Reproduction

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REPRODUCTION IN LIVING ORGANISMS

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Types of Reproduction

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In asexual reproduction, an individual can reproduce without involvement with another individual of that species. The division of a bacterial cell into two daughter cells is an example of asexual reproduction. Asexual reproduction is not, however, limited to single-celled organisms . Most plants have the ability to reproduce asexually and the ant species Mycocepurus smithii is thought to reproduce entirely by asexual means. Reproduction: A Biological Process

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Asexual reproduction is the process by which an organism creates a genetically similar or identical copy of itself without a contribution of genetic material from another individual. Bacteria divide asexually via binary fission ; viruses take control of host cells to produce more viruses; Hydras ( invertebrates of the order Hydroidea ) and yeasts are able to reproduce by budding . These organisms often do not possess different sexes, and they are capable of "splitting" themselves into two or more individuals. On the other hand, some of these species that are capable of reproducing asexually, like hydra , yeast (See Mating of yeasts ] and jellyfish , may also reproduce sexually Asexual Reproduction

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For instance, most plants are capable of vegetative reproduction —reproduction without seeds or spores—but can also reproduce sexually. Likewise, bacteria may exchange genetic information by conjugation . Other ways of asexual reproduction include parthenogenesis , fragmentation and spore formation that involves only mitosis . Parthenogenesis παρθένος parthenos, is the growth and development of embryo or seed without fertilization by a male . Parthenogenesis occurs naturally in some species, including lower plants (where it is called apomixis ), invertebrates (e.g. water fleas , aphids , some bees and parasitic wasps ), and vertebrates (e.g. some reptiles , [1] fish , and, very rarely, birds [2] and sharks [3] ). It is sometimes also used to describe reproduction modes in hermaphroditic species which can self-fertilize

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In biology, fission is the subdivision of a cell (or body, population, or species) into two or more parts and the regeneration of those parts into separate cells (bodies, populations, or species). Binary fission produces two separate cells, populations, species, etc., whereas multiple fission produces more than two cells, populations, species, etc. Fission

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Prokaryotic fission , which is binary fission, is a form of asexual reproduction and cell division used by all prokaryotes , (bacteria and archaebacteria), and some organelles within eukaryotic organisms. This process results in the reproduction of a living prokaryotic cell (or organelle) by division into two parts that each have the potential to grow to the size of the original cell (or organelle). This type of division takes place without the formation of spindles. The single DNA molecule first replicates, then attaches each copy to a different part of the cell membrane. When the cell begins to pull apart, the replicate and original chromosomes are separated.

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Multiple fission of protists Multiple fission at the cellular level occurs in many protists . The nucleus of the parent cell divides several times by mitosis , producing several nuclei. The cytoplasm then separates, creating multiple daughter cells. [4] [5] [6] In apicomplexans , multiple fission is known as protozoal merogony (sometimes treated to be synonymous with schizogony ). Merogony results in merozoites , which are multiple daughter cells within the same cell membrane

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Budding is a form of asexual reproduction in which a new organism grows on another one. The new organism remains attached as it grows, separating from the parent organism only when it is mature. Since the reproduction is asexual, the newly created organism is a clone and is genetically identical to the parent organism. A new organism grows from an outgrowth or bud on the parent. Budding

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Budding of a hydra. A mass of cells divide by mitosis to form a bud , which develops into a small hydra and detaches from the "parent". Such asexual reproduction results in genetically identical individuals.

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Vegetative reproduction Vegetative reproduction is a type of asexual reproduction found in plants where new individuals are formed without the production of seeds or spores by meiosis or syngamy Examples of vegetative reproduction include the formation of miniaturized plants called plantlets on specialized leaves (for example in kalanchoe ) and some produce new plants out of rhizomes or stolon (for example in strawberry ). Other plants reproduce by forming bulbs or tubers (for example tulip bulbs and dahlia tubers). Some plants produce adventitious shoots and suckers that form along their lateral roots. Plants that reproduce vegetatively may form a clonal colony , where all the individuals are clones, and the clones may cover a large area. [ Vegetative Propagation

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Many multicellular organisms form spores during their biological life cycle in a process called sporogenesis . Exceptions are animals and some protists, who undergo gametic meiosis immediately followed by fertilization. Plants and many algae on the other hand undergo sporic meiosis where meiosis leads to the formation of haploid spores rather than gametes. These spores grow into multicellular individuals (called gametophytes in the case of plants) without a fertilization event. These haploid individuals give rise to gametes through mitosis . Spore Formation

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Meiosis and gamete formation therefore occur in separate generations or "phases" of the life cycle, referred to as alternation of generations . Since sexual reproduction is often more narrowl defined as the fusion of gametes ( fertilization ), spore formation in plant sporophytes and algae might be considered a form of asexual reproduction (agamogenesis) despite being the result of meiosis and undergoing a reduction in ploidy . However, both events (spore formation and fertilization) are necessary to complete sexual reproduction in the plant life cycle .

