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