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Flowers and Reproduction (Flower structure and cross pollination.…

- - - - sporophytes are always diploid.
    - - Plant spores undergoes mitosis and grows into an entire new haploid plant called gametophyte.
      - Mammalian gametes are of two types
        
        microgametes
        
        They are small sperm cells.
        
        microgametophytes (male)
        
        grown from microspores
        
        megagametophyte ( female)
        
        grown from megaspores
        
        megagametes
        
        also known as oogamy.
  - - - these are lowermost and outermost of the four floral appendages.
    - - petals together make up corolla. Sepal and petals together constitute flower's perinath.
    - - Above the petals are stamens, collectively called androecium.
      - have two parts
        
        filament
        
        it is the stalk.
        
        anther
        
        pollen is produced here.
        
        neighboring anther cells in a layer called the tapetum act as nurse cells.
    - - constitute gynoecium
      - has three parts
        
        stigma
        
        it catches pollen grains
        
        a style
        
        it elevates the stigma to a useful position
        
        an ovary
        
        where megaspores are produced.
        
        inside the ovary is placentae
        
        it holds ovules.
        
        the ovule has a central mass of parenchyma called a nucellus.
        
        Some nucellus cells enlarge in preparation for meiosis: these are megaspore mother cells or megasporocytes.
      - Gametophytes
        
        Microgametophyte
        
        microspores develope into microgametophyte.
        
        microspores nucleus divides mitotically producing a
        
        Vegetative cells
        
        generative cells
        
        Megagametophyte
        
        embryo sac is multinucleate megagametophyte.
        
        The seven cells are one large central cell with two polar nuclei
        
        three small antipodal cells
        
        an egg apparatus
        
        consisting of two synergids
        
        and an egg.
      - Fertilization
        
        Syngamy of sperm and egg involves both plasmogamy and the fusion of the protoplasts of the gametes and karyogamy.
        
        a large endosperm nucleus is established
        
        both sperm nuclei undergo fusions one with the egg nucleus and the other with the polar nuclei- the process is called double fertilization.
      - Embryo and seed development
        
        Suspensor, which pushes the embryo deep into the endosperm
        
        radicle
        
        epicotyl
        
        hypocotyl
        
        albuminous seed are a mature seed in which endosperm is rather abundant.
        
        if endosperm is sparse or absent at maturity, the seed is exalbuminous.
        
        Seed coat
        
        The integument that surround the nucellus expand and mature into the seed coat.
      - Fruit development
        
        As the ovule develops into a seed, the ovary matures into a fruit.
        
        has three layers.
        
        exocarp is the outer layer
        
        mesocarp is the middle layer
        
        endocarp is the innermost layer.
- - - - the life cycle consist of four types of plants
        
        microgametophytes
        
        megagametophytes
        
        staminate sporophytes
        
        carpellate sporophytes
- - - - has only limited potetntial for growth.