ovule

Examples of ovule in the following topics:

• Hormonal Methods

  • Hormonal contraception is a type of birth control that acts on the endocrine system to prevent ovulation and/or fertilization.
  • Evidence supports the idea that combined hormonal contraceptives work primarily by preventing ovulation.
  • Combined hormonal contraceptives prevent ovulation by suppressing the release of gonadotropins.
  • They inhibit follicular development and prevent ovulation as their primary mechanism of action.
  • Inhibition of follicular development and the absence of a LH surge prevent ovulation.

• 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).

• Uterine (Menstrual) Cycle

  • During menstruation, the body begins to prepare for ovulation again.
  • The sudden change in hormones at the time of ovulation sometimes causes minor changes in the endometrium and light mid-cycle blood flow.
  • After ovulation, under the influence of progesterone, the endometrium changes to a secretory lining in preparation for the potential implantation of an embryo to establish a pregnancy.
  • Normal menstrual flow can occur although ovulation does not occur.

• Ovarian Cycle

  • It is commonly divided into three phases: the follicular phase, ovulation, and the luteal phase.
  • It ends with ovulation.
  • The time immediately surrounding ovulation is referred to as the ovulatory phase or the periovulatory period.
  • After ovulation, the pituitary hormones FSH and LH cause the remaining parts of the dominant follicle to transform into the corpus luteum.
  • It continues to grow for some time after ovulation and produces significant amounts of hormones, particularly progesterone, and to a lesser extent, estrogen.

• 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.