Plant Tissue: Definition, Classification, Distribution and Functions including Mechanical tissues.
- Which tissue is responsible for the secondary growth in dicot stems?
(a) Apical meristem
(b) Intercalary meristem
(c) Lateral meristem
(d) Parenchyma
Answer: (c) Lateral meristem
Explanation: The lateral meristem includes vascular cambium and cork cambium, which are responsible for increasing the thickness (girth) of dicot stems. This secondary growth is crucial for structural support in woody plants. - Collenchyma provides mechanical support primarily to:
(a) Roots
(b) Young stems and petioles
(c) Woody stems
(d) Leaves only
Answer: (b) Young stems and petioles
Explanation: Collenchyma has unevenly thickened walls and is flexible, providing mechanical support to growing regions like young stems and leaf stalks without hindering growth. - Sclerenchyma fibers are dead at maturity due to:
(a) Loss of nucleus
(b) Lignified cell walls
(c) Absence of cytoplasm
(d) Suberin deposition
Answer: (b) Lignified cell walls
Explanation: Sclerenchyma cells develop thick, lignified secondary walls that cut off protoplasm, making them dead at maturity. They provide hardness and strength to plant parts. - Which is a complex tissue?
(a) Parenchyma
(b) Collenchyma
(c) Xylem
(d) Sclerenchyma
Answer: (c) Xylem
Explanation: Xylem is composed of multiple cell types like tracheids, vessels, xylem parenchyma, and xylem fibers, making it a complex tissue responsible for water conduction. - The Casparian strip is found in:
(a) Epidermis
(b) Endodermis
(c) Pericycle
(d) Cortex
Answer: (b) Endodermis
Explanation: The Casparian strip is a band of suberin present in the radial and transverse walls of endodermal cells, regulating the flow of water and solutes into the vascular cylinder. - Which tissue stores food as starch in potato tubers?
(a) Sclerenchyma
(b) Collenchyma
(c) Parenchyma
(d) Aerenchyma
Answer: (c) Parenchyma
Explanation: Parenchyma in potato tubers acts as a storage tissue for starch and other nutrients, making it essential for plant energy reserves. - Sieve tubes and companion cells are components of:
(a) Xylem
(b) Phloem
(c) Epidermis
(d) Periderm
Answer: (b) Phloem
Explanation: Phloem transports organic solutes. Sieve tubes conduct food, while companion cells support and manage metabolic functions of sieve tubes. - Aerenchyma with air cavities is adaptive for:
(a) Deserts
(b) Aquatic habitats
(c) Alpine regions
(d) Dry soils
Answer: (b) Aquatic habitats
Explanation: Aerenchyma forms large air spaces that aid buoyancy and internal aeration in submerged plants, helping survival in water-logged environments. - Which meristem is responsible for leaf elongation in grasses?
(a) Apical meristem
(b) Intercalary meristem
(c) Lateral meristem
(d) Cork cambium
Answer: (b) Intercalary meristem
Explanation: Intercalary meristem is located at nodes and leaf bases in monocots like grasses, helping in regrowth after grazing or mowing. - Cork cambium produces:
(a) Secondary xylem
(b) Secondary phloem
(c) Periderm
(d) Vascular bundles
Answer: (c) Periderm
Explanation: Cork cambium (phellogen) forms the periderm, which replaces the epidermis in older stems and roots. It includes cork (phellem) and phelloderm. - Chlorenchyma is photosynthetic due to:
(a) Chloroplasts in parenchyma
(b) Stomatal guard cells
(c) Mesophyll sclereids
(d) Collenchyma granules
Answer: (a) Chloroplasts in parenchyma
Explanation: Chlorenchyma is a type of parenchyma containing chloroplasts, typically found in mesophyll tissues of leaves where photosynthesis occurs. - Mechanical tissue absent in monocots is:
(a) Sclerenchyma
(b) Collenchyma
(c) Parenchyma
(d) Aerenchyma
Answer: (b) Collenchyma
Explanation: Monocots mostly rely on sclerenchyma for mechanical support. Collenchyma is uncommon in monocots, which usually lack differentiated cortex. - Tracheids differ from vessels by:
(a) Being living
(b) Lacking perforated plates
(c) Conducting food
(d) Presence in angiosperms
Answer: (b) Lacking perforated plates
Explanation: Tracheids have tapered ends and bordered pits but lack perforation plates, unlike vessels which are joined end to end with perforations. - Glandular trichomes secrete:
(a) Water
(b) Resins/oils
(c) Starch
(d) Lignin
Answer: (b) Resins/oils
Explanation: Glandular trichomes are epidermal structures that secrete resins, essential oils, or secondary metabolites for plant defense and attraction. - Pericycle in roots gives rise to:
(a) Root hairs
(b) Lateral roots
(c) Root cap
(d) Endodermis
Answer: (b) Lateral roots
Explanation: The pericycle is a meristematic tissue inside the endodermis. It plays a critical role in the initiation of lateral roots and secondary growth. - Bulliform cells control:
(a) Photosynthesis
(b) Leaf rolling
(c) Stomatal closure
(d) Water storage
Answer: (b) Leaf rolling
Explanation: Bulliform (motor) cells in monocot leaves help conserve water by collapsing and rolling the leaf during water stress. - Which is a dead cell?
(a) Companion cell
(b) Sclereid
(c) Collenchyma
(d) Phloem parenchyma
Answer: (b) Sclereid
Explanation: Sclereids are thick-walled, lignified, dead cells providing rigidity, often found in hard seed coats and gritty pear pulp. - Vascular cambium is derived from:
(a) Procambium
(b) Fascicular + interfascicular cambium
(c) Cork cambium
(d) Calyptrogen
Answer: (b) Fascicular + interfascicular cambium
Explanation: Vascular cambium arises from cambium between xylem and phloem (fascicular) and the parenchyma between vascular bundles (interfascicular). - Hydathodes are involved in:
(a) Photosynthesis
(b) Guttation
(c) Transpiration
(d) Secretion
Answer: (b) Guttation
Explanation: Hydathodes are present at leaf margins and release excess water in liquid form through specialized pores during guttation, especially in humid conditions. - Laticifers contain:
(a) Starch
(b) Latex
(c) Resins
(d) Water
Answer: (b) Latex
Explanation: Laticifers are specialized structures that store and transport latex, a milky fluid containing rubber, alkaloids, and other substances used for defense. - Hypodermis in dicot stems is:
(a) Parenchymatous
(b) Collenchymatous
(c) Sclerenchymatous
(d) Chlorenchymatous
Answer: (b) Collenchymatous
Explanation: The hypodermis in dicot stems is composed mainly of collenchyma, a living mechanical tissue that provides tensile strength and flexibility to growing stems, enabling them to withstand bending forces. - Velamen tissue in orchids is modified:
(a) Cortex
(b) Epidermis
(c) Endodermis
(d) Pericycle
Answer: (b) Epidermis
Explanation: In epiphytic orchids, the velamen is a multi-layered epidermal tissue on aerial roots that absorbs atmospheric moisture and helps reduce water loss. - Heartwood differs from sapwood by:
(a) Being non-conductive
(b) Light color
(c) Higher permeability
(d) Living cells
Answer: (a) Being non-conductive
Explanation: Heartwood is the central, darker, non-functional part of secondary xylem. It is impregnated with oils, resins, and tannins, making it resistant and non-conductive. In contrast, sapwood actively transports water. - Sunken stomata occur in:
(a) Hydrophytes
(b) Xerophytes
(c) Mesophytes
(d) Epiphytes
Answer: (b) Xerophytes
Explanation: Sunken stomata, located in depressions on the leaf surface, minimize water loss by trapping moisture and reducing transpiration—an adaptation seen in desert plants. - Which tissue is absent in monocot roots?
