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21 Cards in this Set

  • Front
  • Back

Alternation of Generations

•Alternation between sporophyte and gametophyte generation


•Gametophytes and sporophytes are two different living plants

Why are mosses and terms limited to living in wet environments?

They have flagellated sperm which need a water medium

Archegonia

Structure in which egg is retained

Antheridia

Structure in which sperm is retained

Sperm in terrestrial plants

Pollen

Advantages of a seed

•Seed contains a dormant sporophyte embryo


•After the fusion of gametes the embryo arrests and remains dormant within the seed until the seed germinates in a favorable environment. The sporophyte then resumes its mitotic division and gives rise to the new adult sporophyte


•Embryo remains viable until it finds a suitable place to live


•Seeds can be dispersed to other habitats allowing the species to spread

Microstrobilus

•Male cones


•Only seen seasonally, mostly in spring


•At the lower branches of the tree


•Very small


•Produce prolific amounts of pollen


•After pollen production, what remains of the cones disappears

Megastrobilus

•Female cones


•Large prominent cones that give rise to trees


•At the higher braces


•Take two or three years to mature and then drop off

Life Cycle of Gymnosperm: Male Gametes

Male cones start with diploid cells called microspore mother cells


These divide by meiosis, halving the chromosome number, producing haploid microspores, each of which then undergoes two successive mitotic division and yields a four-cell pollen grain The pollen grain is the male gametophyte


Eventually the wind disperses the pollen grains

Life Cycle of Gymnosperm: Female Gametes

Megasporocytes which divide by meiosis and produce haploid megaspores. They undergo a series of mitotic divisions repeated over and over again until you get to the female gametophyte which is approximately 2,000 cells. Two of these cells will become the eggs

Pollination

Transfer of pollen to female cone. Female cones have a sticky resin to help pollen adhere to the cone

Ovule

•Located within the ovary


•Location where the egg nucleus is produced


•Eventually hardens and becomes the water-tight seed coat


•Contains the embryo within its walls

Pistol

•Female portion of angiosperm


•Top of the pistol is the stigma


•Long part under stigma is the style


•Ovary is under the style

Stamen

•Male portion of angiosperm


•Anthers - where pollen is produced


•Filaments - anchor anthers to the base of the flower

Double-Fertilization Process: Female Gametophyte

Start off with diploid megaspore mother cells. These divide meiotically and develop four nuclei. Of the four haploid cells, three disintegrate. The surviving one is called the megaspore. The megaspore then divides mitotically into eight nuclei (three mitotic divisions) in the ovule. The nuclei arrange themselves in a distinctive way: three nuclei at the upper end called antipodal cells two nuclei in center of the ovule called the polar nuclei three nuclei toward the bottom -One of these nuclei is the egg nucleus -On either side of the egg nucleus are two other nuclei called synergids

Double-Fertilizaiton Process: Male Gametophyte

In the anthers pollen grains are produced. We have diploid microspore mother cells which undergo meiosis and produce four haploid cells, each of which undergoes mitosis to form a two-celled pollen grain with a haploid nuclei. These pollen grains are then carried either by wind, insect, or animal and lands on the stigma of the flower

How pollen gets to the egg nucleus

One of the cells of the pollen grain is called a tube nucleus. The other is called a generative nucleus. The pollen grain forms a tube that will eventually go all the way down to where the ovule is located. The generative nucleus divides mitotically to form two sperm nuclei and somewhere behind them is the tube nucleus. Generative nucleus gives rise to sperm nuclei, tube nucleus gives rise to tube. When the growth reaches the ovule, the sperm nuclei enter. At the very bottom of the tube is a small opening called a micropyle. The micropyle is the place where the sperm nucleus can enter.

Double-Fertilization Process

First sperm nucleus fuses with the egg nucleus. The resulting structure (zygote) is diploid. The zygote divides mitotically to produce the embryo which will eventually become part of the seed. The second sperm nucleus fuses with the two polar nuclei in the center of the ovule. The resulting structure, called the endosperm, is triploid (two haploid polar nuclei and a haploid sperm nucleus)

Function of Endosperm

Source of nutrition for embryo

Seed

Matured Ovule

Fruit

Matured Ovary