Conclusion

There is not going to be any research here, just an overview on what I have done. I had 2 topics. Reproduction and Issues on sex. Under reproduction, I had two questions. 1) Describe in detail how sexual reproduction takes place in humans. 2) Describe reproduction in other organisms other than mammals. Under Issues on sex, I had the question on whether premarital sex is right or wrong and what are it's consequences.

Reproduction in plants

To round up my final question of research (organisms other than mammals that reproduce), the topic on reproduction and the biojournal in general, I will end off with the topic of research on reproduction in flowering plants. This is my only post where I will talk about something out of the animal kingdom.



Well, firstly we must understand that the flowering plant has male and female organs too. Male organs are collectively called the androecium. The parts include the stamen, which consist of the filament which supports the anthers. The anther contains four microsporangia within which microspores (pollen) are produced by meiosis. Inside the pollen are two (or, at most, three) cells that comprise the male gametophyte. The tube cell (also referred to as the tube nucleus) develops into the pollen tube. The germ cell divides by mitosis to produce two sperm cells.
Female organs are collectively known as the Gynoecium. The gynoecium consists of the stigma, style, and ovary containing one or more ovules. These three structures are often termed a pistil. The stigma functions as a receptive surface on which pollen lands and germinates its pollen tube. The style serves to move the stigma some distance from the ovary. The ovary contains one or more ovules, which in turn contain one female gametophyte, also referred to as the embryo sac.
So for the stigma to even get pollens and reproduce, something known as pollination must occur. This is accomplished by a variety of methods. Entomophyly is the transfer of pollen by an insect. Anemophyly is the transfer of pollen by wind. Other pollinators include birds, bats, water, and humans. Some flowers (for example garden peas) develop in such a way as to pollinate themselves. Flower color is thought to indicate the nature of pollinator: red petals are thought to attract birds, yellow for bees, and white for moths. Wind pollinated flowers have reduced petals, such as oaks and grasses.
The process of pollination being accomplished, the pollen tube grows through the stigma and style toward the ovules in the ovary. The two sperm cells will move down the pollen tube. Once the tip of the tube reaches the micropyle end of the embryo sac, the tube grows through into the embryo sac through one of the synergids which flank the egg. One sperm cell fuses with the egg, producing the zygote which will later develope into the next-generation sporophyte. The second sperm fuses with the two polar bodies located in the center of the sac, producing the nutritive triploid endosperm tissue that will provide energy for the embryo's growth and development.
After fertilization, the zygote divides mitotically. The product of this repeated nuclear division and cell multiplication is an embryo. The seed will now develop. The development consists of a conversion of the integument of the ovule into a resistant seed coat, the development of the endosperm, and the development of the embryo. All these events take place within the original ovary.
A section through a nearly mature seed will reveal an embryo consisting of two large cotyledons with a small epicotyl between them attached to the hypocotyl. Most or all of the endosperm has been absorbed by the cotyledons and the integuments of the ovule have grown into a seed coat. The basal portion of the embryo is termed the radicle. The epicotyl develops into the above ground structures of the plant (stem, leaves, flowers). The radicle develops into the true root system while the hypocotyl develops into the transition zone between root and stem.
The seed will usually lay in the ovary wall which has been devloped into a fruite. The seed will then disperse by either wind, air, animals or water and germinate themselves.
I thank http://io.uwinnipeg.ca/~simmons/lb4pg12.htm and http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookflowers.html for the info

