General Q&A for Class 12 · Page 252
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What is meant by a thallus?
A thallus is a plant body lacking differentiation into true roots, stems, and leaves. This simple organization characterizes algae and primitive bryophytes
- GeneralClass 12All
Represent schematically the life cycle of a gymnosperm.
Gymnosperm life cycle (heterosporous, with alternation of generations): Sporophyte (2n) → Male/Female Cones ↓ Male cone: Microsporophylls → Microsporangia → Microspore mother cells → Meiosis → Microspores → Pollen grains (male gametophyte) Female cone: Megasporophylls → Megasporangia (ovules) → Megaspore mother cells → Meiosis → Megaspores → Female gametophyte → Ar
- GeneralClass 12All
Discuss the economic importance of bryophytes.
(a) Soil erosion prevention: Dense mats protect soil from rain impact (b) Soil formation: Pioneer species (Sphagnum) fill ponds/lakes, creating peat soil (c) Water retention: Sphagnum absorbs large water volumes—used for plant transport (d) Peat production: Compressed, fossilized Sphagnum forms peat: Fuel source Soil amendment (
- GeneralClass 12All
Discuss major pigments and cell wall composition of different classes of algae.
Class Pigments Cell Wall Composition Chlorophyceae Chlorophyll a, b Inner cellulose + outer pectose layer Phaeophyceae <td
- GeneralClass 12All
What are the functions of following structures in algae? (b) Mention the pigments and reserve food material.
(a) Functions: Holdfast: Anchors alga to substratum Frond: Leaf-like photosynthetic structure Air bladder: Provides buoyancy for optimal light exposure (b) Brown algae characteristics: Pigments: Chlorophyll a & c, carotenoids, fucoxanthin Reserve food: Laminarin, m
- GeneralClass 12All
Discuss phylogenetic classification system, numerical taxonomy, cytotaxonomy and chemotaxonomy.
Phylogenetic Classification Basis: Evolutionary relationships and common ancestry Assumption: Taxa share common ancestors; classification reflects phylogeny Numerical Taxonomy (Phenetics) Method: Computer-based analysis of numerous characters Features: Characters assigned numerical codes Equ
- GeneralClass 12All
Discuss artificial and natural classification systems.
Artificial Classification System Basis: Superficial morphological characters (habit, flower color, leaf number) Limitations: Emphasizes vegetative characters (environmentally influenced) Separates closely related species Assigns equal importance to all characters regardless of evolutionary significance Natural Class
- GeneralClass 12All
Discuss the economic importance of pteridophytes.
(a) Soil conservation: Bind soil on slopes, preventing erosion (b) Medicinal applications: Dryopteris yields anthelmintic (anti-parasitic) compounds (c) Ornamental value: Ferns cultivated for aesthetic foliage (d) Food source: Marsilea provides edible starch for some communities (e) Industrial use: Equisetum stems used for scouring ut
- GeneralClass 12All
What is the dominant phase of pteridophytes and how is it formed?
The sporophyte is dominant in pteridophytes: Formation sequence: Spore mother cells in sporangia undergo meiosis → haploid spores Spores germinate → prothallus (small gametophyte) Prothallus bears antheridia and archegonia Flagellated antherozoids swim to archegonia (requires water) Fertilization
- GeneralClass 12All
Give five main characteristics of brown algae.
Pigmentation: Chlorophyll a & c, fucoxanthin (xanthophyll) imparts brown coloration Habitat: Predominantly marine; abundant in temperate and cold waters Morphological diversity: Range from simple filaments (Ectocarpus) to massive kelps (>100 meters) Storage products: Laminarin (polysaccharide), mannitol (suga
- GeneralClass 12All
(a) Discuss the structure of carpel. (b) Discuss post-fertilization development in angiosperms.
(a) Carpel structure (female reproductive organ): Stigma: Terminal receptive surface for pollen adhesion Style: Elongated tube connecting stigma to ovary Ovary: Basal chamber containing one or more ovules Integuments: Protective layers around ovule Nucellus: Megasporangium tissue (b)
- GeneralClass 12All
Discuss double fertilization.
Double fertilization is unique to angiosperms: Pollination: Pollen grain lands on stigma Pollen tube growth: Grows through style, reaches ovule via micropyle Gamete discharge: Two male gametes released into embryo sac First fertilization (Syngamy): Male gamete + Egg cell → Zygote (2n) Second fertilization (Triple fusion)</str
- GeneralClass 12All
What are different cells present in the embryo sac? Discuss their fate.
Embryo sac structure (seven cells, eight nuclei): Cell Type Number Fate After Fertilization Egg cell 1 Fuses with male gamete → Zygote → Embryo
- GeneralClass 12All
a) Draw a well-labelled diagram of Funaria representing gametophyte and sporophyte. (b) Explain sexual reproduction in brown algae.
(a) Funaria structure: Gametophyte: Leafy shoot with rhizoids, main axis, and leaves Sporophyte: Capsule, seta (emerging from gametophyte) (b) Sexual reproduction in brown algae: Exhibits isogamous, anisogamous, or oogamous patterns Gametes are typically pyriform (pear-shaped) with two
- GeneralClass 12All
Explain the haplo-diplontic condition in bryophytes and pteridophytes.
Haplo-diplontic life cycle features both multicellular haploid and diploid phases: In Bryophytes: Dominant phase: Independent, photosynthetic gametophyte (haploid) Sporophyte: Dependent on gametophyte for nutrition; consists of foot, seta, and capsule In Pteridophytes: Dominant phase: Independent, vascularized <s
- GeneralClass 12All
Represent schematically the type of life cycle pattern exhibited by most algae.
Most algae exhibit a haplontic life cycle: Haploid Gametophyte (n) → Gametes (n) → Syngamy → Zygote (2n) → Meiosis → Haploid Spores (n) → Gametophyte (n) Key features: Dominant phase is haploid Only the zygote is diploid Meiosis occurs immediately after fertilization (zygotic meiosis)
- GeneralClass 12All
Define microsporangiate and macrosporangiate.
Microsporangiate strobili (male cones): Bear microsporophylls with microsporangia producing microspores (pollen) Macrosporangiate strobili (female cones): Bear megasporophylls with megasporangia (ovules) producing megaspores
- GeneralClass 12All
What is the storage food in different classes of algae?
Class Storage Product Chlorophyceae Starch Phaeophyceae Laminarin, Mannitol Rhodophyceae <p
- GeneralClass 12All
Draw a well-labelled diagram of Fucus.
Fucus exhibits typical brown algae morphology with: Holdfast: Anchoring structure Stipe: Stem-like portion Frond: Photosynthetic blade with midrib Air bladders: Gas-filled structures providing buoyancy
- GeneralClass 12All
Give two general characteristics of angiosperms.
Reproductive structures: Produce flowers containing specialized reproductive organs; seeds develop within fruits (mature ovaries) Habitat diversity: Exhibit remarkable ecological adaptability, occupying virtually all terrestrial and many aquatic habitats