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Unit 6 – Lecture 6
Alternation of Generations
 type of reproduction
utilizing asexual
& sexual means
Alternation of Generations
 offspring generations
alternate between being
haploid [1n] in one
generation to being
diploid [2n] the next.
Alternation of Generations
 in some plants, the
sporophyte is a
completely different
plant than the
gametophyte.
 in others, the
gametophyte
is something
we really don’t see.
Alternation of Generations
 Sporophyte [2n]
produces spores [1n]
through meiosis
 sporophyte is the
typical “adult plant”
that we see
Alternation of Generations
 Spores [1n] produce
gametophytes [1n]
through
mitosis
Alternation of Generations
 Gametophyte [1n]
produces gametes [1n]
through mitosis
Alternation of Generations
 Gametes [1n] fuse
in fertilization to
produce zygote [2n]
Alternation of Generations
 Zygote [2n] grows to
become embryo [2n]
Alternation of Generations
 Embryo [2n] grows
to become
sporophyte [2n]…
 etc.
Alternation of Generations
 non-vascular and non-seed plants MUST have water
to reproduce.
 flagellated sperm must swim to egg
 gametophyte can be very
small, but visible –
1cm or less.
Other Asexual Reprod Methods
 vegetative reproduction – new plant forms from
existing plant part (roots)
 fragmentation – new plant forms from a cutting of the
original plant.
Seed Plants
 are vascular…
 two varieties:
 gymnosperm – produce cones
 angiosperm – produce flowers
Angiosperms
 produce flowers and seeds inside of a fruit
 petals, pistil, stamen, etc.


petals attract pollinators
fruit attracts organisms which can spread seeds
Angiosperms
Angiosperms
Angiosperms
 are either monocot or dicot
 cotyledon – the seed “leaves” or sides / food supplies
 don’t need to know these directly:



have different types of xylem & phloem
have different types of veination
have differences in petal arrangement
Seed Production
Germination
 germination – zygote growing into new plant
 requirements:




water
suitable temperature
oxygen
time
Germination
 germination – zygote growing into new plant
 requirements:
light
 other:
 freezing – apples
 soaking in salt
water – coconuts
 fire – many
conifers
 cannot be halted
