Plant Reproduction and Development Chapter 28 Angiosperm Life

Plant Reproduction and Development Chapter 28

Angiosperm Life Cycles • Dominant form is the diploid sporophyte seed • In flowers, haploid spores formed by meiosis develop into gametophytes fertilization mature sporophyte DIPLOID HAPLOID meiosis (within anther) meiosis (within ovary) gametes (sperm) microspores (mitosis) male gametes gametophyte megaspores (eggs) (mitosis) female gametophyte

Flower Structure STAMEN (male reproductive part) filament anther CARPEL (female reproductive part) stigma style ovary • Nonfertile parts – Sepals – Receptacle • Fertile parts – Male stamens – Female carpels ovary) OVULE (forms within ovary) petal (all petals combined are the flower’s corolla) sepal (all sepals combined are the flower’s calyx) receptacle

Kinds of Flowers • Perfect flowers – Have both male and female parts • Imperfect flowers – Are either male or female – Same plant may have both male and female flowers – Sexes may be on separate plants

Pollen Formation • Each anther has four pollen sacs • Inside the pollen sacs, cells undergo meiosis and cytoplasmic division to form microspores • Microspores undergo mitosis to form pollen grains

Egg Formation • Ovules form inside the ovary of a flower • Protective integuments form around the ovule • Inside, cells divide by meiosis to form haploid megaspores • All megaspores but one disintegrate

Pollination • Transfer of pollen grains to a receptive stigma • Pollen can be transferred by a variety of agents • When a pollen grain lands on the stigma it germinates

Seed Formation • Fertilization of the egg produces a diploid sporophyte zygote • The zygote undergoes mitotic divisions to become an embryo sporophyte • Seed: A mature ovule, which encases an embryo sporophyte and food reserves inside a protective coat

Structure of a Seed • Protective seed coat is derived from integuments that enclosed the ovule • Nutritious endosperm is food reserve • Embryo has one or two cotyledons – Monocot has one – Dicot has two

Seed Dispersal • Fruit structure is adapted to mode of dispersal • Some modes of seed dispersal: – Wind currents – Water currents – Animals

Asexual Reproduction • New roots or shoots grow from extensions or fragments of existing plants • Proceeds by way of mitosis • All offspring are genetically identical (unless mutation occurs)

Natural Clones • Forest of Quaking Aspen in Utah – 47, 000 trees are genetically identical shoots – Roots are all interconnected • Oldest known clone – Ring of Creosote bushes in Mojave desert that is 11, 700 years old

Seed Germination • Process by which the plant embryo resumes growth after seed dispersal • Depends upon environmental factors – Temperature – Soil moisture – Oxygen levels

Splitting the Seed Coat • Imbibition – Water molecules move into a seed • As water moves in, the seed swells and the coat ruptures

Growth of a Bean Plant primary leaf hypocotyl two cotyledons primary root branch root

Growth of a Corn Plant

Hormones and Development • Genes governing the synthesis of hormones are activated in some cells but not others • This can start different cell lineages down different developmental pathways • Hormones interact with other gene products and with the environment to affect growth and development