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Transcript
Sexual Reproduction in Plants The Seed The seed is the product of sexual reproduction in most plants. The seed contains an embryo, a food supply and a seed coat that keeps it from drying out. Seed-bearing plants can be classified into two groups based on seed structure. The two groups are called Angiosperms and Gymnosperms. Angiosperms Angiosperms are flowering plants The seeds form inside the flower When mature the seeds are enclosed in a case. Sexual Reproduction in Angiosperms The flowers produced by angiosperms contain the plant’s reproductive organs The female reproductive organs are called the pistil The male reproductive organs are called the stamen Pollination In order for the seeds to develop, pollen grains from the anthers must reach the stigma of the pistil. This process is called pollination There are two types of pollination used by angiosperms; Self-pollination - the males and female gametes come from the same plant Cross –pollination – the male and female gametes come from two different plants. The two most common agents of crosspollination are wind and insects. Fertilization The pollen grain must grow a pollen tube to reach the ovule When the pollen reaches the ovule a zygote and a cotyledon are formed. The cotyledon contains stored food. Gymnosperms Gymnosperms do not produce flowers Produce seeds inside the cones Seeds have a coat that protects them but are not inside a case Sexual Reproduction in Gymnosperms Gymnosperms produce their seeds inside cones. For this reason they are called conifers. In some species male and female cones are produced on separate trees. In most conifers male and female cones are produced by each tree. Pollination and Fertilization Pollination proceeds the same as in angiosperms Fertilization also requires the formation of a pollen tube to allow the pollen to reach the egg. Plants without seeds Plants such as mosses and ferns reproduce through spores Like gametes spores are haploid however, a spore can develop into a new plant without fertilization. The mature form called a sporophyte will release the spores Under the correct conditions the spore will develop into a gametophyte. The two main advantages for dispersal are; that they are light and that they can survive unfavourable conditions by staying dormant until the conditions are ideal.