28.1 Reproductive Strategies

By: Sarah Moran
Started 3/6 6:50 pm; Finished 3/6 8:40 pm

Overview of the life cycle and anatomy of flowering plants
Plants differ from animals in regards to reproduction such that they have two multicellular stages in their life cycle. A diploid stage alternates with a haploid stage.
  • Sporophyte - the diploid plant that produces haploid spores by meiosis; is dominant, produces flowers
  • Spores divide by mitosis to become haploid gametophytes that produce gametes.
Flowers are the reproductive structures of angiosperms. They contian two types of spores.
  • Microspores - develop into male gametophytes, pollen grains
  • Megaspores - develop into female gametophyte, embryo sac within an ovule of an ovary
  • Pollen grains contain sperm that travel to the embryo sac and fertilizes the egg, which becomes a zygote.
  • The ovule develops into a seed; the ovary into a fruit, which disperses the seeds.
Flowering plants are adapted to land.
  • Gametophytes are protected within the sporophte.
  • A thick wall develops to protect pollen grains.
  • External water is unneeded for fertilization due to pollen tubes.
  • A seed coat protects the growing embryo.

A. Flowers
Flowers develop in response to environmental signals, such as day length. Flowers may develop from he shoot apical meristem or from auxillary buds.
  1. Sepals - The most leaflike of flower parts, they are usually green and protect the bud of the developing flower.
  2. Petals - After the flower has opened, a whorl of petals appears. Their color, size, and shape attracts pollinators.
  3. Stamens - These are the male parts of flowers.
    1. Anther - a sac-like container, from which pollen grains and microspores develop.
    2. Filament - a slender stalk
  4. Carpel - the vaselike female portion of the flower at its very center.
    1. Stigma - enlarged sticky knob
    2. Style - slender stalk
    3. Ovary - enlarged base that encloses the ovules; if there are multiple carpels fused together, the ovary is compound with several chambers.
      1. Ovules - play a role in production of female gametophytes
  5. Not all flowers have all parts. Those that do are complete; those that do not are incomplete. Flowers with both stamens and carpels are bisexual, perfect. Those with only one of the two are imperfect, unisexual. If bisexual flowers are on one plant, it is monoecious. If on two, it is dioecious.external image 016_flower.jpg

B. Life Cycle of Flowering Plants
  1. Development of the Male Gametophyte
    1. Anthers contain four pollen sacs, each full of microsporocytes, which undergoes meiosis to produce four microspores.
    2. Microspores with haploid nuclei undergo mitosis, resulting in two cells wth finely sculptured walls - pollen grains.
    3. Pollen grains are at first immature and contain a tube cell, which will produce a pollen tube, and a generative cell, which will divide to produce two sperm.
  2. Development of the Female Gametophyte
    1. Ovaries contain ovules, which have a central mass of parenchyma cells covered by tissue called integuments, except for openings called micropyles.
    2. Megasporocytes are enlarged parenchyma cells. They undergo meiosis to produce four haploid megaspores. Three are nonfunctional. The functional one divides mitotically until there are eight nuclei.
    3. Cell walls form to make seven cells; one is binucleate.
    4. The female gametophyte (or embryo sac) consists of one egg cell, two synergid cells, one central cell, two polar nuclei, an three antipodal cells.
  3. Development of Sporophyte
    1. Walls separating pollen sacs in the anther break down when pollen grains are mature.
    2. Pollination is the transfer of pollen from the anther to the stigma of a carpel. Self-pollination is done by just one plant; cross-pollination requires two plants.
    3. Pollinators assist in cross-pollinaton. Other adaptations include carpels that mature only after the anthers have released pollen.
    4. When pollen grains land on stigmas, it germinates to make a pollen tube. The pollen tube passes between the stigma and style to reach the micropyle, a pore of the ovule.
    5. Double fertilization occurs: one sperm nucleus unites with one polar nuclei of the central cell to form a 3n endosperm cell. The zygote undergoes mitosis to become an embryo, a young sporophyte. The endosperm cell does so to become the endosperm, the tissue that will nourish the developing embryo and seedling.

Works Cited:
Double Fertilization in Flowering Plants. Prod. Kosasihiskandarsjah. Youtube.com. 03 May 2008. Web. 6 Mar. 2011.
Farabee, M. J. "Flowering Plant Reproduction." Estrella Mountain Community College, 2001. Web. 6 Mar. 2011. http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookflowers.html.
Mader, Sylvia S. "Reproduction In Plants." Biology. Student Ed. 9th ed. Boston: Glencoe/McGraw Hill, 2007. 496-99. Print.

What are the major components of the female and male parts of flowering plants?

28.2 - Seed Development

By:Laura Martin
Started 12:38 Mar 06; Finished 3:05 Mar 06
external image moz-screenshot-2.pngexternal image moz-screenshot-3.png
Cliffs notes on Seed Development

A. Development of the Eudicot Embryo
  1. Zygote Stage - Directly after double fertilization, the endosperm cell begins to divide, as well as the zygote, which divides asymmetrically.
  2. Proembryo Stage -Of these newly formed cells, one is small with dense cytoplasm, and is destined to become the embryo. This cell divides repeatedly, creating what is called the proembryo. The other cell also divides repeatedly, forming an elongated structure called the basal cell. At the proembryo stage, the endosperm resembles a mass of tissue that surrounds the embryo. The suspensor, which transfers nutrients to the embryo, is a separate structure and will disintegrate later.
  3. Globular Stage - The proembryo divides more, becoming globe shaped. The cells on the outer layer of the proembryo will become dermal tissue, as they divide in a specific direction to produce a single outer layer of cells. At the globular stage, it is already determined that the cells near the suspensor will become a root, whereas the cells on the other end will eventually form a shoot.
  4. Heart Stage - At the heart stage, the embryo becomes roughly heart shaped because of the cotyledons' appearance. The cotyledons (seed leaves), appear because of the rapid rate of cell division.
  5. Torpedo Stage - The cotyledons enlarge, giving the embryo an enlarged and elongated torpedo shape. The tissues begin to differentiate, and the root and shoot apical meristems are distinguishable, as well as the ground meristem. The root apical meristem is responsible for the growth of the plant that is below the ground, and the shoot apical meristem is responsible for above-ground growth. At this stage, the endosperm also gets smaller.
  6. Mature Embryo Stage - At the mature embryo stage, the embryo now has the epicotyl (the shoot apical meristem), the hypocotyl, and the radicle (the root apical meristem). The epicotyl is located between the cotyledons, and contributes to shoot development. The hypocotyl contributes to stem development, and is located below the cotyledons. At the core of the embryo, the procambium will become part of the plant's vascular tissue. The seed coat forms, and protects the embryo as it develops further.

external image plant_embryogenesis.jpg

B. Monocots Versus Eudicots
There are a few major differences between seed development in monocots and eudicots:
  • Monocots have one cotyledon, where eudicots have two
  • Monocots absorb and store nutrients differently. In addition to storing nutrients, the monocot cotyledon will absorb nutrients from the endosperm and pass them to the embryo. In eudicots, the cotyledons sore all the nutrients that the embryo uses.

Works Cited:
Mader, Sylvia S. "Reproduction In Plants." Biology. Student Ed. 9th ed. Boston: Glencoe/McGraw Hill, 2007. 502-03. Print.

Question: What are the names for the differentiated parts of the mature embryo, and what functions will they eventually serve?