Questions and Answers
What is a megaphyll?
Which types of ferns possess megaphylls?
Both eusporangiate and leptosporangiate ferns
What are two reasons for the evolution of megaphylls?
What does the telome theory suggest about megaphyll evolution?
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What is a telome?
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What is true about fronds?
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What is a compound frond composed of?
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Climbing ferns exhibit determinate leaf growth.
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What defines Polypodiopsida?
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What are fern sporophytes characterized by?
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What do sori represent on fern fronds?
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What does the annulus in a sporangium do?
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What is the structure of a prothallus?
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How does a new sporophyte initially depend on the gametophyte?
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What is apogamy?
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What is apospory?
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What describes vegetative reproduction in ferns?
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Some fronds look the same when comparing fertile and sterile fronds.
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Study Notes
Ferns and Megaphylls
- Ferns are characterized by the presence of megaphylls, large leaves with multiple veins.
- Both eusporangiate and leptosporangiate ferns possess megaphylls, highlighting their evolutionary significance.
Megaphyll Definition and Function
- Megaphylls are defined by having a leaf trace gap, allowing efficient water conduction and nutrient transport.
- The evolution of megaphylls is linked to environmental adaptations and demands for better vascular systems to prevent overheating.
Evolutionary Theories
- The telome theory proposes that structures in plants evolve due to environmental pressures affecting the development of ultimate branches, or telomes.
Fern Structure and Features
- Fronds, the leaves of ferns, may vary in thickness, typically being one cell layer thick or leathery. They often exhibit dichotomous venation patterns.
- Types of fronds include entire, pinnatifid, and compound, with compound fronds consisting of lamina and petiole along with pinna and petiolule attached to the rachis.
Climbing Ferns and Growth Patterns
- Climbing ferns exhibit indeterminate leaf growth and can create dense thickets, sometimes becoming aggressive invaders in ecosystems.
Polypodiopsida Classification
- True ferns are classified under Polypodiopsida, characterized as homosporous and displaying high diversity.
Sporophyte Characteristics
- Fern sporophytes are the dominant form, featuring rhizomes (underground stems), fronds, and adventitious roots, with siphonostelic rhizomes contributing to their structure.
Reproductive Structures
- Frond surfaces display sori, which may be clustered and are responsible for spore production; these may be exposed or covered by protective structures called indusia.
- In sporangia, the annulus plays a crucial role in spore dispersal; it forms, inverts as it dries, then snaps back to release spores into the wind.
Gametophyte and New Sporophyte Development
- The prothallus, which is the gametophyte stage, is small and membranous, featuring rhizoids and gametangia on its ventral surface.
- Sperm produced by antheridia are multiflagellate, while archegonia develop near the prothallus notch.
- The new sporophyte initially relies on the gametophyte for nutrition during early development stages.
Alternative Reproductive Methods
- Apogamy refers to the formation of a sporophyte directly from a gametophyte, which can occur in either haploid or triploid forms.
- Apospory involves the formation of a 2n gametophyte directly from the sporophyte, showcasing an alternative reproductive strategy.
Vegetative Reproduction
- Some ferns reproduce vegetatively through rhizomes that divide, allowing the emergence of separate plants.
- Certain species generate bulbils, small plantlets that detach and grow independently.
Dimorphism in Ferns
- In dimorphic ferns, there is a notable visual difference between fertile and sterile fronds, which can impact reproductive strategies.
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Test your knowledge on megaphylls and their significance in ferns with these flashcards. Each card provides a definition or important fact about megaphylls and their role in plant biology. Perfect for students of botany and plant sciences.
