NEET Anatomy of Flowering Plants Previous Year Questions with Solutions

Transverse section of a typical monocot stem (e.g., maize, grass) reveals the following distinct anatomical features:

• • Epidermis: Single outermost layer with cuticle; trichomes (epidermal hairs) are generally absent.
• • Hypodermis: A few layers of thick-walled, lignified sclerenchymatous cells providing mechanical strength to withstand bending and wind stress. It is NEVER parenchymatous or collenchymatous.
• • Ground tissue: Large, conspicuous parenchymatous tissue extending from hypodermis to the center without differentiation into cortex, endodermis, pericycle, and pith.

Vascular bundles display iconic diagnostic hallmarks:

• • Scattered distribution: A large number of vascular bundles are scattered throughout the ground tissue; peripheral bundles are smaller and more densely arranged than larger central ones.
• • Bundle sheath: Each vascular bundle is enveloped by a sclerenchymatous bundle sheath.
• • Conjoint and closed: Vascular bundles are conjoint (xylem and phloem on same radius), collateral, and closed (cambium is absent, precluding secondary growth).
• • Phloem composition: Composed of sieve tubes and companion cells; phloem parenchyma is absent.
• • Water cavity: A lysigenous cavity (water-containing cavity) is formed by the breakdown of inner protoxylem vessels.

Statement (1) claims "Hypodermis is parenchymatous", directly contradicting the presence of a sclerenchymatous hypodermis. Hence, Statement (1) is incorrect.

The stomatal apparatus consists of the stomatal aperture (pore), two guard cells flanking the pore, and surrounding specialized subsidiary cells derived from epidermal tissue.

In dicots, guard cells are bean-shaped or kidney-shaped. The outer walls of guard cells (away from the stomatal pore) are thin, while the inner walls (facing and bordering the stomatal pore) are highly thickened and inelastic. Cellulose microfibrils are oriented radially rather than longitudinally, facilitating aperture opening when guard cells become turgid.

The question asks which component possesses thin outer walls and highly thickened inner walls. This is the hallmark anatomical definition of guard cells.

Collenchyma is a simple permanent tissue consisting of living cells characterized by unevenly thickened corners due to deposition of cellulose, hemicellulose, and pectin. They possess living protoplasts and chloroplasts, providing mechanical flexibility to growing stems and petioles. Calling collenchyma "dead" is factually false (sclerenchyma is the dead mechanical tissue).

In gymnosperms, xylem lacks vessels (except in order Gnetales). Water conduction occurs primarily through tracheids. Thus, the statement that gymnosperms lack vessels in their xylem is universally true in standard plant taxonomy.

Statement I is false and Statement II is true, leading directly to Option (2).

In grasses, certain adaxial epidermal cells along the veins modify themselves into large, empty, colourless cells called bulliform cells (or motor cells).

When the bulliform cells have absorbed water and are turgid, the leaf surface is exposed. When they are flaccid due to water stress, they cause the leaves to curl inward to minimize water loss via transpiration.

The primary physiological function is mediating inward curling of leaves in monocots.

Endarch and exarch refer exclusively to developmental arrangements of primary xylem elements (protoxylem and metaxylem). Secondary xylem formed by vascular cambium does not exhibit endarch/exarch differentiation:

In stems, protoxylem lies towards pith (centre) and metaxylem towards periphery (endarch). In roots, protoxylem lies towards the periphery and metaxylem towards the centre (exarch):

NCERT states verbatim: "In stems, the protoxylem lies towards the centre (pith) and the metaxylem lies towards the periphery of the organ. This type of primary xylem is called endarch. In roots, the protoxylem lies towards periphery and metaxylem lies towards the centre. Such arrangement of primary xylem is called exarch."

Vascular cambium activity is modulated by seasonal climatic fluctuations in temperate regions:

NCERT states verbatim: "In winter, the cambium is less active and forms fewer xylary elements that have narrow vessels, and this wood is called autumn wood or late wood."

The diminished mitotic rate of cambial fusiform initials during winter is the direct physiological cause for the anatomical traits (fewer elements, narrow vessels) of late wood. Hence, Reason R correctly explains Assertion A.

Analyzing the veracity of anatomical statements according to NCERT:

Analyzing the specific errors planted in the distractors:

Only Statements A and D are factually and technically correct. Option (3) is the required answer.

During secondary growth in dicot stems, the increase in girth tears the outer cortical and epidermal layers. A secondary lateral meristem arises in the cortex:

At certain regions, the phellogen cuts off closely arranged parenchymatous complementary cells instead of cork cells. These cells rupture the epidermis, forming lens-shaped apertures called lenticels that permit exchange of gases between the atmosphere and internal cortical tissues $\implies$ (a)-(iii).

Plant tissues are systematically organized into meristematic and permanent tissues based on division capability and cellular uniformity:

Checking (a)-(ii) narrows down candidates to Option (1). Verifying (b)-(iv), (c)-(i), and (d)-(iii) confirms complete 100% agreement with Option (1).

In young dicot stems, cambium present between primary xylem and primary phloem within a vascular bundle is the intrafascicular cambium (primary lateral meristem):

- Pair (1): Large, empty, colorless epidermal cells on the adaxial surface of grass leaves are bulliform (motor) cells, which control leaf rolling to minimize transpiration (subsidiary cells flank stomatal guard cells). - Pair (2): In leaves, vascular bundles are encased by a layer of tightly packed cells known as the bundle sheath (conjunctive tissue is the parenchymatous tissue between xylem and phloem in roots). - Pair (4): The loose, thin-walled parenchymatous cells produced by phellogen that rupture the epidermis are complementary cells, forming lenticels (spongy parenchyma is the loosely arranged mesophyll tissue in leaves).

In arborescent dicotyledonous trees undergoing multi-year secondary growth, the secondary xylem differentiates into two concentric zones: - Heartwood (Duramen): The innermost, central cylinder of secondary xylem. Tracheids and vessels become non-functional and plugged by balloon-like parenchymatous ingrowths called tyloses. Deposition of aromatic tannins, resins, oils, gums, and essential oils imparts a dark brown or black colour, durable decay-resistance, and massive mechanical tensile strength. It does not conduct water. - Sapwood (Alburnum): The peripheral, outer region of secondary xylem. It contains living xylem parenchyma and unobstructed tracheary elements that are actively involved in the conduction of sap (water and dissolved mineral salts) from roots to leaves. It is distinctly lighter in colour.

Statement (3) claims that sapwood is the "innermost secondary xylem". Because sapwood is strictly peripheral, statement (3) is anatomically false and is the required answer.

In all roots (dicot and monocot), vascular bundles are arranged radially (xylem and phloem on alternating radii). Feature (c) specifies "conjoint and closed", which is characteristic of stems, completely ruling out root options.

In monocot stems (e.g., maize), vascular bundles are numerous and scattered throughout the large conspicuous parenchymatous ground tissue (atactostele). Each bundle is surrounded by a sclerenchymatous bundle sheath.

Monocot stem vascular bundles are closed because they lack vascular cambium (incapable of secondary growth). Furthermore, phloem parenchyma is characteristically absent in monocots, and water-containing cavities (protoxylem lacunae) are present within the bundles.

All four listed features (a, b, c, d) match the NCERT textbook description of a monocotyledonous stem verbatim.