GK: Class 12 General Q&A · Page 169
3,658 free answers on GK (General) for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
Give a brief description of guard cells
Guard cells are specialized epidermal cells that regulate stomatal aperture (pore). Structural Features: Shape Variation: Dicots:Bean-shaped (kidney-shaped) Monocots (Grasses):Dumb-bell shaped (with bulbous ends and narrow middle) Cellular Characteristics: <l
- GeneralClass 12All
What do you understand by protoxylem and protophloem?
Protoxylem and protophloem are the first-formed primary vascular tissues during plant development. Protoxylem: Definition: The earliest-formed primary xylem Cell characteristics:Narrow vessels/tracheids with annular or spiral thickening Flexibility: Extensible walls (allows elongatio
- GeneralClass 12All
What are the main water transporting elements in flowering plants?
Solution: The xylem tissue contains two primary water-conducting elements: Tracheids Vessels (vessel elements) Comparative Analysis: Feature Tracheids Vessels
- GeneralClass 12All
What do you mean by sclereids?
Sclereids (also called stone cells) are one of the two forms of sclerenchyma tissue. Structural Characteristics: Shape:Spherical, oval, or cylindrical Cell Wall:Highly thickened with extensive lignin deposition Lumen: Very narrow cavity (almost obliterated) <li
- GeneralClass 12All
Give a short description of parenchymatous cells.
Parenchyma is the most abundant and versatile simple permanent tissue in plants. Morphological Features: Shape: Generally isodiametric (spherical, oval, polygonal, rounded) Cell Wall:Thin, cellulosic primary walls Intercellular Spaces: May be closely packed or have small to large air
- GeneralClass 12All
What are the different types of meristems found in flowering plants w.r.t. position? Name them and describe any one.
Based on position in the plant body, meristems are classified as: Apical meristems Intercalary meristems Lateral meristems Detailed Description of Apical Meristems: Definition: Meristems located at the tips (apices) of roots and shoots. Characteristics: Shape: D
- GeneralClass 12All
Which type of cells are found in the secondary cortex?
Parenchymatous cells Formation & Structure: Produced by phellogen (cork cambium) towards the inner side Also called phelloderm Living cells with thin cellulosic walls Store nutrients and provide flexibility to the bark
- GeneralClass 12All
Give one function of the heartwood.
Provides mechanical support to the stem. Additional Functions: Structural integrity: Prevents buckling under wind stress No conduction: Dead cells filled with tannins, resins, oils Decay resistance: Aromatic compounds repel microorganisms and insects Commercial value: Used in furniture (teak, mahogany) Contrast with
- GeneralClass 12All
Which type of growth takes place in plants with the help of lateral meristems?
Secondary growth (increase in girth/diameter) Process Overview: Lateral meristems include: Vascular cambium → produces secondary xylem (wood) and secondary phloem Cork cambium (Phellogen) → produces cork (phellem) and secondary cortex (phelloderm) Taxonomic Distribution: Common in dicots and gymnosperms; absent in mos
- GeneralClass 12All
Name the material deposited on the radial and tangential walls of endodermal cells.
Suberin Biochemical Nature: Suberin is a lipophilic (waxy) biopolymer composed of: Long-chain fatty acids Phenolic compounds Glycerol Physiological Role: Forms Casparian strips that create an impermeable barrier, forcing water and minerals through the symplastic pathway (cell-to-cell), enabling selective uptake and pr
- GeneralClass 12All
Which type of arrangement of vascular bundles is seen in the roots of angiosperms?
Radial arrangement Structural Details: In radial vascular bundles: Xylem and phloem lie on different radii Alternating patches of xylem and phloem Conjunctive tissue (parenchyma) separates them Exarch protoxylem (towards periphery) Functional Advantage: This arrangement facilitates efficient lateral
- GeneralClass 12All
Define epidermis.
Epidermis is the outermost single-layered protective tissue of the primary plant body (roots, stems, leaves). Comprehensive Definition: The epidermis comprises: Compactly arranged parenchymatous cells (no intercellular spaces) Cuticle on the outer surface (waxy cutin layer) Stomata for gas exchange Trichomes (epiderma
- GeneralClass 12All
Which phloem element closely associates with the sieve tube elements?
Companion cells Mechanistic Insight: Companion cells are specialized parenchymatous cells connected to sieve tube elements via plasmodesmata (cytoplasmic bridges). Since mature sieve tubes lack nuclei, companion cells: Control sieve tube metabolism Maintain pressure gradients for translocation Regulate loading/unloading of photoassimilates</s
- GeneralClass 12All
What is the location of protoxylem in a dicot stem?
Protoxylem lies towards the centre (pith) in dicot stems. Advanced Explanation: This arrangement is called endarch condition (proto = first; endo = inside). The sequence of xylem differentiation is: Protoxylem (innermost, smaller vessels) → Metaxylem (outermost, larger vessels) Contrast with Roots: In roots, protoxylem is exarch (
- GeneralClass 12All
In which two forms does sclerenchyma exist in the body of plants?
Solution: Sclerenchyma fibres (elongated, pointed cells) Sclereids (short, isodiametric stone cells) Detailed Comparison: Feature Sclerenchyma Fibres Sclereids <st
- GeneralClass 12All
What is the name given to the specialised regions of active cell division in plants?
Solution:Meristems (or meristematic tissues) Expanded Explanation: Meristems are regions of undifferentiated cells capable of continuous division (mitosis). Based on position, they are classified as: Apical meristems: At root and shoot tips (primary growth) Intercalary meristems: At leaf bases and internodes (grasses) Lateral
- GeneralClass 12All
Distinguish between families Solanaceae, Liliaceae and Fabaceae on the basis of gynoecium characteristics. Also write economic importance of any one of the above family.
Solution: Family Gynoecium Solanaceae Bicarpellary, syncarpous, superior ovary, bilocular, oblique septum, axile placentation, many ovules <stro
- GeneralClass 12All
a) What is fruit? (b) Define parthenocarpic fruit. (c) Describe various zones of fruit by taking any fleshy fruit.
Solution: (a)Fruit: A mature, ripened ovary developed after fertilization, containing seeds. (b)Parthenocarpic fruit: A fruit that develops without fertilization, hence seedless. Examples: Banana, seedless grapes, pineapple (induced parthenocarpy) (c)Zones of a Fleshy Fruit (Mango&mdash
- GeneralClass 12All
Give two examples that develop from different part of the angiospermic plant other than radicle. Name the roots which are modified for respiration.
Solution: Adventitious Roots (Not from Radicle): Stilt roots (maize): Arise from lower nodes of stem Prop roots (banyan): Arise from branches of stem Roots Modified for Respiration: Pneumatophores (respiratory roots) in Rhizophora, Avicennia—grow vertically upward with lenticels<
- GeneralClass 12All
What is a floral diagram? Explain with a diagram.
Solution: Floral Diagram: A diagrammatic representation showing: Number of parts in each whorl Arrangement of parts Fusion and overlapping Relationship between whorls Key Features: Mother axis (position indicated by a dot) Br