Amphibian reproduction

Now on reproduction of amphibians. For the purpose of reproduction most amphibians are bound to have fresh water. They need to be laid in damp places because of their jellylike characteristic and because there is no shell which means the eggs would quickly dry out and the young would die before they even had a chance to develop if not in water. When the eggs are laid, the male releases sperm over the female's eggs as they are laid. During this time, the male is in a posture called Amplexus which may be inguinal (male grasping the female in front of the her back legs) or axillary (male grasping the female in front of the her hands).
Several hundred frog species in adaptive radiations (e.g. Eleutherodactylus), however, do not need any water whatsoever. They reproduce via direct development, an ecological and evolutionary adaptation that has allowed them to be completely independent from free-standing water. Almost all of these frogs live in wet tropical rainforests and their eggs hatch directly into miniature versions of the adult, passing through the tadpole stage within the egg.
Several species have also adapted to arid and semi-arid environments, but most of them still need water to lay their eggs. Symbiosis with single celled algae that lives in the jelly-like layer of the eggs has evolved several times. The larvae (tadpoles or polliwogs) breathe with exterior gills.
Other kinds of fertilisation include those by salamanders whereby the male deposits a packet of sperm called a spermatophore onto the ground. The female then pulls it into her cloaca where fertilization occurs internally. Some caecilians and tailed frogs use internal fertilization where the male deposits sperm directly into the female's cloaca via an intromittent organ.
Amphibians laying their eggs in water normally leave them alone, but those laying eggs on land usually watch over them to protect them from predators. A few have developed strange ways to guard their eggs until they have hatched. The Surinam toad (Pipa pipa) of South America carries its eggs in pockets of skin on its back until the froglets hatch three months later. The gastric brooder (Rheobatrachus silus) of Australia no sooner lays its eggs than it swallows them! The eggs incubate in the frog's stomach where acid production ceases until the froglets hatch and crawl out through their mother's mouth.
Once hatched, the larva feed on yolk from their egg until they are able to find food for themselves. Then, they start to transform gradually into the adult's appearance. This process is called metamorphosis. Typically, the animals then leave the water and become terrestrial adults.
I thank http://www.eoearth.org/article/Amphibian_morphology_and_reproduction and wikipedia for the information.

Reproduction in fish

Let us move on to fish. Well, most fishes are egg-layers. They lay eggs that are then fertilized by the male when the males spray semen on them, some species lay their eggs on a substrate like a rock or on plants, while others scatter their eggs and the eggs are fertilized as they drift or sink in the water column. Some fish species use internal fertilization and then disperse the developing eggs or give birth to live offspring. The eggs contain yolk which supplies the embryo with food, and albumen - a protein- which protects it. The embryo obtains its oxygen from the water by diffusion, and the young fish, or larvae, hatch after a few days.

Yet many fish also bear live young. Live-bearing fishes may be ovoviviparous, in which the eggs essentially simply hatch within the female, or viviparous, in which the unborn young are supplied nourishment through the mother's tissues.

In some ovoviviparous fishes the embryo develops in the egg while the egg is still within its follicular covering within the ovary, and ovulation (or release of the egg) and birth occur at the same time. In other ovoviviparous forms the eggs are released from the protective follicles into the cavity of the hollow ovary, where development continues.

In some viviparous fishes the walls of the egg follicle are in intimate contact with the embryo, supplying it with nourishment. In the viviparous sharks, a part of the oviduct, or egg channel, is developed into a uterus, where the modified yolk sacs of the young are closely joined to pockets within the uterus. In live-bearing fishes and in some egg-layers, fertilization occurs internally, and methods have been evolved for introducing the sperm into the female's body. In sharks the pelvic fins of the male are modified into intromittent organs called myxoptergia, and in the male topminnows the anal fin is modified into a similar-functioning intromittent organ called the gonopodium.

At least three modes of reproduction--heterosexual, hermaphroditic, and parthenogenetic--are found in fishes. In the most common form, heterosexual reproduction, there are separate male and female parents, but even here there is considerable variation. In some live-bearing fishes, the female is able to store sperm for up to 8 or even 10 months, and this sperm is used to fertilize new batches of eggs as they develop. In some cases, a female may carry sperm from several males at once.

In hermaphroditic reproduction, a single fish is both male and female, produces both eggs and sperm (either at the same time or at different times), and mates with other similar hermaphroditic fishes. External self-fertilization occurs in one hermaphroditic fish, which sheds egg and sperm simultaneously. In another, internal self-fertilization may occur. In certain fishes there is a time sequence of hermaphroditism, young fishes reversing their sex as they grow older.

In parthenogenetic reproduction, unfertilized eggs develop into embryos. This is known to exist in at least one fish species, Poecilia formosa, of the Amazon River; however, even though development proceeds without fertilization in some of these females, mating with a male is still required to stimulate egg development.

Parental care also shows great diversity. Some fishes, like the Atlantic herring, form huge schools of males and females and freely shed their eggs and sperm (milt), and then abandon the eggs. Other fishes build nests and care for both the eggs and newly hatched young. Others have evolved methods of carrying the eggs with them, commonly in their mouths, but also in gill cavities or in special pouches on the body.

I thank www.lookd.com/fish/reproduction.html for the info

Reptile reproduction

Ok, having dealt with birds, let me move on to reptiles. Firstly, most reptiles lay eggs. Reptiles that lay eggs are called oviparous. Some reptiles bear live young, and the term for this is viviparous. We will focus more on oviparous reptiles.

