Question

Explain the transverse section of dicot leaf with a neat labelled diagram. (4 Marks)

Answer 1

The transverse section of dicot leaf shows the following structures:
(i) Upper epidermis: This is the outermost layer made of single layered parenchymatous cells without intercellular spaces. The outer wall of the cells are cuticularized. Stomata are less in number. (1 Mark)
(ii) Lower epidermis: It is a single layer of parenchymatous cells with a thin cuticle. It contains numerous stomata. Chloroplasts are present only in guard cells. The lower epidermis helps in the exchange of gases. The loss of water vapour is facilitated through this chamber. (1 Mark)
(iii) Mesophyll: The tissue present between the upper and lower epidermis is called mesophyll. It is differentiated into Palisade parenchyma and Spongy parenchyma. (1 Mark)
a) Palisade parenchyma:
It is found just below the upper epidermis. The cells are elongated. These cells have more number of chloroplasts. The cells do not have intercellular spaces and they take part in photosynthesis.
b) Spongy parenchyma:
It is found below the palisade parenchyma tissue. Cells are almost spherical or oval and are irregularly arranged. Cells have intercellular spaces. It helps in gaseous exchange.
(iv) Vascular bundles:
Vascular bundle are present in mid-rib and lateral veins. Vascular bundles are conjoint, collateral and closed. Each vascular bundle is surrounded by a sheath of parenchymatous cells called bundle sheath. Each vascular bundle consists of xylem lying towards the upper epidermis and phloem towards the lower epidermis. (1 Mark)