Petal: Often brightly coloured and scented. Many have nectaries make nectar. Draws attedtion of insects and animals. Protects soft stamen and pistil.Stamen: Male reproductive system. Also called the androecium. Each one is made up of two parts: a) Anther. b)Filament.
Anther: Structures that produces pollen grains. Pollen grains consist of the male gametes.Filament: A long stalk which supports the anther.Stigma: A sticky structure at the apex of the style . Place where pollen grains adhere.
Style: A stalk that joins the stigma to the ovary. Connects the stigma to the ovary. Holds the stigma in the air to collect pollen. May nourish pollen tube following pollination.Ovule: Contains female gametes. Form the seeds.
Pedicel: Supports the flower in the best position for pollination.
Ovary: Structures that protects ovules. Forms the fruits. Stores one or more ovules from which the female gametes develop.Receptacle: Supports ovary. It may swell and encloses the ovary to form the certain part of fruits. Examples: apple and strawberry.
1) Pollen grains are formed in the anther.2) Each pollen mother cell will go through meiosis to produce four haploid microspores (n).
3) A tube nucleus and generative nucleus formed after the nucleus of each microspore divides by mitosis.4) The microspores develop into pollen grains. Eventually the microspores develop into pollen grains.
5) Pollination is the process in which mature pollen grains from the anther are transferred to the stigma of a flower.
Formation of Embryo Sac in the Ovule1) The ovule develops from the ovarian tissue at the base of the carpel.2) It has a diploid embryo sac mother cell (2n).3) Every ovule has a protective outer layers of cells named the integuments.
4) The embryo sac mother cell (2n) goes through meiosis to form megaspores (n) which is a row of four haploid cells.5) The four megaspores are linearly arranged.6) Usually one becomes funtional and develops further.
7) Three of four megaspores will degenerate, leaving one in the ovule.8) The remaining one haploid cell develops to form the young embryo sac.9) The megaspore will grow and enlarges, filling up most of the ovule.
10) The megaspore divides mitotically 3 times to form 8 nucleatic gametocytes and embryo sac, 8 nuclei within the cytoplasm of a single cell have no cell walls.11) Antipodal cells are produced after the migration of the 8 nuclei to one end of the cell.
During the growth of the pollentube, the generative nucleus whichfollows closely behind the tube nucleusdivides by mitosis to produce two malegamete nuclei.Pollen tube grows down the style into thestigma and towards the ovule.
Double fertilisation means aprocess where a diploid zygote andtriploid nucleus are formed.In the embryo sac, one malegamete nucleus fuses with the egg cellforming a diploid zygote (2n) .The other male gamete nucleus fuseswith the two polar nuclei forming atriploid (3n) .
Thus, in an embryo sac,2 fusions takeplace simultaneously.After fertilisation, the diploid zygotedivides by mitosis forming theembryo.The triploid zygote also undergoesrepeated mitotic division to form theendosperm which becomes the ediblepart of the fruit.
Upon reaching the micropyle, the tubenucleus disintegrates.Besides, the tip of the tube burstsopen, the male nuclei then enter theembryo sac.Double fertilisation is unique toangiosperms which occur in the ovule.
The division of triploid nucleus is veryimportant to give rise to theendosperm that nourishes the embryoand growing seedling.It also helps to form the foodstoring tissue of the seed.The synergid cells and the antipodalcells degenerate.
Ensures the genetic informationof the parent plants is passeddown to the next generation.Existing variation among the nextgeneration.Ensures the survival of the species.
For protection of the seed and aids inthe dispersal of the seeds.Ensures the survival of floweringplants in changing environment.Ensures the successful germination ofa seed into a new plant.Ensures the continuity of the plantspecies.
Growth in Multicellular OrganismsGrowth: Is a permanent process (irreversible) with an increase in the body mass, size and number of cells. Involves quantitative changes in solid matter, dry mass and the amount of cytoplasm.
Development: The changes in shape, function and complexity associated with growth. Involves qualitative changes that are related to differentiation and specialisation to perform specific functions.
Cell division stage: The number of cells of an organism rises by mitosis. One cell divides by mitosis in geometric progression. For example : 1 2 4 8 16 cells, and so on.
Cell enlargement stage: Also known as cell elongation. Vacuolation is important in cell enlargement of plants. The volume and size of cells increase through the intake of water and other substances from the environment by osmosis and diffusion.
Cell differentiation stage: Cells growth begins to differ from each other to form specialised and permanent cells with specific functions. For instance, the neurones and specific types of blood cells in animals, the xylem and phloem cells in plants.
The process of GrowthInvolves elongation and branchingof roots and shoots.Brought about by apical meristems.Importance :- produces xylem andphloem .
Cells of the primary meristem continue todivide, thereby elongating the root. Cells of the primary meristem stopdividing and cease to be meristematic. Cells elongate and expandthrough absorbing nutrients and water through osmosis.Cells differentiate into particular tissue types which is also called zone of maturation.
Nucleus Small vacuoles Cytoplasm Vacuoles enlarging Small vacuoles fuse to form a large central vacuoleCytoplasm and nucleus push towards the cell margin
Thanks to: Pn Prema a/p Kuttam Pillai (GPM SMK Aminuddin Baki, Chemor) Liew Bih Ling (Thinkquest Manager) Gan Wan Yeat, Exploring, Penerbitan Fajar Bakti Sdn. Bhd, Shah Alam, 2006.