Biology · Anatomy of Flowering Plants · NEET
'Dorsiventral' means the two surfaces are different (dorsal = upper, ventral = lower). In a dicot leaf, the upper side faces the sun and holds the palisade parenchyma, while the lower side holds the spongy parenchyma and more stomata. Because the top and bottom are built differently, the leaf is called dorsiventral. A dicot leaf normally lies flat with one side facing up, so this is the common type you see.
Palisade parenchyma cells are elongated (long), arranged vertically and parallel to each other, tightly packed, and placed on the adaxial (upper) side just below the upper epidermis. Spongy parenchyma cells are oval or round, loosely arranged, placed below the palisade cells, and have many large air spaces between them. Palisade does most photosynthesis (more chloroplasts, near light); spongy allows gas exchange through the air spaces.
The palisade parenchyma. It sits on the upper (adaxial) side closest to sunlight, its cells are tall and tightly packed with many chloroplasts, so it traps the most light and carries out most of the photosynthesis. The spongy layer below also has chloroplasts but its main job is gas exchange through the air spaces.
In a vertical (transverse) section through the lamina, a dorsiventral leaf shows three parts: (1) Epidermis — covers both the upper (adaxial) and lower (abaxial) surfaces and has a cuticle; the lower epidermis usually has more stomata. (2) Mesophyll — the ground tissue between the two epidermis layers, made of parenchyma, split into palisade and spongy parenchyma. (3) Vascular system — the vascular bundles in the veins and midrib, each surrounded by a bundle sheath of thick-walled cells.
The abaxial (lower) epidermis generally bears more stomata than the adaxial (upper) epidermis. The upper epidermis may even lack stomata. Having fewer stomata on the sun-facing upper side helps the leaf reduce water loss, since the top surface gets more heat and light.
Mesophyll is made of parenchyma, which is a simple permanent tissue (one cell type). In leaves this parenchyma contains chloroplasts and carries out photosynthesis, so it is specially called mesophyll. Both palisade and spongy layers are parenchyma; they are not xylem or phloem (those form the complex vascular tissue inside the veins).
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a leaf whose upper and lower sides are different. The upper side has tall palisade cells and the lower side has loose spongy cells with air spaces. Dicot plants have this type of leaf.
Mesophyll is the ground tissue between the upper and lower epidermis. It is made of parenchyma cells full of chloroplasts and carries out photosynthesis. In a dicot leaf it is split into palisade and spongy parenchyma.
Because the top of the leaf faces the sun. Palisade cells are tall, tightly packed and full of chloroplasts, so placing them near the light lets them absorb the most sunlight and do the most photosynthesis.
Each vascular bundle in the veins and midrib is surrounded by a layer of thick-walled bundle sheath cells. This layer protects and supports the xylem and phloem inside the vein.
A dorsiventral (dicot) leaf has different upper and lower sides, mesophyll split into palisade and spongy parenchyma, and more stomata on the lower surface. An isobilateral (monocot) leaf has similar surfaces, mesophyll NOT split, and stomata on both surfaces. NEET often tests this exact difference.
