Reproduction in Angiosperms IB Topic 9.3.1-9.3.3

Reproduction in flowering plants Flowering plants contain their reproductive organs in the flower Flowers are often hermaphrodite structures  both male and female parts

Draw and Label … A diagram showing the structure of a dicotyledonous animal pollinated flower Sepal, petal, anther, filament, stigma, and ovary See Figure 10.27 (Clegg)

The Buttercup Flower

Parts of the flower Sepals: Collectively called the calyx Enclose the flower in the bud and are usually small, green, and leaf like Petals: Collectively called the corolla Often colored and conspicuous (may attract insects and other animals) Stamens: The male part of the flower Consist of anthers (housing pollen grains) and the filament (stalk) Carpels: The female part of the flower There may be one or many & they may be fused together or free standing Each carpel consists of an ovary and a stigma (which receives pollen)

Addressing some vocabulary … Pollination: is the transfer of pollen from a mature anther to a receptive stigma The pollen may come from the anthers of the same flower or flowers of the same plant Self pollination Or, the pollen may come from flowers on a different plant of the same species Cross pollination

So, how is that pollen transferred? Typically by insects and wind Insect pollinated plants typically produce nectar which attracts insects to the flower Although in some species, pollen can be transferred by: Birds Bats Running water

What comes after pollen transfer … ? FERTILIZATION!!! Can only occur after pollen has landed on the stigma and has germinated there Fertilization is the fusion of male and female gametes to form a zygote

What’s double fertilization? The pollen grain produces a pollen tube, which grows down between the cells of the style and into the ovule The pollen tube delivers two male nuclei One fuses with the egg The other fuses with another nucleus  triggers the formation of the food store for the developing embryo

Fertilization in a flowering plant

How are seeds formed and dispersed? Seeds develop from the fertilized ovule After fertilization: The zygote grows by mitotic division (embryonic root, stem, and cotyledon) As the seed matures, the outer layers become the protective seed coat (testa) and the whole ovary develops into the fruit. The water content of the seed decreases The seed moves into a dormancy period

The Seed The seed is a form in which the flowering plant may be dispersed Seed dispersal is the carrying of the seed away from the vicinity of the parenting plant Wind, animals, water, and explosive mechanisms help disperse seeds

The structure of a dicotyledonous seed (broad bean seed)