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Flowers II Modified Flowers and Sexual Reproduction.

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Presentation on theme: "Flowers II Modified Flowers and Sexual Reproduction."— Presentation transcript:

1 Flowers II Modified Flowers and Sexual Reproduction

2 Bracts zAdditional floral structures outside the calyx zMay be leaflike or petal-like zThe showy white or pink "petals" of dogwood are bracts

3 Tepals zSepals are brightly colored and identical to the petals

4 Complete and Incomplete flowers zFlowers containing all four floral appendages are known as complete flowers zFlowers lacking any of the four floral structures are known as incomplete flowers zFlowers of grasses possess neither sepals nor petals

5 Perfect and Imperfect Flowers zPerfect flowers have both stamens and carpels zImperfect flowers lack either stamens or carpels *Unisexual flowers *Male flowers called staminate *Female flowers called pistillate or carpellate

6 Plants with Unisexual Flowers zMonoecious plants have both male and female flowers on a single individual zDioecious plants are either male or female with only unisexual flowers on a single individual

7 Ovary Position zSuperior ovary - sepals, petals, and stamens are inserted beneath the ovary zInferior ovary - sepals, petals and stamens are inserted above the ovary

8 Flower symmetry zRegular flower displays radial symmetry zIrregular flowers display bilateral symmetry

9 Inflorescence zFlowers grouped in clusters zSometimes what appears as a single flower is actually an inflorescence zSunflower, daisies, and dogwood flower common examples zThe arrangement of flowers in the inflorescence varied with many patterns possible: spike, umbel, head, and catkin

10 Inflorescence Types Spike Umbel Catkin Head

11 Sexual Reproduction in Flowers

12 Meiosis occurs: zStamens y in pollen chambers of anther zCarpels y in developing ovules in ovary

13 Pollen development -1 zMicrospore mother cells become distinct in the pollen chambers zEach MMC undergoes meiosis to produce 4 microspores zEach microspore develops into a pollen grain, the male gametophyte

14 Pollen chamber in anther

15 Pollen development - 2 zMicrospore nucleus undergoes mitosis to produce xgenerative nucleus xtube nucleus zMicrospore wall modified into pollen wall zWhen mature pollen are released from the anthers

16 Pollen wall zIntine - inner layer zExine - outer layer zExine may be ornamented with spines, ridges, or pores

17 Pollen - Male gametophyte Tube nucleus Generative nucleus Exine Intine

18 Pollen Types Ragweed Thistle Oak

19 Ovule zOne or more ovules develop within the ovary zOvule is surrounded by integuments zOpening in integuments is known as the micropyle

20 Ovule development - 1 zOne cell becomes distinct as a megaspore mother cell zThe megaspore mother cell undergoes meiosis to produce four megaspores zThree degenerate leaving one surviving megaspore

21 Ovule development - 2 zSurviving megaspore undergoes three mitotic divisions to producing 8 nuclei zThese 8 nuclei are distributed with 3 near the micropyle end of the ovule, 3 at the opposite end and 2 (polar nuclei) in the center zOne of the nuclei at the micropyle end is the egg zThis mature female gametophyte is often called the embryo sac

22 Ovule - Female Gametophyte Polar nuclei Integuments Egg Micropyle

23 Pollination zTransfer of pollen from the anther to the stigma zSelf-pollination - same flower zCross- pollination - from one flower to another zPollen transfer occurs mainly by animals or wind

24 Animal Pollinated Flowers zFlowers brightly colored and fragrant zEssential oils attract zNectar produced zColor patterns may be nectar guides zPollen larger, sticky, and not abundant

25 Wind Pollinated Flowers z Flowers small and inconspicuous often an inflorescence z Often lacking sepals and petals; no nectar z Pollen small, dry, light, and abundant yOne ragweed plant can release one billion pollen grains (1 million tons/yr in NA) Stigma Ovary

26 POLLEN zStudy of pollen called palynology has applications in many diverse fields: petroleum geology, anthropology, archeology, criminology, and medicine zWhen pollen is released by wind- pollinated plants, only a very tiny percentage reaches the stigma - remainder settles back to earth.

27 Pollen tube growth zPollen grain germinates on compatible stigma zPollen tube begins growing down into the style towards the ovary zGenerative nucleus divides mitotically producing two non-motile sperm. zPollen tube continues to grow until it reaches the micropyle of an ovule

28 Pollen tube growth Pollen Pollen tube Ovary Ovule

29 Pollen tube growth Pollen Pollen tube Ovary Ovule **** Sperm

30 Double fertilization zA distinctive feature of angiosperms zBoth sperm involved in fertilization. zOne sperm fertilizes the egg to produce a zygote z Second sperm fuses with the two polar nuclei producing the primary endosperm nucleus which develops into endosperm

31 Fertilization Polar nuclei Egg ** Pollen tube Sperm

32 Double fertilization zSperm + Egg -----> Zygote zSperm + 2 polar nuclei > Primary Endosperm Nucleus

33 Endosperm zA nutritive tissue for the developing embryo. zMajor food source for the human population zEndosperm reserves in wheat, rice, and corn are especially important food sources

34 Following fertilization zSepals, petals, and stamens drop off zOvary greatly expands becoming a fruit zEach fertilized ovule becomes a seed zInteguments of the ovule develop into the seed coat

35 Summary z1. Meiosis reduces the number of chromosomes from diploid to haploid z2. The flower is the unique reproductive structure of angiosperms z3. Pollination is the transfer of pollen from anther to stigma occurring through the action of wind or animals z4. In angiosperms reproduction is accomplished through the process of double fertilization.


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