(a) Epidermis
(b) Cortex
(c) Cambium
(d) Pith
Answer: (c) Cambium
Explanation: Unlike dicot roots, monocot roots lack vascular cambium, hence do not undergo secondary growth. Their vascular bundles are radial and arranged in multiples (polyarch). - Lenticels permit:
(a) Water absorption
(b) Gas exchange
(c) Photosynthesis
(d) Food storage
Answer: (b) Gas exchange
Explanation: Lenticels are spongy openings in the periderm (outer bark) that allow exchange of gases (O₂ and CO₂) between internal tissues and the atmosphere, especially in woody stems. - Bundle sheath in C₄ plants contains:
(a) Chloroplasts
(b) Sclereids
(c) Trichomes
(d) Laticifers
Answer: (a) Chloroplasts
Explanation: In C₄ plants, bundle sheath cells surround vascular bundles and contain large chloroplasts that carry out the Calvin cycle. This spatial separation of photosynthetic processes increases efficiency. - Which is a living mechanical tissue?
(a) Sclerenchyma
(b) Collenchyma
(c) Xylem fibers
(d) Cork
Answer: (b) Collenchyma
Explanation: Collenchyma provides mechanical support in young growing parts of the plant. It is made up of living cells with unevenly thickened cell walls rich in cellulose and pectin. - Hydathodes are located on:
(a) Roots
(b) Leaf margins
(c) Stem internodes
(d) Flower petals
Answer: (b) Leaf margins
Explanation: Hydathodes are pore-like structures at leaf tips or margins involved in guttation, the release of excess water in liquid form, particularly at night. - Quiescent center is found in:
(a) Shoot apex
(b) Root apex
(c) Vascular cambium
(d) Cork cambium
Answer: (b) Root apex
Explanation: The quiescent center is a group of slowly dividing cells in the root apical meristem. It maintains meristematic activity and replaces damaged cells when needed. - Which tissue provides tensile strength to mature plant organs?
(a) Parenchyma
(b) Sclerenchyma
(c) Collenchyma
(d) Aerenchyma
Answer: (b) Sclerenchyma
Explanation: Sclerenchyma fibers are thick-walled, lignified dead cells that provide rigidity and strength to mature parts of the plant such as stems, bark, and veins. - Sieve plates are characteristic of:
(a) Tracheids
(b) Vessels
(c) Sieve tubes
(d) Companion cells
Answer: (c) Sieve tubes
Explanation: Sieve tubes in phloem have sieve plates—porous end walls that allow movement of photosynthates (mainly sucrose) between adjacent sieve elements. - In monocot stems, mechanical support is primarily due to:
(a) Collenchyma
(b) Sclerenchyma hypodermis
(c) Parenchyma
(d) Vascular bundles
Answer: (b) Sclerenchyma hypodermis
Explanation: In monocots, collenchyma is absent. The outer layer (hypodermis) has sclerenchyma that reinforces the stem’s strength and protects vascular bundles. - The tissue that regenerates damaged parts in plants is:
(a) Permanent tissue
(b) Meristematic tissue
(c) Epidermis
(d) Endodermis
Answer: (b) Meristematic tissue
Explanation: Meristematic cells divide actively and can differentiate into any tissue type, playing a crucial role in regeneration and wound healing. - Stone cells (sclereids) are abundant in:
(a) Leaf mesophyll
(b) Pear fruit and nut shells
(c) Root cortex
(d) Shoot apex
Answer: (b) Pear fruit and nut shells
Explanation: Sclereids or stone cells are short, thick-walled dead cells that impart hardness to plant parts like pear fruit flesh and seed coats of nuts. - Vascular bundles in dicot roots are:
(a) Scattered
(b) Radial
(c) Concentric
(d) Collateral
Answer: (b) Radial
Explanation: In dicot roots, xylem and phloem are arranged alternately on different radii, forming a radial pattern, suitable for water and nutrient transport. - Which tissue controls stomatal opening?
(a) Epidermal cells
(b) Guard cells
(c) Subsidiary cells
(d) Bulliform cells
Answer: (b) Guard cells
Explanation: Guard cells flank each stoma and regulate its opening by changing turgor pressure, thereby controlling gas exchange and transpiration. - The periderm replaces the:
(a) Cortex
(b) Epidermis
(c) Endodermis
(d) Pith
Answer: (b) Epidermis
Explanation: During secondary growth, the periderm (formed by cork cambium) replaces the outer epidermis and provides protection against water loss and pathogens. - Which is NOT a component of phloem?
(a) Sieve tubes
(b) Companion cells
(c) Phloem parenchyma
(d) Tracheids
Answer: (d) Tracheids
Explanation: Tracheids are elongated, lignified, dead cells involved in water conduction and are part of xylem, not phloem. - Lysigenous cavities in aerenchyma result from:
(a) Cell division
(b) Cell lysis
(c) Cell expansion
(d) Wall thickening
Answer: (b) Cell lysis
Explanation: Lysigenous aerenchyma forms when cortical cells break down or lyse to create air spaces, allowing internal aeration in aquatic plants. - Tyloses are balloon-like structures in:
(a) Phloem
(b) Heartwood xylem
(c) Epidermis
(d) Cortex
Answer: (b) Heartwood xylem
Explanation: Tyloses are outgrowths of parenchyma cells into xylem vessels, blocking them as they transition to non-functional heartwood, helping resist pathogen entry.
- Which meristem produces cortex and pith?
(a) Procambium
(b) Ground meristem
(c) Protoderm
(d) Cork cambium
Answer: (b) Ground meristem
Explanation: Ground meristem is a primary meristematic tissue that differentiates to form the ground tissues of the plant — namely, cortex, pith, and mesophyll. These tissues contribute to storage, photosynthesis, and structural functions. - Hydromorphic tissues in hydrophytes lack:
(a) Chloroplasts
(b) Mechanical tissues
(c) Stomata
(d) Aerenchyma
Answer: (b) Mechanical tissues
Explanation: In hydrophytes (aquatic plants), mechanical tissues like collenchyma and sclerenchyma are reduced or absent due to the buoyant support provided by water. This allows for a more flexible and lightweight structure. - Companion cells are connected to sieve tubes via:
(a) Plasmodesmata
(b) Sieve pores
(c) Pit membranes
(d) Middle lamella
Answer: (a) Plasmodesmata
Explanation: Plasmodesmata are microscopic channels that traverse the cell walls, allowing cytoplasmic continuity between sieve tube elements and companion cells for coordinated transport and communication. - Which tissue stores water in succulent plants?
