Bryophytes, Pteridophytes, and Gymnosperms are the three groups ofplants that bear archegonia. The life cycle of gymnosperms involves:
● Reproduction: The gymnosperms are heterosporous produces haploid microspores and megaspores. The micro and megaspores are produced within sporangia that are borne on sporophylls. The spores are arranged spirally along an axis to form lax or compact strobili or cones.
● Male gamete: The microsporangia or male strobili are strobili bearing microsporophylls and microsporangia. The microspores develop into amale gametophytic generation which is highly reduced and is confined to a limited number of cells. This reduced gametophyte is called a pollen grain which develops within the microsporangia.
● Female gamete: The microsporangia or female strobili are the cones bearing megasporophylls with ovules or megasporangia. The male or female cones or strobili can be borne on the same tree as in Pinus or, of needle-like on the different trees as in Cycas. From one of the cells of the nucellus, the megaspore mother cell is differentiated. The nucellus is protected by envelopes and the composite structure that is called an ovule. The ovules are borne on megasporophylls which may get clustered to form the female cones. To form four megaspores the megaspore mother cell divides meiotically. Within the megasporangium or nucellus, one of the megaspores is enclosed and develops into a multicellular female gametophyte that bears two or more archegonia or female sex organs. Within the megasporangium, the multicellular female gametophyte is also retained.
● Fertilization: The pollen grain is released from the microsporangium, and is carried through air currents, and comes in contact with the opening of the ovules develops on megasporophylls. In the ovules, the pollen tube carrying the male gametes grows towards archegonia, and near the mouth of the archegonia, they discharge their contents. The zygote develops into an embryo and the ovules into seeds after completing fertilization.Answered by Abhisek | 1 year ago
Describe the important characteristics of gymnosperms.
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|
How would you distinguish monocots from dicots?
Differentiate between syngamy and triple fusion
Differentiate between homosporous and heterosporous pteridophyte