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