Males and females possess different reproductive organs. The male possesses two testicles, housed inside the body. The male also has a copulatory organ, either a single penis (turtles and tortoises, crocodilians) or a pair of hemipenes (lizards, snakes) that can often be seen as two bulges behind the cloaca at the base of the tail. The penis or hemipenis is not connected to the urinary tract, and is strictly an organ of reproduction. A female has ovaries which store eggs.

For fertilization, a male reptile inserts either one of his two hemipenes into the female's cloaca, or the single penis is inserted. Before actual copulation, the pair usually engages in some type of ritualized courtship. After copulation, sperm can be stored for up to six years, and this stored sperm can fertilize subsequent clutches without additional contact by a male.
Using the green iguana as an example, even without a male present to fertilize eggs, a healthy adult female may begin developing eggs. The process begins with the ovaries, where eggs are stored. Follicles begin developing in the ovaries. Each follicle is composed of a tiny egg and a sac filled with yolk. The follicles then detach and move into the oviducts where the egg white is added, and then a shell is placed around the yolk and white. The female usually will not eat for three to six weeks prior to laying her eggs.

A gravid female would naturally dig a large burrow in moist soil (often along a riverbank) in the wild when she wants to lay her eggs. Then, she will deposit the eggs and completely cover the hole, hiding any evidence of her activities.

Female pythons are one of only a few groups of reptiles to care for her eggs after oviposition. A female will coil around her eggs until they hatch, protecting the eggs and providing temperature regulation, as well. Crocodilians also assist the hatchlings as they emerge from their nests, and will guard them for a while after hatching.

In the species that give birth to live young, some species show a degree of maternal care. Some skinks will assist the neonates by helping them escape from their birth sacs. The Solomon Island skink gives birth to one very large offspring after a long gestation period and while pregnant, she will eat very little. Snakes, such as the boas and garter snakes also give birth to live young.

Now back to egss. In captivity, eggs are usually removed and placed in an incubator. Vermiculite is moistened with bottled water and the eggs are buried halfway. Eggs should be handled carefully, and care should be taken to not change the position that they were in when deposited.

The eggs of some species are hard (turtles, tortoises, crocodilians and some lizards, especially geckos), and those of others are more leathery (snakes and most lizards) Incubation time can vary from about 45 days (in small lizards) to over a year (for some tortoises).
When it is time for the baby to hatch, the neonate uses its egg tooth (also called caruncle) to cut through the eggshell. The baby will usually remain in the egg for 12-48 hours after it pokes its head through the egg. During that time, any remaining yolk still attached to the hatchling will be absorbed.
Babies hatched from eggs, as well as those that are born alive from the female, are able to fend for themselves as soon as they are up and walking around/slithering.

I thank www.exoticpetvet.net/reptile/rerepro.html for the information

Animal reproduction

Ok, sadly, I'm out of ideas for the topic on premarital sex and its consequences, so let us go back to my initial topic, on sexual reproduction. So I will now formulate a third question, describe sexual reproduction in other organisms other than mammals.

So, let us first deal with verterbraes. I will begin with birds. Birds reproduce by sexual reproduction, males having paired testes lying in the bodity cavity, and females having only a functional left ovary and oviduct. Firstly, a stimulus occurs weeks in advance of the breeding season in the birds. This ensures the male arrives on the breeding grounds with the testes fully developed and the female has enlarged of the female reproductive organs, development of eggs in the ovaries, formation of the brood patch, and so on. These enlarged testes secrete greater amounts of male hormones that may brighten skin colors and stimulate singing and courtship behavior.

After mating, copulation occurs, in which the male mounts the female from behind. Both sexes hold their tails to the side and turn back the feathers around the cloaca (the common opening of the bird's alimentary canal and excretory and reproductive systems), so that the swollen lips of the male's and female's cloacae can come into contact. In some birds, such as geese and ducks there is a grooved, erectile penis inside the male's cloaca that guides the sperm, which have been stored in a nearby sac, into the female. In passerines, there is no penis, and copulation amounts to a brief "cloacal kiss" during which the sperm are transferred out of the testis, into the vas deferens and into the female
Once transferred, the sperm remain for a while in storage at the lower end of the oviduct, and then swim to the upper end of that duct to fertilize the egg. Consequently, there is considerable variation among species in the frequency of copulations, how long it takes for the egg to be laid and how many eggs are actually laid. But in order for an egg to form, the sperm must meet the egg in the oviduct before the layers of the egg form.

