Asexual Reproduction in Animals Group 3 Nina Bansil Kenneth Calabia Josef Franz Cruz I. Introduction Asexual reproduction is reproduction which does not involve meiosis, ploidy reduction, or fertilization. Only one parent is involved in asexual reproduction. A more stringent definition is agamogenesis which refers to reproduction without the fusion of gametes. Asexual reproduction is the primary form of reproduction for single-celled organisms such as the archaea, bacteria, and protists.
Many plants and fungi reproduce asexually as well. While all prokaryotes reproduce asexually (without the formation and fusion of gametes), mechanisms for lateral gene transfer such as conjugation, transformation and transduction are sometimes likened to sexual reproduction. A lack of sexual reproduction is relatively rare among multicellular organisms, for reasons that are not completely understood.
Current hypotheses suggest that, while asexual reproduction may have short term benefits when rapid population growth is important or in stable environments, sexual reproduction offers a net advantage by allowing more rapid generation of genetic diversity, allowing adaptation to changing environments. Paramecium is a group of unicellular ciliate protozoa, which are commonly studied as a representative of the ciliate group, and range from about 50 to 350 ? m in length. Simple cilia cover the body, which allow the cell to move with a synchronous motion (like a caterpillar).
There is also a deep oral groove containing inconspicuous compound oral cilia (as found in other peniculids) used to draw food inside. They generally feed on bacteria and other small cells. Osmoregulation is carried out by a pair of contractile vacuoles, which actively expel water from the cell absorbed by osmosis from their surroundings. Paramecia are widespread in freshwater environments, and are especially common in scums. Recently, some new species of Paramecia have been discovered in the oceans.
Certain single-celled eukaryotes, such as Paramecium, are examples for exceptions to the universality of the genetic code: in their translation systems a few codons differ from the standard ones. It reproduces in two ways: asexually by simple binary fission and sexually by conjugation. Binary fission, or prokaryotic fission, is the form of asexual reproduction and cell division used by all prokaryotes, some protozoa, and some organelles within eukaryotic organisms. This process results in the reproduction of a living prokaryotic cell by division into two parts which each have the potential to grow to the size of the original cell.
Mitosis and cytokinesis are not the same as binary fission; specifically, binary fission cannot be divided into prophase, metaphase, anaphase, and telophase because prokaryotes have no nucleus and no centromeres. The ability of some multicellular animals, such as echinoderms and flatworms, to regenerate two whole organisms after having been cut in half, is also not the same as binary fission. Neither is vegetative reproduction of plants. Conjugation, on the other hand, is a type of sexual reproduction. During this process, two individuals of different mating types come together and form a cytoplasmic bridge between them.
This is followed by a complex set of divisions and degenerations of the macronuclei and micronuclei that ultimately results in an exchange in genetic material between the conjugants analogous to the sexual reproduction seen in multicellular organisms. Hydra is another type of organism that can reproduce asexually. It is a genus of simple fresh-water animal possessing radial symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa. [1][2] They can be found in most unpolluted fresh-water ponds, lakes and streams in the temperate and tropical regions by gently sweeping a collecting net through weedy areas.
They are usually a few millimeters long and are best studied with a microscope. Biologists are especially interested in hydras due to their regenerative ability and because they appear to undergo senescence (aging) very slowly, if at all. It undergoes budding to reproduce asexually. Budding is a form of asexual reproduction in which a new organism grows on another one. It stays attached, while it grows. Only when it is fully grown does it detach from the parent organism. Since the reproduction is asexual, the newly created organism is a clone and is genetically identical to the parent organism.
The experiment was done to know more about small organisms like hydra and paramecium, and on how they reproduce asexually. II. Materials Paramecium sp. ( in binary fission ) Hydra sp. ( budding ) III. Procedure IV. Results V. Discussion Paramecium: The paramecium approximates a prolate spheroid, rounded at the front and pointed at the back. The pellicle is a stiff but elastic membrane that gives the paramecium its definite shape. Covering the outer edge are hairlike structures, called cilia. On the side, beginning near the front end continuing down half way, is the oral groove, which collects food until it is swept into the cell mouth.
