Which one of the following is a correct statement? [2012]a)Pteridophyt...
(1) Gametophyte of bryophytes bears protonemal & leafy stage. (2) In gymnosperm female gametophyte is not free living. (3) They are present in Marchantia or which is a bryophyte. (4) Origin of seed habit started in pteridophyte Selaginaella.
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Which one of the following is a correct statement? [2012]a)Pteridophyt...
Explanation:
The correct statement is option D, which states that the origin of seed habit can be traced in pteridophytes. Let's understand why this statement is correct.
Pteridophytes and Seed Habit:
1. Introduction to Pteridophytes:
Pteridophytes are a group of vascular plants that reproduce and disperse through spores. They include ferns, horsetails, and clubmosses. Pteridophytes have a dominant sporophyte generation and a reduced gametophyte generation.
2. Origin of Seed Habit:
The seed habit is the defining characteristic of gymnosperms and angiosperms. Seeds provide several advantages over spores, such as protection, nourishment, and dormancy. The origin of the seed habit can be traced back to the pteridophytes.
3. Evolution of Seeds in Pteridophytes:
During the evolution of pteridophytes, some species developed structures called sporangia, which protected the spores. These sporangia were initially exposed to the environment and lacked any protective covering. However, over time, modifications occurred, leading to the development of structures called sporophylls.
4. Development of Sporophylls:
Sporophylls are specialized leaves that bear sporangia. In some pteridophytes, sporophylls became modified to form structures called sporangiophores. These sporangiophores protected the sporangia and facilitated spore dispersal.
5. Seed-Like Structures:
In certain pteridophytes, the sporangiophores became further modified, leading to the development of seed-like structures. These structures had protective coverings and contained spores. They provided some advantages similar to seeds, such as protection and dispersal.
6. Seed-like Structures in Pteridophytes:
The seed-like structures found in pteridophytes are not true seeds. They lack an embryo and nutritive tissue. However, they represent an intermediate stage in the evolution of seeds.
7. Significance of Seed-like Structures:
The presence of seed-like structures in pteridophytes indicates a gradual transition from spore dispersal to seed dispersal. This transition marked the origin of the seed habit, which later evolved and became highly developed in gymnosperms and angiosperms.
Therefore, it is correct to say that the origin of the seed habit can be traced in pteridophytes. These seed-like structures found in certain pteridophytes represent an intermediate stage in the evolution of seeds.
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