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REPRODUCTION IN PLANTS 13 FEBRUARY 2013 Lesson Description In this lesson, we will: Look at types of reproduction Look at the reproductive mechanisms in three groupings of plants o bryophytes o pteridophytes o gymnosperms Key Concepts Types of Reproduction Asexual Reproduction Also known as vegetative reproduction - spores (n) are produced in the sporophyte (2n) by meiosis Only one parent or individual There are three types of asexual reproduction o Sideways shoots o Lateral buds on underground storage organs o Stems produce new roots when cut from main plant Advantages of asexual reproduction Quick and efficient Only 1 parent required Desirable genetic characteristics not lost Disadvantages of asexual reproduction Genetically identical to parents no genetic variation Competition for resources occurs Sexual Reproduction Sexual reproduction – fusion of gametes Gametophyte grows and releases gametes (n) More than 1 parent required Advantages of sexual reproduction Genetic variation occurs Reduces chances of parasites and diseases moving from parents to offspring New species can develop as a result of genetic variation (evolution) Disadvantages of sexual reproduction Only half the population can produce offspring A mate is required and wind or animals are needed for pollination Desirable genetic characteristics are not guaranteed to be passed on Populations take a long time to build up Diagram showing the generalised alternation of generations in plants: (Solutions for all Life Sciences, Macmillan, p57) Plants alternate sexual and asexual generations. Mechanisms of Reproduction Bryophytes A moss gametophyte generation with sporophyte generation attached: (Solutions for all Life Sciences, Macmillan, p58) Bryophytes are homosporous Gametophyte generation is dominant Male and female shoots are separate Male sperms swim to the eggs in the female shoot Sporophyte found on female gametophyte Pteridophytes Structure of the sporophyte generation of a typical fern: (Solutions for all Life Sciences, Macmillan, p60) Sori under leaves contain haploid spores produced by meiosis in sporangia The fern is homosporous Spores develop into gametophyte (heart shaped thallus) Reproductive organs under thallus Sperm swims to fertilize egg Sporophyte develops from diploid embryo Gymnosperms Needles and cones of a pine tree: (Solutions for all Life Sciences, Macmillan, p64) Gymnosperms produce male and female spores - they are heterosporous Male cones produce many microspores which become pollen Wind carries the male gametophyte generation (pollen) from the male cone Female cones produce ovules that contain female gametophytes Pollen lands on ovule and a tube grows down to carry sperm cell to egg cell in ovule. The ovule grows into a seed. Gametophyte generation housed entirely in the sporophyte generation. Question Question 1 (Adapted from Solutions for all Life Sciences, Macmillan, p68) a.) In what ways do the sperm of mosses and ferns differ from those of the spermatophytes? b.) What is the reason for the difference in structure of the sperm mentioned in question (a)? c.) Why do gymnosperms and grasses produce more pollen than the rest of the spermatophytes? d.) How have the spermatophytes achieved total independence from water for reproduction? e.) Why has reducing the gametophyte generation been an advancement for the spermatophytes? f.) Explain why most angiosperms are able to produce less pollen than gymnosperms. (3) (2) (2) (2) (3) (2) Question 2 (Adapted from Solutions for all Life Sciences, Macmillan, p70) a.) b.) c.) d.) Explain the terms ‘sexual’ and ‘asexual’. Why do most higher forms of organisms use sexual reproduction? What does it mean when a plant is said to be hermaphrodite? Draw up a table in which you compare the advantages and disadvantages of asexual and sexual reproduction. Links Plant Reproduction: Asexual Reproduction (Britannica.com) http://www.youtube.com/watch?v=NfPP2CQGuC0 Reproduction in plants http://www.youtube.com/watch?v=f44CBkneep4 Plant reproduction.mov http://www.youtube.com/watch?v=ZvBMQIrlhYw (2) (2) (2) (16)