There is an opening near the back end called the anal pore. The contractile vacuole and its radiating canals — referred to previously for osmoregulation of the organism, are also found on the outside of a paramecium. The paramecium is very commonly mistaken as a blepharisma. The paramecium contains cytoplasm, trichocysts, the gullet, food vacuoles, the macronucleus. Paramecium are capable of both sexual and asexual reproduction. Asexual reproduction is the most common, and this is accomplished by the organism dividing transversely.
The macronucleus elongates and splits. Under ideal conditions, Paramecium can reproduce asexually two or three times a day. Normally, Paramecium only reproduces sexually under stressful conditions. This occurs via gamete agglutination and fusion. Two Paramecium join together and their respective micronuclei undergo meiosis. Three of the resulting nuclei disintegrate, the fourth undergoes mitosis. Daughter nuclei fuse and the cells separate. The old macronucleus disintegrates and a new one is formed. This process is usually followed by asexual reproduction. Hydra:
Hydra has a tubular body secured by a simple adhesive foot called the basal disc. Gland cells in the basal disc secrete a sticky fluid that allows for its adhesive properties. At the free end of the body is a mouth opening surrounded by one to twelve thin, mobile tentacles. Each tentacle, or cnida (plural: cnidae), is clothed with highly specialised stinging cells called cnidocytes. Cnidocytes contain specialized structures called nematocysts, which look like miniature light bulbs with a coiled thread inside. At the narrow outer edge of the cnidocyte is a short trigger hair called a cnidocil.
Upon contact with prey, the contents of the nematocyst are explosively discharged, firing a dart-like thread containing neurotoxins into whatever triggered the release which can paralyse the prey, especially if many hundreds of nematocysts are fired. Hydra has two main body layers separated by mesoglea, a gel-like substance. The outer layer is the epidermis, and the inner layer is called the gastrodermis. The cells making up these two body layers are relatively simple. Hydramacin is a bactericide recently discovered in Hydra; it protects the outer layer against infection.
The nervous system of Hydra is a nerve net, which is structurally simple compared to mammalian nervous systems. Hydra does not have a recognizable brain or true muscles. Nerve nets connect sensory photoreceptors and touch-sensitive nerve cells located in the body wall and tentacles. Respiration occurs by diffusion through the epidermis. Some excretion and transportation also occur in this manner. When food is plentiful, many hydras reproduce asexually by producing buds in the body wall, which grow to be miniature adults and simply break away when they are mature.
When conditions are harsh, often before winter or in poor feeding conditions, sexual reproduction occurs in some hydras. Swellings in the body wall develop into either a simple ovary or testes. The testes release free-swimming gametes into the water, and these can fertilise the egg in the ovary of another individual. The fertilized eggs secrete a tough outer coating, and, as the adult dies, these resting eggs fall to the bottom of the lake or pond to await better conditions, whereupon they hatch into miniature adults. Hydras are hermaphrodites and may produce both testes and an ovary at the same time.
Many members of the Hydrozoa go through a body change from a polyp to an adult form called a medusa. However, all hydras remain as polyps throughout their lives. VI. Conclusion Some of organisms living in the face of the planet can reproduce asexually or sexually, base on some factors. Usually, when the circumstance is favourable, these organisms reproduce asexually, without the use of a partner. But when in harsh circumstances, such as when food is scarce, the organism does not have the full capacity to reproduce on its own, so it needs a partner to fulfil the role.
It’s just like we as person; we have the tendency to have so much pride, always saying we can do anything on our own, proving ourselves the capacities we have. But when we face stressful conditions, we unwillingly break the wall that sets aside from us to the world and seeks attention and caring from people whom we love and trust… That’s life. VII. Reference www. wikipedia. org Lab Manual Josef Franz Cruz Exercise 12. 2 My Family’s Variety of Fingerprints 1. Left Father Right 2. Right Left Mother 3. Right Left Sister 4. Brother Right Left 5. Me Right Left
