I. Background
A. Flowers
1. Flowers are the organ of sexual reproduction
a. Seeds within a fruit
b. Require double fertilization
2. Angiosperms have vessel elements in their xylem and sieve-tube members in their phloem
B. Classes of flowering plants
1. Monocots
a. Typically herbaceous
b. Examples: Lilies, grasses, corn, palms, and orchids
c. Parallel leaf venation
d. Floral parts in 3s or multiples of 3
e. Fibrous root system
f. Scattered vascular bundles
g. One cotyledon in the seed
h. Persistent endosperm in the mature seed
2. Dicots
a. May be herbaceous or woody
b. Examples: Roses, oak trees, potatoes, and daisies
c. Netted leaf venation
d. Floral parts in multiples of 4 or 5
e. Taproot system
f. Vascular bundles arranged in a ring
g. Two cotyledons in the seed
h. Endosperm absent in the mature seed
II. Morphology of Flowering Plants
1. Flowers consist of sepals, petals, stamens, and carpels arranged in whorls around a stalk (peduncle)
a. Sepals and petals are sterile modified leaves
b. Stamens and carpels are fertile modified leaves
c. A flower with all four parts is complete
d. A flower missing any of the four parts is incomplete
e. A flower with both stamens and carpels is perfect
f. A flower having stamens or carpels (but not both) is imperfect
2. Sepals
a. Sepals function in protecting the other flower parts while it is a bud
b. The sepals are collectively referred to as the calyx
3. Petals
a. The petals are typically brightly colored to attract animal pollinators
b. The petals are collectively referred to as the corolla
4. Stamen
a. The stamens each have a filament (stalk) and an anther
b. In the anther microspores develop into pollen grains
i. Each pollen grain has two sperm
5. Carpel
a. Female reproductive organs located in the center of the flower
b. Produce ovules which ultimately may develop into seeds
c. The female portion of the flower is sometimes referred to as a pistil
i. The pistil may consist of a single carpel (simple pistil) or several fused carpels (compound pistil)
d. Each pistil has a stigma at the distal end
i. Pollen grain lands
e. Each pistil has a style (neck) and an ovary
i. Contains the ovule
f. Each ovule contains a female gametophyte that produces one egg and two polar nuclei
g. After fertilization the ovule develops into a seed
III. Life Cycle of Flowering Plants
A. Double fertilization
1. Flowering plants have a dominant sporophyte generation
a. Gametophyte is reduced to just a few cells
2. Ovules contain a megasporocyte
a. Megasporocyte undergoes meiosis to produce 4 haploid megaspores
3. Only one megaspore develops
a. Megaspore divides mitotically
b. Develops into the female gametophyte (embryo sac)
4. The female gametophyte consists of only 8 cells
a. Three of these cells participate in fertilization
i. One egg
ii. Two haploid polar bodies
5. The anther contains microsporocytes
a. Microsporocytes undergo meiosis to produce 4 haploid microspores
6. Each of the microspores develops into the male gametophyte
a. The male gametophyte is the pollen grain
7. Pollination involves transfer of the pollen grain to the style of the flower
a. Pollen grain lands on a style of the same species
b. Pollen grain grows a pollen tube down through the stigma to the ovaries
8. Both sperm enter the embryo sac
9. Fertilization involves both sperm
a. Referred to as double fertilization
i. One sperm fertilizes the egg resulting in a diploid zygote
ii. The other sperm fuses with the two haploid polar nuclei forming a triploid cell
10. The triploid cell develops into endosperm
a. Endosperm is a nutritive material for the embryo
b. Endosperm is persistent in monocot seeds
c. Endosperm is absorbed into the cotyledons in dicot seeds
IV. Development of Seeds and Fruit
A. Seeds and fruits develop after fertilization
1. Fruits protect the seeds from desiccation
2. Fruits may aid in dispersal of seeds by wind, water, or animals
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