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Seeds are prominent because of their __.
What are the advantages?
great survival value
- i. Protection and stored food are available to the embryo even in critical stages of germination and establishment
- ii. It igives the seed a great selective advantage over their free-sporing relatives and ancestors over plants that shed their spores
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a. All are __
i. Produce __ and __ that give rise to __ and __
ii. Seed producing is an extreme form of heterospory that has been modified to form an __(the structure that develops into the seed)
1. The seed is a __
2. An __ consists of a __, the structure in which megaspores are produced, surrounded by one or two additional layers of tissue, the __
- heterosporous
- megaspores and microspores
- megagametophytes and microgametophytes
- ovule
- matured ovule containing an embryo
- immature ovule
- megasporangium
- integuments
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What led to the evolution of the ovule?
- 1. Retention of megaspores within the megasporangium (aka: nucellus)
- 2. Reduction in number of megaspore mother cells to one
- 3. Survival of one for the four megaspores
- 4. Formation of female gametophye inside the single functional megaspore—the formation of an endosporic female gametophyte that is no longer free living and is retained within the megasporangium
- 5. Development of the embryo, or young sporophyte, wthin the female gametophyte retained within the megasporangium
- 6. Formation of an integument that completely envelops the megasporangium, except for an opening at its apex called the micropyle
- 7. Modification of the apex of the megasporangium to receive microspores, or pollen grains
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Progression to development of Egg
Explain Elkinsia.
- i. nucellus and 4-5 integumentary lobes with little to no fusion; they curved inward at their tips, forming a ring around the apex of the nucellus
- 1. Ovules were surrounded by dichotomously branched, sterile structures called cupules
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I. Components of a Seed: Embryo, Stored Food, and Seed coat
a. Ovule consists of a __
b. When ready for fertilization, the nucellus contains a __
c. After fertilization, the integuments become the __, and a seed is formed
- nucellus enveloped by one or two integuments with a micropyle
- megagametophyte composed of nutritive tissue and archegonia
- seed coat
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I. Phyla of Seed Plants
a. Seed-bearing plants called__
b. All seed plants have __, which are large leaves with several veins, but are modified to needles or scales in some groups
c. Phyla?
- seed ferns
- megaphylls
- i. Confers ii. Cycads iii. Gingki iv. Gnetophyes v. Anthophyta
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I. Seed Ferns
a. Remains of seed ferns are common fossils in rocks of Carboniferous age
i. __ were so fernlike that these plants were long regarded as ferns
1. __: Oliver and Scott discovered they had seedsà gymnosperms
- Large, pinnately compound fronds
- 1905
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Structure of seed ferns
Living or not?
tall, woody trees
Fronds: borne at the top of the stem, or trunk and the fronds had microsporangia and seeds
extinct
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