(a) Chlorenchyma
(b) Hydrenchyma
(c) Aerenchyma
(d) Collenchyma
Answer: (b) Hydrenchyma
Explanation: Hydrenchyma is a specialized water-storage parenchyma tissue found in succulent plants like cacti and euphorbias. It helps them survive prolonged dry periods by retaining water in large central vacuoles. - The hypodermis of Pinus needles is:
(a) Parenchymatous
(b) Collenchymatous
(c) Sclerenchymatous
(d) Chlorenchymatous
Answer: (c) Sclerenchymatous
Explanation: In gymnosperms like Pinus, the hypodermis is made of sclerenchymatous cells that are lignified and provide rigidity and protection against desiccation and physical damage. - Open vascular bundles have:
(a) No cambium
(b) Cambium between xylem-phloem
(c) Phloem only
(d) Xylem only
Answer: (b) Cambium between xylem-phloem
Explanation: Open vascular bundles, characteristic of dicot stems, contain a cambium layer between xylem and phloem. This allows secondary growth and thickening of the stem over time. - Which tissue transports hormones in plants?
(a) Xylem
(b) Phloem
(c) Parenchyma
(d) Sclerenchyma
Answer: (b) Phloem
Explanation: Phloem is responsible not just for transporting organic food like sucrose, but also plant growth regulators (hormones) such as auxins and gibberellins throughout the plant. - The epidermis of roots develops:
(a) Cuticle
(b) Root hairs
(c) Stomata
(d) Trichomes
Answer: (b) Root hairs
Explanation: Root epidermal cells differentiate into root hairs, which are extensions that increase surface area for efficient water and nutrient absorption from the soil. - P-protein is found in:
(a) Xylem sap
(b) Phloem sap
(c) Latex
(d) Resins
Answer: (b) Phloem sap
Explanation: P-proteins are phloem proteins involved in sealing sieve tubes during injury. They play a defensive role by preventing loss of sap and entry of pathogens. - Which is NOT a function of parenchyma?
(a) Storage
(b) Photosynthesis
(c) Mechanical support
(d) Wound healing
Answer: (c) Mechanical support
Explanation: Parenchyma serves in storage, photosynthesis, and regeneration. Mechanical support is mainly provided by specialized supportive tissues like collenchyma and sclerenchyma. - Interfascicular cambium arises from:
(a) Procambium
(b) Medullary rays
(c) Pericycle
(d) Endodermis
Answer: (b) Medullary rays
Explanation: The interfascicular cambium originates from the parenchyma cells of the medullary rays located between vascular bundles. It contributes to the formation of the vascular cambium ring in dicots. - Myrosin cells in Brassica store:
(a) Starch
(b) Glucosinolates
(c) Latex
(d) Tannins
Answer: (b) Glucosinolates
Explanation: Myrosin cells are specialized idioblasts in Brassica species. They store glucosinolates, which are hydrolyzed to produce defense compounds like isothiocyanates upon herbivore attack. - Velamen absorbs moisture through:
(a) Active transport
(b) Capillary action
(c) Root pressure
(d) Osmosis
Answer: (b) Capillary action
Explanation: Velamen, a spongy multi-layered epidermis in epiphytic orchids, absorbs atmospheric moisture through capillarity — crucial for survival without direct soil contact. - Which tissue is multinucleate?
(a) Sieve tube
(b) Laticifer
(c) Sclereid
(d) Tracheids
Answer: (b) Laticifer
Explanation: Articulated laticifers are elongated, multinucleated cells formed by the fusion of multiple cells. They store and transport latex, which helps in defense and wound healing. - Mesophyll is differentiated into palisade and spongy in:
(a) Monocot leaves
(b) Dicot leaves
(c) Hydrophytes
(d) Xerophytes
Answer: (b) Dicot leaves
Explanation: In dorsiventral (dicot) leaves, mesophyll is divided into palisade parenchyma (upper, photosynthetic) and spongy parenchyma (lower, for gas exchange). This differentiation optimizes light absorption and internal aeration. - Quiescent center is resistant to:
(a) Drought
(b) Radiation damage
(c) Pathogens
(d) Herbivory
Answer: (b) Radiation damage
Explanation: The quiescent center in root apices consists of cells with minimal division, reducing the risk of replication-associated DNA damage from radiation or stress, thus protecting root meristems. - Girdling experiments prove:
(a) Water transport via xylem
(b) Organic nutrient transport via phloem
(c) Mineral absorption
(d) Hormone signaling
Answer: (b) Organic nutrient transport via phloem
Explanation: Girdling removes phloem in a ring from the stem. The accumulation of sugars above the ring and death below it proves phloem’s role in transporting organic nutrients. - Which tissue is absent in roots?
(a) Epidermis
(b) Stomata
(c) Endodermis
(d) Pericycle
Answer: (b) Stomata
Explanation: Stomata are specialized structures for gaseous exchange, present in aerial parts (leaves, stems), not in roots, which rely on root hairs and general diffusion for gas exchange. - Transfer cells specialize in:
(a) Short-distance solute transport
(b) Mechanical support
(c) Water storage
(d) Photosynthesis
Answer: (a) Short-distance solute transport
Explanation: Transfer cells have cell wall ingrowths that enhance surface area, facilitating rapid and efficient transport of solutes over short distances, particularly in sites of intense transport like phloem loading zones. - Which tissue provides maximum mechanical strength to plants?
(a) Parenchyma
(b) Collenchyma
(c) Sclerenchyma
(d) Aerenchyma
Answer: (c) Sclerenchyma
Explanation: Sclerenchyma cells are thick-walled and lignified, providing the highest degree of rigidity and mechanical support. They occur as fibers or sclereids in various plant parts. - Protophloem differs from metaphloem by:
(a) Being smaller and non-functional early
(b) Having companion cells
(c) Lacking sieve plates
(d) Being lignified
Answer: (a) Being smaller and non-functional early
Explanation: Protophloem matures early in rapidly elongating plant parts and often becomes non-functional or crushed soon after formation. In contrast, metaphloem develops later and remains functional for longer. - In submerged hydrophytes, the dominant mechanical tissue is:
(a) Sclerenchyma
(b) Collenchyma
(c) Parenchyma
(d) Chlorenchyma
Answer: (c) Parenchyma
Explanation: Hydrophytes rely on water for mechanical support, so their tissues are soft and flexible. Parenchyma dominates, often forming aerenchyma for buoyancy and internal gas exchange. - Trichomes are derived from:
(a) Epidermis
(b) Cortex
(c) Pericycle
(d) Pith
Answer: (a) Epidermis
Explanation: Trichomes are hair-like extensions of epidermal cells that aid in reducing transpiration, reflecting sunlight, and providing protection against herbivores and pathogens. - Which structure prevents apoplastic water movement in roots?
(a) Pericycle
(b) Casparian strip
(c) Passage cells
(d) Hypodermis
Answer: (b) Casparian strip
Explanation: Casparian strips are bands of suberin in endodermal cell walls that block passive apoplastic flow, forcing water to enter the symplastic pathway through the plasma membrane. - Girdled trees die due to disruption of:
(a) Xylem transport
(b) Phloem transport
(c) Cambial activity
(d) Root pressure
Answer: (b) Phloem transport
Explanation: Girdling removes the phloem, halting translocation of photosynthates to the roots. Starved roots die, leading to the death of the entire tree over time. - Which is NOT a component of xylem?
