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Transcript
Flowering Plants Reproduction Chapter 35 Angiosperms • The largest and most successful group of plants • Can reproduce both sexually and asexually • Advantages: – Sexual – genetic variation – Asexual – rapid and efficient • Disadvantages: – Sexual – requires time and energy – Asexual – lack of genetic variation Alternation of Generations • Diploid sporophyte generation – larger and nutritionally independent – Produces haploid spores by meiosis • Haploid gametophyte generation – located in the flower; microscopic and totally dependent on the sporophyte – Gives rise to the gametes by mitosis Flower structure • Complete flowers: – All four whorls • Sepals (all together = calyx) • Petals (all together = corolla) • Stamen – male flower part – Filament, anther • Carpel (a.k.a. pistil) – female flower part – Stigma, style, ovary Pollination • Self-pollination – within the same flower or another flower on the same plant • Cross-pollination – pollen grains travel to another plant – Insects, birds, small mammals, wind and water can all serve as agents Tricks to prevent inbreeding • Self-pollination reduces genetic variation and may concentrate ‘bad’ genes • Incomplete flowers – separate male and female flowers • Timing variation – pollen is shed at a time when stigma is not receptive • Self-incompatibility – a plant has the ability to identify and reject its own pollen Coevolution • Plants and their animal pollinators are usually closely adapted to each other – Colors, scents • Animals may also have adaptations – Physical features and even behavior Fertilization • Pollen grains lands on stigma • One cell grows a thin pollen tube through the style to the ovary • The 2nd cell in the pollen grain divides to form 2 sperm cells which travel down the tube to the ovule • One sperm cell fertilizes the egg and form a zygote • The other sperm cell joins with 2 polar nuclei and forms a triploid endosperm which will nourish the embryo • This process is called double fertilization Seeds • Contain an embryonic plant and food stored in the cotyledons or endosperm • Surrounded by a protective seed coat • Germination – seed sprouts and relies on stored food until leaves are functional • Fruits are mature, ripened ovaries Asexual reproduction • Rhizome – horizontal, underground stem that can branch in many directions • Bulb – underground bud with thick leaves that store food • Runners – horizontal, aboveground stems • Suckers – shoots that branch off of underground roots