In: Biology
2a. What is the large diploid cell that begins to develop into a pollen grain? What type of cell division takes place to form four haploid microspores?
2b. Define the term pollination as it takes place in Pines.
2c. Even though pine trees are monoecious, that is they contain both male and female cones, they reproduce by cross-fertilization. Explain.
2a. Diploid sporogenous mothercells undergo meosis and form haploid microspores.In the telophase stage four haploid cells are formed called tetrad. Tetrad seperate and final cell division occurs in cytoplasm.In the prophase I of meosis, leptopene stage - 2 chromatid appear thread like followed by zygotene - pairing of homologus chromosome takes place and then diploptene - seperation of paired chromosome and in diakenesis chromosome maximum contraction.Nuclear and chromosomal arrangement occurs during meosis . Ribosome restoration in metaphase followed by cytokinesis. Prophase is followed by meosis II generating tetrad.Microsporocytes interconnected by cellwall and finally form callose. Callose wall are surrounded the cell to produce tetrad at the second mitotic division.
2b. Pine trees are wind pollinated where transfer of pollen from male cone to female cone occurs as the flowers do not have nectar and pollen to attract bees and butterflies. Sperm nucleoid fertlizes egg in the female cone and mature by 2 years.
2c. Male and female cone occurs on the same plant.Female cone is seen in higher branches at the top.Male cone is seen in the lower branches it prevent the pollen from falling on the female flowers. As the pollen to drift upwards from male cone is tough pollen reaches the female cone by wind from another plant.When the pollen lands on the female cone it develops into long thin tube to the centre where egg is deposited.Genetic information in pollen combines with egg and form fertlised embryo which further develops to seeds.