(a) Tracheids
(b) Vessels
(c) Xylem parenchyma
(d) Companion cells
Answer: (d) Companion cells
Explanation: Companion cells are part of phloem and aid sieve tube elements. Xylem comprises tracheids, vessels, xylem fibers, and xylem parenchyma — all aiding water conduction and support. - The tissue responsible for rhythmic growth in bamboo is:
(a) Apical meristem
(b) Intercalary meristem
(c) Lateral meristem
(d) Cork cambium
Answer: (b) Intercalary meristem
Explanation: Intercalary meristems are found at internodes and base of leaves in grasses and bamboos, allowing rapid and rhythmic elongation even after cutting or grazing. - Lignin is absent in:
(a) Sclerenchyma
(b) Tracheids
(c) Collenchyma
(d) Vessels
Answer: (c) Collenchyma
Explanation: Collenchyma provides flexible support and has cellulose and pectin-rich walls, whereas sclerenchyma and xylem elements (tracheids and vessels) have lignin-rich, rigid secondary walls. - Hydathodes discharge water through:
(a) Water stomata
(b) Lenticels
(c) Cuticle
(d) Plasmodesmata
Answer: (a) Water stomata
Explanation: Hydathodes are specialized structures, often located at leaf tips or margins, that release water droplets through a process called guttation. These modified stomata remain permanently open. - Which tissue forms the edible part of an apple?
(a) Sclereids
(b) Parenchyma
(c) Collenchyma
(d) Phloem fibers
Answer: (b) Parenchyma
Explanation: The fleshy, juicy part of an apple is mainly made of parenchymatous cells that store sugars and water, making the fruit edible and nutritious. - Vascular bundles in dicot leaves are:
(a) Conjoint collateral
(b) Radial
(c) Concentric
(d) Closed
Answer: (a) Conjoint collateral
Explanation: In dicot leaves, xylem and phloem are located together in the same vascular bundle (conjoint), with xylem on the upper side and phloem on the lower side. - Stone cells (sclereids) are found in:
(a) Potato tubers
(b) Guava fruit
(c) Cactus stems
(d) Grass leaves
Answer: (b) Guava fruit
Explanation: Sclereids (stone cells), particularly brachysclereids, give a gritty texture to fruits like guava and pear. They provide mechanical protection and prevent herbivory. - Which meristem produces vascular tissues?
(a) Protoderm
(b) Procambium
(c) Ground meristem
(d) Calyptrogen
Answer: (b) Procambium
Explanation: Procambium is a primary meristem that gives rise to primary xylem and phloem, which are responsible for conducting water and nutrients in young plant organs. - Sieve tube elements lack:
(a) Sieve plates
(b) Nucleus at maturity
(c) Cellulose walls
(d) Plasmodesmata
Answer: (b) Nucleus at maturity
Explanation: Sieve tube elements lose their nuclei at maturity, making them dependent on companion cells for metabolic activities and coordination. - Kranz anatomy is characterized by:
(a) Large bundle sheath cells with chloroplasts
(b) Sunken stomata
(c) Multiple epidermis
(d) Well-developed aerenchyma
Answer: (a) Large bundle sheath cells with chloroplasts
Explanation: Kranz anatomy is seen in C₄ plants where bundle sheath cells form a wreath around vascular bundles and carry out the Calvin cycle, optimizing CO₂ fixation. - Which tissue regenerates bark after injury?
(a) Vascular cambium
(b) Cork cambium
(c) Apical meristem
(d) Intercalary meristem
Answer: (b) Cork cambium
Explanation: Cork cambium (phellogen) forms the protective outer bark (periderm), replacing damaged epidermis after wounding or during secondary growth. - Companion cells are absent in:
(a) Angiosperms
(b) Gymnosperms
(c) Pteridophytes
(d) Bryophytes
Answer: (b) Gymnosperms
Explanation: Gymnosperms have albuminous cells, which are structurally and functionally similar to companion cells but not derived from the same mother cell. - The hypodermis of maize stems is:
(a) Collenchymatous
(b) Sclerenchymatous
(c) Parenchymatous
(d) Chlorenchymatous
Answer: (b) Sclerenchymatous
Explanation: In monocots like maize, the hypodermis (just beneath the epidermis) is made of sclerenchymatous cells that offer mechanical strength and protection. - Resin ducts in conifers are lined by:
(a) Epithelial cells
(b) Guard cells
(c) Sclereids
(d) Trichomes
Answer: (a) Epithelial cells
Explanation: Epithelial cells surrounding resin ducts synthesize and secrete resins, which deter herbivores and pathogens and help seal wounds. - Which tissue allows gaseous exchange in woody stems?
(a) Hydathodes
(b) Lenticels
(c) Stomata
(d) Cuticle
Answer: (b) Lenticels
Explanation: Lenticels are porous structures in the periderm that facilitate gaseous exchange in woody stems where stomata are absent. - In roots, lateral roots originate from:
(a) Cortex
(b) Endodermis
(c) Pericycle
(d) Epidermis
Answer: (c) Pericycle
Explanation: The pericycle is a meristematic tissue located just inside the endodermis, capable of giving rise to lateral roots and part of the vascular cambium. - Which tissue is dead but functional?
(a) Collenchyma
(b) Phloem parenchyma
(c) Tracheids
(d) Sieve tubes
Answer: (c) Tracheids
Explanation: Tracheids are non-living at maturity but functional in conducting water and providing support. In contrast, sieve tubes are living but lack nuclei. - Bulliform cells are modified:
(a) Epidermal cells
(b) Mesophyll cells
(c) Bundle sheath cells
(d) Stomatal cells
Answer: (a) Epidermal cells
Explanation: Bulliform cells are large, vacuolated epidermal cells in monocot leaves. They help in leaf rolling and unrolling during water stress. - The periderm includes all EXCEPT:
(a) Cork
(b) Cork cambium
(c) Secondary cortex
(d) Vascular cambium
Answer: (d) Vascular cambium
Explanation: Periderm includes cork (phellem), cork cambium (phellogen), and phelloderm (secondary cortex). Vascular cambium is a separate lateral meristem responsible for secondary vascular tissues. - Lysigenous cavities are common in:
(a) Xerophytes
(b) Hydrophytes
(c) Epiphytes
(d) Halophytes
Answer: (b) Hydrophytes
Explanation: In hydrophytes, lysigenous cavities form through cell lysis, creating large air spaces (aerenchyma) that aid in buoyancy and internal gas exchange. - Which tissue stores tannins?