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Meiosis and gamete formation therefore occur in separate generations or "phases" of the life cycle, referred to as alternation of generations . Since sexual reproduction is often more narrowly defined as the fusion of gametes ( fertilization ), spore formation in plant sporophytes and algae might be considered a form of asexual reproduction (agamogenesis) despite being the result of meiosis and undergoing a reduction in ploidy . However, both events (spore formation and fertilization) are necessary to complete sexual reproduction in the plant life cycle.

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Fungi and some algae can also utilize true asexual spore formation, which involves mitosis giving rise to reproductive cells called mitospores that develop into a new organism after dispersal. This method of reproduction is found for example in conidial fungi and the red alga Polysiphonia , and involves sporogenesis without meiosis. Thus the chromosome number of the spore cell is the same as that of the parent producing the spores

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Fragmentation is a form of asexual reproduction where a new organism grows from a fragment of the parent. Each fragment develops into a mature, fully grown individual. Fragmentation is seen in many organisms such as animals (some annelid worms, turbellarians and sea stars ), fungi, and plants. Some plants have specialized structures for reproduction via fragmentation Fragmentation

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Most lichens , which are a symbiotic union of a fungus and photosynthetic algae or bacteria, reproduce through fragmentation to ensure that new individuals contain both symbionts. These fragments can take the form of soredia , dust-like particles consisting of fungal hyphae wrapped around photobiont cells.

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Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis , involving the halving of the number of chromosomes ; and fertilization , involving the fusion of two gametes and the restoration of the original number of chromosomes. During meiosis, the chromosomes of each pair usually cross over to achieve homologous recombination . Sexual Reproiduction

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The evolution of sexual reproduction is a major puzzle. The first fossilized evidence of sexually reproducing organisms is from eukaryotes of the Stenian period, about 1 to 1.2 billion years ago. [1] Sexual reproduction is the primary method of reproduction for the vast majority of macroscopic organisms, including almost all animals and plants . Bacterial conjugation , the transfer of DNA between two bacteria , is often mistakenly confused with sexual reproduction, because the mechanics are similar.

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Plant reproduction is the production of new individuals or offspring in plants , which can be accomplished by sexual or asexual means. Sexual reproduction produces offspring by the fusion of gametes , resulting in offspring genetically different from the parent or parents. Asexual reproduction produces new individuals without the fusion of gametes, genetically identical to the parent plants and each other, except when mutations occur. In seed plants , the offspring can be packaged in a protective seed , which is used as an agent of dispersal. In Plants

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Sexual reproduction in flowering plants involves the production of male and female gametes , the transfer of the male gametes to the female ovules in a process called pollination . After pollination occurs, fertilization happens and the ovules grow into seeds with in a fruit . After the seeds are ready for dispersal , the fruit ripens and by various means the seeds are freed from the fruit and after varying amounts of time and under specific conditions the seeds germinate and grow into the next generation.

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The anther produces male gametophytes , the sperm is produced in pollen grains , which attach to the stigma on top of a carpel , in which the female gametophytes (inside ovules) are located. After the pollen tube grows through the carpel's style, the sex cell nuclei from the pollen grain migrate into the ovule to fertilize the egg cell and endosperm nuclei within the female gametophyte in a process termed double fertilization .

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The resulting zygote develops into an embryo, while the triploid endosperm (one sperm cell plus two female cells) and female tissues of the ovule give rise to the surrounding tissues in the developing seed. The ovary, which produced the female gametophyte(s), then grows into a fruit , which surrounds the seed(s). Plants may either self-pollinate or cross-pollinate . Nonflowering plants like ferns , moss and liverworts use other means of sexual reproduction.

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Human reproduction is any form of sexual reproduction resulting in the conception of a child , typically involving sexual intercourse between a man and a woman. During intercourse, the interaction between the male and female reproductive systems results in fertilization of the woman's ovum by the man's sperm , which after a gestation period is followed by childbirth . The fertilization of the ovum may nowadays be achieved by artificial insemination methods, which do not involve sexual intercourse In Human

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The human male The male reproductive system contains two main divisions: the testes where sperm are produced, and the penis . In humans, both of these organs are outside the abdominal cavity . Having the testes outside the abdomen facilitates temperature regulation of the sperm, which require specific temperatures to survive about 2-3 °C less than the normal body temperature i.e. 37°C. If the testicles remain too close to the body, it is likely that the increase in temperature will harm the spermatozoa formation, making conception more difficult

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The human female The female reproductive system likewise contains two main divisions: the vagina and uterus , which act as the receptacle for semen, and the ovaries , which produce the female's ova. The vagina is attached to the uterus through the cervix , while the uterus is attached to the ovaries via the Fallopian tubes . At certain intervals, the ovaries release an ovum, which passes through the fallopian tube into the uterus.

