States the Unifying features of archegoniated .
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Answer:
Explanation:Alternation of generation in archegoniates
1. Alternation of generation In Archegoniates Made by: Sumit Sangwan Botany hons. 2nd year
2. What is alternation of generations? • First time demonstrated by Hofmeister(1851) • Life cycle of a plant is called alternation of generations. • Haploid and diploid generation alternating during life cycle -Sporophyte ie. Multicellular , spore forming diploid plant str. -Gametophyte ie. Multicellular haploid plant structure, forms gametes.
3. Alternation of generations in different plants • Depends on type of plant • Bryophytes(mosses and ferns) - dominant generation-haploid phase - main plant body is composed of gametophyte • Pteridophytes and gymnosperms - dominant generation- diploid phase - main plant body is composed of sporophyte.
4. Significance: • Better chance for survival • Better adapted to environment • Newer varieties develop • Variations are produced during meiosis
5. Alternation of generation in Bryophytes • Haploid phase (n) is gametophytic generation or sexual phase. • Bears reproductive organs - produce antherozoids and eggs • Gametophytic stage - longer lived ,conspicuous as compared to sporophyte. • Gametophytic stage is dominant in life cycle.
6. • Diploid phase (2n) or the sporophytic stage - gametic union results into the formation of zygote which develops into sporophyte. • Meiosis in SMC(spore mother cell) - spore formed - germinate to form gametophyte again. - cycle continues with alternation b/w gametophye and sporophyte. • Sporophyte dependent on gametophyte • Heteromorphic alternation of generation.
7. Life cycle : Marchantia sp.
8. Funaria (moss): life cycle
9. Difference between moss and liverwort life cycle • GAMETOPHYTE I. presence of protonema II. Symmetry III. Rhizoids • SPOROPHYTE I. Development of embryo II. Capsule organization. III. Photosynthetic system in cell layers of capsule in mosses and absence in liver worts. IV. Presence of air pores,columella
10. Alternation of generation in Pteridophytes
11. • Haploid phase (n) is gametophytic generation or sexual phase. • Bears reproductive organs -anthredia and archegonia • Anthredia and archegonia - flagellate antherozoids and egg respectively. • Gametophyte may be monoecious as in homosporous sp. / dioecious in heterosporous sp. • Gametophyte is independent in Pteris and dependent in Selaginella.
12. • Diploid phase (2n) or sporophytic stage • Formed from zygote after fertilization. • Meiosis in SMC(spore mother cell) - non motile haploid spore formed - germinate to form gametophyte again. - cycle continues with alternation b/w gametophye and sporophyte. • All spore formed may be of one type ie.homosporous species(Lycopodium,Dryopteris)
13. • Spores formed may be of two types ie. Heterosporous species (Selaginella,Marsilea): - microspores/male spores developed in male sporangia -germinate to form male gametophyte • Megaspores/female spore developed in megasporangia. - -germinate to form female gametophyte • Sporophyte is dominant phase in life cycle • independent of the gametophyte (prothallus) and grows to a much greater size. • sporophytes are differentiated into stems, leaves and roots and shows well developed conducting tissues
14. Alternation of generation in gymnosperms
15. -GAMETOPHYTIC STAGE • Dependent on sporophyte for protection and nutrition • Haploid gametophyte found within mature sporophyte. • Two type of spores produced: - Microspore ie. Male spore, undergoes mitosis to form multicellular male gametophyte ie. Pollens grain which are contained within the pollen cones. - Megaspore ie.large, female spore, undergo mitosis in order to produce the multicellular female gametophyte. The female gametophyte is housed in the ovulate cones which are larger and generally easier to see than the male pollen cones.
16. Male cone
17. Female cone
18. • The haploid stage will continue as long as the male and female gametophytes are kept separate. • In spring, the tree release large amounts of pollen - pollen grains that contain the male gametophyte travel by air and hopefully land on an ovulate cone. • pollen tube develops in order for the newly produced male gamete to reach and fertilize the female gamete.
19. Seed • Following fertilization, the zygote develops into a sporophyte embryo, and the whole ovule transforms into the seed. • The seed contains the embryo’s food supply and has a tough seed coat • In a typical pine, seeds are shed from the cones about 2 years after pollination • When conditions are favorable, it germinates • Eventually, it grows into a sporophyte.
Altrenation of generations:
All plants undergo a life cycle that takes