BIOL 1120 Lecture Notes - Lecture 21: Pollen Tube, Zygote, Parthenogenesis
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Chapter 41: Plant Reproduction
I. Flower Characteristics via Coevolution
A. Plants and insects have coevolved.
1. Plants with structures that were more enticing to insects were favored (3 basic attractants for
a. Some plants offered a food incentive.
b. Some plants offered a sexual attractant.
i. Scent of a receptive female
ii. Shape of a receptive female
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c. Other plants provided a nursery for developing insect larvae.
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2. Insects that recognized and located particular plants had a competitive edge.
B. Insects are effective carriers of pollen from flower to flower as they visit to gather food.
II. Flower Components (Fig. 41.11, p. p. 837)
A. The specialized parts of the flower grow from the modified end of the floral shoot—the receptacle.
1. Non- fertile components
a. Sepal (collectively called the calyx) are the outermost green, leaflike parts.
b. Petals (collectively called the corolla) are the colored parts located between the reproductive
structures and the sepals.
2. Fertile components
a. Stamens (male parts) are located inside the corolla.
i. Often the stamen consists of a slender stalk (filament ) capped with an anther.
ii. Inside the anthers are pollen sacs in which pollen grains develop.
b. Carpels (female parts) collectively called the pistil .
i. Located in the central part of the flower
ii. Vessel-shaped structure with an expanded lower chamber (ovary), slender column
(style ), and upper surface (stigma) for pollen landing.
iii. In the ovary eggs develop, fertilization occurs, and seeds mature.
B. Flowers differ from the other tissues of the plant in their fragrance and colors (carotenoids and
anthocyanins), which are attractive to pollinators.
C. Complete Flowers have all four of the above floral parts.
D. Incomplete Flowers are lacking at least one of the four floral parts.
E. Perfect Flowers have both male and female parts.
F.Imperfect Flowers lack the parts of one sex (may, or may not, be on the same plant)
1. Monoecious plants have male (staminate) and female (pistilate) flowers on the same plant (ex.
corn, cucurbits, pines, etc.).
2. Dioecious plants have male and female flowers on separate plants (ex. hollies, gingkoes,
mulberries, willows, etc.).
III. Male Gametophyte (Pollen grain) Formation (Fig. 41.15, p. 839)
A. Diploid microspore mother cells in the anthers divides by meiosis to form four haploid
B. Each microspore will divide to form pollen grains each containing two cells.
1. One cell (generative cell ) in each pollen grain will produce 2 sperm cells.
2. The other cell (tube cells ) will form the pollen tube.
IV. Female Gametophyte (Embryo sac) Formation (Fig. 41.15, p. 839)
A. Diploid megaspore mother cells in an ovule divides by meiosis to produce haploid megaspores .
B. One of which will undergo mitosis three times to produce a cell with eight nuclei.
C. The nuclei migrate to different parts of the cell resulting in an embryo sac with seven cells (Fig.
41.17, p. 840).
1. One cell has two nuclei and will become the endosperm which will eventually provide
nutrition for the embryo.
2. Another cell will be the egg.
V. From Pollination to Fertilization (Fig. 41.26, p. 846-847)
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