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Chapter 12 Flowers and Fruits Flowers Sexual reproductive organs of flowering plants angiosperms, most diverse plant group produce new generations thru sexual reproduction – embryo develops into a seed Parts of a Flower

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Chapter 12 l.jpg

Chapter 12

Flowers and Fruits


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Flowers

  • Sexual reproductive organs of flowering plants

    • angiosperms, most diverse plant group

    • produce new generations thru sexual reproduction – embryo develops into a seed


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Parts of a Flower

  • Receptacle – flower parts attach here at the swollen area near the penduncle – stalk of the flower

  • Sepal – outer whorl of floral parts – all the sepals are called a calyx

  • All the petals together make up the corolla which form the next whorl

    • both are sterile parts of the plant and function to attract pollinators


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Sexual Reproduction Parts

  • Male part is the stamen

    • produce pollen grains that produce sperm

    • made up of the anther and filament

  • Female part is the pistil

    • inside 1 to many ovules – in each ovule is a single egg

    • made of the stigma and the style

  • Egg and sperm fuse in the ovule and develops into the seed

  • Ovary of flower and sometimes associated parts – becomes fruit that protects seed(s) and help in dispersal


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Stamens

  • Produce the pollen grains

  • 4 pollen-containing chambers fused into an anther that make pollen grains that are released thru a slit or thru the top

  • Anther generally supported on a stalk called the filament

  • Collection of stamens is a androecium

    • variation in number and arrangement of stamens, attachment of anther to filament, way release pollen from anther


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Stamen Arrangements

Magnolias have dozens of stamens

Some have free stamens and others are fused at filaments


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Pistils

  • Contain at least one ovule in their ovary and may be 1 or more per flower, some have one ovary with several carpels fused at the edge

    • ovary is called the carpel

  • Enlarged lower end is the ovary and the stigma is usually on a stalk and receives the pollen

    • stalked is called the style

    • raise the stigma to enhance pollination


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Female Reproductive Parts

  • Carpels/pistil have no gender

  • Specialized structure called the embryo sac in the ovule that is female

  • All the carpels collectively called the gynoecium

  • Indicators for how many carpels

    • chamber for each carpel is a section in an orange

    • stigmas or style may also reflect the number of carpels

    • lilies have 3 seed chambers and 3 stigma but only one style – made from 3 styles that fused together from 3 carpels

    • 4 lobes on the stigma with 4 fused carpels


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Petals

  • Often colorful, fragrant parts of flower

  • Collective petals are called the corolla – usually the most noticeable and attractive part - #, size, color and odor distinguish between flowers

  • Petals can be free, fused in short tube with large lobes, fused into long tube that encompasses most of the corolla – honeysuckle

    • aids in pollination


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Flower Symmetry

Radially symmetrical – petals develop equally

Bilaterally symmetrical – petals do not develop equally


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Floral Part Arrangements

  • a – spiral – magnolia

  • b – whorls – lily

  • c – petal like sepals and radial symmetry – daffodils

  • d – bilateral symmetry – pansy

  • e – petals fused into a tube – cape primrose


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Sepals

  • Flowers usually have a specific number of petal that they corresponds to the number of stamens, carpel and sepal

    • magnolia – hard to separate petals from sepals

  • Leaf-like sepals protect immature flower

    • may resemble petals like in the lily – call them tepals

    • 4 o’clocks have a calyx (sepals) that look like a corolla (petals) but they have no petals

  • Sepals may fuse into a tube and calyx may be radially or bilaterally symmetrical

  • Number of sepals also can reflect the number of other flower parts

    • same number of sepals and petals – look down from above they alternate

  • Protect inner parts of flower – prevent drying out

    • often fall off at maturity or after pollination and fertilization


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Embryo and Endosperm

  • Plants have a sexual reproduction part to their life cycle

  • Creates the embryo in a seed that matures into a plant – requires the formation an egg and sperm for fertilization

  • Most cells have diploid numbers of chromosomes

    • 1 set from each parent

  • Gametes are haploid – these are the reproductive cells

    • have only ½ the number of chromosomes – meiosis

    • fertilization produces a zygote that is diploid


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Life Cycle

  • Sperm is made in the pollen grain in the anther

  • Egg made in embryo sac in the ovule

  • Pollen grain and egg are gametophytes of flowering plants

  • Zygote grows in ovule becomes first cell of new organism


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Double Fertilization

  • Fertilization requires that pollen grains from anther to receptive stigma of a pistil

  • Embryo sac forms with a stalk and 1 or 2 integuments that develop into seed coat

  • Pollen reaches stigma and germinates to make pollen tube down style into the ovary

    • pollen that forms the pollen tube is the tube cell

    • 2nd cell in pollen grain is the generative cell as it divides and makes 2 sperm – move to a small opening in ovule called micropyle


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Double Fertilization (cont)

  • The 2 sperm move into embryo sac thru synergids which are cells next to the egg

    • send out chemicals so that pollen can find the egg

  • Sperm #1 – fertilizes the egg to form zygote

  • Sperm #2 fuses with the polar nuclei which are haploid near the mid region of the ovule to make a triploid cell = 3 sets of chromosomes

    • usually forms the endosperm in the seed – food for the embryo

  • Ovule matures into the seed

  • Many insects visit but only pollen form same species sticks tightly to stigma while rest falls off easily

  • Flowers can be used identify plants


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Reproductive Morphology

  • Helps to explain diversity

  • Flowering plants way out number any other group of plants

  • Diversity in shape, size and forms

    • from the reproductive success in a wide variety of habitats = based on the development of the flower

      • seed, fruit, pollination and the methods by which these things are distributed


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Variation in Basic Parts

  • Some flowers lack sepals, petals, stamens or pistils

  • Grasses have 3 stamens, 1 functional carpel (may have 2 non-functioning ones), no petals or sepals

  • Others have either stamens or carpels but not both


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Flower Types

  • Complete flower – has all major parts – sepal, petals, stamens and pitils

  • Incomplete flower – lacks one or more of the above parts

  • Perfect flower – has and androecium (collection of carpels) and a gymnoecium (collection of stamens) even if petals and sepals are missing


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Position of the Ovary

  • Superior ovary – base of the ovary above the sepals, petals and stamen – St John’s wort

  • Inferior ovary – the sepals, petals and pistil rest on top of the ovary – daffodil

  • Incomplete ovary – ovary surrounded by the receptacle and the petals and stamens branch from the receptacle above the ovary - rose


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Monocot and Dicot Flowers

  • Identified by the number of their floral parts

  • Monocots – flower parts occur in 3 or multiples of 3

    • 3 petals, 3 sepals, 6 stamens, 1 pistil with 3 chambers

    • mostly herbaceous plants – non-woody

  • Dicots – flower parts in 4 or 5 or multiples of 4 or 5

    • 80% of all angiosperms – herbaceous and woody


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