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Lecture 4 - Lecture 4 COLINATION OF THE LAND invasion of...

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Lecture 4 COLINATION OF THE LAND- invasion of the land plants!!! Plants probably descended from group of green algae called charophytes or Stone worts Difference between plants and algae Plants have this aerial portion covered with a waxy Cuticle- this helps prevent desiccation of drying out of plant tissues by evaporation Plants have something called a Stomata- these things are tiny pores that dot the surface of leaves and facilitate the gas exchange (Algae lack both of those) Plants have a multi-cellular Gametangia – sex organ (while algae have a unicellular gametangia. each plant gametangium has a later of sterile non-reproductive cells that surrounds and protects the delicate gametes (eggs and sperm cells) . in plants the fertilized egg develops into a multi-cellular embryo (young plant) within the female gametangium. Thus the embryo is protected during it’s development. Plants produce spores by meiosis, and algae produce spores by either meiosis or mitosis In algae, the fertilized egg develops away from he gametangium, in some, the gametes are released before fertilization while in other the fertilized egg is released. The plant life cycle alternates haploid and diploid cycles : Basic Life Cycle of a Plant
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The Gametophyte generation- rise to haploid gametes by mitosis- two gametes fuse diploid portion of the life cycle begins. The Gametophyte itself is a Haploid Generation. The Sporophyte generation- produces haploid spores by meiosis first stage of the gametophyte generation. The sporophyte itself is a diploid generation. Haploid Gametophytes Produces Antheridia (male Gametangia)- This produces sperm cells or Haploid Gametophytes produces archegonia (female gametangia) – which produces a single egg Sperm and Egg both fuse and enters the … Zygote Embryo Spore Haploid (n) Gametophyte Generation Gametophyte Fertilization Diploid (2n) Sporophyte Generation Sporophyte Meiosis
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One sperm cell fertilizes the egg to form the zygote this is a diploid Zygote and is the first stage in the sporophyte generation. divides by mitosis and develops into a multi-cellular embryo (young sporophyte plant) embryo development takes place with in the archegonium(protected as it develops) mature sporophyte has special cells called sporogenous cells (spore producing cells also called spore mother cells)
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