Set-I: Past Entrance Papers

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(c) Medullary rays (pith rays or wood rays) are sheets or ribbons of cells running from the inside of the plant to the outside. That is, they run at right angles to the xylem and phloem, which run vertically. While the plant is alive, these medullary cells are alive. In dicot stems, the cambium which is present between the primary xylem and primary phloem is called intrafascicular cambium. The cells of medullary rays near this intrafascicular cambium become meristematic and form interfascicular cambium. This leads to the formation of a continuous ring of cambium. Other options can be corrected as: Few epidermal cells in the vicinity of guard cells become specialised in their shape and size and are called subsidiary cells.
The parenchymatous cells which lie between the xylem and the phloem are called conjunctive tissue.
A spongy layer of irregular chlorophyll-bearing cells interspersed with air spaces that fill the interior part of the leaf below the palisade layer is called spongy parenchyma.

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(c) Regeneration of damaged growing grass following grazing is largely due to intercalary meristem. It is the meristem which oocurs between mature tissues. It is found in grasses and regenerates parts damaged by the grazing herbivores.

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(a) In the dicot root, the vascular cambium originates from tissues located below the phloem bundles and a portion of pericycle tissue above the protoxylem. Vascular cambium is the meristematic layer that is responsible for cutting off vascular tissues (xylem and phloem). In the young stem, it is present in patches as a single layer between the xylem and phloem.

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(d) Xylem is a type of complex tissue. it translocates water, mineral salts, organic nitrogen, and hormones.

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(c) Casparian strip is a band of cell wall material deposited in the radial and transverse walls of the endodermis. Casparian strip is made of suberin and sometimes lignin.

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(a) Grasses are monocots and monocots usually do not have secondary growth. Palm-like monocots have anomalous secondary growth.

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(b) Secondary tissues are generated from the growth of a cambium. Vascular cambium gives rise to secondary xylem to the inside, and to secondary phloem to the outside.

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(d) Root hair are lateral tubular outgrowths that develop from the outer cells of zone of maturation or root hair zone.

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(a) Cortex is the region present between epidermis and stele.

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(d) The leaf and stem epidermis of the plant is covered with pores called stomata. Each stomata is surrounded by a pair of specialised epidermal cells known as guard cells which are in some cases further surrounded by another category of less modified epidermal cells known as subsidiary cells which provide support to the guard cells.

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(a) In monocot root, a large number of vascular bundles are arranged in the form of a ring around the central pith. Vascular bundles are closed because there is no cambium present between the xylem and phloem.

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(d) Vascular bundles in monocotyledons are considered as closed because cambium is absent in the vascular system and thus they lack secondary growth in the thickness.

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(d) Lenticels are lens-shaped openings formed in bark due to secondary growth. They permit gaseous exchange in woody trees. They also contribute to transpiration but in minute amounts because the suberised complementary cells present beneath the pore prevent excessive water loss.

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(c) In dicot stems, the cells of cambium present between the primary xylem and primary phloem is the intrasfascicular cambium. The cells of medullary rays, adjoining these intrafascicular cambium become meristematic and form the interfascicular cambium. Thus, a continuous ring of cambium is formed.

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(b): Lateral meristems are the meristems which are present along the lateral sides of the stem and roots. They divide only in the radial direction. Intrastelar or vascular cambium ring formed by intra-fascicular (also called fascicular) and inter-fascicular cambium; and cork cambium (phellogen) are examples of this type of meristem. These meristems are responsible for the increase in the girth of stems and roots.

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(d) \(\mathrm{C}_{4}\) plants show the kranz type of anatomy. In kranz anatomy, the mesophyll is undifferentiated and its cells occur in concentric layers around vascular bundles. The vascular bundles are surrounded by large-sized bundle sheath cells which are arranged in wreath-like manner in one to several layers. In \(\mathrm{C}_{4}\) plants there are two carboxylation reactions, first in mesophyll chloroplast and second in bundle sheath chloroplast. RuBP is present in bundle sheath chloroplasts where \(\mathrm{C}_{3}\) cycle takes place.

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(b) The epidermal surface of the leaf exhibits 1,000 to 60,000-minute openings called stomata. The stomata are bordered by two specialized epidermal cells – the guard cells which in some cases are accompanied by subsidiary cells. The walls of guard cells are unevenly thickened. Each guard cell has a thick, inelastic inner wall and a thin, elastic outer wall. Stomatal aperture is present in between the guard cells. Guard cells are not always surrounded by accessory cells or subsidiary cells.

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(d) Vessels are the integral component of the xylem. These are typically found in flowering plants (angiosperms) but absent from most of the gymnosperms such as conifers. Vessel elements are the main feature distinguishing the hardwood of angiosperms from the softwood of conifers. Gymnosperms are also called as ‘softwood spermatophytes’ because they lack thick-walled vessels rendering them softwood plants; because vessels impart strength to wood.

