Question

Explain briefly the following terms with suitable examples –
(i) Protonema
(ii) Antheridium
(iii) Archegonium
(iv) Syngamy
(v) Sporophyll
(vi) Isogamy

Answer 1

Hint: Protonema is the first stage in the life cycle of mosses (bryophytes). Antheridium are the male sex organs and archegonium are female sex organs in bryophytes, pteridophytes. Mature leaves bear a group of sori. Such fronds are called sporophyll. Sexual reproduction takes place through spores. Isogamy occurs commonly in unicellular algae.

Complete Answer:
(i) Protonema – It is a creeping, green, branched and frequently filamentous stage. It is a haploid, independent, gametophytic stage in the life cycle of mosses. It is produced from the spores and gives rise to new plants.
Examples – Funaria, polytrichum and sphagnum.

(ii) Antheriduim – It is multicelluar jacketed male sex organ in bryophytes and pteridophytes. It produces biflagellate antherozoids.
Example: Marchantia (Bryophytes)

(iii) Archegonuim – It is multicellular jacketed, flask shaped female sex organs. It has neck, swollen venter and produces a single female gamete called egg.
Example: Bryophytes, pteridophytes and gymnosperms.

(iv) Syngamy – When one of the male gametes fuses with an egg cell to form zygote, it is called syngamy. The zygote develops into an embryo. It can be observed in angiosperms during double fertilization.

(v) Sporophyll – It is a leaf that bears sporangia. They may be microsporophyll or megasporophyll. Sporophyll aggregate to form cones or strobili.
Example: Sporophyll of fern, Microsporophyll and megasporophyll of Selaginella.

(vi) Isogamy – It is the fusion of two gametes that have similar structure.
Example: Chlamydomonas, Ectocarpus, Ulothrix.

Note:
- The gametophyte in mosses is differentiated into prostrate protonema and an erect gametophore (leafy stage) Antheridium produces biflagellate motile anthropoids, female sex organs called archegonium is flask-shaped with tubular neck and swollen venter and produces single egg. Archegonium first appears in bryophytes.
- During double fertilization one male gamete fuses with egg cells to form syngamy, other male gamete fuses with the diploid secondary nucleus to produce primary endosperm nucleus (PEN). This is a unique event in angiosperms.