TOPIC 4 BRYOPHYTES C 1 What ecological roles do bryophytes play Why are they important to the global C cycle a Bryophytes contribute to plant biodiversity b Bryophytes Primary form of carbon storage in many northern ecosystems Important in the global C cycle i Sphagnum peat mosses in particular they store 400 billion metric tons of organic ii Sphagnum dominated peat lands take up 2 of Earths total surface 1 2 the size of the U S iii The C they store is NOT readily decayed Bryophytes are important initial colonizers of bare rock and soil surfaces Maintain soil moisture Recycle nutrients in forest vegetation What distinguishes bryophytes and vascular plants from green algae are the bryophytes and vascular plants called the Embryophytes 2 Why Recognize that Embryophytes and plants are terms that are used synony mously Bryophytes Vascular plants and Green Algae most classes make up the Streptophyte clade and share many similarities However due to certain distinctions from Green Algae the Bryophytes and Vascular plants diverged further into another clade Embryophytes aka land plants Distinctions between the Embryophytes Bryophytes and Vascular plants and green algae 1 The presence of male and female gametangia antheridia and archegonia respectively with protective layer called sterile jacket layer 2 Retention of the developing multicellular embryo within the archegonium female gametophyte allowing matrophy nourishment of embryo by the gametophyte Evolutionarily an advantage because it allowed for multi cellular diploid sporophytes with each cell being genetically equivalent to the originally fertilized egg 3 The presence of a multicellular diploid sporophyte each cell of which is genetically equivalent to the fertilized egg resulting in increased meioses and an amplification of the number of haploid spores that can be produced following each fertilization event This is an advantage to early plants as they began to live on land Many spores fertilization event helped compensate for low fertilization rates when water become scarce 4 Multicellular sporangium hollow structure where spores are produced consisting of a ster jacket layer and sporogenous the internal tissue that actually produces the spores 5 Meiospores with walls containing sporopollenin Sporopollenin The most decay and chemical resistant biopolymer known This would be significant to land plants because it enables Bryophyte spores to survive dispersal through the air from one moist site to another 6 Tissues produced by an apical meristem ile Charophytes the closest related green algae group lack all of these characteristics that Bryophytes and Vascular plants share These characteristics are correlated with the existence of plants on land 3 5 What distinguishes bryophytes from vascular plants Distinctions between Bryophytes and Vascular plants a Bryophytes lack vascular tissue i Vascular tissue The water and food conducting tissues called xylem and phloem ii Some bryophytes have specialized conducting tissue but the cell walls are NOT lignified like those in vascular plants b Differences in life cycles i Both exhibit alternating heteromorphic gametophytic and sporophytic generations but ii In the Bryophytes the gametophytic generation is dominant larger and free living The sporophyte generation is smaller and permanently attached to and nutritionally dependent on its parental gametophyte iii While in the vascular plants the sporophyte generation has become independent is able to branch and is larger than the gametophyte How are the terms bryophytes and Phylum Bryophyta being used differ 4 Are bryophytes monophyletic paraphyletic or polyphyletic ently in the text Bryophytes Paraphyletic Group does NOT include all of the descendants from a single common ancestor The text refers to Bryophytes as the clade that includes liverworts hornworts and mosses Phylum Bryophyta refers to only mosses the most recognizable member of the clade Describe the bryophyte body both sporophytic and gametophytic stages some terms listed under 6 will be useful to do so How do the leaves and stems of bryophytes differ from the leaves and stems of vascular plants Which pores in the bryophyte body are homologous to the stomata of vascular plants and which are analogous Why is the bryophyte body typically thin Bryophytes exhibit alternating heteromorphic gametophytic and sporophytic generations Gametophyte The haploid n gamete producing generation a Large and free living b Generally flat and dichotomously branched c Some are thalli singular Thallus meaning they have an undifferentiated body not differenti d Some thalloid gametophytes have surface pores ated into roots stems and leaves Surface pores analogous Specialized adaptation on upper surface for increasing CO2 uptake permeability Ex surface pores on the thalloid liverwort Marichantia while at the same time reducing water loss to stomata in sporophytes of vascular plants f Some Bryophytes are thalli but some are leafy Some liverworts and mosses ARE differentiated into leaves and stems but they are controversially considered not to be true leaves because they occur in the gametophytic generation and do not contain xylem and phloem Like vascular plants do analogous to waxy cuticle found on leaves of vascular plants occurs on g Surface layers the surfaces of some Bryophytes Reduces water loss gas exchange h Rhizoids The way in which both leafy and thalloid bryophytes are attached to a substrate Rhizoids anchor the gametophyte but do NOT absorb water or inorganic ions like vascular plants do May be multi or unicellular Absorption occurs directly throughout entire gametophyte reason that bryophytes are so thin facilitates the uptake of water and CO2 i Male and female sex organs both have protective jacket layers j Some go through Protonema staga The first stage of the haploid stage Sporophyte The diploid 2n spore producing generation a Small unbranched and permanently attached to nutritionally dependent on the gametophyte b The embryo of the sporophyte develops from the zygote within the female sex organ archegonium c A mature sporophyte is usually differentiated into a foot attached to gametophyte a seta a stalk a single sporangium aka capsule spore producing structure d Sporophyte produces spores via meiosis within the sporangium that is encased in a wall con taining sporopollenin significant for land plants e The sporophyte epidermis of some bryophytes Hornworts and mosses contain stomata that
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