Chapter 20 REPRODUCTION OF FLOWERING PLANTS

A. Asexual Reproduction Parent plant produces progeny that are genetically identical to it and to each other (clones). Clones can develop from portions of stems, leaves or roots.

Asexual reproduction is advantageous when environmental conditions are stable.

B. Sexual Reproduction Parent plant produces progeny that are genetically diverse. Involves alternation of generations.

1. Flowers Reproductive organs of angiosperms. Function to: ] attract pollinators ] bring eggs & sperm together ] form fruit ] protect developing seeds

Most flowers have 4 whorls: ] Whorl 1 – Calyx (outermost) [sepals] ] Whorl 2 - Corolla [petals] ] Whorl 3 - Stamens [male reproductive organs] ] Whorl 4 – Pistil (innermost) [female reproductive organs]

Complete flowers - possess all 4 parts (sepals, petals, stamens & carpels). Incomplete flowers - lack one or more of the 4 parts. Perfect flowers - have stamens & carpels. Imperfect flowers - have either stamens or carpels. Monoecious - plant with  &  flowers. Dioecious - plant with either  or  flowers.

2. Gamete Formation ] Sperm formation  Mature sporophyte produces flowers with anthers.  Anthers consist of 4 pollen sacs - each contains numerous microspore mother cells.

 Each microspore mother cell divides by meiosis - gives rise to 4 haploid microspores.  Microspores divide by mitosis - give rise to microgametophytes (pollen grains) containing: F 1 vegetative cell F 1 generative cell

] Egg formation Ovary  Mature sporophyte produces flowers with ovule(s).  Each ovule contains a megaspore mother cell.

 Megaspore mother cell divides by meiosis - gives rise to 4 haploid megaspores: F 3 degenerate F 1 persists & enlarges  Enlarged megaspore undergoes 3 mitotic divisions - gives rise to megagametophyte (embryo sac).

Mature megagametophyte consists of 8 haploid nuclei, but only 7 cells: F 1 large, central cell - contains 2 haploid nuclei (polar nuclei) F 1 egg F 5 support cells (will degenerate)

3. Pollination Transfer of pollen from anther to stigma. ] Wind-pollinated flowers are usually small, greenish, odorless & produce large quantities of pollen. Include oak, cottonwood, ragweed & grasses ] Animal-pollinated flowers are usually large, colored, scented & produce nectar. Most angiosperms

4. Double Fertilization  Pollen lands on stigma of same species.  Pollen tube grows down style to ovule.  Two sperm descend pollen tube. F 1 sperm fertilizes egg; forms the zygote (2n) F 1 sperm fertilizes polar nuclei; forms endosperm (3n) Ovule Style

C. Seeds and Fruits 1. Seed Development & Dormancy ] Zygote divides to form embryo. F dicot embryo forms 2 cotyledons (seed leaves). v cotyledons absorb endosperm F monocot embryo forms 1 cotyledon v most endosperm remains intact until after germination

Monocot seed Dicot seed Seeds consist of a plant embryo, food source (endosperm) & a seed coat. Seed coat

Mature seeds enter a period of dormancy (temporary suspension of growth & development). ] allows time for plant to disperse seeds. ] allows seeds to postpone germination until environmental conditions are favorable.

2. Fruit Formation Fruits consist of the mature, ripened ovaries of flowers (and receptacles, in some) Fruits function to: ] protect seeds from drying out ] aid in seed dispersal

Types of Fruits ] Simple fleshy fruits - have 1 or more united carpels. F Drupe - hard pit; 1 seed/carpel Ex. olive, cherry, peach, plum, coconut F Berry - fleshy core; many seeds/carpel Ex. grape, tomato, pepper F Pome - tough core; pulp derived from receptacle Ex. apple, pear

] Complex fleshy fruits - have multiple separate carpels. F Aggregate - develop from 1 flower Ex. blackberry, strawberry, raspberry F Multiple - develop from tight clusters of flowers Ex. pineapple

] Dehiscent dry fruits - mature fruit splits, releasing seeds Ex. bean, pea, peanut ] Indehiscent dry fruits - mature fruit remains around seed(s) Ex. hickory, acorn, maple, sunflower, corn

3. Seed Dispersal and Germination ] Dispersal  animals  wind  water (coconuts)  explosive seed pods

] Germination Resumption of growth & development after dormancy is broken. Usually requires: F water - expands seed & ruptures seed coat; triggers metabolic changes F a source of energy (starch in endosperm or cotyledons) F oxygen - required for production of ATP

May also require: F exposure to light of certain intensity F several days at a particular temperature F passing through digestive tract of an animal F exposure to fire

Monocot development Dicot development