Botany LS1203 - Plant Biology
Life Cycles
The descriptions given here for the three types of life cycles found in eukaryotic
organisms assume that the organisms described are multicelllular.
The descriptions also assume that the only ploidy numbers
involved are diploid (2n) and haploid (1n).
Animal Kingdom: Gametic Life Cycle
In the gametic life cycle, the gamete (egg or sperm) is the only haploid
cell produced.
meiosis
fertilization
mitosis
2n multicelled -------->
1n gamete -----------> 2n zygote
--------> 2n multicelled
Fungi Kingdom: Zygotic Life Cycle
In the zygotic life cycle, the zygote is the only diploid cell produced.
mitosis
fertilization
meiosis
mitosis
1n multicelled --------> 1n
gamete -----------> 2n
zygote --------> 1n spore --------> 1n multicelled
Plant Kingdom: Sporic Life Cycle
In the sporic life cycle, you see alternating multicelled 2n and 1n generations.
A sporophyte is a multicelled 2n plant that makes 1n spores by meiosis.
A spore undergoes mitosis to form a multicelled 1n plant, the gametophyte.
A gametophyte makes gametes by mitosis.
meiosis
mitosis
mitosis
fertilization
mitosis
2n sporophyte --------> 1n spore ------->
1 n gametophyte --------> 1 n gamete ----------->
2n zygote --------> 2n sporophyte
Algae
You can find examples of all three types of life cycles, including a three
generation variation of the sporic life cycle, among the algae.
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12 September 2002.