(a) Parenchyma
(b) Sclerenchyma
(c) Collenchyma
(d) Epidermis
Answer: (a) Parenchyma
Explanation: Parenchyma cells can store various secondary metabolites like tannins, alkaloids, and resins, which function in defense and protection. - Open vascular bundles allow:
(a) No secondary growth
(b) Secondary growth via cambium
(c) Radial symmetry
(d) Scattered arrangement
Answer: (b) Secondary growth via cambium
Explanation: In dicot stems, open vascular bundles contain a cambial layer that enables the formation of secondary xylem and phloem, allowing the stem to increase in girth. - Passage cells are found in:
(a) Epidermis
(b) Endodermis
(c) Pericycle
(d) Cortex
Answer: (b) Endodermis
Explanation: Passage cells are thin-walled, unsuberized endodermal cells found opposite protoxylem poles. They facilitate water and mineral movement into the stele. - Which tissue transports amino acids?
(a) Xylem
(b) Phloem
(c) Parenchyma
(d) Sclerenchyma
Answer: (b) Phloem
Explanation: Along with sugars, phloem translocates organic nitrogen compounds such as amino acids from leaves to various parts of the plant. - Which tissue contains the thickest cell walls?
(a) Parenchyma
(b) Collenchyma
(c) Sclerenchyma
(d) Meristem
Answer: (c) Sclerenchyma
Explanation: Sclerenchyma cells have extremely thick, lignified secondary walls, which can occupy 90% of the cell volume, offering great mechanical strength. - The vascular cambium is an example of:
(a) Apical meristem
(b) Lateral meristem
(c) Intercalary meristem
(d) Protoderm
Answer: (b) Lateral meristem
Explanation: Vascular cambium lies parallel to the plant axis and facilitates secondary growth by adding secondary xylem and phloem. - In C₃ plants, bundle sheath cells:
(a) Lack chloroplasts
(b) Contain Rubisco
(c) Have Kranz anatomy
(d) Perform C₄ cycle
Answer: (a) Lack chloroplasts
Explanation: Unlike C₄ plants, C₃ plants do not have Kranz anatomy, and their bundle sheath cells typically lack chloroplasts or are not photosynthetically active. - Which tissue gives rise to adventitious roots?
(a) Epidermis
(b) Pericycle
(c) Endodermis
(d) Cortex
Answer: (b) Pericycle
Explanation: Pericycle is a lateral meristem that initiates the development of lateral and adventitious roots, especially in dicot plants.
- Phellogen produces:
(a) Secondary xylem
(b) Cork (phellem) outward and phelloderm inward
(c) Vascular tissues
(d) Root hairs
Answer: (b) Cork (phellem) outward and phelloderm inward
Explanation: Phellogen, also called cork cambium, is a secondary lateral meristem that divides periclinally to form cork (phellem) on the outer side and phelloderm (secondary cortex) on the inner side. Together, these form the periderm, replacing the epidermis during secondary growth. - The primary function of hydathodes is:
(a) Photosynthesis
(b) Guttation
(c) Transpiration
(d) Nectar secretion
Answer: (b) Guttation
Explanation: Hydathodes are specialized structures typically located at the tips or margins of leaves. They discharge liquid water through a process called guttation, driven by root pressure, especially during high soil moisture and low transpiration at night or early morning. - Which structure is absent in monocot stems?
(a) Vascular bundles
(b) Cambium
(c) Epidermis
(d) Ground tissue
Answer: (b) Cambium
Explanation: Monocot stems contain closed vascular bundles, meaning they lack a cambium layer between xylem and phloem. As a result, monocots generally do not undergo secondary growth, unlike dicots which possess open bundles with vascular cambium. - Laticifers are important for:
(a) Water transport
(b) Latex secretion (e.g., rubber, opium)
(c) Photosynthesis
(d) Mechanical support
Answer: (b) Latex secretion (e.g., rubber, opium)
Explanation: Laticifers are specialized cells or ducts that synthesize and store latex, a milky fluid containing defensive compounds like alkaloids, terpenes, and resins. They play a protective role against herbivores and pathogens and are the source of commercial products like natural rubber. - The Casparian strip is composed of:
(a) Cellulose
(b) Suberin and lignin
(c) Pectin
(d) Cutin
Answer: (b) Suberin and lignin
Explanation: The Casparian strip, found in the radial and transverse walls of endodermal cells in roots, is a hydrophobic barrier made of suberin and lignin. It blocks passive apoplastic movement of water and solutes into the vascular cylinder, ensuring selective uptake through the symplast. - In tissue culture, totipotency is exhibited by:
(a) Sclerenchyma
(b) Parenchyma
(c) Tracheids
(d) Mature sieve tubes
Answer: (b) Parenchyma
Explanation: Parenchyma cells are living, undifferentiated, and capable of cell division. Under appropriate in vitro conditions, they can exhibit totipotency — the ability to regenerate into an entire organism. This forms the basis of plant tissue culture and micropropagation techniques.
Stele: Types & Evolution
- The term “stele” refers to:
(a) Entire plant body
(b) Central vascular cylinder of roots/stems
(c) Leaf venation pattern
(d) Epidermal layer
Answer: (b) Central vascular cylinder of roots/stems
Explanation: Stele refers to the central part of the root or stem containing the vascular tissues (xylem and phloem), pericycle, and sometimes pith. It lies within the endodermis. - The most primitive type of stele is:
(a) Eustele
(b) Siphonostele
(c) Protostele
(d) Atactostele
Answer: (c) Protostele
Explanation: Protostele is the most basic and ancient type of stele with a solid xylem core surrounded by phloem, found in primitive vascular plants like Rhynia and Lycopodium. - In a protostele, xylem is surrounded by:
(a) Pith
(b) Cortex
(c) Phloem
(d) Endodermis
Answer: (c) Phloem
Explanation: In protostele, xylem occupies the center and is completely encircled by phloem; it lacks a central pith. - Which stele has a central pith?
(a) Protostele
(b) Siphonostele
(c) Actinostele
(d) Plectostele
Answer: (b) Siphonostele
Explanation: Siphonostele features a parenchymatous pith in the center, surrounded by vascular tissues; typical of ferns like Pteridium. - Eustele is characteristic of:
(a) Ferns
(b) Dicot stems
(c) Monocot roots
(d) Bryophytes
Answer: (b) Dicot stems
Explanation: In eustele, vascular bundles are arranged in a ring around the central pith, as seen in dicot stems like Helianthus. - Atactostele is found in:
(a) Dicot roots
(b) Monocot stems
(c) Fern rhizomes
(d) Gymnosperm wood
Answer: (b) Monocot stems
Explanation: Atactostele is characterized by scattered vascular bundles throughout the ground tissue, common in monocots such as maize. - Solenostele differs from dictyostele in having:
(a) Scattered bundles
(b) Non-overlapping leaf gaps
(c) Central pith
(d) Radial symmetry
Answer: (b) Non-overlapping leaf gaps
Explanation: Solenostele has leaf gaps that do not overlap, while dictyostele has multiple overlapping leaf gaps separated by parenchymatous tissues. - The stele in Selaginella stem is a:
(NEET 2020, TGT 2019)
(a) Eustele
(b) Protostele (actinostele)
(c) Siphonostele
(d) Atactostele
Answer: (b) Protostele (actinostele)
Explanation: Selaginella has an actinostele, a type of protostele with star-shaped xylem and radiating arms, typical of its primitive vascular system. - Polycyclic stele is observed in:
(a) Tree ferns (e.g., Cyathea)
(b) Grasses
(c) Pine stems
(d) Orchid roots
Answer: (a) Tree ferns (e.g., Cyathea)
Explanation: Polycyclic stele has two or more concentric rings of vascular tissues, often found in large ferns like Cyathea. - The endodermis separates:
(a) Epidermis from cortex
(b) Cortex from stele
(c) Xylem from phloem
(d) Pith from pericycle
Answer: (b) Cortex from stele
Explanation: The endodermis is the innermost layer of the cortex and acts as a selective barrier between the cortex and the stele. - Which stele type evolved first?
