ANGIOSPERMS (FLOWERING PLANTS)

• Angiosperms are subdivided into monocotyledonous (monocots) and dicotyledonous plants (dicots)
• Monocotyledon: One cotyledon, seed leaf, and one seed leaf
• Dicotyledon: A plant with two cotyledons in the seed.
• The sporophyte generation is the dominant generation- represented by an adult flowering plant
• Have true roots, stems, leaves and flowers, not a thallus
• Monocots have an adventitious root system

  Dicots have a taproot systems, consists of a main root with lateral roots
• The stem grows upright and consists of nodes and internodes. It has strengthening tissue
• The stem bears its leaves in a favourable position to absorb sufficient sunlight and cardon dioxide for photosynthesis
• The stem positions its flowers in such a way that they can be easily pollinated, and the fruits in sich a way that seeds can be dispersed
• Vascular tissue (xylem and phloem) are present. They occur in vascular bundles in flowering in plants
• Leaves are the main organs for photosynthesis
• The leaves of monocotyledonous plants have parallel veins

  Dicotyledonous plants have net venation- one or more veins
• Flowers are the sexual reproductive organs
• A flower consists of three main parts

  perianth (corolla and/ or calyx)

  androecium (stamen)

  gynoecium (pistil)
• In monocotyledonous flowers, the perianth consists of a single whorl (floral ring). Corolla and calyx fused to form a single tube called the perigone

  
• In dicotyledonous flowers, the perianth is differentiated into two whorls: the corolla (petals) and the calyx (sepals)

  
• The stamens are the male sex organs in which pollen grains (male spores) are produced in pollen sacs (male sporangium)
• The pistil, consisting of a sticky stigma, a long style and an ovary, composes the female sex organ
• The ovule (containing female sporangium with female spores) is located inside the ovary
• During pollination, a ripe pollen grain lands on receptive stigma
• After pollination the pollen grain germinates (in sugar solution on stigma) and develops into two male gametes
• Fertilisation in Angiosperms

  
• The germinating pollen grain, containing the two male gametes, represents the male gametophyte
• One of the female spores (in sporangium, in ovule, of ovary) forms embryo sac (female gametophyte)
• The embryo sac inside the ovule contains an ovum and two polar nuclei
• The pollen tube grow down the style into the ovary and penetrates the ovule and eventually the embryo sac to release two male gametes
• During fertilisation, one of the male gametes fuses with ovum to form a zygote- beginning of the next sporophyte generation
• No water is needed for fertilisation
• The other male gamete fuses with two polar nuclei in embryo sac to form endosperm, food for the developing embryo
• The zygote develops into an embryo, which enters a dormant phase
• The fertilised ovule develops into a seed that contains the embryo, endosperm and tests (hard seed coat)
• Seeds are dispersed by the wind, water, insects or animals
• Testa ruptures when water is present and the seed germinates
• Radicle of the germinating seed gives rise to the root and the plumule to the stem of the new vegetative plant- represents the sporophyte generation
• Life Cycle of Angiosperms