14.4 The Life Cycle of Flowering Plants Biology 1001 November 25, 2005
Jan 19, 2016
14.4 The Life Cycle of Flowering Plants
Biology 1001
November 25, 2005
Alternation of GenerationsFigure 29.5!!
Angiosperms, like all plants, have an alternation of generations type of life cycle The two generations are
heteromorphic The gametophytes highly are
reduced and dependent on the sporophytes
The gametes and spores are non-motile
Flower Structure The flower is an angiosperm
structure specialized for sexual reproduction
It is a specialized shoot with up to four rings of modified leaves called floral organs: sepals, petals, stamens, and carpels Sepals and petals are sterile organs Stamens, the male reproductive organs,
consist of an anther and a filament Carpels, the female reproductive
organs, consist of the stigma, the style, and the ovary
Figure 30.7!!
Flower Variety
Figure 38.2!,!! – An Overview of Angiosperm Reproduction
Figure 30.10!,!! - The life cycle of an angiosperm
Development of the Gametophytes The flowers on the sporophyte produce microspores and
megaspores that form male and female gametophytes The male gametophytes are the pollen grains, which develop
within microsporangia in the anther The female gametophyte is the embryo sac, and it develops
within the megasporangium within the ovule, which develops in the ovary
Each pollen grain has two haploid cells, a generative cell that divides to produce two sperm, and a tube cell that produces a pollen tube
The embryo sac consists of 8 haploid nuclei partitioned into 7 cells: the egg, two synergids, three antipodal cells, and two polar nuclei
Gametophyte DevelopmentFigure 38.4
Pollination and Fertilization Pollination is the transfer of pollen from the anther to the
stigma of the carpal After pollination, the pollen tube grows through the style and
into the ovary and the generative cell divides into the two sperm cells, which are discharged near the embryo sac
Pollination precedes and is necessary for fertilization to occur Fertilization is the union or syngamy of the egg and sperm In angiosperms, a process called double fertilization occurs
One sperm fertilizes the egg forming the diploid zygote and the other combines with the two polar nuclei to form the triploid endosperm, which develops into a nutrient supply for the seed
After fertilization, the ovule matures into the seed
The Co-evolution of Flowers & Pollinators
Co-evolution refers to reciprocal evolutionary adaptations of two interacting species
Animals interact with plants by helping to disperse their pollen and seeds, meanwhile receiving a benefit by eating nectar, seeds, and fruits of the plant
Wind and water are also means of pollen and fruit dispersal
Figure 30.13!•Bee Pollinators•Hummingbird Pollinators•Bat Pollinators