(a) Siphonostele
(b) Protostele
(c) Eustele
(d) Atactostele
Answer: (b) Protostele
Explanation: Protostele is the earliest and simplest stele type in evolutionary terms. It gave rise to siphonostele and then eustele. - In roots, the stele is typically:
(a) Eustele
(b) Protostele
(c) Siphonostele
(d) Atactostele
Answer: (b) Protostele
Explanation: Most roots, especially in early stages, exhibit a protostele with a central xylem core surrounded by phloem arranged in a radial pattern. - The pericycle is part of the stele and gives rise to:
(a) Root cap
(b) Lateral roots
(c) Root hairs
(d) Endodermis
Answer: (b) Lateral roots
Explanation: The pericycle, a layer just inside the endodermis, is a part of the stele and initiates the development of lateral and adventitious roots. - Amphiphloic siphonostele is found in:
(a) Fern rhizomes (e.g., Adiantum)
(b) Dicot stems
(c) Monocot roots
(d) Conifer wood
Answer: (a) Fern rhizomes (e.g., Adiantum)
Explanation: Amphiphloic siphonostele has phloem on both sides of the xylem and is common in some fern rhizomes like Adiantum. - Which plant has a eustele?
(a) Equisetum
(b) Pinus
(c) Helianthus (sunflower)
(d) Marsilea
Answer: (c) Helianthus (sunflower)
Explanation: Helianthus, a dicot, shows eustele with distinct vascular bundles arranged in a ring. Pinus has a polycyclic variant of eustele. - Stele without leaf gaps is:
(a) Siphonostele
(b) Protostele
(c) Eustele
(d) Dictyostele
Answer: (b) Protostele
Explanation: Protostele lacks leaf gaps, while siphonosteles and dictyosteles have them due to leaf trace formation. - In monocots, vascular bundles are:
(a) Arranged in a ring
(b) Scattered (atactostele)
(c) Concentric
(d) Radial
Answer: (b) Scattered (atactostele)
Explanation: Monocot stems like those of wheat and maize show atactostele with vascular bundles scattered in the ground tissue. - The stele of Equisetum is a:
(a) Protostele
(b) Siphonostele with canals
(c) Eustele
(d) Dictyostele
Answer: (b) Siphonostele with canals
Explanation: Equisetum possesses a siphonostele containing carinal canals, which are water-conducting cavities derived from the protoxylem. - Which is NOT a component of stele?
(a) Pericycle
(b) Vascular tissues
(c) Pith
(d) Endodermis
Answer: (d) Endodermis
Explanation: Endodermis forms the boundary of the stele; it is part of the cortex, not the stele itself. - The evolution of stele involved:
(a) Reduction in xylem solidity
(b) Loss of phloem
(c) Disappearance of pith
(d) Radial to collateral bundles
Answer: (a) Reduction in xylem solidity
Explanation: Evolution proceeded from solid xylem core in protostele to hollow siphonostele with pith and finally dissected bundles in eustele. - Polycyclic eustele is seen in:
(a) Ferns
(b) Gymnosperms (e.g., Cycas)
(c) Angiosperms
(d) Mosses
Answer: (b) Gymnosperms (e.g., Cycas)
Explanation: Cycas has multiple concentric rings of vascular bundles in its stem, a condition termed polycyclic eustele. - Medullary rays in eustele function in:
(a) Water conduction
(b) Lateral transport and storage
(c) Mechanical support
(d) Photosynthesis
Answer: (b) Lateral transport and storage
Explanation: Medullary rays, also called pith rays, are parenchymatous tissues running radially between vascular bundles, aiding in lateral conduction and storage. - Amphivasal bundles are characteristic of:
(a) Monocot stems
(b) Some monocot roots (e.g., Dracaena)
(c) Dicot stems
(d) Fern rhizomes
Answer: (b) Some monocot roots (e.g., Dracaena)
Explanation: In amphivasal (leptocentric) bundles, phloem is surrounded by xylem. This anomalous vascular arrangement is seen in plants like Dracaena and Yucca. - The Casparian strip is located in the:
(a) Pericycle
(b) Endodermis
(c) Epidermis
(d) Xylem
Answer: (b) Endodermis
Explanation: The Casparian strip is a suberized, impermeable band in the radial and transverse walls of endodermal cells. It prevents uncontrolled apoplastic flow of water and solutes into the stele. - Which stele type has overlapping leaf gaps?
(a) Solenostele
(b) Dictyostele
(c) Protostele
(d) Eustele
Answer: (b) Dictyostele
Explanation: In dictyostele, multiple leaf traces exit the vascular cylinder, forming overlapping leaf gaps. It is typical of advanced ferns like Dryopteris. - In Marsilea, the stele is:
(a) Protostele
(b) Siphonostele
(c) Eustele
(d) Atactostele
Answer: (b) Siphonostele
Explanation: Marsilea, an aquatic fern, possesses a siphonostele with a well-developed central pith and phloem on both sides of xylem (amphiphloic siphonostele). - The stele concept was proposed by:
(a) Strasburger
(b) Van Tieghem and Douliot
(c) Haberlandt
(d) Schmidt
Answer: (b) Van Tieghem and Douliot
Explanation: The concept of stele was introduced in 1886 by Van Tieghem and Douliot, who described the central vascular cylinder and its variations. - Which plant has a plectostele?
(a) Adiantum
(b) Lycopodium clavatum
(c) Equisetum
(d) Pinus
Answer: (b) Lycopodium clavatum
Explanation: In plectostele, xylem is dissected into plates embedded in phloem. This type of stele occurs in some species of Lycopodium (club mosses). - In dicot roots, vascular bundles are:
(a) Conjoint collateral
(b) Radial
(c) Concentric
(d) Scattered
Answer: (b) Radial
Explanation: In dicot roots, xylem and phloem occur on separate radii forming a radial arrangement, which is typical of roots with protostelic organization. - The primary function of stele is:
(a) Protection
(b) Conduction and support
(c) Photosynthesis
(d) Storage
Answer: (b) Conduction and support
Explanation: The stele contains xylem and phloem, which function in transporting water, minerals, and food throughout the plant, and also provide mechanical support.
Normal and anomalous secondary growth in stems and roots in plants.
