Question

8. Explain briefly the following terms with suitable examples
(i) protonema
(ii) antheridium
(iii) archegonium
(iv) diplontic
(v) sporophyll
(vi) isogamy





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Answer 1

Answer:

1. Protonema: It appears due to germination of spore in Moss. It is the gametophytic stage which is creeping green branched and filamentous. From the leafy stage of moss gametophyte appears. Example: Funaria.
2. Antheridium: It is multicellular, jacketed, male sex organ. Each antheridium which is usually round or club shaped is surrounded by jacket protecting the mass of androcytes. Androcytes or sperm mother cells from number of sperms are male gametes. Example: Marchantia, Funaria, Ferns.
3. Archegonium: Archegonium is female sex organ in bryophytes and pteridophytes and gymnosperms. It bears a tubular neck and swollen, lower venter. Neck usually contains one or many neck Canal cells. In venter egg (oosphere) and venter Canal cell are present. Example: Marchantia, Funaria, Ferns, Pinus etc.
4. Diplontic life cycle: It is found in all seed bearing plants i.e. gymnosperms and angiosperms. The dominant vegetative phase is diploid (sporophytic). The sporophyte bears sex organs which produce gametes. Thus meiosis occurs at the time of gamete formation (gametogenesis). The gametic fusion results in the production of zygote which gives rise to diploid sporophyte again.
5. Sporophyll: Modified leaf bearing sporangia are called sporophylls. They may be of two types i.e. Microsporophylls and Megasporophylls. Microsporophylls bear microsporangia and Megasporophylls bear megasporangia. They may get clustered to form male cones and female cones respectively. e.g. Sporophyll- Ferns. Microsporophylls and Megasporophylls - Pinus.
6. Isogamy: It is the fusion of gametes, where both the fusing gametes and morphologically and physiologically identical. e.g. Chlamydomonas.

Answer 2

Answer:

i) Protonema is the haploid stage in the bryophyte lifecycle where thread-like chain of cells are formed Ex: In mosses protonema develops directly from a spore.

ii) Antheridium – The male sex organ, producing male gametes in bryophyte and pteridophytes is called antheridium. Ex: many fungi and algae have antheridia during their reproductive phases.

iii) Archegonium is a female reproductive organ of bryophytes which is flask-shaped and produces a single egg. Observed in pteridiophytes, gymnosperms, bryophytes, they are jacketed and multicellular, possessing a neck and a swollen venter.

iv) Diplontic – Life cycle in which dominant free living phase is diploid, generating haploid gametes. Ex: Sargassum

v) A leaf which bears sporangia is called as sporophyll, which may be microsporophyll or megasporophyll. These structures combine to form strobini(cones) Ex: Pinus

vi) Isogamy – Sexual reproduction that takes place through fusion of two gametes which can be flagellated and similar in size or non-flagellated (non-motile) but similar in size. Such reproduction is called isogamy. Ex: Ectocarpus