Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.
The vertical section of a dorsiventral (dicotyledonous) leaf through the lamina shows three main parts: epidermis, mesophyll, and vascular system.
The epidermis covers both the upper surface (adaxial epidermis) and lower surface (abaxial epidermis) of the leaf and bears a conspicuous cuticle. The abaxial epidermis generally bears more stomata than the adaxial epidermis. The adaxial epidermis may even lack stomata.
The mesophyll lies between the upper and lower epidermis. It possesses chloroplasts and carries out photosynthesis. It is made up of parenchyma with two types of cells. The palisade parenchyma is adaxially placed and consists of elongated cells arranged vertically and parallel to each other. The spongy parenchyma consists of oval or round, loosely arranged cells situated below the palisade cells, extending to the lower epidermis. There are numerous large air cavities between these cells.
The vascular system includes vascular bundles seen in the veins and the midrib. Their size depends on the size of veins, which vary in thickness in reticulate venation. The vascular bundles are surrounded by a layer of thick-walled bundle sheath cells.
Labelled Diagram: The diagram should show the vertical section of the leaf with the following labels: Adaxial epidermis (upper), Cuticle, Palisade parenchyma, Spongy parenchyma with air cavities, Vascular bundle (showing Xylem and Phloem), Bundle sheath cells, Abaxial epidermis (lower), and Stomata.
Explanation
This question tests the student's understanding of the anatomical structure of dorsiventral leaves, typically found in dicotyledonous plants. The answer must cover all three main tissue systems - epidermis, mesophyll, and vascular system - with specific details about cell types and their arrangement. The diagram is essential for a complete answer as it visually represents the spatial arrangement of tissues. Key differentiating features from isobilateral leaves (like differentiated mesophyll into palisade and spongy parenchyma, and stomata distribution) should be highlighted.
Solution Steps
Step 1: Identify the three main parts of dorsiventral leaf from vertical section - epidermis, mesophyll, and vascular system.
Step 2: Describe epidermis with adaxial and abaxial surfaces, cuticle, and stomata distribution.
Step 3: Describe mesophyll differentiation into palisade parenchyma and spongy parenchyma with their arrangement and air cavities.
Step 4: Describe vascular system with vascular bundles, bundle sheath cells, and reticulate venation.
Step 5: Draw and label the vertical section diagram showing all parts.