- Normal secondary growth in dicot stems involves:
(a) Apical meristem only
(b) Vascular cambium and cork cambium
(c) Intercalary meristem
(d) Phelloderm division
Answer: (b)
Explanation: In dicots, secondary growth is initiated by the vascular cambium (producing secondary xylem and phloem) and cork cambium (forming periderm). - Anomalous secondary growth in Bougainvillea stems results from:
(a) Scattered vascular bundles
(b) Multiple concentric cambium rings
(c) Absence of cork cambium
(d) Medullary bundles
Answer: (b)
Explanation: Bougainvillea shows successive cambia that form multiple concentric rings of vascular tissue, a type of anomalous growth. - In dicot roots, vascular cambium originates from:
(a) Cortex
(b) Conjunctive tissue and pericycle
(c) Endodermis
(d) Epidermis
Answer: (b)
Explanation: The vascular cambium in dicot roots develops from conjunctive tissue (between xylem and phloem) and the pericycle (opposite protoxylem). - Which plant shows anomalous growth due to interxylary phloem?
(a) Dracaena
(b) Yucca
(c) Salvadora
(d) Boerhaavia
Answer: (c)
Explanation: Salvadora shows patches of phloem embedded in secondary xylem (interxylary phloem). - Cork cambium (phellogen) in stems is derived from:
(a) Epidermis
(b) Cortex or pericycle
(c) Pith
(d) Vascular cambium
Answer: (b)
Explanation: In stems, phellogen typically originates from the outer cortex or sometimes the pericycle. - Monocots lack normal secondary growth due to:
(a) Thin stems
(b) Absence of vascular cambium
(c) Parallel venation
(d) Fibrous roots
Answer: (b)
Explanation: Most monocots lack vascular cambium in their vascular bundles, restricting them to primary growth only. - In Dracaena, anomalous growth involves:
(a) Cork cambium only
(b) Secondary thickening meristem (STM)
(c) Fascicular cambium
(d) Intercalary meristem
Answer: (b)
Explanation: Dracaena shows anomalous secondary growth due to STM, which adds vascular bundles centrifugally. - Heartwood differs from sapwood in:
(a) Light color
(b) Being non-conductive, dark, and resin-filled
(c) Higher water content
(d) Presence of living cells
Answer: (b)
Explanation: Heartwood is darker, non-functional, and often filled with tannins, resins, and tyloses, unlike sapwood. - Anomalous secondary growth in Amaranthus stems features:
(a) Concentric cambia
(b) Accessory cambia forming circular rings
(c) Interxylary phloem
(d) Included phloem
Answer: (b)
Explanation: In Amaranthus, accessory cambial rings produce concentric zones of vascular tissues. - Vascular cambium activity in dicot stems produces:
(a) Primary phloem only
(b) Secondary xylem inward, secondary phloem outward
(c) Cork cells
(d) Periderm
Answer: (b)
Explanation: The vascular cambium produces secondary xylem toward the inside and secondary phloem outward. - Periderm in older stems replaces:
(a) Pith
(b) Epidermis
(c) Cortex
(d) Endodermis
Answer: (b)
Explanation: Periderm (phellogen, phellem, phelloderm) forms the protective covering, replacing the epidermis in older stems. - Anomalous secondary growth in Boerhaavia involves:
(a) STM
(b) Successive rings of cambia
(c) Interxylary phloem
(d) Medullary bundles
Answer: (b)
Explanation: Boerhaavia exhibits multiple rings of cambia, forming successive layers of vascular tissues. - Lenticels function in:
(a) Water absorption
(b) Gas exchange through periderm
(c) Photosynthesis
(d) Food storage
Answer: (b)
Explanation: Lenticels are pores in the bark that allow exchange of gases between internal tissues and the atmosphere. - Which plant shows normal secondary growth?
(a) Zea mays (maize)
(b) Cocos nucifera (coconut)
(c) Mangifera indica (mango)
(d) Dracaena marginata
Answer: (c)
Explanation: Mango, a dicot, undergoes typical secondary growth via vascular and cork cambium. - Included phloem (interxylary phloem) is characteristic of:
(a) Yucca
(b) Chenopodiaceae family
(c) Cycas
(d) Pinus
Answer: (b)
Explanation: Many members of Chenopodiaceae (e.g., Beta vulgaris) have strands of phloem embedded within xylem. - Secondary growth in dicot roots results in:
(a) Increased root length
(b) Increased girth and vascular tissue
(c) Adventitious root formation
(d) Root hair proliferation
Answer: (b)
Explanation: Secondary growth adds xylem and phloem, increasing root diameter. - Anomalous growth in monocots (e.g., Yucca) is due to:
(a) Cork cambium
(b) Secondary thickening meristem (STM)
(c) Fascicular cambium
(d) Intercalary meristem
Answer: (b)
Explanation: STM is responsible for secondary thickening in certain monocots like Yucca. - Tyloses are found in:
(a) Sapwood
(b) Heartwood
(c) Phloem
(d) Cambium
Answer: (b)
Explanation: Tyloses are balloon-like parenchyma extensions that block xylem vessels in heartwood. - In Bignonia, anomalous growth features:
(a) Concentric cambia
(b) Furrowed xylem with phloem patches
(c) Interxylary phloem
(d) Medullary bundles
Answer: (b)
Explanation: Bignonia has wedges of phloem embedded in secondary xylem (furrowed pattern). - Normal secondary growth is absent in:
(a) Eucalyptus
(b) Dalbergia
(c) Oryza sativa (rice)
(d) Tectona grandis (teak)
Answer: (c)
Explanation: Rice is a monocot with closed vascular bundles, preventing secondary growth. - Cork cambium in roots arises from:
(a) Epidermis
(b) Pericycle
(c) Endodermis
(d) Cortex
Answer: (b)
Explanation: In roots, the cork cambium (phellogen) originates from the pericycle. - Nyctanthes (night jasmine) shows anomalous growth with:
(a) Interxylary phloem
(b) Multiple accessory cambia
(c) Medullary bundles
(d) STM
Answer: (b)
Explanation: Successive accessory cambia form additional vascular tissues in Nyctanthes. - Vascular cambium is initially:
(a) Continuous cylinder
(b) Fascicular (in bundles) + interfascicular (between bundles)
(c) Absent in stems
(d) Radial in arrangement
Answer: (b)
Explanation: The cambium ring forms by joining fascicular (within bundles) and interfascicular (between bundles) cambium. - Anomalous secondary growth occurs in:
(a) Some dicots and monocots
(b) Only dicots
(c) Only monocots
(d) Gymnosperms exclusively
Answer: (a)
Explanation: Both dicots (Boerhaavia, Bougainvillea) and monocots (Dracaena) may show anomalous growth. - Medullary bundles are seen in:
(a) Dracaena
(b) Mirabilis jalapa
(c) Bougainvillea
(d) Yucca
Answer: (b)
Explanation: Medullary bundles are vascular bundles found in the pith region, as in Mirabilis. - Secondary growth in dicots increases:
(a) Root length only
(b) Stem and root girth
(c) Leaf size
(d) Flower production
Answer: (b) Stem and root girth
Explanation: Secondary growth involves vascular and cork cambium activity, adding secondary xylem and phloem which increases girth (diameter) of stems and roots. - In Beta vulgaris (beetroot), anomalous growth includes:
(a) Concentric cambia
(b) Supernumerary cambia producing interxylary phloem
(c) STM
(d) Furrowed xylem
Answer: (b) Supernumerary cambia producing interxylary phloem
Explanation: In Beta vulgaris, multiple accessory cambia form secondary vascular tissues with patches of phloem embedded within xylem (interxylary phloem). - Vascular cambium is more active:
(a) In roots than stems
(b) Toward the inner side (producing more xylem)
(c) In monocots
(d) During primary growth
Answer: (b) Toward the inner side (producing more xylem)
Explanation: The vascular cambium produces more secondary xylem on the inner side than phloem on the outer side, leading to wood formation. - Anomalous growth in monocot stems (Agave) results in:
(a) Annual rings
(b) Massive parenchyma with embedded vascular bundles
(c) Cork formation
(d) Heartwood deposition
Answer: (b) Massive parenchyma with embedded vascular bundles
Explanation: In Agave, the secondary thickening meristem (STM) produces parenchyma tissue with scattered vascular bundles—a type of anomalous secondary growth. - Bark includes all tissues:
(a) Inside vascular cambium
(b) Outside vascular cambium
(c) Inside cork cambium
(d) Only cork cells
Answer: (b) Outside vascular cambium
Explanation: Bark is a collective term for tissues outside the vascular cambium, including secondary phloem, cork cambium, cork, and phelloderm.
