Presentation on theme: "Modified Flowers and Sexual Reproduction"— Presentation transcript:
1 Modified Flowers and Sexual Reproduction Flowers IIModified Flowers and Sexual Reproduction
2 Bracts Additional floral structures outside the calyx May be leaflike or petal-likeThe showy white or pink "petals" of dogwood are bracts
3 TepalsSepals are brightly colored and identical to the petals
4 Complete and Incomplete flowers Flowers containing all four floral appendages are known as complete flowersFlowers lacking any of the four floral structures are known as incomplete flowersFlowers of grasses possess neither sepals nor petals
5 Perfect and Imperfect Flowers Perfect flowers have both stamens and carpelsImperfect flowers lack either stamens or carpelsUnisexual flowersMale flowers called staminateFemale flowers called pistillate or carpellate
6 Plants with Unisexual Flowers Monoecious plants have both male and female flowers on a single individualDioecious plants are either male or female with only unisexual flowers on a single individual
7 Ovary PositionSuperior ovary - sepals, petals, and stamens are inserted beneath the ovaryInferior ovary - sepals, petals and stamens are inserted above the ovary
9 Inflorescence Flowers grouped in clusters Sometimes what appears as a single flower is actually an inflorescenceSunflower, daisies, and dogwood flower common examplesThe arrangement of flowers in the inflorescence varied with many patterns possible: spike, umbel, head, and catkin
12 Meiosis occurs: Stamens Carpels in pollen chambers of anther in developing ovules in ovary
13 Pollen development -1Microspore mother cells become distinct in the pollen chambersEach MMC undergoes meiosis to produce 4 microsporesEach microspore develops into a pollen grain, the male gametophyte
19 Ovule One or more ovules develop within the ovary Ovule is surrounded by integumentsOpening in integuments is known as the micropyle
20 Ovule development - 1One cell becomes distinct as a megaspore mother cellThe megaspore mother cell undergoes meiosis to produce four megasporesThree degenerate leaving one surviving megaspore
21 Ovule development - 2Surviving megaspore undergoes three mitotic divisions to producing 8 nucleiThese 8 nuclei are distributed with 3 near the micropyle end of the ovule, 3 at the opposite end and 2 (polar nuclei) in the centerOne of the nuclei at the micropyle end is the eggThis mature female gametophyte is often called the embryo sac
23 Pollination Transfer of pollen from the anther to the stigma Self-pollination - same flowerCross- pollination - from one flower to anotherPollen transfer occurs mainly by animals or wind
24 Animal Pollinated Flowers Flowers brightly colored and fragrantEssential oils attractNectar producedColor patterns may be nectar guidesPollen larger, sticky, and not abundant
25 Wind Pollinated Flowers Flowers small and inconspicuous often an inflorescenceOften lacking sepals and petals; no nectarPollen small, dry, light, and abundantOne ragweed plant can release one billion pollen grains (1 million tons/yr in NA)StigmaOvary
26 POLLENStudy of pollen called palynology has applications in many diverse fields: petroleum geology, anthropology, archeology, criminology, and medicineWhen pollen is released by wind-pollinated plants, only a very tiny percentage reaches the stigma - remainder settles back to earth.
27 Pollen tube growth Pollen grain germinates on compatible stigma Pollen tube begins growing down into the style towards the ovaryGenerative nucleus divides mitotically producing two non-motile sperm.Pollen tube continues to grow until it reaches the micropyle of an ovule
30 Double fertilization A distinctive feature of angiosperms Both sperm involved in fertilization.One sperm fertilizes the egg to produce a zygoteSecond sperm fuses with the two polar nuclei producing the primary endosperm nucleus which develops into endosperm
33 Endosperm A nutritive tissue for the developing embryo. Major food source for the human populationEndosperm reserves in wheat, rice, and corn are especially important food sources
34 Following fertilization Sepals, petals, and stamens drop offOvary greatly expands becoming a fruitEach fertilized ovule becomes a seedInteguments of the ovule develop into the seed coat
35 Summary1. Meiosis reduces the number of chromosomes from diploid to haploid2. The flower is the unique reproductive structure of angiosperms3. Pollination is the transfer of pollen from anther to stigma occurring through the action of wind or animals4. In angiosperms reproduction is accomplished through the process of double fertilization.
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