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Q8(iv):
Explain briefly the following terms with suitable examples:- (iv) diplontic
Solution :
1. Theoretical Definition of Diplontic Life Cycle
The diplontic life cycle is a biological pattern of alternation of generations characterized by the dominance of the diploid ($2n$) sporophytic phase. In this life cycle, the organism exists primarily as a multicellular diploid individual, while the haploid ($n$) phase is severely reduced to only the gametes (sperm and egg) formed through meiosis [Per Biological Principles of Alternation of Generations].
2. Schematic Representation of Diplontic Cycle
3. Sequential Analysis of the Diplontic Cycle
- Step 1: Dominant Phase: The main plant body is diploid ($2n$), representing the sporophyte. It produces haploid gametes through the process of meiosis [By Genetic Reduction Law].
- Step 2: Gametogenesis: Meiotic division occurs in specialized cells (meiocytes), resulting in the production of haploid gametes ($n$). These gametes represent the only haploid stage in the life cycle.
- Step 3: Fertilization (Syngamy): The haploid gametes fuse to restore the diploid condition, forming a zygote ($2n$). The zygote undergoes mitotic divisions to develop into the multicellular diploid sporophyte, thereby completing the cycle.
4. Comparative Context
| Feature | Diplontic Cycle |
|---|---|
| Dominant Phase | Sporophyte ($2n$) |
| Haploid Stage | Only Gametes |
| Examples | All seed-bearing plants (Gymnosperms and Angiosperms), Fucus (algae) |
5. Biological Significance
The diplontic life cycle is highly adaptive for terrestrial survival. Because the diploid state contains two sets of chromosomes, it provides a "backup" copy of genetic information, allowing for masking of deleterious recessive mutations, which is evolutionarily advantageous for complex organisms [Per Evolutionary Biology Theory of Genetic Redundancy].
Final Solution: The diplontic life cycle is a pattern where the diploid sporophyte is the dominant, independent, and photosynthetic phase of the plant. The haploid gametophytic phase is reduced to a single-celled or few-celled gamete stage. Representative examples include all Gymnosperms and Angiosperms.
More Questions from Class 11 Biology Plant Kingdom EXERCISES
- Q1: What is the basis of classification of algae?
- Q2: When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?
- Q3: Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
- Q4: Mention the ploidy of the following: protonemal cell of a moss; primary endosperm nucleus in dicot, leaf cell of a moss; prothallus cell of a ferm; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.
- Q5: Write a note on economic importance of algae and gymnosperms.
- Q6: Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
- Q7: What is heterospory? Briefly comment on its significance. Give two examples.
- Q8(i): Explain briefly the following terms with suitable examples:- (i) protonema
- Q8(ii): Explain briefly the following terms with suitable examples:- (ii) antheridium
- Q8(iii): Explain briefly the following terms with suitable examples:- (iii) archegonium
- Q8(v): Explain briefly the following terms with suitable examples:- (v) sporophyll
- Q8(vi): Explain briefly the following terms with suitable examples:- (vi) isogamy
- Q9(i): Differentiate between the following:- (i) red algae and brown algae
- Q9(ii): Differentiate between the following:- (ii) liverworts and moss
- Q9(iii): Differentiate between the following:- (iii) homosporous and heterosporous pteridophyte
- Q10: Match the following (column I with column II) Column I Column II (a) Chlamydomonas (i) Moss (b) Cycas (ii) Pteridophyte (c) Selaginella (iii) Algae (d) Sphagnum (iv) Gymnosperm
- Q11: Describe the important characteristics of gymnosperms.
CBSE Solutions for Class 11 Biology Plant Kingdom
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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