Describe the internal structure of a sunflower leaf.

(N/A) The sunflower leaf is a dorsiventral leaf,which means its upper and lower surfaces are different. Its internal structure consists of three main parts:
$1$. Epidermis: It covers both the upper (adaxial) and lower (abaxial) surfaces. It is covered by a waxy cuticle. Stomata are more abundant on the lower surface.
$2$. Mesophyll: This tissue is located between the upper and lower epidermis and is differentiated into two types of parenchyma cells:
$(a)$ Palisade parenchyma: Located below the upper epidermis,these are elongated,vertically arranged cells rich in chloroplasts for photosynthesis.
$(b)$ Spongy parenchyma: Located below the palisade cells,these are oval or round cells with large intercellular spaces for gaseous exchange.
$3$. Vascular System: It consists of vascular bundles found in the veins and midrib. Each bundle is surrounded by a layer of thick-walled bundle sheath cells. Xylem is located towards the upper side,and phloem is located towards the lower side.