis. Therefore, they contain the largest number of chloroplasts per cell. Moreover, a plant leaf contains one or two cells-thick palisade mesophyll layers. In addition, intercellular air space occurs between the tightly packed palisade mesophyll cells.

Figure 1: Palisade Mesophyll

Furthermore, palisade mesophylls are cylindrical cells. They contain chloroplasts near the cell wall. This help to take optimal advantage of the light. In addition, the slight separation of palisade mesophyll cells provides the maximum absorption of carbon dioxide. It’s interesting to note that leaves in sunny areas contain many layers of palisade cells, while leaves in shade areas, leaves near the ground, and old leaves contain a single layer of palisade mesophylls.

What is Spongy Mesophyll

The spongy mesophyll is the other layer of photosynthetic cells occurring in C3 plants. However, these cells occur towards the lower epidermis, beneath the palisade mesophyll layer. The cells of the spongy mesophyll are irregular-shaped and loosely packed. The main function of the spongy mesophyll is to undergo photosynthesis. However, the number of chloroplasts in the spongy mesophyll is fewer than the number of chloroplasts in the palisade mesophyll. The most important feature of spongy mesophyll is the presence of large spaces of air between cells.

Figure 2: Palisade and Spongy Mesophyll

Moreover, the large spaces occurring between the spongy mesophyll are important for air exchange. During photosynthesis, carbon dioxide gas needs to come into the cells while removing oxygen and water vapor. Therefore, the air spaces between spongy mesophyll are extremely humid. This process is called a gaseous exchange. Thus, another function of spongy mesophyll is gas exchange.

Similarities Between Palisade Mesophyll and Spongy Mesophyll

• Palisade mesophyll and spongy mesophyll are two types of mesophylls occurring in plant leaves.
• They are photosynthetic cells and occur in plants that undergo the C3 carbon fixation pathway.

Difference Between Palisade Mesophyll and Spongy Mesophyll

Definition

Palisade mesophyll refers to one or more layers of cells located directly under the epidermal cells of the adaxial leaf blade surface, while spongy mesophyll refers to the mesophyll tissue comprising cells of irregular shape, some of them lobed, separated by large spaces in which the atmosphere is humid.

Anatomy

Palisade mesophyll contains tightly packed columnar cells, while spongy mesophyll consists of randomly assembled, irregularly shaped cells.

Occurrence

Moreover, palisade mesophyll occurs towards the upper epidermis, while spongy mesophyll occurs towards the lower epidermis.

Chloroplast Number

Palisade mesophyll contains the highest number of chloroplasts, while spongy mesophyll contains less number of chloroplasts.

Function

The main function of palisade mesophyll is to undergo photosynthesis, while the main function of spongy mesophyll is to undergo gas exchange.

Conclusion

In brief, palisade and spongy mesophyll are two types of mesophylls that occur in the plant leaf. They occur in plants that undergo the C3 pathway. Both types of mesophylls are photosynthetic. Palisade mesophylls are found towards the upper epidermis of the plant leaf. They are columnar cells that are tightly packed. Palisade mesophylls contain the highest number of chloroplasts. In addition, the palisade mesophyll’s main function is photosynthesis. In comparison, spongy mesophylls occur towards the lower epidermis. They are irregular-shaped cells that are randomly assembled. Spongy mesophyll contains fewer chloroplasts. But the main function of spongy mesophyll is gas exchange. Therefore, the main difference between palisade and spongy mesophyll is their structure.

References:                     

1. “Palisade Mesophyll.” Encyclopedia.com. 
2. “Spongy Mesophyll.” Encyclopedia.com. 

Image Courtesy:

1. “Angiosperm Leaf Palisade Mesophyll in Nymphea (36909777763)” By Berkshire Community College Bioscience Image Library – Own work (CC0) via Commons Wikimedia
2. “Multicolor fluorescence image of living HeLa cells” By Zephyris – Own Work (CC-BY SA 3.0) via Commons Wikimedia