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The fertilization of the ovum with the sperm occurs at the ampullary-isthimic junction only that is why not all the intercourses result in pregnancy. The ovum meets with Spermatozoon , a sperm may penetrate and merge with the egg, fertilizing it with the help of certain hydrolytic enzymes present in the acrosome . The fertilization usually occurs in the oviducts , but can happen in the uterus itself. The zygote then becomes implanted in the wall of the uterus, where it begins the processes of embryogenesis and morphogenesis .

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The ova, which are the female sex cells, are much larger than the spermatozoon and are normally formed within the ovaries of the female fetus before its birth. They are mostly fixed in location with in the ovary until their transit to the uterus, and contain nutrients for the later zygote and embryo . Over a regular interval, in response to hormonal signals, a process of oogenesis matures one ovum which is released and sent down the Fallopian tube.

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Pregnancy is the period of time during which the fetus develops, dividing via mitosis inside the female. During this time, the fetus receives all of its nutrition and oxygenated blood from the female, filtered through the placenta , which is attached to the fetus' abdomen via an umbilical cord . This drain of nutrients can be quite taxing on the female, who is required to ingest slightly higher levels of calories .

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Once the fetus is sufficiently developed, chemical signals start the process of birth, which begins with the fetus squeezing through the vagina, and eventually out of the mother. The newborn, which is called an infant in humans, should typically begin respiration on its own shortly after birth. Not long after, the placenta is passed as well. The end of the umbilical cord attached to the child's abdomen eventually falls off on its own.

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Birth control is an umbrella term for several techniques and methods used to prevent fertilization or to interrupt pregnancy at various stages. Birth control techniques and methods include contraception (the prevention of fertilization), contragestion (preventing the implantation of the blastocyst ) and abortion (the removal or expulsion of a fetus or embryo from the uterus ). Contraception includes barrier methods , such as condoms or diaphragm , hormonal contraception , also known as oral contraception, and injectable contraceptives Birth control

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Contraception includes barrier methods , such as condoms or diaphragm , hormonal contraception , also known as oral contraception, and injectable contraceptives . [1] Contragestives, also known as post-coital birth control, include intrauterine devices and what is known as the morning after pill . [2]

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Mechanisms of action and terminology The function of birth control can be classified by the stage of reproduction during which it is active. A form of birth control which prevents the sperm from fertilizing the egg is a contraceptive agentA form of birth control which acts after fertilization to prevent or interrupt the implantation of the embryo into the uterine lining is a contragestive agentAfter implantation has occurred, an agent which ends gestation by terminating the pregnancy is an abortifacient

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The term contraception is a contraction of contra , which means against , and the word conception , meaning fertilization. [8] The word contragestion is likewise a combination of contra and gestation . French scientist Étienne-Émile Baulieu coined the word in 1985 because he felt that there was a need for a technical term to describe the prevention of implantation, which did not fit the traditional definitions of either contraception or abortion . [

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Sexually transmitted disease ( STD ), also known as a sexually transmitted infection ( STI ) or venereal disease ( VD ), is an illness that has a significant probability of transmission between humans by means of human sexual behavior , including vaginal intercourse , oral sex , and anal sex . While in the past, these illnesses have mostly been referred to as STDs or VD, in recent years. Sexually Transmmited Diseases(STDs)

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sexually transmitted infections ( STIs ) has been preferred, as it has a broader range of meaning; a person may be infected , and may potentially infect others, without having a disease . Some STIs can also be transmitted via the use of IV drug needles after its use by an infected person, as well as through childbirth or breastfeeding .

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Prevention is key in addressing incurable STIs, such as HIV & herpes. Sexual health clinics fight to promote the use of condoms and provide outreach for at-risk communities. The most effective way to prevent sexual transmission of STIs is to avoid contact of body parts or fluids which can lead to transfer with an infected partner. Not all sexual activities involve contact: cybersex , phonesex or masturbation from a distance are methods of avoiding contact.

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Vaccines Vaccines are available that protect against some viral STIs, such as Hepatitis A , Hepatitis B , and some types of HPV . Vaccination before initiation of sexual contact is advised to assure maximal protection.

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Condoms Condoms and female condoms only provide protection when used properly as a barrier, and only to and from the area that it covers. Uncovered areas are still susceptible to many STDs . In the case of HIV, sexual transmission routes almost always involve the penis, as HIV cannot spread through unbroken skin, thus properly shielding the insertive penis with a properly worn condom from the vagina or anus effectively stops HIV transmission .

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Female Foeticide The killing of women exists in various forms in societies the world over. However, Indian society displays some unique and particularly brutal versions, such as dowry deaths and sati. Female foeticide is an extreme manifestation of violence against women. Female foetuses are selectively aborted after pre-natal sex determination,

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