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FLOWERS AND REPRODUCTION (INFLORESCENCES AND POLLINATION (DETERMINATE…

- - - - MICROGAMETOPHYTE
        
        microspore develop from microgametophytes. the microspore nucleus divides mitotically producing a large vegetative cell and small generative cell which subsequently divides and form two sperm cells.
      - MEGAGAMETOPHYTE
        
        within the ovule the surviving megaspore develops into a megagametophyte. The female gametophyte that arises from a megaspore of a heterosporous plant. In angiosperms, the megagametophyte is the embryo sac.
    - - syngamy of sperm and egg involves both plasmogamy and karyogamy. the pollen tube tip brust and releases both sperm cell in which one migrates through synergids protoplasm towards the egg. sperm cells plasma membrane breaks down and loses most of its protoplasm. the sperm nucleus enters the egg then is drawn to and fuses with the egg nucleus establishing a diploid zygote nucleus.
    - - the flower stalk is pedicel and very end of the axis where the other flower parts are attache is receptacle. sepals are the lowermost and outermost layer. all the sepals together are reffered to as calyx. above the sepals on the receptacle are petals which together make up corolla. above the petals known as stamens collectively called androecium. carpels constitute the gynoecium.
    - - as the endosperm nucleus proliferates, the zygote also begins to grow into small clusters of cells parts of which later becomes a short stalk like structurewhich pushes the embryo deep into the endosperm. a mature seed in which endosperm is rather abundant is an albuminous seed. if endospem is sparse or absent at maturity, the seed is exalbuminous.
    - - sporophytes are always diploid. have cells that are capable of undergoing meiosis and result in haploid spores. the spores undergoes mitosis and grows into a new haploid plant called gametophyte which produce gametes. they produce male gametophyte known as microgametophyte and female gametophyte known as megagametophyte which come from microspore and megaspore respectively.
    - - as the ovule develops into a seed, the ovary matures into a fruit. development varies with the nature of the carpels as well as the nature of mature fruits. often three layers become distinct during growth, the exocarp, the mesocarp and the endocarp. the entire fruit wall whether composed of one, two, or all three layers is the pericarp.
- - - - A species may have individuals that produce only staminate flowers and others that produce only carpellate flowers-this is dioecy and the species is said to be dioecious. monoecy is the condition of having staminate flowers located on the same plant as carpellate flowers; monoecious species include cuttails and corn.
    - - the evolution of animal mediated pollination had a dramatic impact on the evolution of flowering plant. The shape of the flower is important as pollinator actually makes contact with it. Most flowers are radially symmetrical known as actinomorphic. In some flowers, there is a bilateral symmetrical known as zygomorphic.
    - - self-pollination is inhibited by compatibility barriers, chemical reactions between pollen and carpels that prevent pollen growth. In one incompatibility system, as a pollen tube grows, the stigma and style test proteins on the tube surface which when produced block the further growth of the pollen tube.
    - - When pollen is transported by wind, this is called anemophily. Many of the world's most important crop plants are wind-pollinated. These include wheat, rice, corn, rye, barley, and oats. Wind pollinated individuals produce up to several thousand small flowers;calthough each flower is tiny, the entire plant has large total stigmatic surface area.
    - - when the stigma and style become mature, there may be no living pollen left in the flower;thus, all pollination is effected by younger flowers just opening their anthers. on plants with many flowers that do not open simultaneously, older flowers could be self-pollinated by freshly opened flowers of the same plant.
    - - the ovary and ovule must be well protected from pollinators. deeply burrried ovaries are known as inferior ovaries and partially burried ovaries is called half inferior ovary.
    - - cross pollination is the pollination of a carpel by pollen from a different individual and self pollination is pollination of a carpel by pollen from the same flower or another flower on the same plant.many mechanisms have evolved that decrease the probability of self-pollination and increase the chance of cross-pollination with its accompanying genetic diversity.