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

Joanna Tatomir, Jeremy Battista
  • Author
    Joanna Tatomir

    Joanna holds a PhD in Biology from the University of Michigan and is currently working towards a degree in Veterinary Medicine at Michigan State University. She has taught a combination of ESL and STEM courses to secondary and university students.

  • Instructor
    Jeremy Battista

    Jeremy has a master of science degree in education.

Learn about the definition and function of mesophyll cells as well as the structure and primary role of spongy mesophyll and palisade parenchyma in photosynthesis. Updated: 12/19/2021

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Mesophyll

All living organisms engage in cellular respiration in order to produce the energy needed to carry out basic metabolic functions such as growth, reproduction, and tissue repair. Plants perform respiration in a unique way, by converting light energy into chemical energy. This process is known as photosynthesis. In order to carry out photosynthesis, plants have developed numerous structural and physiological adaptations, such as the use of chloroplasts in place of mitochondria as the powerhouse for the plant cell.

Leaf Structure

In plants, leaves represent the main site of photosynthesis. Leaves are comprised of three layers, the upper epidermis, the lower epidermis, and a layer of mesophyll cells in between these two layers. The upper epidermis represents the adaxial, or top, side of the leaf. This layer is one cell in thickness and is covered by the cuticle, a waxy surface that prevents water loss through the epidermis. The lower epidermis is referred to as the abaxial, or lower, surface of the leaf.

The epidermis contains stomata, specialized pores that represent the main sites for gas exchange in plants. A pair of guard cells controls when the stomata are opened or closed. Epidermal cells lack chlorophyll, the light absorbing pigment associated with photosynthesis. However, the guard cells surrounding each stomata contain chlorophyll.

What is Mesophyll?

Mesophyll in plants refers to the middle layer of cells found in leaves. The term mesophyll is derived from the Greek word mesos, meaning ''middle,'' and the Greek word phyllo, or ''leaf.'' So mesophyll literally translates into ''middle leaf.''

Mesophyll definition: the middle cell layer of a leaf containing chloroplasts and representing the main site of photosynthesis

Plants possess three different types of tissue: dermal, vascular and ground tissue. The mesophyll of leaves represents a type of ground tissue. Plant ground tissue refers to any non-dermal or non-vascular cell type. The function of ground tissue is dependent on where it is located. In leaves, the main function of the mesophyll is to facilitate the process of photosynthesis

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Mesophyll Cells

There are two types of mesophyll cells, or mesophyll tissue- palisade parenchyma and spongy parenchyma (also known as spongy mesophyll). The function and location of these two cell types will be further discussed in the sections below.

Palisade Parenchyma

The palisade parenchyma represents the first type of mesophyll cell. The cells of the palisade parenchyma are shaped like pillars that are tightly bunched together. There can be as many as three layers of palisade parenchyma cells, depending on the plant species.

Parenchyma cells are characterized as totipotent. Totipotency refers to a cell capable of turning into any cell type in an organism. The palisade parenchyma cells found in the mesophyll are located directly below the upper epidermis. Unlike other plant cells, which often contain a secondary cell wall, the palisade parenchyma cells found in the mesophyll only have a single cell wall that contributes to its flexibility.

When compared to the other cells of a leaf, the palisade parenchyma contains a large number of chloroplasts. Because the parenchyma constitutes a majority of the tissue found in leaves, this region represents the primary site where a majority of photosynthesis occurs in a plant. This layered arrangement of the cells contained in leaves is characteristic of dicotyledons (dicots), flowering plants with seeds that produce two embryo leaves. In monocotyledons (monocots), or grassy plants with seeds that produce a single embryo leaf, the mesophyll cells are not differentiated. Instead, monocot leaves primarily consist of spongy parenchyma cells. This cell type will be discussed in the next section.

Spongy Mesophyll

Spongy parenchyma, or spongy mesophyll, represents the second cell type found in plant leaves. This layer of cells is located just below the palisade parenchyma tissue and directly above the lower epidermis in dicots. In monocots, spongy parenchyma represents the only cell type found in the mesophyll.

Unlike the palisade parenchyma, the spongy parenchyma possesses an irregular arrangement with large spaces in between each cell. These gaps facilitate carbon dioxide diffusion between the cell and gas exchange via the stomata, which open into these spaces in the lower epidermis of dicots and in both epidermal layers of monocots.

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Frequently Asked Questions

What is the difference between palisade mesophyll and spongy mesophyll?

The palisade mesophyll are pillar-shaped cells bunched closely together. Spongy mesophyll contains irregularly shaped cells with wide gaps between them to facilitate gas exchange via the stomata. Monocot leaves only possess spongy mesophyll, while dicots leaves have both palisade and spongy mesophyll.

What is the function of the spongy mesophyll in a leaf?

The spongy mesophyll contains irregularly shaped cells with wide gaps between them in order to facilitate carbon dioxide diffusion and gas exchange via the stomata. Spongy mesophyll also contains chloroplasts responsible for photosynthesis.

What is the function of mesophyll?

Mesophyll represents the middle layer of cells located between the epidermal layers of a leaf. Mesophyll contains many chloroplasts, and therefore represents the main site of photosynthesis in plants.

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