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Reproductive differences between gymnosperms and angiosperms: gymnosperms: 1) ovules attached to amegasporophyll - megasporophylls often arranged in a.

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Presentation on theme: "Reproductive differences between gymnosperms and angiosperms: gymnosperms: 1) ovules attached to amegasporophyll - megasporophylls often arranged in a."— Presentation transcript:

1 reproductive differences between gymnosperms and angiosperms: gymnosperms: 1) ovules attached to amegasporophyll - megasporophylls often arranged in a megastrobilus (ovulate cone)

2 2) a) megagametophytes consist of many cells; b) eggs produced in archegonia

3 3) microsporangia attached to surface of a microsporophyll - microsporophylls often arranged in a microstrobilus (staminate cone)

4 4) microgametophytes are very small - produce sperm (not in antheridia) - are pollen grains 5) pollination by wind dispersal of pollen 6) pollen tube grows to an ovule and sperm is released - sperm have flagella and swim to egg, but not through external water 7) seeds develop on surface of megasporophylls - seeds are not enclosed (naked) gymnosperm = naked seed

5 CHARACTERISTICGYMNOSPERMS Placement of ovulesAttached to megasporophylls, in a megastrobilus Size of megagametophyteMany cells ArchegoniaPresent Placement of microsporangia (pollen sacs) Attached to microsporophylls, in a microstrobilus Size of microgametophytesVery small; several cells AntheridiaAbsent PollinationMostly by wind dispersal of pollen SpermHave flagella; swim through ovule to reach egg Seed locationOn surface of megasporophylls; not enclosed (naked)

6 angiosperms: 1) ovules (and seeds) are enclosed within ovaries; - part of flower structure angiosperm = vessel seed 2) megagametophytes consist of only a few cells - produce eggs, but not in archegonia 3) microsporangia carried on stamens; part of flower structure 4) sperm do not have flagella 5) double fertilization occurs

7 CHARACTERISTICGYMNOSPERMSANGIOSPERMS Placement of ovulesAttached to megasporophylls, in a megastrobilus Located in an ovary, within a flower Size of megagametophyteMany cellsA few cells ArchegoniaPresentAbsent Placement of microsporangia (pollen sacs) Attached to microsporophylls, in a microstrobilus Located on a stamen, within a flower Size of microgametophytes Very small; several cellsExtremely small, a few cells AntheridiaAbsent PollinationMostly by wind dispersal of pollen Various mechanisms - wind, insect, bat, rodent, etc. SpermHave flagella; swim through ovule to reach egg No flagella; deposited at egg Seed locationOn surface of megasporophylls; not enclosed in a fruit ("naked") Located enclosed in a fruit that develops from the ovary Double fertilizationAbsentPresent

8 Flower Structure: flower stalk (peduncle) and floral appendages attached to it receptacle floral appendages = sterile appendages and fertile appendages sterile appendages = sepals and petals sepals petals

9 fertile appendages = stamens and carpels stamens - are specialized microsporophylls - include: filament anther

10 carpels modified megasporophylls? - produce a tubular pistil - each has a stigma ; an ovary; a style

11 5) double fertilization - megagametophyte of angiosperms usually has seven cells - one egg, two synergids, three antipodals - each with one 1n nucleus - one central cell containing TWO 1n nuclei = polar nuclei

12 pollination - pollen is transferred from pollen sac to a stigma pollen germination pollen tube grows through style, to an ovule - releases two sperm into the ovule 1) one sperm (1n) fuses with the egg (1n) - produces zygote (2n) 2) second sperm fuses with two polar nuclei -produces a triploid (3n) primary endosperm nucleus

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14 following double fertilization: - zygote develops into embryo (within the ovule) - the primary endosperm nucleus produces endosperm tissue (all cells with 3n nuclei) - will provide nutrients to the embryo - integuments harden to form seed coat ** produces a seed, consisting of: - seed coat - endosperm (not present in gymnosperms) - sometimes a perisperm - embryo

15 In flowering plants, ovules are enclosed in ovaries - ovaries undergo changes as seeds form - produces a fruit - will usually enlarge may become fleshy may become dry, or hard

16 fruit - provides additional protection for the embryo - contributes to seed dispersal

17 typical flower structure varies with species common variations include variation in appendages: # of each type size color shape other variations: placentation type: placenta placentation

18 parietal placentation: - ovules attached to side walls of ovary - ovary with one or more locules

19 axile placentation: - ovules attached to partitioning walls in ovary - ovary has two or more locules

20 free central placentation: - ovules attached to central column of tissue - ovary has one locule

21 basal placentation: - ovule(s) attached to base of ovary - ovary has one locule

22 fusion of various floral appendages coalescence e.g. formation of tubular corolla adnation

23 variations in ovary placement: hypogynous flowers - ovary is superior - other appendages attached lower

24 epigynous flowers - receptacle tissue surrounds ovary - other appendages attached above the ovary - ovary is inferior

25 perigynous flowers - basal portion of sepals, petals, and stamens form structure that surrounds the ovary - ovary is superior

26 variations related to presence or absence of floral appendages: complete flowers incomplete flowers perfect flowers imperfect flowers staminate flower carpellate flower

27 species with imperfect flowers may be monoecious or dioecious: monoecious species dioecious species

28 Embryo structure - seed and embryo structure also varies with species - embryo includes a root-shoot axis, and one or two cotyledons - root-shoot axis consists of a) the radicle b) the plumule - includes epicotyl andembryonic leaves attached c) the hypocotyl

29 - one or two cotyledons attached at hypocotyl/epicotyl junction - two classes of flowering plants - dicots, have two cotyledons - monocots, have one cotyledon - cotyledons are food-storage organs - may remain small - may become thick and fleshy

30 monocot embryos include additional protective tissue layers: - the coleoptile - the coleorhiza


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