GYMNOSPERMS REPRODUCTION AND LIFE CYCLE THE NAKED SEEDS

SPERMOPHYTA (Gymno & Angio) seed plants Vascular tissue Use seeds for reproduction Cell walls with cellulose Don’t require water for reproduction Dominant sporophyte Microscopic gametophyte

BODY PLAN – Gymno only! Dominant diploid sporophyte Have roots, stems, leaves, vascular tissue Leaves = large or needle like Have two types of cones –Produce spores  gametophyte Gametophyte depends on sporophyte for nutrition Gametophyte = naked seed produced on outside of cone

ADVANTAGES Transfer of pollen grains and development of pollen tube eliminates the need for water for sexual reproduction Gametophyte is very reduced and does not develop in the soil as an independent generation, instead the tiny gametophyte is contained and protected within the moist reproductive tissue of the sporophyte Evolution of the seed = protection of the dormant embryo from drying out, cold …and is used to disperse the seed to new habitats

DIVERSITY CYCADS Grow in tropical and subtropical regions Look like palms except they have naked seeds produced by big cones Abundant 300 million years ago –were the food of herbivorous dinosaurs and the fate of both of these groups of organisms was probably closely linked.

DIVERSITY GINKO This is a monotypic division, a single species of a single genus, Ginkgo biloba the maidenhair tree.. Ginkgo biloba was preserved in the gardens of Buddhist monasteries in China and Japan where it was encountered by Westerners in the eighteenth century. It has turned out to be a valuable street tree because of its unusual foliage and tolerance of pollution.

DIVERSITY CONIFER Conifer leaves are needle or scale-like often large and can dominate the plant life in some ecosystems their stems continue to expand in width as well as length throughout the life of the plant The older parts of the stem become woody, which provides a further distinction from the seedless vascular plants of which there are no surviving woody representatives. EX. Pine, Spruce, Cedar, Fir, Juniper…

THE CONIFER LIFE CYCLE NAKED SEEDS  BIG TREES

The Dominant Sporophyte Diploid Produces male and female cones

BEGIN WITH DOMINANT SPRORPHYTE = MATURE TREE The plant produces both male and female cones MALE CONES ARE SMALL AND PRODUCE POLLEN GRAINS FEMALE CONES ARE LARGE

The Male Cone Appears in the sring Cells in the cone divide by meiosis and produce small haploid spores  pollen grains Pollen Grain = immature male gametophyte Pollen grains are released into the air

Pollen grains

FEMALE CONES More familiar Larger spores form by meiosis = haploid egg Female gametophyte stay inside tissue of parent sporophyte

POLLINATION Pollen grain carried to female cone via wind When it arrives inside the female cone, each pollen grain forms a tiny pollen tube Pollen Grain + Pollen Tube = Mature male gametophyte Pollen tube grows into female gametophyte until it reaches an egg

FERTILIZATION Occurs deep within the protective tissues of the parent sporophyte A sperm nucleus from the pollen grain unites with the egg  zygote In Pine it takes 15 months from pollination to fertilization

DEVELOPMENT OF THE EMBRYO Zygote cells undergo mitosis  embryo  sporophyte plant Embryo surrounded by food storage tissue (part of gametophyte) Protective coat of sporophyte tissue develops around embryo and food By the time the food runs out, embryo has chlorophyll and can make its own