Anatomy or internal structure of a Monocot leaf


In this resource, I gave a detailed account of the internal or anatomical structure of a monocot leaf as it appears under the compound microscope. The various tissues present in the monocot leaf and their functions were also discussed. Some of the most frequently asked questioned were also included along with this resource for the benefit of the readers.

Introduction

Monocot leaves are the leaves that appear on plants produced from seeds with single cotyledon like Maize, Rice, Grass, Wheat, etc. Monocot leaves are said to be isobilateral leaves as both the surface of the leaves are with the same coloration. The leaves are usually ribboned like with parallel venation. Parallel venation means veins in the leaf are arranged in a parallel fashion. We are studying the anatomy of the leaf means, we are studying the internal structure or arrangement of various tissues arranged internally in the leaf. The various tissues present inside the leaf will carry out some specific functional activities for the leaf. By mounting a thin section of a monocot leaf like that of a grass leaf or maize leaf on a clean glass slide and after staining can be observed under a Compound microscope, we can get a clear view of the arrangement of its various tissues in an orderly fashion.

Internal organization of various tissues in monocot leaf

The following are the various tissues and their functional activities of monocot leaf:-

  1. Upper epidermis
  2. It is the uppermost layer or adaxial layer of a monocot leaf. It is a single-layered tissue made of cubical or barrel-shaped cells and is arranged closely with no intercellular spaces in between them. Chloroplasts cannot be seen in these cells. The upper epidermis on its outer surface is covered by a thin cuticle.

    In a monocot leaf, an equal number of stomata are present on both the surfaces of the epidermis. Such a condition is usually described as Amphi stomatic condition. A few cells present in the upper epidermis are enlarged to form motor cells called bulliform cells. These cells are larger when compared to other epidermal cells. These cells will be helpful for the monocot leaves to roll over themselves to reduce the surface area exposed to sunlight and become shrunken during hot midday time to reduce the rate of transpiration. It is an adaptation for monocot leaves to check the loss of water from their surface during the hot summertime.

    In both upper and lower epidermal layers of monocot leaf, an equal number of stomata are present. But in dicot leaves, more stomata are present in the upper epidermal layer and fewer stomata in the lower epidermal layer. In the case of monocot leaf, the two guard cells which form the stoma are dum-bell shaped. But the two guard cells which form stoma in dicot leaves are kidney or bean-shaped.

  3. Mesophyll
  4. Mesophyll is a green ground tissue present in between upper epidermis and lower epidermis. In monocot leaf, mesophyll tissue is not differentiated into palisade parenchyma and spongy parenchyma as in the case of a dicot leaf. The tissue of monocot leaf consists of only one kind of cells that are small oval or spherical or irregular shaped spongy parenchyma cells with chloroplasts and chlorophyll. This tissue is present in 6-7 layers with large intercellular spaces in between them. In between the epidermal layers of the monocot leaf, undifferentiated spongy parenchyma with fewer chloroplasts and chlorophyll is present and thus both the surfaces of the leaf appear to be with the same coloration. This mesophyll tissue is concerned with the photosynthesis process in the leaves of these plants.

  5. Vascular bundles
  6. Vascular bundles represent the veins of the leaves. Vascular bundles are present within the mesophyll tissue. Each vascular bundle consists of xylem and phloem complex tissues surrounded by bundle sheath. The bundle sheath layer of the vascular bundle is made of large barrel-shaped endodermal cells. The cells of this layer usually store starch granules. Hence it is also known as a starch sheath. Xylem tissue of a vascular bundle is present towards the upper epidermis of the leaf. Xylem complex is a complex permanent tissue consists of xylem tracheids, xylem vessels, xylem parenchyma, and xylem fibers. Xylem in a vascular bundle is concerned with the conduction of water and dissolved minerals.

    Phloem tissue in the vascular bundle is present towards the lower epidermal surface of the leaf. Phloem is a complex permanent tissue made of sieve tubes and sieve pores, companion cells, phloem parenchyma, and phloem fibers. Phloem tissue in a leaf is concerned with the conduction of dissolved food materials (usually glucose).

    Vascular bundles in monocot leaf are described as conjoint, collateral, and closed with endarch xylem. As xylem and phloem are present on the same radius, the vascular bundle is described as conjoint and collateral. The vascular bundle is described as closed as there is no cambium present between xylem and phloem. Xylem vessels are of two types-protoxylem and metaxylem vessels. Protoxylem vessels are newly formed young vessels while metaxylem vessels old and well-matured vessels. Xylem bundles are described here as endarch because the protoxylem vessels face towards the upper epidermis. Vascular bundles help in the transport of water, dissolved minerals, and dissolved food materials in the leaf. Vascular bundles also provide strength to the leaf.

  7. Lower epidermis
  8. Below the undifferentiated mesophyll tissue a single layer of epidermis is present. This layer is present on the abaxial (lower) surface of the leaf. The cells are cubical or barrel in shape and are arranged very closely without any intercellular spaces. The same number of stomata is present as in the upper epidermis. Through the stomata of the upper and lower epidermis exchange of gases occur through the diffusion method. Just above the stomata of the epidermal layers of both the surfaces of the leaf, air cavities or sub-stomatal chambers are present. These air cavities act as a storehouse of carbon dioxide or water vapor till they diffuse.


Most frequently asked questions:-

  1. What are bulliform cells and give its functional role.
    Ans. Bulliform cells are large bubble-shaped epidermal cells present in groups on the upper surface of monocot leaves. These cells help in the roling of leaves to reduce the loss of water during hot midday times.

  2. State the difference in shape of guard cells of stomata in dicot and monocot leaves.
    Ans. The guard cells of stoma are kidney or bean-shaped in dicot leaves and dumbel-shaped in monocot leaves.

  3. What are the tissues present in the veins of leaves.
    Ans. The veins of leaves represent vascular bundles that include xylem and phloem tissues.

  4. How can you distinguish a monocot leaf from dicot leaf in their internal structure.
    Ans. Mesophyll tissue is differentiated into palisade and spongy parenchyma in dicot leaves while the mesophyll is undifferentiated and contain only spongy parenchyma in monocot leaves.
    The guard cells in dicot leaf are kidney-shaped while monocot leaf are dumbel-shaped.

  5. Name the type of venation observed in dicot and monocot leaves.
    Ans. In dicot leaf reticulate venation and in monocot leaf parallel venation.

  6. What is the functional role of mesophyll tissue in a leaf.
    Ans. Mesophyll tissue contain chloroplasts and chlorophyll and this tissue help in photosynthesis to prepare carbohydrate food.

  7. What are sub-stomatal chambers?
    Ans. The cavities present above the stomata on the lower epidermis of a leaf are known as sub-stomatal chambers. They store CO2 or water vapor in these cavities till they diffuse.

  8. What is bundle-sheath in monocot leaf?
    Ans. The thick cells present around the vascular bundles that include starch granules in monocot leaf is known as bundle-sheath or starch-sheath.

Here is a video of the anatomy and internal structure of a Monocot leaf:-


Comments

No responses found. Be the first to comment...


  • Do not include your name, "with regards" etc in the comment. Write detailed comment, relevant to the topic.
  • No HTML formatting and links to other web sites are allowed.
  • This is a strictly moderated site. Absolutely no spam allowed.
  • Name:
    Email: