Chapter 23b-Angiosperms. Double Fertilization The ovule is the site of meiosis and ultimately the formation of the seed.

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1 Chapter 23b-Angiosperms Double Fertilization The ovule is the site of meiosis and ultimately the formation of the seed. The ovule develops one or more layers of sterile tissue, the integuments along with a megasporocyte, which is embedded in the nucellus. The megasporocyte divides by meiosis to produce the haploid megaspores. Of the four megaspores, generally only one remains. Within the embryo sac, cell walls develop around some of the nuclei, forming the egg and 2 other cells, the synergids. Other nuclei are not enclosed in cell walls. Some of these, the polar nuclei, are located in the central region of the embryo sac. This shows the mature ovule with the embryo sac fully developed. Note that the egg and synergids are located at the micropylar end and that the polar nuclei are not far from the same end. The pollen tube grows through the micropyle and the 2 sperm nuclei are released. The phenomenon of two sperm nuclei combining with different nuclei from the female gametophyte is termed double fertilization, a phenomenon nearly unique to angiosperms.

2 Flowers Vary in their Architecture A flower with all four parts is a complete flower. If it lacks one or more parts, it is an incomplete flower. If a flower has both androecium and gynoecium (male and female) it is called a perfect flower. If only one sex is present, it is an imperfect flower. Symmetry is also used to characterize flowers Regular symmetry is when all the flower parts Sedum Irregular symmetry is when the flower parts are not equal. Pisum Flower parts may be free or united (fused). In Sedum, the petals, sepals, stamens, and pistils are completely separate and free. Sedum In Narcissus, the petals are fused over part of their length to form a tube.

3 Ovary position also varies. In some plants, the ovaries are clearly situated above the point of attachment of the other flower parts. In other plants, the ovaries appear to be placed below the point of attachment of the other flower parts. Superior ovary in Tulipa. Inferior ovary in Narcissus. A cluster of flowers is called an inflorescence

4 Angiosperms-Fruits Fruits are derived from the ovary of the flower. Fruits protect seeds, aid in seed dispersal, and can be a factor in seed germination. Fruit structure is highly constant for the same species in different environments and therefore fruits are used in classification. Fruits are of three types: Simple fruits are derived from a single ovary, the ovary may have one or more carpels. Aggregate fruits are derived from many separate ovaries of a single flower, all attached to a common receptacle. Carpels Stamen Raspberry flower Carpel (fruitlet) Stigma Ovary Stamen Raspberry fruit Aggregate fruit

5 Multiple fruits are the enlarged ovaries of multiple flowers that more or less fuse together. Flower Pineapple inflorescence Each segment develops from the carpel of one flower Pineapple fruit Multiple fruit A simple fruit the almond The almond has only a single carpel with one ovule. A simple fruit the legume, found in peas, beans, etc. Legumes have a single ovary and carpel, but there are multiple ovules. Fruits may be dehiscent (splits open) or indehiscent. Additional simple, dehiscent fruits: Follicle (Ex: Magnolia) The follicle develops from a single carpel and opens along only 1 side. Capsule (Poppy) Capsules are simple fruits derived from compound ovaries

6 Simple fruits can also be indehiscent, either dry or fleshy. Nuts are one type of dry, indehiscent fruit. Other dry, indehiscent simple fruits include: achene The sunflower seed is actually an achene; the shell is the pericarp. Other dry, indehiscent simple fruits include: caryopsis The seeds of corn and other grasses. The caryopsis differs from the achene in that the pericarp is firmly attached to the seed. Other dry, indehiscent simple fruits include: samara The winged fruits of maples and elms. The wings are outgrowths from the ovary wall. One of the most common fleshy simple fruits is the drupe. Plants that produce drupes include The almond is also a drupe, but we don t see the fleshy part. The initial fleshy pericarp eventually dries and becomes the hard covering of the seed.

7 Other fleshy, simple fruits include: Berry Berries are derived from a compound ovary, and many seeds are embedded in the fleshy pericarp. The tomato is a berry. Other fleshy, simple fruits include: Pepo The cucurbits (watermelon, cucumber, squash) are pepos. Pepos are specialized berries except with a rind that is a layer of tissue from the receptacle. Other fleshy, simple fruits include: Hesperidium A heperidium is another specialized berry and includes the citrus fruits. The thick peel that has numerous oil cavities is the exocarp and mesocarp. Other fleshy, simple fruits include: Pome The pome is derived from an inferior ovary.

8 Study outline for Chapter 23b-Angiosperms Label the angiosperm life cycle with the terms below: sporophyte gametophyte anther filament pollen sac pollen integuments micropyle ovule polar nuclei synergids egg sperm endosperm embryo seed seedling stigma style ovary pollen tube embryo sac Use the figure above to describe the angiosperm life cycle. Please include an explanation of double fertilization in your answer.

9 Study outline for Chapter 23b-Angiosperms Define the following term of floral characteristics: complete flower incomplete flower perfect flower imperfect flower Define the following term of floral characteristics and be able to recognize each characteristic. regular flower irregular flower free floral parts fused floral parts superior ovary inferior ovary inflorescence panicle umbel compound umbel spike solitary disc flowers ray flowers What are the 3 types of fruits? Define simple fruit. Define aggregate fruit. Define multiple fruit. Define dehiscent. Define indehiscent. Define the following fruit types and know two examples for each type of fruit. Dry, simple fruits legume follicle capsule nut achene samara caryopsis Which of the fruits listed above are dehiscent? Which of the fruits listed above are indehiscent? Fleshy, simple fruits drupe berry hesperidium pepo pome Aggregate fruit