Set-II: Past Entrance Papers

Hint

(a) The vascular tissue of the root is characterised by the radial arrangement of vascular bundles i.e., xylem and phloem occur in separate patches on alternate radii. The number of xylem and phloem groups varies from two to six. But tetrarch condition (four vascular bundles) is more common. Monocot root generally has more than six vascular bundles (polyarch). Vascular bundles in dicot stems are conjoint, collateral or bicollateral, endarch and open. They are arranged in a ring.

In monocot stems the vascular bundles are conjoint, collateral, endarch and closed. They are scattered in the ground tissue.

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(b) Vessels are long tubelike structures ideally suited for the conduction of water and solutes. These are made up of a row of cylindrical cells arranged in longitudinal series. The partition walls of these cells are perforated and as such the entire structure becomes tubelike. The region of the wall where perforations occur is known as the perforation plate. Vessels are found in the wood of almost all the angiosperms except certain primitive members of the order ranales (vessel less dicots), e.g., Trochodendron, Tetracentron, Drimys, Pseudowintera, etc.

Vessels also occur in some pteridophytes, such as Selaginella, and in the members of order Gnetales of gymnosperms (e.g., Genetum, Ephedra, and Welwitschia).

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(a) Inulin is a water-soluble fructosan. It is a common reserve food in members of family compositae. Pectin in a mucopolysaccharides and occur in plant cell walls. At the time of fruit ripening, wall pectins hydrolyse to give constituent sugars.

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(b) In plants during vascularisation, differentiation of procambium occurs followed by the formation of primary phloem and xylem simultaneously.

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(d) Endodermis is single-layered structure which separates the cortex from the stele. The cells of endodermis are barrel-shaped without intercellular spaces, living and containing starch. The radial and tangential walls of endodermal cells possess thickenings of lignin, suberin, and cutin in the form of strips or bands, which are known as Casparian bands or Casparian strips.

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(a) Casparian strip is a band of cell wall material that is deposited in the radial and transverse walls of the endodermis of roots. It is made up of suberin and sometimes lignin. It regulates water and mineral uptake by the roots. 

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(b): The innermost layer of the soft cortex is called as endodermis. This uniseriate layer is characterised by the presence of Casparian strips. This thickening was first observed by Caspary, in 1865 and hence the name.

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(b) Bordered pits are found in the vessel wall. In bordered pits, the thickening material over arches the pit cavity in such a way that a pit chamber opens to the interior by a pit aperture.

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(d) A bicollateral vascular bundle is characterised by xylem being sandwiched between phloem. Here there are two cambium rings e. g., Cucurbita.

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(b) Vascular cambium produces secondary xylem and secondary phloem. It is developed from the procambium which is an embryonic tissue, hence it is primary in origin. It is secondary in function for it forms the secondary tissues like secondary xylem, secondary phloem, and secondary medullary rays. The cambium is a radially one-cell thick zone of meristematic cells.

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(c) In monocot leaf, mesophyll cells are not differentiated into palisade and spongy tissues. But there is well-differentiated mesophyll cells in the dicot stem. Also in the upper epidermis, there are some large cells found in groups which are called bulliform cells. The venation pattern in the monocot is parallel.

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(d) Phloem is the food conducting tissue of plants. The sieve tubes are food-conducting elements of the plants. It is proposed that food is translocated by mass flow or by streaming currents of protoplasm.

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(a) Angular collenchyma occurs in, Cucurbita. It has thickening at the angles and there are no intercellular spaces. It is generally found in leaf petioles.

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(a) Grafting is a technique in which cambium bearing shoot (scion = graft) of one plant is joined to cambium bearing stump (root system = stock) of a related plant through different unions like tongue grafting, wedge grafting, etc. In grafting union between stock and scion produces an undifferentiated mass of cells called callus. Therefore, for union between stock and scion in grafting, the first to occur is the formation of callus. Callus is more or less corky secondary tissue developed lay woody plants over a wound. It is derived from the cambium.

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(b) Pericycle of root produces lateral roots. The endodermis is followed by the pericycle. Usually, it is a continuous layer but in some monocots, it is interrupted by xylem and phloem. It is the site of origin of lateral roots and cork cambium. The root branches are, therefore described as endogenous in origin.

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(c) Collenchyma occurs in climbing stems. Collenchyma occurs in the stem and petioles of dicot herbs. Due to the deposition of pectin, it has a high water-retaining capacity. Since pectin appears at the angles, it becomes a spongy tissue. The collenchyma is a mechanical tissue that gives tensile strength to the plant.

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(c) Collenchyma is found in the epidermis of the dicot stem and petioles and is abundant in climbing stems. Collenchyma occurs as hypodermis (below the epidermis) and also above the petiole in dicots providing tensile strength. So, the correct answer is ‘Dicot herbs.’

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(a) Monocot leaves possess intercalary meristem. Intercalary meristem are responsible for localised growth. Perhaps they have been separated or detached from the mother meristem e.g., meristem present at the base of leaves in many monocots, in the internode of grasses, at the top of peduncles of Plantago, and Taraxacum, etc.

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(a) Death of protoplasm is a pre-requisite for vital functions like transport of sap. Xylem is a dead tissue and does not have protoplasm, xylem performs the function of transporting water or sap inside the plant from roots to leaves.

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a) The tunica corpus concept was given by Schmidt (1924) which was based on the plane of divisions of cells. According to this concept, there are two portions in shoot apex-tunica and corpus. The tunica shows only anticlinical divisions and thus it is responsible for surface growth. The corpus shows divisions in all planes and thus responsible for volume growth.

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(a) Pith and cortex do not differentiate in monocot stem. Since numerous vascular bundles lie scattered, the ground tissue system in a monocot stem is distinguishable into hypodermis and ground parenchyma.

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(a) In hypodermis or outer cortical cells, a layer becomes meristematic which is known as cork cambium or phellogen. This phellogen also cuts off cells both on its outer side and inner side. The cells cut off on the outer side are phellem or cork cells and cells cut off on the inner side are phelloderm or secondary cortex.

The phellem or cork cells are dead and have deposition of a fatty substance called suberin (i.e., cork cells are suberized). Suberin is impervious to water and thus cork cells are buoyant (i.e., float on water).

Phellem, phellogen, and phelloderm collectively constitute periderm.

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(a) The meristem that helps in increasing girth is the lateral meristem. The lateral meristem is responsible for lateral growth of the plant i.e., growth in thickness e.g., cambium and cork cambium. It divides only periclinally or radially and is responsible for the increase in girth or diameter.

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(c) Tunica corpus theory, given by Schmidt (1927) is related to shoot apex or stem apical meristem. According to it, tunica is the outer zone of the shoot apex while corpus is the inner zone. Tunica forms protoderm that gives rise to the epidermis of the stern and leaves. Corpus is the inner mass that undergoes divisions to form procambium and ground meristem.

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(b) Smut is a disease of cereals, corn, grasses, and sorghum caused by many species of fungi. The smuts are multicellular fungi characterized by their large numbers of teliospores. The smuts get their name from a Germanic word for dirt because of their dark, thick-walled, and dust-like teliospores. They are mostly Ustilaginomycetes and can cause plant disease.

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(b) Transition of radial vascular bundle in root to conjoint vascular bundle in stem occurs in transition zone which is generally hypocotyl. Hypocotyl is the part of the embryonal axis below the level of cotyledons.

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(d) A leaf primordium grows into the adult leaf lamina by means of apical meristem first and later marginal meristems.

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(a) Procambium is the derivative of shoot apical meristem and forms vascular strand.

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(b) Dicots possess a tap root system.