Leaf Anatomy: Internal Structure and Functionality Explained

Introduction

A leaf is the principal component of the plant, which is found above the ground. One of the essential characteristics of a leaf is that it is generally green in colour. Leaves are the structure responsible for photosynthesis, and leaf anatomy plays an essential role in this process. This article deals with Leaf anatomy, i.e. the internal structure of a leaf, parts and functions. 

 Leaf anatomy, i.e., the internal structure of a leaf, comprises the epidermal tissue, the mesophyll tissue and the vascular tissue. The epidermis is the outermost layer; mesophyll is the middle layer, and vascular bundles are scattered. 

Leaf

The leaf is known as the kitchen of the plant. They are the primary organ responsible for photosynthesis, which is how the plant obtains its energy or food. The presence of chlorophyll gives them their green hue.

Function of Leaf

• Photosynthesis: The most crucial function of a leaf is photosynthesis. They include chloroplasts that help in photosynthesis. Phloem tissue transports the prepared food to other sections of the plant
• Help plants to breathe- The epidermis of the leaf contains guard cells that manage and regulate the microscopic holes under the surface of the leaves, allowing the plant to breathe. Stomata are the name for these pores. Stomata control the flow of water into and out of the cell. It is also in charge of the gas exchange throughout the epidermis
• Food storage: The leaves of several plants have been adapted to store food. Succulent leaves are common in these plants, as they are in xerophytic plants

Leaf Anatomy, Parts and Functions

Each leaf consists of the following layers-

Epidermis

• The epidermis covers the upper and lower surface of a leaf. The epidermis is usually a single layer of densely packed cells. It manages exchange between the plant and its environment by limiting water loss, managing gas exchange, transmitting sunlight for photosynthesis, and deterring herbivores
• The epidermis secretes a special waxy suberin cuticle, preventing water from evaporating from the leaf tissue. This layer may be thicker in the top epidermis in dry regions than in wet climates
•  The cuticle prevents water loss while also preventing carbon dioxide absorption and oxygen excretion. Stomata (singular, stoma), or “little mouths,” perform these duties via regulating water loss, O2 release, and CO2 intake. Stomata are more plentiful in the lower epidermis of most leaves, decreasing water loss due to direct sunlight

Mesophyll

•  Mesophyll is made up of the tissues that make up most of the leaf’s interior. Most plant photosynthesis occurs in this tissue.  It is made up of thin-walled parenchyma cells or collenchyma cells containing chloroplasts. The mesophyll is made up of two layers in flowering plants and ferns
• The higher Palisade layer absorbs most sunlight and performs the majority of photosynthesis. Many chloroplasts may be found in the columnar cells of the palisade layer. By permitting CO2 diffusion and H2O capillary flow, slight but precise separations between the cells optimise the availability of the raw materials for photosynthesis. Leaves exposed to direct sunlight may have up to five layers of palisade cells, whereas shadow leaves may only have one
•   More spherical cells with fewer chloroplasts are seen in the spongy bottom layer. The cells are loosely packed, with bigger, open areas between them

Vascular tissues

• The veins of leaves are predominantly made up of vascular tissue, with parenchymal pith and collenchyma around them
• Water and minerals are transported from the roots and stem into and throughout the leaves by an upper layer of the Xylem. Dead cells with substantially thickened yet pitted cell walls make up Xylem. When stomatal evaporation begins the transpirational pull, the cells are oriented end-to-end, straw-like, allowing hydrogen bonds between water molecules (cohesion) to drag each other (and hitch-hiking mineral ions) through the xylem columns
• Sugars created in the leaves (“sugar sources”) are transported to portions of the plant that require these fuels (“sugar sinks”) by living cells of the lower layer of phloem, which are likewise organised in bundles of straw-like columns but linked by sieve plates and plasmodesmata
• Sugars generated in leaves are actively transported and concentrated by partner cells in the phloem, enabling water to follow and raise the pressure, resulting in sap flow from source to sink
•  Vascular tissue, like guard cells, uses osmosis to achieve movement without muscles. Because osmosis is a passive, totally physical process, this achievement is all the more astounding

Internal Structure of a Monocot and Dicot leaf

Internal anatomy of a Monocot leaf

• The epidermis of a monocot leaf is divided into upper and lower layers. Parenchyma cells make up the epidermis. The outer wall of the epidermis has cuticles, and the upper and lower epidermis have stomata. Bulliform cells are big and thin-walled cells found in the top epidermis
•  Palisade and spongy parenchyma are not distinguished in mesophylls. The cells are organised in an uneven pattern with intercellular gaps. Chloroplasts are found in these cells
• Vascular bundles: There are several vascular bundles, some of which are small and some enormous. A parenchymatous bundle sheath surrounds each vascular bundle, i.e., conjoint, collateral and closed vascular bundles. Xylem is found in the top epidermis, while phloem is found in the lower epidermis

Internal anatomy of a Dicot leaf

•   A dicotyledonous leaf has a dorsiventral epidermis. It has two epidermal layers. The epidermis is typically a single layer of densely packed cells
• Palisade cells are found underneath the top epidermis in the palisade parenchyma. One layer of elongated cylindrical cells makes up this structure
•  Spongy parenchyma: This type of parenchyma comprises irregularly shaped cells that are loosely oriented towards the lower epidermis. They enclose large intercellular gaps and air cavities. A few chloroplasts can be found in the cells
•  Vascular tissues: This type of tissue is found in the veins. These are conjoint, collateral, and closed vascular bundles. A dense covering of thin-walled parenchymatous cells surrounds each vascular bundle. Border parenchyma or bundle sheath is the name given to this layer

Conclusion

It is concluded that leaves play a significant role in plants. Leaf shape and function are essential for nutrient generation, plant defense development, and survival. This is emphasised because, despite their small size compared to the size of the plant or tree, they are numerous, resulting in many photosynthetic reactions and an abundance of nutritional material. The entire interior structure of a leaf serves the function of a plant’s development, supporting animal existence.