Explain Dorsiventral (Dicotyledonous) Leaf
in detail....
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Answers
Answer:
(i) Epidermis: A dicotyledonous leaf is generally dorsiventral. It has upper and lower epidermis. The epidermis is usually made up of a single layer of cells that are closely packed. The cuticle on the upper epidermis is thicker than that of lower epidermis. The minute openings found on the epidermis are called stomata.
(ii) Mesophyll: The ground tissue lying between the two epidermal layers is known as the mesophyll. It is differentiated into (a) Palisade parenchyma and (b) Spongy parenchyma.
(a) Palisade parenchyma: Palisade cells occur below the upper epidermis. In consists of one layer of elongated cylindrical cells. They are closely packed. They contain numerous chloroplasts. It manufactures starch by photosynthesis.
(b) Spongy parenchyma: It consists of irregularly shaped cells, loosely arranged towards the lower epidermis. They enclose large intercellular spaces and air cavities. The cells contain a few chloroplasts. Spongy cells help in the diffusion of gases through the spaces between them.
(c) Vascular tissues: It is located in the veins. Vascular bundles are conjoint, collateral and closed. Each vascular bundle is surrounded by a compact layer of thin-walled parenchymatous cells. This layer is known as border parenchyma or bundle sheath.
It is the uppermost single layer made up of parenchymatous cell, but sometimes multilayer eg: Ficus
cuticle covers the upper layer
The stomata is less in the upper suface. The stomata is more in number in lower epidermis.
Mesophyll is differentiated in two parts I. e., upper palisade and lower spongy parenchyma.
Palisade cells has chloroplasts.Hence they are major seat of photosynthesis
Spongy parenchyma has less chloroplasts and it's stores food
Vascular bundle with colourless bundle sheath (in C4 plants)
vascular bundle withn xylem towards upper side and phloem towards lower side