Plant reproduction Chapter 38

Fig. 38.3

Plant life cycle Alteration of generations Haploid (n) Diploid (2n) Sporophyte: Diploid plant produces haploid spores by meiosis Gametophyte: Haploid plant produces diploid zygotes by fertilization

Angiosperms Gametophyte generation very small Enclosed within the parent sporophyte Pollen grains: Male gametophytes Embryo sac: Female gametophytes Gametes produced in separate structures

Life cycle

Flower structure Sepals Protect the flower Petals Attract pollinators Stamens: male structures Filaments: “stalks” Anther: swollen portion at the top

Flower structure Carpels: female structures Ovules: develops into seeds Ovary: contains ovules Style: slender neck-like structure Stigma: top collects pollen

Flower structure

Seed Development

Male gametophytes Pollen formation Pollen sacs in anther Microspore: (mother cell) Meiosis 4 haploid cells 4 pollen grains Inside is a generative cell Divides later to form 2 sperm

Female gametophytes Egg formation Ovules Contain a megaspore mother cell Undergoes meiosis 4 haploid cells 3 die (disintegrate) one lives Undergoes mitosis 8 haploid nuclei Arranged in specific order in embryo sac

Female gametophytes 1 at opening of embryo sac (egg cell) 2 (single cell) at center polar bodies 2 contained in cells called synergids on either side of the egg cell 3 called antipodals at opposite end from egg cell

Fertilization Pollen sticks to sugary substance on stigma Grows pollen tube Reaches ovule Pollen grain divides into two sperm One of the synergids degenerates Tube penetrates the ovule

Fertilization Double fertilization 2 sperm are used 1. Sperm fertilizes egg-zygote (2n) 2. Sperm fuses with polar bodies Forms endosperm (3n)

Fertilization

Seed formation Ovule develops into a seed Ovary develops into a fruit Endosperm develops first Stores food for seed Most monocots & some eudicots White coconut meat-endosperm White part of popcorn-endosperm

Seed structure Seed coat: Protective covering Cotyledons: Seed leaf Help with embryo development Dormancy Imbibition: Uptake of water–starts germination

Fig. 38-8 Seed coat Epicotyl Hypocotyl Radicle Cotyledons (a) Common garden bean, a eudicot with thick cotyledons Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle (b) Castor bean, a eudicot with thin cotyledons Scutellum (cotyledon) Pericarp fused with seed coat Endosperm Coleoptile Epicotyl Hypocotyl Coleorhiza Radicle (c) Maize, a monocot

Fig. 38-9 Foliage leaves Cotyledon Epicotyl Hypocotyl Cotyledon Cotyledon Hypocotyl Hypocotyl Radicle Seed coat (a) Common garden bean Foliage leaves Coleoptile Coleoptile Radicle (b) Maize

Fruit Development

Fruit formation Ovary Simple fruits: Single carpel-pea, nectarines Aggregate fruits: Separate carpels Raspberry Multiple fruits: Group of flowers-pineapples

Fig. 38-10 Stigma Carpels Style Stamen Flower Petal Ovary Stamen Sepal Stigma Ovary (in receptacle) Ovule Ovule Pea flower Raspberry flower Pineapple inflorescence Apple flower Each segment develops from the carpel of one flower Remains of stamens and styles Carpel (fruitlet) Stigma Sepals Seed Ovary Stamen Seed Receptacle Pea fruit Raspberry fruit Pineapple fruit Apple fruit (a) Simple fruit (b) Aggregate fruit (c) Multiple fruit (d) Accessory fruit

Asexual reproduction Genetically identical individuals Vegetative reproduction Cuttings Spider plants Fragmentation Roots give rise to new plants (Aspens) Apomixis (seeds produced asexually) Dandelions