Root-steam Transition.
- The root-stem transition zone occurs in the:
(a) Root apex
(b) Hypocotyl
(c) Epicotyl
(d) Cotyledons
Answer: (b) Hypocotyl
Explanation: The hypocotyl is the embryonic region connecting the root and shoot, where vascular transition from radial (root) to collateral (stem) occurs. - During transition, root vascular bundles change from:
(a) Collateral to radial
(b) Radial to collateral
(c) Concentric to amphivasal
(d) Bicollateral to radial
Answer: (b) Radial to collateral
Explanation: Roots show radial bundles (xylem and phloem alternate), whereas stems have collateral bundles (xylem internal, phloem external). - In dicots, the transition involves:
(a) Splitting and twisting of vascular tissues
(b) Fusion of cortex and pith
(c) Disappearance of pericycle
(d) Formation of medullary rays
Answer: (a) Splitting and twisting of vascular tissues
Explanation: Xylem and phloem strands split, twist, and reorganize into the ring arrangement found in stems. - The exarch condition in roots becomes endarch in stems due to:
(a) Change in protoxylem position
(b) Protoxylem shifting from periphery to center
(c) Loss of metaxylem
(d) Phloem inversion
Answer: (a) Change in protoxylem position
Explanation: Root protoxylem lies at the periphery (exarch); in stems, it shifts toward the center (endarch condition). - Which plant shows a “direct” or “fused” type of transition?
(a) Cucurbita
(b) Ranunculus
(c) Pisum sativum (pea)
(d) Helianthus
Answer: (c) Pisum sativum (pea)
Explanation: In pea, root and shoot vascular systems connect directly with minimal rearrangement. - The transition zone is absent in:
(a) Dicots
(b) Monocots with adventitious roots
(c) Gymnosperms
(d) Pteridophytes
Answer: (b) Monocots with adventitious roots
Explanation: In monocots, adventitious roots arise directly from stem tissue, so no transition is required. - During transition, the pericycle:
(a) Forms cambium
(b) Fragments and merges with phloem
(c) Develops root hairs
(d) Becomes endodermis
Answer: (b) Fragments and merges with phloem
Explanation: Pericycle loses its identity and its cells contribute to phloem and other tissues in the stem. - In Medicago, transition involves:
(a) Vascular strands splitting into four bundles
(b) Loss of xylem
(c) Cortex transforming into pith
(d) Epidermal thickening
Answer: (a) Vascular strands splitting into four bundles
Explanation: The single vascular cylinder splits into four strands that rotate and form a ring. - The endodermis in roots:
(a) Disappears during transition
(b) Forms stomata
(c) Becomes pith in stems
(d) Develops Casparian strips in stems
Answer: (a) Disappears during transition
Explanation: Endodermis with Casparian strip degenerates in the hypocotyl; not found in stems. - Vascular transition is most complex in:
(a) Tap-rooted dicots
(b) Monocots
(c) Hydrophytes
(d) Epiphytes
Answer: (a) Tap-rooted dicots
Explanation: Tap-rooted dicots like Ricinus show significant rearrangement from radial to collateral bundle types. - In monocots, root-stem transition is:
(a) Identical to dicots
(b) Absent or simplified
(c) Involves cork cambium
(d) Centered in mesocotyl
Answer: (b) Absent or simplified
Explanation: Monocots produce adventitious roots directly from the stem, bypassing complex vascular transition. - The protoxylem gap during transition is filled by:
(a) Metaxylem
(b) Parenchyma or conjunctive tissue
(c) Phloem fibers
(d) Sclereids
Answer: (b) Parenchyma or conjunctive tissue
Explanation: As vascular tissues split, parenchyma fills the gap and maintains continuity. - Which plant exhibits a “gradual” transition type?
(a) Pisum
(b) Vicia
(c) Cucurbita
(d) Zea mays
Answer: (c) Cucurbita
Explanation: In Cucurbita, vascular rearrangement occurs gradually over an extended hypocotyl region. - The pith in stems originates from:
(a) Cortex
(b) Ground meristem of the hypocotyl
(c) Endodermis
(d) Pericycle
Answer: (b) Ground meristem of the hypocotyl
Explanation: During transition, central parenchyma from ground meristem forms the pith of the stem. - During transition, the xylem axis splits in:
(a) Dicots only
(b) Dicots and some gymnosperms
(c) Monocots only
(d) Bryophytes
Answer: (b) Dicots and some gymnosperms
Explanation: Xylem strands divide and rearrange in dicots and gymnosperms to form a ring-like pattern. - The Casparian strip is lost in the transition zone because:
(a) Endodermis degenerates
(b) Xylem absorbs it
(c) Phloem becomes active
(d) Pericycle thickens
Answer: (a) Endodermis degenerates
Explanation: Casparian strip is a feature of the endodermis, which degenerates in the transition zone. - In Lathyrus, vascular bundles rearrange into:
(a) Two bundles
(b) Four bundles
(c) Scattered bundles
(d) Concentric rings
Answer: (b) Four bundles
Explanation: Like Medicago, Lathyrus has vascular tissue splitting into four bundles that rotate to form a ring. - The primary function of root-stem transition is:
(a) Photosynthesis
(b) Continuity of vascular tissues
(c) Mechanical support
(d) Water storage
Answer: (b) Continuity of vascular tissues
Explanation: The transition ensures uninterrupted transport between root and shoot systems. - Which tissue remains continuous during transition?
(a) Endodermis
(b) Pericycle (partially)
(c) Cortex
(d) Epidermis
Answer: (b) Pericycle (partially)
Explanation: While endodermis and cortex degenerate, the pericycle fragments but contributes to stem phloem. - In gymnosperms, root-stem transition resembles:
(a) Monocots
(b) Dicots
(c) Bryophytes
(d) Pteridophytes
Answer: (b) Dicots
Explanation: Like dicots, gymnosperms show rearrangement from radial roots to collateral stems.
