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Q9(iii):
Differentiate between the following:- (iii) homosporous and heterosporous pteridophyte
Solution :
Step 1: Conceptual Definitions
In Pteridophytes, the reproductive cycle is characterized by the production of spores within specialized structures called sporangia. The differentiation between homosporous and heterosporous conditions is based on the morphological and functional uniformity or dimorphism of these spores.
- Homospory: A condition where the sporophyte produces only one type of spore. These spores are morphologically identical and typically germinate to produce a monoecious gametophyte (prothallus) bearing both antheridia and archegonia. [Ref: Biological principle of reproductive uniformity].
- Heterospory: A condition where the sporophyte produces two distinct types of spores: smaller microspores and larger megaspores. This is an evolutionary precursor to the seed habit. [Ref: Evolutionary biology, specifically the development of the seed habit in Tracheophyta].
Step 2: Analytical Comparison
| Feature | Homosporous Pteridophytes | Heterosporous Pteridophytes |
|---|---|---|
| Spore Differentiation | Single type of spore produced. | Two types: Microspores and Megaspores. |
| Gametophyte | Generally monoecious. | Dioecious (Microspore forms male gametophyte; Megaspore forms female). |
| Evolutionary Status | Primitive condition. | Advanced, precursor to seed habit. |
| Representative Genera | Dryopteris, Pteris. | Selaginella, Salvinia, Azolla. |
Step 3: Visual Representation of Spore Morphology
Step 4: Theoretical Justification
The transition from homospory to heterospory represents a significant shift in resource allocation. In heterosporous plants [e.g., Selaginella], the female gametophyte is partially retained on the parent sporophyte, providing protection and nutrition to the developing embryo. This physiological interdependence is recognized as an essential evolutionary bridge toward the establishment of the seed, where the embryo is nurtured within the ovule [Per the Principles of Plant Evolution].
Final Solution: Homosporous pteridophytes produce spores of a single type resulting in monoecious gametophytes, whereas heterosporous pteridophytes produce microspores and megaspores that result in separate male and female gametophytes, representing an evolutionary trend toward seed formation.
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(iv): Explain briefly the following terms with suitable examples:- (iv) diplontic
- 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
- 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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