Tag: internal structure of root, stem and leaf

Transpiration is the evaporative loss of water by plants. It occurs mainly through the stomata in the leaves. Usually the lower surface of a dorsiventral (often dicotyledonous) leaf has a greater number of stomata while in an isobilateral(often monocotyledonous) leaf. There are almost equal number of stomata on both surfaces.

Dorsiventral leaves orient themselves at an angle to the main axis and perpendicular to the direction of sunlight. Most dicots have dorsi-ventral leaves that are net-veined, including most trees, bushes, garden plants and wildflowers. Mesophyll is the ground tissue between the upper and lower epidermis. In dorsiventral leaf, it is differentiated into palisade parenchyma and spongy parenchyma. Palisade parenchyma lies towards the upper epidermis and consists of one, two or three layers of elongated cells, densely packed with no intercellular spaces and contains chloroplast

In the vascular bundles of dicot leaves, xylem and phloem are present on same radius and also present side by side. So they are called collateral and conjoint. Cambium is absent between xylem and phloem. So, It is called closed vascular bundle.

A dorsiventral organ is one that has two surfaces differing from each other in appearance and structure, as an ordinary leaf. This term has also been used as a synonym for dorsoventral organs, those that extend from a dorsal to a ventral surface. Dorsi-ventral leaves which usually orient at an angle to the main axis and held perpendicular to the direction of sunlight. An isobilateral leaf is usually vertically oriented to expose both surfaces to the sun. The leaves hang vertically to expose one face directly to the drying sun, then the other face. They have equal numbers of stomata in matching quantities and surface qualities of cuticle on both faces of the leaf. Epistomatic leaf has stomata on the upper surface only. Hypostomatic leaf having stomata on the underneath, i.e., foliar abaxial surface.

In a dorsiventral leaf the phloem is present towards the lower surface of the leaf. Xylem lies towards upper epidermis and is composed of annular and spirally thickened vessels, tracheids, fibres and xylem parenchyma. The vascular bundles are conjoint, closed and collateral. Mid vein bundle is large, while others are small. 

Palisade cells contain the largest number of chloroplasts per cell, which makes them the primary site of photosynthesis in the leaves of those plants that contain them, converting the energy in light to the chemical energy of carbohydrates. Beneath the palisade mesophyll are the spongy mesophyll cells, which also perform photosynthesis. Spongy cells acts well in high intensity light.

In dorsi ventral leaf, mesophyll is the ground tissue that occurs between the two epidermal layers. It is exclusively composed of chlorenchyma cells. The mesophyll is characteristically differentiated into two regions namely, an upper palisade parenchyma and a lower spongy parenchyma. Palisade parenchyma is composed of two or three layers of elongated, compactly arranged chlorenchyma cells. Intercellular spaces are absent. The cells contain a very large number of chloroplasts. Spongy parenchyma is composed of a few layers of loosely arranged spherical or oval chlorenchyma cells with prominent intercellular spaces. These cells contain very few chloroplasts. In isobilateral leaf, mesophyll is ground tissue that occurs between the two epidermal layers. It is composed of many layers of loosely arranged, spherical or oval chlorenchyma cells. Intercellular spaces are prominent. Mesophyll is not differentiated in spongy and palisade tissue. 
Therefore, the correct answer is option B.

Dorsiventral leaf - Mesophyll is the ground tissue that occurs between the two epidermal layers. It is exclusively composed of chlorenchyma cells. The mesophyll is characteristically differentiated into two regions namely, an upper palisade parenchyma and a lower spongy parenchyma. Palisade parenchyma is composed of two or three layers of elongated, compactly arranged chlorenchyma cells. Intercellular spaces are absent.

In dorsiventral leaves, mesophyll is the ground tissue that occurs between the two epidermal layers. It is exclusively composed of chlorenchyma cells. The mesophyll is characteristically differentiated into two regions namely, an upper palisade parenchyma and a lower spongy parenchyma. Dorsiventral leaves are present in dicots. In an isobilateral leaves, undifferentiated mesophyll is present. These leaves are present in monocots. Dorsiventral leaves are absent in extremely xerophytic leaves and hydrophytic leaves. 
Thus, the correct answer is option D.