3.5 Seed Plants

Progymnosperms

• extinct

• first naked seed plants

• transitional group

Structures that allowed seed plants to survive on dry land:

1. Seed

2. Pollen

Seed coat

protects embryo

endosperm

stores food for developing embryo

Seed

Micogametophytes

• male

• pollen grains

• dispersed by wind or pollinator

Megagametophyts

• develope within ovule

• enclosed within diploid sporophyte tissue in angiosperms

Monoecious

male and female on same plant

dioecious

male and female on separate plants

gymnosperms characteristic

• dominant sporophyte

• gametophyte small and not independent

• lack flowers and fruits

• unclear monophyletic or paraphyletic

Conifers

• dominant, most diverse

• monoecious

• needle like leaves with thick cuticle

• softwood

Cycads

• slow growing gymnosperms

• resembles palm trees

• dioecious

• flagellated sperm

Ginkgos

• no longer found in the wild

• dioecious

• pollen with flagellated sperm

• fan shaped leaves

Gnetophytes

• Three unusual genera: ephedra, gnetum, welwitschia

• Dioecious

• angiosperm like features most like because of convergent evolution

Female and male cones- conifers

• megastrobilus produces megagametophyte

• microstrobilus/pollen cone produces microgametophyte

Gamete production in megastrobilus

1. sporogenesis: diploid megasporocyte divides via miosis, 1 large haploid cell survive and becomes megaspore

2. Gametogenesis: megaspore divides via mitosis and developes into megagametophyte with egg cell inside (containing archegonium)

Gamete production in microstroblius

1. Sporogenesis: diploid microsporocyte divides via meiosis into 4 haploid microspores: tetrad

2. Gametogenesis: one microspore divides via mitosis to produce generative cell and tube cell. Generative cell divides via mitosis to produce two sperm cell. Tube cell grows into pollen tube that sperm travel down to fertilize

Conifer Life cycle

• micro and mega sporocytes undergo meiosis to produce haploid gametes

• Archegonium has sticky pollen to trap micropyle to pollinate

• pollen tube grows toward gametophyte

• one sperm nuclei fertilizes egg → embryo→seed

• can take 1-2 years after pollination

Angiosperms

• flowering plants

• success due to flowers and fruits

• sporophyte dominant

• monophyletic

• monocots dicots

Flowers

• modified stems bearing modified leaves

• houses gametophytes

• have both male and female

Flowers: monoecious

• separate male and female flowers on same plants

flowers: dioecious

separate male and female plants

Angiospore female gamete production

• meiosis in megasporocyte→ 4 megaspores (1 large)

• 1 megaspore survives produces 8 nuclei and 7 cells via mitosis

• 3 cells at each end of embryo sac: antipodal cells, synergids and egg

• central cell contains polar nuclei ( cell with 2 nuclei)

Angiospores male gamete production

• meiosis of mother spore cells in microsporangium produces 4 microspores

• each microspore forms pollen grain

• pollen contains 2 cells

• generative and pollen tube

Double fertilization

• pollen lands on stigma and pollen tube begins to grow

• First fertilization: 1 sperm+1 egg= diploid zygote

• Second fertilization: other sperm fuses with polar nuclie= triploid cell

• zygote develops into embryo with radicle and one or two cotyledons

Basal angiosperms

• branched off before monocots and dicots

• magnolidae

Monocots

• do not produce true wood, herbaceous

• only primary growth at apical meristems

• One cotyledon

• parallel veins

• scattered vascular tissue

• fiberous roots

• pollen is monosulcate

• flower is three or multiples of three

eudicots

• produce true wood

• primary and secondary growth

• wood is proleferating xylem

• two cotyledon

• network veins in leaves

• vascular tissue in ring pattern

• tap rool with lateral roots

• pollen is trisulcate

• flower parts in 4, 5 or multiples of 4 and 5