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SEED PLANTS: SUBPHYLUM SPERMOSIDA
Fig 22.5 pg 470
- members of Spermopsida produce seeds instead of spores
- better dispersal
- seed coat that surrounds developing embryo
- embryo will grow for a while but will remain dormant until conditions
are right for germination into new plant
Diagram structure of a typical seed pg 470
A. FORMATION OF SEEDS fig 25.9 pg. 539
- seeds begin to develop once sperm fertilizes egg
- zygote develops into embryo inside seed
- cotyledon is seed that contains stored food for embryo once it
germinates
- structures of seeds are name according to their attachment to
cotyledon(s)
1. epicotyl: part of seed that develops into stem
- has apical meristem tissue
2. hypocotyls: structure beneath epicotyl
- attached to radicle that will develop into primary root
- has apical meristem tissue
Diagram a typical seed in more detail pg 539
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B. SEED DEVELOPMENT
- begin to germinate once they absorb water
- causes endosperm & cotyledon to swell & crack
- radical emerges as primary root
- some seeds develop instantly into plants; others enter dormancy
when embryo is alive but not growing
- dormancy allows seeds to be dispersed further from parent
C. THE SPERMOPSIDA (SEED PLANTS)
- members of Spermopsida are most successful & plants because:
1. Production of seeds: allows dispersal
2. Production of cones/flowers: attracts pollinators
3. Co-evolution with animals
- key reproductive structures of spermopsida include:
i) seeds
ii) cones
iii) flowers
- Subphylum divided into:
i) Gymnopserms
ii) Angiosperms
GYMNOSPERMS
A. CONES Fig 22.7 pg 472
- gymnosperm = naked seed
- specialized reproductive leaves called scales
- several scales grouped to form male & female cones
1. pollen cones: produce male gametophytes called pollen
2. seed cones: produce female gametophytes called eggs
- after fertilization in female cone  seed develops on scales
unprotected
B. CLASSES three main classes
1. Cycadae: palm-tree like
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2. Gingkoae: only one species, Gingko biloba
3. Coniferae: most abundant & widespread
C. CONIFERS: THE EVERGREENS
- very long, thin leaves called needles
- fall off every fall or gradually every few years
1. Life Cycle
- dominant sporophyte stage
- microsporangia inside male pollen cones produce immature pollen
grains
- megasporangia inside female seed cones produce ovules (with eggs
inside)
- pollen grains released & land near ovule
- pollen grain splits & grows a pollen tube that grows into ovary
- inside pollen tube are two sperm nuclei (one will fertilize egg)
- resulting zygote develops into embryo inside seed
Diagram life cycle of typical conifer pg 534
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ANGIOSPERMS (protected seed)
A. FLOWERS
Fig 25.4 pg 535, fig 25.5 pg 536
- flowers: mini-stems consisting of specialized leaves involved in
reproduction though process called pollination
1. sterile leaves - sepals & petals don’t produce gametophytes
a) sepals: outermost leaves, often green, resemble true leaves
- protect flower bud while developing
b) calyx: sepals & flower
c) petals: second circle of leaves, brightly coloured
- entire collection = corolla
- attract insects & pollinators
2. Fertile leaves – stamen & carpels
a) stamen: male part, long filament supports anther (where
microsporangium produce microspores)
b) carpel: female part, several fertile leaves that have rolled up
to protect female gametophyte
c) pistil: one or more carpels
- ovary with several ovules, stalk called style, top of stalk is
stigma
Diagram a typical angiosperm flower pg 535
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B. CLASSES
- two subclasses - separated based on structure of seed
1. monocotyledenae – 1 cotyledon (seed leaf)
2. dicotyledenae- 2 cotyledons
Characteristic
Example
Monocots
Annuals: Tulips
Veins in leaves
Flower parts
Vascular bundles in
stems
Vascular bundles in
roots
Growth of stems
Parallel
Multiples of 3
Scattered
Dicots
Woody trees: Deciduous
trees
Branched
Multiples of 4 or 5
Ring
Alternating
xylem/phloem
None
Xylem forms X; phloem
in between
Yes
C. LIFE CYCLE Fig 25.6 pg 537
1. Inside Ovary
 diploid megaspore mother cells produces 4 haploid cells (meiosis)
*3 will die*
 remaining will undergo mitosis to produce 8 haploid nuclei
 8 are enclosed within membrane called embryo sac
 3 nuclei clump to form polar nuclei
 one of 3 will become egg
 other 2 lie on either side of egg nucleus
 remaining 3 die
2. Inside Anther
 diploid microspore mother cell produces 4 haploid microspores
(meiosis)
 each becomes immature pollen grain
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 pollen grain lands on female gametophyte, nucleus divides
(mitosis) produces 2 haploid nuclei
 one is tube nucleus which produces pollen tube then dies
 other is generative nucleus that divides (mitosis) produce 2
sperm cells
 pollen grains released when anther dries out
3. Pollination: transfer of pollen from anther to stigma; two types
a. self-pollination: plant pollinates itself
b. cross-pollination: plant pollinates another
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pollen grain on stigma  grows pollen tube from tube nucleus
generative nucleus divides to produce 2 sperm cells
pollen tube extends towards embryo sac inside female
double fertilization; one sperm fertilizes egg nucleus to form
diploid zygote; other fertilizes two polar nuclei to form triploid
endosperm
endosperm provides food for embryo
after fertilization, parts of ovule thicken to form seed
ovary wall begins to form fruit that holds seeds
fruit aids in dispersal by attracting insects & animals
COEVOLUTION OF FLOWERING PLANTS & ANIMALS
- particularly in angiosperms
- animals are integral part of reproduction (& survival of plant
species)
- attract insects (instead of using wind), birds, & animals by
producing flowers that produce liquid pollen; nectar
- pollinators travel from one flower to next, carrying pollen = vector
pollination
- flower structure has evolved to target specific pollinators
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e.g. colour, markings, odour, shape of flowing all ensure specific
pollinators
- production of fruit aids in dispersal
- animals attracted to colour, odour, taste of fruit
- eat fruit & seeds
- seeds have tough seed coat  out with wastes (natural fertilizer!)
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