Biology XI:3 Plant Kingdom(5 Division Angiosperms)

Division Angiosperms Large group of plants inhabiting a wide range of habitats The pollen grains and ovules are developed in structures called flowers. Seeds enclosed by fruits Range from tiny, almost microscopic, specimens (Wolfia) to tall trees like Eucalyptus Two main groups are: Monocotyledons − having one cotyledon in their seeds Dicotyledons − having two cotyledons in their seeds The male sex organ in a flower is a stamen. Each stamen consists of: a slender filament an anther at the tip The anther produces pollen grains by meiosis. The female sex organ is a pistil or carpel Each pistil consists of: an ovary a style a stigma The ovary encloses one or more ovules. Within the ovule (the highly reduced female gametophyte) embryo sacs are present. Embryo sac is a seven-celled, eight-nucleated structure. Embryo sac contains One egg cell Two synergids Three antipodal cells One central cell The polar nuclei fuse to form a secondary nucleus (diploid). Pollen grains, after dispersal from anthers are carried by the wind or other agents to the stigma of the pistil; termed as pollination Fertilisation in angiosperms is termed as double fertilisation. The synergids and antipodals degenerate after fertilisation. The ovules develop to form seeds, and the ovaries develop into fruits. LIFE CYCLE OF AN ANGIOSPERM