Mesophyll Cells Function, Types & Structure: What is Mesophyll?

In addition to facilitating gas exchange, the spongy parenchyma also contains chloroplasts. Therefore, these spongy mesophyll cells also possess photosynthetic capabilities. The spongy parenchyma thus contributes to photosynthesis in dicot leaves and represents the main source of photosynthesis in monocot leaves.

Mesophyll Structure

The diagram below represents a cross-section of a dicot leaf. The structures shown include:

1. Cuticle: waxy coating over the epidermis
2. Upper epidermis: epidermal cells located on the upper surface of the leaf
3. Palisade parenchyma: columnar cells comprising the upper layer of the mesophyll
4. Spongy parenchyma: irregular cells forming the lower layer of the mesophyll
5. Lower epidermis: epidermal cells located on the lower surface of the leaf
6. Stomata: openings in the epidermis that facilitate gas exchange
7. Guard cells: a pair of cells that controls when the stomata open or close
8. Xylem: vascular tissue responsible for transporting water from the roots to the rest of the plant
9. Phloem: vascular tissue responsible for transporting nutrients from the leaves to the other parts of a plant
10. Vascular bundle: the combination of xylem and phloem

The diagram of a dicot leaf.

The image below shows the cross-section of a dicot leaf as viewed under a microscope. The cross-section shows a single layer of cells on the upper epidermis of the leaf in teal. The palisade parenchyma is just below the epidermis in purple. The spongy parenchyma is located just below the palisade cells. In the center of the diagram is the vascular bundle, containing the xylem and the phloem. The single layer of cells beneath the spongy parenchyma is the lower epidermis.

Cross-section of a dicot leaf.

The image below shows the cross-section of a monocot leaf as viewed under a microscope. The cross-section shows a single layer of upper epidermal cells on the upper surface of the leaf. At the lower surface of the leaf is a single layer of lower epidermal cells. The spongy parenchyma is located between these two layers. Vascular bundles can be seen distributed throughout the mesophyll.

Cross-section of a monocot leaf.

Lesson Summary

Plant leaves represent the primary photosynthetic structures in plants. The upper layer of the leaf consists of a single layer of cells known as the upper epidermis. The bottom layer of the leaf is known as the lower epidermis, which also contains a single layer of cells. The mesophyll is located in between the two epidermal layers and represents the site of photosynthesis in a plant. Unlike the epidermal cells, mesophyll cells contain chloroplasts, the organelles responsible for converting light energy into chemical energy. The mesophyll consists of two different cell types- the palisade parenchyma and the spongy parenchyma.

In dicot plants (with seeds producing two embryo leaves), the palisade parenchyma consists of pillar-shaped cells located just below the upper epidermis. Below the palisade parenchyma in dicots is the spongy parenchyma, which contains spaces to facilitate carbon dioxide diffusion and gas exchange via the stomata found on the lower surface of the leaf. In monocot plants (with seeds producing a single embryo leaf), the leaves contain spongy parenchyma in between two layers of epidermal cells. Both palisade and spongy parenchyma contain chloroplasts responsible for photosynthesis.