The birds will be laid in nests that vary from burrows(penguins) to leaf piles(turkeys). When eggs are laid, all birds will incumbate their eggs by supplying heat from their bodies. That heat may be considerable, since the normal temperature of a bird is around 100 to 112 Fahrenheit. Once incubation begins the bird seldom leaves the nest, and then not long, because the eggs will not hatch if they get too cold. During incubation the eggs have to be turned once or twice a day so that they will be heated evenly and the membranes of the embryo will not adhere to the shell.

So now a bit more about a bird egg. The egg cell of a bird is really what we call the yolk. The yolk is the food supply for the developing embryo. The nucleus of the bird's egg can be found in the middle of a white spot which is found on top of the yolk. The egg that female bird lays is covered in layers of albumen (a material like jelly), two membranes and a hard shell. The shell and the membranes protect and support the egg. The albumen feeds the developing embryo with water and protein. The albumen, membranes and shell are added to the yolk layer-by-layer as it passes down a tube called the oviduct inside the hen's body.

When the egg actually hatches, the characteristics again vary species to species. Some hatch naked, while others hatch with their full feathers. Some are blind, others can already move. Thus, there is a lot of difference which makes bird reproduction very fascinating.

I thank www.stanford.edu/group/stanfordbirds/text/essays/Copulation.html, http://www.saburchill.com/chapters/chap0034.html and www.newton.dep.anl.gov/natbltn/400-499/nb456.htm for the info.

Abortion

Having shown you the contraceptive methods available to prevent unwanted pregnancies I will elaborate on what to do if you have them. One way is through abortion. This is a very controversial topic because it involves human lives. It also involves women's rights so one must consider both parties involved. In most countries, this is only done in the first trimester of pregnancy when people don't consider the fetus a life. So I shall not dwell on the moral aspects, but more on the scientific part of abortion itself.

Intentional abortion is also known as Induced abortion. There are 2 main methods, surgical and medical.

Surgical methods include suction-aspiration or vacuum abortion during the first 12 weeks. Manual Vacuum aspiration (MVA) abortion, consists of removing the fetus or embryo by suction using a manual syringe. MVA can be used in very early pregnancy, and does not require cervical dilation. Electric vacuum aspiration (EVA) abortion uses an electric pump.

Surgical techniques are sometimes referred to as 'Suction (or surgical) Termination Of Pregnancy' (STOP). From the 15th week until approximately the 26th, dilation and evacuation (D&E) is used. D&E consists of opening the cervix of the uterus and emptying it using surgical instruments and suction.
Dilation and curettage (D&C), the second most common method of abortion. Curettage refers to cleaning the walls of the uterus and embryo with a curette. The World Health Organization recommends this procedure when MVA is unavailable.
Other techniques must be used to induce abortion in the second trimester. Premature delivery can be induced with prostaglandin; this can be coupled with injecting the amniotic fluid with caustic solutions containing saline or urea.

After the 16th week of gestation, abortions can be induced by intact dilation and extraction (IDX), which requires surgical decompression of the fetus's head before evacuation. IDX is sometimes called "partial-birth abortion," which has been banned in the United States.

A hysterotomy abortion is a procedure similar to a caesarean section, and is performed under general anesthesia because it is considered major abdominal surgery. It requires a smaller incision than a caesarean section and is used during later stages of pregnancy.
From the 20th to 23rd week of gestation, an injection to stop the fetal heart can be used as the first phase of the surgical abortion procedure to ensure that the fetus is not born alive.

The second type of abortion is medical, in which only drugs is used to induce abortion. The first wave of drugs is usually either an injection of methotrexate or a dose of mifepristone in tablet form.
Mifepristone binds to the progesterone receptor to block progesterone. Progesterone is necessary for pregnancy maintenance. Mifepristone also softens and dilates the cervix, and causes decidual necrosis (which leads to placental detachment).
Methotrexate blocks an enzyme necessary for DNA synthesis, thus inhibiting the growth of rapidly dividing placental trophoblastic cells.

Both drugs are then followed up by A prostaglandin analog--a dose of misoprostol in tablet form, or gemeprost. Misoprostol works by softening and dilating the cervix, and binding to myometrial cells to cause strong uterine contractions. Contractions cause expulsion of the embryo.

Having shown you all the methods of abortion if you have an unwanted pregnancy, I would end my topic on issues of sex here.

I thank wikipedia and wikimedia for the info and pics