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(b) In monocot stem vascular bundles are oval-shaped. In this, xylem and phloem are present on the same radii, and also present side by side. So they are also called Collateral and Conjoint vascular bundles. In the vascular bundles, cambium is absent between xylem and phloem, So these are closed vascular bundles. In the xylem, protoxylem is towards the centre, and the metaxylem is towards the periphery. So, it is a endarch xylem. In the protoxylem, some of the cells, disintegrate, and form into a lysigenous cavity, called Protoxylem lacuna. eg: Maize.

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(c) Vascular bundle consists of complex tissues, the phloem, and the xylem. In dicots, between xylem and phloem, cambium is present which helps in secondary growth. This type of vascular bundle is called open. While in monocots cambium is absent, so these are called closed vascular bundles.

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(a) Companion cell is a type of cell found within the phloem of flowering plants. Each companion cell is usually closely associated with a sieve element. They remain connected with sieve cells by plasmodesmata. They help in loading of phloem sieve cells with sugars through active transport.

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(b) Ground tissue can be defined as all the tissues except epidermis and vascular bundles. Ground tissue constitutes the interior of organs except vascular system. It consists of simple tissues such as parenchyma, collenchyma, and sclerenchyma. Parenchymatous cells are usually present in the cortex, pericycle, pith, and medullary rays, in the primary stems and roots. The ground tissue system of the leaves is called mesophyll.

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(b) In the dicot stem, cambium is present between xylem and phloem, such vascular bundles are called open. In the monocot stem, the cambium is absent, such vascular bundles are called closed. Cambium are the meristematic cells which produces secondary xylem and phloem.

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(a) Barley is a monocotyledonous plant. The vascular bundle of the stem is conjoint, collateral, exarch, and closed (because cambium is absent). It is also scattered throughout the ground tissue.

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(d) Palisade parenchyma is absent in leaves of Sorghum. It is a monocot plant where the parenchyma tissues of the leaves are not differentiated into palisade and spongy.

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(a) Xylem is the principal water-conducting tissue of the plant. It consists of four types of cells-tracheids, vessels, xylem fibres and xylem parenchyma.

Xylem vessels are hollow, elongated cells with open ends and pitted walls. Cells walls are lignified. At maturity, nucleus is absent in vessels.

The constituent cells of the phloem are sieve elements (sieve cells, sieve tubes), companion cells, phloem fibres, and phloem parenchyma cells.

Sieve tube members are long, slender, tube-like cells joined end to end, to form long tubular channels the sieve tubes. Sieve tube members possess specialized sieve areas on the end walls called sieve plates. Young sieve-tube members have abundant cytoplasm but there is no nucleus. The nucleus disintegrates during their development.

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(c) The tissues which develop from apical meristem and procambium are known as primary tissues and these constitute the primary structures of the plant body. The development of the primary tissues causes the stem to grow in length and to some extent in thickness. Stem and root in dicotyledons show secondary growth as they have the development of secondary vascular tissues (i.e., secondary xylem and secondary phloem) in them. Flowers, fruits, and leaves are primary tissues.

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(a) The root system of a plant develops from the hypocotyl of the embryo of a seed.

The root shows the following four regions these usually merge into one another, without distinct boundaries between them. 

The zones, successively from the apex to the base are-
(i) Root cap zone: The apex of each root is covered by a cushion of thin-walled cells known as root cap. (ii) Region of cell division: It lies just behind the root cap. It is the main growing region of the root where active cell divisions take place.
(iii) Region of elongation: The region of elongation is responsible for the growth in the length of the root.
(iv) Region of maturation: Epidermal cells of this region give out small, thin, cylindrical unicellular outgrowths, known as root hairs. These are the main absorbing organs of the root.

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(d) Parts of typical root: root cap, meristematic growing region, zone of elongation, root hair zone, zone of meristematic cells.

Apical meristem is terminal in position and responsible for the terminal growth of the plant. Apical meristem is present at all root tips and shoot tips.

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(a) The major storage component of Avocado fruit is oil. It is stored in specialized mesocarp cells called idioblast.

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(a) In monocotyledons the seeds are generally endospermous. The internal structure of grain can be studied in a longitudinal section. It shows two distinct regions upper large region, the endosperm, and the lower smaller region, the embryo. The endosperm is surrounded by a special one-cell thick layer, called the aleurone layer. It is filled with aleurone grains which are proteinaceous in nature. Other components of this layer are phytin, carbohydrates and small amounts of phospholipids are also present.

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(c) Chlorenchyma or assimilatory parenchyma are parenchymatous cells that possess abundant chloroplasts in them. They are capable of photosynthesis. A spore capsule of moss can perform photosynthesis because of the presence of chlorenchyma cells in them.

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(b) In the apices of some roots, (e.g., Zea mays or maize), there is a central region of cells that normally does not divide. This central inactive region was called the quiescent centre by F.A.L. Clowes (1959, 1961). The cells of this region have lesser amounts of RNA and DNA so they have small nuclei. These cells also have a lower rate of protein synthesis. Mitochondria and endoplasmic reticulum are less developed. The cells of the quiescent centre are usually inactive. However, if already existing meristematic cells are injured or become inactive due to any other reason, the cells of the quiescent centre become active.

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