Q . 1 : What are lenticels? What are their function?
Ans: Lenticels are small elliptical openings formed on the surface of dicot stem during secondary growth. They serve as passages for gas exchange. A lenticel has an opening formed by the rupture of the epidermis. At its bottom are several thin-walled and loosely arranged parenchyma cells, called complementary cells. The intercellular spaces between them enables the ventilation of internal tissues.
Q.2 : What is guttation?
Airs : When the root pressure is high and transpiration is low, certain plants lose water in the form of drops from the margins, or tips of leaves. This is known as guttation. Guttation takes place through specialised pores called hydathodes present near vein endings. Gullation takes place during night period and guttaled water may contain minerals and some excreatory products. This occurs in plants like Colocasia, Tomato, Balsm, Cucurbits, Grasses etc.
Q. 3: What are Casparian thickenings? How are they significant?
Ans: Casparian or transverse thickenings are thickenings on the walls of endodennis cells due to the deposition of lignin or suberin. It was discovered by Caspar. They regulate the movement of water solutes and also enables the selective filtration of solutes.
Q. 4 : What is phellum (Cork)? Give its function?
Ans : Phellurn (cork) is the impervious, resistant and protective tissue formed from cork cambium. It consists of dead and suberised cells, called cork cells. Phellum protects the inner tissues from desiccation, injuries due to heat, cold, attack of other organisms, etc.
Q. S : What is turgor pressure or pressure potential? What is its significance in plants?
Ans : The outwardly directed hydrostatic pressure exerted by the expanding protoplast on the cell wall, in response to the osmotic entry of water into the cell. Turgor Pressure is essential for the maintenance of form and mechanical strength of succulent parts and for the opening and closing of stomata.
Q. 6 : What is a tap root system? Name three modifications of it giving one example for each.
Ans : The root system is composed of a vertically growing primary root and its branches. The
primary root is prolongation of the radicle. The modification of taproot system include
(1) Storage roots eg: Carrot,
(ii) Perumatophores or breathing roots - eg: Rhizophora,
(iii) Buttress roots eg: bombax.
Parallel venation:- When the veins are parallel and do not form a network, it is called parallel venation. Lt is characteristic ofmonocots. They are of following types,
a. Pinnate : (Unicostate) The leaf has a prominent midrib and it gives off lateral veins which run parallel to each other towards the margin or apex of leaf.
b. Palmate : (multicostate) The leaf arranged in form of palms. eg: (a) Unifoliate eg: Citrus (b) Bifoliate.
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