Plant Anatomy (GATE - XL)

Correct answer.
Meristematic tissues consist of cells that are in a state of division or retain the power division. These are present in root and shoot apex.

In monocotyledon roots, vascular bundles are present as hexarch or polyarch system. Pith is large and well-developed. Cambium is absent.
Hence, A and D both characters are absent in monocotyledon roots.

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The concept of stele was developed in the late 19th century by French botanists P. E. L. van Tieghem and H. Doultion as a model for understanding the relationship between shoot and root, and for discussing the evolution of vascular plant morphology.

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Tuber of sweet potato is the modification of tap root.
Carrot is modification of tap root.

Correct answer. Runner, Stolon and Sucker are sub-aerial stem modifications.

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Xylem is one of the two types of transport tissues in vascular plants. Almost all plant cells produce primary cell walls. The major component of most primary walls in xylem is a disorganised network of cellulose fibrils, which allows the wall to stretch and expand as the cell grows. The secondary wall is deposited on the inner side of the primary wall during and after the cell has elongated or enlarged. The cellulose fibrils in the secondary wall are arranged in a regular fashion with alternating layers at fixed angles to the main axis of the cell. This reinforces the plant cell while preserving the elastic nature of the primary wall. Most of the cell types in xylem can be distinguished based on the shape and features of the secondary cell wall.
The walls of tracheids are made up of lignin. Xylem parenchyma cells store water, mineral nutrients and carbohydrates, and respond to wounding. Sclerenchyma cells of xylem provide mechanical support, defense and water transport.

A. Suberin is a waxy substance found in higher plants. Suberin is a main constituent of cork and is named after the cork oak, quercus suber.
B. Abnormal secondary growth does not follow the pattern of a single vascular cambium of a thick hair clit, producing xylem to the inside and phloem to the outside. Some dicots have anomalous secondary growth, e.g. bougainvillea and dracaena. Withania shows normal secondary growth.
C. In angiosperms, intercalary meristems occur only in monocots (in particular, grass) stems at the base of nodes and leaf blades and respond to primary growth of stem and root.
Hence, B and C are false.

Haplostele consists of a cylindrical core of xylem surrounded by a ring of phloem. An endodermis generally surrounds the stele. A centrarch (protoxylem in the center of a metaxylem cylinder) haplostele is prevalent in members of the rhyniophyte grade, such as rhynia.

Correct answer. In hydrophytes, root hairs are absent and root cap is replaced by root pocket.

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Sclerenchymatous cells are dead and lack protoplasm is correct, but them being the longest cells of the plant kingdom is not the correct explanation of assertion.

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In older stems, the woody trunk is differentiated into two regions. The outer light coloured region is called sap wood or alburnum, and central dark coloured region is called heartwood or duramen. The cells of sapwood are living and functional. They take part in conduction of water and storage of food. The heartwood consists of dead cells. During the growth process, the rings of sapwood gradually process and convert into heartwood. The living cells of sapwood lose their protoplast and water content. The lumen of the xylem vessels gets blocked in growth of the parenchyma cells.
Hence, both A and R are true.

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In dicot stem, vascular bundles are conjoint, collateral and open.
Scattered vascular bundles are a characteristic feature of monocot stem.

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Monocotyledonous plants have no secondary growth because secondary growth takes place by the activity of cambium and cork cambium.

Correct answer.
Apical meristem is an undifferentiated tissue at the tip (apex) of shoots and roots formed of meristematic cells and is responsible for growth of root and stem.