ovule

Examples of ovule in the following topics:

• Characteristics of Gymnosperms

  • This term comes from the fact that the ovules and seeds of gymnosperms develop on the scales of cones rather than in enclosed chambers called ovaries.
  • The other type of cones, the larger "ovulate" cones, make megaspores that develop into female gametophytes called ovules .
  • Incredibly, this whole sexual process can take three years: from the production of the two sexes of gametophytes, to bringing the gametophytes together in the process of pollination, and finally to forming mature seeds from fertilized ovules.
  • This is the cone that produces ovules.

• Life Cycle of a Conifer

  • Female cones (ovulate cones) contain two ovules per scale.
  • One megaspore mother cell (megasporocyte) undergoes meiosis in each ovule.

• Double Fertilization in Plants

  • After pollen is deposited on the stigma, it must germinate and grow through the style to reach the ovule.
  • The pollen tube is guided by the chemicals secreted by the synergids present in the embryo sac; it enters the ovule sac through the micropyle.
  • The fertilized ovule forms the seed, whereas the tissues of the ovary become the fruit, usually enveloping the seed.
  • Shown are the stages of embryo development in the ovule of a shepherd's purse (Capsella bursa).

• Female Hormones

  • LH also plays a role in the development of ova, as well as in the induction of ovulation and stimulation of estradiol and progesterone production by the ovaries.
  • Estradiol is the reproductive hormone in females that assists in endometrial regrowth, ovulation, and calcium absorption; it is also responsible for the secondary sexual characteristics of females.
  • Slowly-rising levels of FSH and LH cause the growth of follicles on the surface of the ovary, which prepares the egg for ovulation.
  • The spike in LH causes ovulation: the most mature follicle ruptures and releases its egg .
  • Following ovulation, the ovarian cycle enters its luteal phase and the menstrual cycle enters its secretory phase, both of which run from about day 15 to 28.

• The Life Cycle of an Angiosperm

  • Therefore, they generate microspores, which will produce pollen grains as the male gametophytes, and megaspores, which will form an ovule that contains female gametophytes.
  • The ovule, sheltered within the ovary of the carpel, contains the megasporangium protected by two layers of integuments and the ovary wall.
  • When a pollen grain reaches the stigma, a pollen tube extends from the grain, grows down the style, and enters through the micropyle, an opening in the integuments of the ovule.
  • After fertilization and some growth in the angiosperm, the ripened ovule is produced.
  • The formation of the seed completes the process of reproduction in seed plants (started with the development of flowers and pollination), with the embryo developed from the zygote and the seed coat from the integuments of the ovule.

• Angiosperm Flowers

  • Styles, stigmas, and ovules constitute the female organ: the gynoecium or carpel.
  • The ovary houses one or more ovules, each of which will develop into a seed upon fertilization.

• Development of the Seed

  • The seed, along with the ovule, is protected by a seed coat that is formed from the integuments of the ovule sac.
  • The seed coat forms from the two integuments or outer layers of cells of the ovule, which derive from tissue from the mother plant: the inner integument forms the tegmen and the outer forms the testa.
  • The ovules after fertilization develop into the seeds.

• Sexual Reproduction in Angiosperms

  • The ovary, which may contain one or multiple ovules, may be placed above other flower parts (referred to as superior); or it may be placed below the other flower parts (referred to as inferior) .
  • Once fertilization is complete, the resulting diploid zygote develops into the embryo; the fertilized ovule forms the other tissues of the seed.
  • The ovule wall will become part of the fruit.
  • As shown in this diagram of the embryo sac in angiosperms, the ovule is covered by integuments and has an opening called a micropyle.

• Female Reproductive Anatomy

  • At ovulation, one follicle ruptures and one egg is released .
  • When an egg is released at ovulation, the fimbrae help the non-motile egg enter into the tube, the passage to the uterus.
  • At ovulation, the follicle ruptures, releasing the egg.

• Contraception and Birth Control

  • There are many methods of birth control, including barriers to sperm, hormones that prevent ovulation, sterilization procedures, and "natural" methods.
  • Natural methods include avoiding intercourse when ovulation is occurring ("natural family planning) or withdrawing the penis from the vagina before ejaculation.
  • A woman's body temperature may rise a degree Celsius at ovulation and the cervical mucus may increase in volume, becoming more pliable.