Post on 29-May-2015
Sexual reproduction
Life cycles and the alternation of generations
Sexual reproduction in animals
Animals have diploid body cells and haploid gametes
The diploid body cells are made by mitosis The haploid gametes are made by meiosis At fertilization the haploid sperm and egg
fuse to produce the diploid zygote. This then divides many times by mitosis to
grow into a new individual
Sexual reproduction in plants
In flowering plants there are two distinctive phases of life cycle:
the diploid sporophyte and the haploid gametophyte
Sexual reproduction in plants
The diploid sporophyte produces haploid spores by meiosis.
The spores develop into the haploid gametophyte, which then produces haploid gametes by mitosis
Sexual reproduction in plants
In plants such as mosses and ferns, the main plant is the diploid sporophyte.
It produces (genetically different) haploid spores by meiosis
Sexual reproduction in plants
The spore grows into the gametophyte, which produces (genetically identical) gametes by mitosis.
Sexual reproduction in plants
In flowering plants the water dependent gametophyte stage in the life cycle is much reduced.
The dominant stage in the life cycle is the sporophyte
Essential terms to know
Spore A haploid cell that can be dispersed It is the product of meiosis of a diploid cell
Essential terms to know
Gamete A haploid cell, produced by mitosis of haploid cells. It can fuse with another gamete to produce a diploid
zygote
Essential terms to know
Sporophyte A multicellular plant that is diploid and
produces spores.
Essential terms to know
Gametophyte A multicellular plant that is haploid and
produces gametes
Essential terms to know
NB These terms have been defined in terms of plant kingdoms. A fungal spore is very different!!!!
Essential terms to know
Alternation of generations Terrestrial plants that have a life cycle with a
multicellular gametophyte and multicellular sporophyte generation which alternates are said to have a life cycle that shows “alternation of generations”