General Q&A for Class 12 · Page 246
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
Discuss epidermal tissue system in detail.
Solution: The epidermal tissue system forms the outermost protective layer of the primary plant body, comprising: Epidermis Stomata Epidermal Appendages (Trichomes and Root Hairs) EPIDERMIS: Structural Characteristics: Usually single-layered (except in some x
- GeneralClass 12All
Write a descriptive note on phloem and its elements in angiosperms.
Phloem is a complex permanent tissue responsible for translocation of organic nutrients (primarily sucrose) from sources (leaves) to sinks (roots, fruits, storage organs). Components of Angiosperm Phloem: Phloem comprises four types of elements: Sieve Tube Elements Companion Cells Phl
- GeneralClass 12All
Differentiate between collenchyma and sclerenchyma.
Both collenchyma and sclerenchyma are simple permanent tissues providing mechanical support, but differ significantly in structure and function. Feature Collenchyma Sclerenchyma 1. Cellular State<
- GeneralClass 12All
Define periderm.
Periderm is the secondary protective tissue that replaces the epidermis in stems and roots undergoing secondary growth. Comprehensive Definition: Periderm is a complex tissue formed during secondary growth, comprising three components: Phellogen (Cork Cambium) - Meristematic layer Phellem (Cork) - Oute
- GeneralClass 12All
Why are annual rings formed in the flowering plants of temperate regions?
Annual rings (also called growth rings) are concentric circular bands visible in the cross-section of woody stems, formed due to seasonal activity of vascular cambium. Mechanism of Formation: Temperate Climate Characteristics: Distinct seasons: Spring (warm, wet) → Summer → Autumn → Winter (cold, dry) Seasonal ca
- GeneralClass 12All
What do you understand by secondary medullary rays?
Secondary medullary rays (also called vascular rays or xylem/phloem rays) are radially oriented parenchymatous bands that traverse through secondary vascular tissues. Formation: During secondary growth in dicot stems: Vascular cambium produces secondary xylem (inward) and secondary phloem (outward) At certain locations, cambia
- GeneralClass 12All
Differentiate between primary and secondary growth of plants.
Aspect Primary Growth Secondary Growth Definition Increase in length of roots and stems Increase in girth/diameter of roots and stems <td
- GeneralClass 12All
What are bulliform cells? What role do they play?
Bulliform cells (also called motor cells) are large, specialized epidermal cells found in grass leaves (monocots). Location: Present on the adaxial (upper) epidermis Arranged in groups in the valleys between veins Often aligned along the longitudinal axis of the leaf Structura
- GeneralClass 12All
Give a short description of the vascular system of dorsiventral leaves.
Solution: The vascular system in dorsiventral (dicot) leaves consists of vascular bundles present in veins and midrib. Structural Organization: Arrangement: Reticulate venation (net-like pattern) Midrib (central vein) → Secondary veins → Tertia
- GeneralClass 12All
Which tissue in leaves performs photosynthesis?
esophyll is the primary photosynthetic tissue in leaves. Definition: Mesophyll is the ground tissue present between the upper (adaxial) and lower (abaxial) epidermis. Structural Features: Composed of chlorophyll-rich parenchyma cells (chlorenchyma) Cells contain numerous chloroplasts
- GeneralClass 12All
What are the two types of epidermis found in leaves of flowering plants?
Solution: Leaves have two distinct epidermal layers: Adaxial Epidermis (Upper Epidermis) Abaxial Epidermis (Lower Epidermis) Detailed Comparison: Feature Adaxial Epidermis Abaxial Epidermis</st
- GeneralClass 12All
Comment upon the pericycle present in stems and roots of angiosperms.
Pericycle is a component of the ground tissue system, located inner to the endodermis. Comparative Analysis: Plant Part Pericycle Characteristics Dicot Root • Parenchymatous cells</st
- GeneralClass 12All
Give two differences between the internal structure of dicot and monocot stem w.r.t. hypodermis and vascular bundle.
olution: Character Dicotyledonous Stem Monocotyledonous Stem 1. Hypodermis Composed of collenchymatous cells (thin-walled, with angular thickening at corners)
- GeneralClass 12All
Why is endodermis also called the starch sheath in dicot stem?
abundantly filled with starch grains. Structural Features: Endodermis in Dicot Stems: Innermost layer of cortex (boundary between cortex and stele) Single-layered, barrel-shaped cells No intercellular spaces (compactly arranged) Living cells with prominent nucleus Rich in starch grains (am
- GeneralClass 12All
Why do monocotyledonous roots not undergo any secondary growth?
Monocotyledonous roots lack secondary growth due to the absence of vascular cambium. Detailed Explanation: Primary Requirement for Secondary Growth: Vascular cambium (fascicular + interfascicular) Cork cambium (phellogen) Why Monocots Lack Cambium: Embryological Constraint: Mon
- GeneralClass 12All
Discuss the location of conjunctive tissue. Which cells constitute this tissue?
Conjunctive Tissue (also called connective tissue) is a component of the ground tissue system in roots. Location: In angiosperm roots with radial vascular bundles: Located in the patches between xylem and phloem Since xylem and phloem occupy different radii, the intervening spaces contain conjunctive tissue <st
- GeneralClass 12All
What are trichomes? Write their function in angiosperms.
Trichomes are epidermal appendages (outgrowths) found on the surface of plants. Structural Diversity: Based on Cellularity: Unicellular: Single-celled (root hairs, cotton fibers) Multicellular: Multi-celled (common in shoot systems) Based on Branching: Branched: Stellate (star-shaped) tri
- 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