Introduction to Reproduction
Reproduction is important because the survival of a species depends on its reproductive success. Reproductive success is being able to produce fertile offspring, or offspring that are able to pass on genes to the next generation.
There are two different types of reproduction. They are asexual reproduction and sexual reproduction. Asexual reproduction involves one parent. The one parent makes clones of itself in order to reproduce. The parent passes on all of its genes to the offspring. The four types of asexual reproduction are binary fission, budding, fragmentation (regeneration), and vegetative propagation. In sexual reproduction, there are two parents. The two parents make genetically variable offspring when they reproduce. The offspring is genetically variable because each parent passes half of its genes to their offspring.
There are two different types of reproduction. They are asexual reproduction and sexual reproduction. Asexual reproduction involves one parent. The one parent makes clones of itself in order to reproduce. The parent passes on all of its genes to the offspring. The four types of asexual reproduction are binary fission, budding, fragmentation (regeneration), and vegetative propagation. In sexual reproduction, there are two parents. The two parents make genetically variable offspring when they reproduce. The offspring is genetically variable because each parent passes half of its genes to their offspring.
Mitosis and Meiosis
Mitosis
Mitosis make cells such as skin cells. After the process of mitosis, two cells are created. Not only are two cells created, but the cells are exact copies of each other. Each cell has a full set of chromosomes at the end of the process. These cells are called diploid cells. Along with this, mitosis is reproduction.
Mitosis has only one set of steps. The first step is Interphase, the non-dividing phase in which DNA replicates and no chromosomes are visible. The step after this is Prophase, the phase in which chromosomes appear, spindle fibers are formed, and the nucleus dissolves. After Prophase is Metaphase, the phase in which the chromosomes line up in the middle of the cell. After this is Anaphase, the phase in which sister chromatids move apart to opposite sides of the cell. Finally, the last phase is Telophase, the phase in which two cells form.
Mitosis has only one set of steps. The first step is Interphase, the non-dividing phase in which DNA replicates and no chromosomes are visible. The step after this is Prophase, the phase in which chromosomes appear, spindle fibers are formed, and the nucleus dissolves. After Prophase is Metaphase, the phase in which the chromosomes line up in the middle of the cell. After this is Anaphase, the phase in which sister chromatids move apart to opposite sides of the cell. Finally, the last phase is Telophase, the phase in which two cells form.
Meiosis
Meiosis makes sex cells. These cells are called gametes. Four of these sex cells are made, with the exception of females. These cells are also variable, which means the for example, four sperm cells will be different. These cells also have half the number of chromosomes. These cells are called haploid cells. However, unlike mitosis, meiosis is not actual reproduction. In order to be considered reproduction, fertilization needs to occur.
Meiosis has two sets of steps. The first step is interphase, the non-dividing phase in which DNA replicates and no chromosomes are visible. After interphase is Prophase I, the phase in which chromosomes duplicate, the nucleus dissolves, spindle fibers form, and cross in-over occurs. Metaphase I comes after. In this phase, chromosomes line up in the middle with homologous pair. Anaphase I then occurs, homologous chromosomes separating. After Anaphase I is Telophase I, the phase in which two cells form, each having one homolog in it. After this, Prophase II occurs, in which chromosomes appear, spindle fibers are formed, and the nucleus dissolves. During Metaphase II, the chromosomes line up in the middle. After this, Anaphase II occurs, sister chromatids moving apart. Finally, Telophase II takes place, and four haploid cells are formed.
Meiosis has two sets of steps. The first step is interphase, the non-dividing phase in which DNA replicates and no chromosomes are visible. After interphase is Prophase I, the phase in which chromosomes duplicate, the nucleus dissolves, spindle fibers form, and cross in-over occurs. Metaphase I comes after. In this phase, chromosomes line up in the middle with homologous pair. Anaphase I then occurs, homologous chromosomes separating. After Anaphase I is Telophase I, the phase in which two cells form, each having one homolog in it. After this, Prophase II occurs, in which chromosomes appear, spindle fibers are formed, and the nucleus dissolves. During Metaphase II, the chromosomes line up in the middle. After this, Anaphase II occurs, sister chromatids moving apart. Finally, Telophase II takes place, and four haploid cells are formed.
Human Reproduction Systems
Male Reproductive System
There are nine parts to the male reproductive system. One part is the testes. The testes is responsible for making sperm cells and testosterone. Testosterone is a hormone that increases muscle size, hair, and sex drive. The sack that hols the testes is called the scrotum, another part of the system. The scrotum moves up and down in order to keep the testes at a lower temperature than the body. Along with these, the vas deferens is the tube that delivers sperm from the testes to the penis. Another part is the seminal vesicle. The seminal vesicle creates semen, a fluid that carries sperm. Another part is the urethra, a vessel the delivers semen and urine out of the body. It serves both as the reproduction system and excretory system.
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The epididymis, another part, stores sperm. The bladder holds urine. Along with this, the prostate creates an alkaline solution to combat the acidic female vagina. And finally, the bulborethral gland is responsible for pre-ejaculated fluids to clean the urethra.
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Female Reproductive System
There are five parts to the female reproductive system. One part are the ovaries. The ovaries is the location of eggs, the gametes of a female. Each woman has about 300,000 eggs and only release 300 in lifetime during menstruation. The ovaries also releases two hormones, estrogen and progesterone.
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The second part are the Fallopian tubes, also known as the oviducts. The Fallopian tubes are the site of fertilization and has cilia along the walls to help move the egg along. The third part is the uterus, an organ that is the size and shape of pear. The uterus is also known as the womb and is where the embryo develops. The walls thicken and shed each month, which is also known as a woman's period. The wall is the uterus is known as the endometrium, the fourth part of the female reproductive system. The endometirum is the site of embryo implantation. However, if there is no embryo development present, it sheds during a woman's period. The final part of the female reproductive system is the cervix. The cervix is the entrance and exit of the uterus.
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The Menstrual Cycle
The menstrual cycle occurs in women and is controlled by hormones secreted by the pituitary gland and the ovaries. There are three phases of the menstrual cycle. Throughout the menstrual cycle, the hormone estrogen, which is released from the ovaries, controls all. The whole cycle starts with the release of GnRH from the hypothalamus, which stimulates FSH. The first phase is called the follicular phase. In this phase, the egg is being being matured and the follicle develops. The hormone FSH (follicle stimulating hormone) is released by the pituitary gland, due also to the release of estrogen. The second phase is the luteal phase. In this phase, ovulation occurs, which is when the egg is released from the follicle due to an increase in LH (luteinizing hormone) because of estrogen, and estrogen also halts the release of FSH. LH is released from the pituitary gland. The follicle becomes the corpus luteum which releases progesterone from the ovaries. Progesterone prepares the female for pregnancy by thickening the endometrium. However, when the egg is not fertilized, the corpus luteum dies, progesterone and estrogen levels drop, resulting in menstruation, or the shedding of the endometrium. The menstrual cycle occurs within an average of 28 days.
Reproduction in Jellyfish
Jellyfish reproduction has many stages. In the medusa/ adult stage of a jellyfish, they can reproduce sexually. In order to do this, sperm and eggs are released into the water. This forms a planula, a free-swimming or crawling larval. In this stage, the planula attaches itself to the bottom of a smooth rock or another structure and grows into a polyp, the next stage of jellyfish life. A polyp looks like a small sea anemone. During this lengthy stage which could last for numerous months and years, the polyp grows through asexual reproduction. The polyps clone themselves and bud into the next stage, called ephyra. From here, it grows into an adult medusa jellyfish. [1]