Reproduction is the process by which a living organism is able to produce new individuals of its own kind. Unlike other life processes such as nutrition, respiration, etc., it is not essential to maintain the life of an individual organism. But it is important for the existence and continuity of the species.
Reproduction ensured continuity of life on earth.
It is a bridge to hereditary transmission.
It involves a continuation of characters from the parents to daughter cells by copying DNA (Deoxyribose Nucleic Acid) molecules present in the chromosomes of the cell.
Copying DNAs is also not a foolproof exercise, even minute changes bring about variation in the blueprint of the offsprings.
The useful variations are retained while the harmful ones do not go beyond.
Actually, variations help the species to withstand drastic environmental changes, thus saving the species from becoming extinct and promoting its survival for a longer time.
This inbuilt tendency of variation is the “basis” for Evolution.
Asexual Reproduction: It is extremely useful as a means of rapid multiplication. It is common in lower plants and animals.
Different forms of Asexual Reproduction:
Fission: In unicellular organisms when a cell becomes fully mature, it splits into two or more parts. It is called the fission. In organisms such as Amoeba,
Budding: A bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully
mature, detach from the parent body and become new independent individuals.
Spore Formation: Spores are small, the bulb-like structure which develops at the top of the erect hyphae of the fungus-plant, when released into the air germinate, into new individuals after landing into food or soil.
Fragmentation: It is the accidental process when the broken pieces of an organism (fragments) grows into a complete organism. Example, fragmentation in Spirogyra.
Regeneration: When simple animals like a hydra, planaria develop a new individual from their broken older part it is known as regeneration. It is carried out by specialized cells which grow large numbers of cells.
Vegetative Propagation: A mode of reproduction in which parts like the stem, root, leaves develop into new plants under favorable conditions.
Benefits:
Plants can bear flowers, fruits more quickly than those produced from seeds.
Growing banana, orange, rose, jasmine that have lost the capacity to produce seeds.
Sexual Reproduction: When reproduction takes place as a result of the fusion between two gametes, one from each parent, it is called sexual reproduction.
This process of fusion between two gametes is called fertilization.
The formation of gametes involves an exchange of chromosomal (genetic) fragments between homologous chromosomes causing genetic recombination which leads to variation.
Sexual Reproduction in Plants: It occurs mostly in flowering plants.’ In fact, flowers are the reproductive organ of plants.
Sexual reproduction in flowering plants
Sepals are green structures that protect the inner parts when the flower is in bud stage.
Petals are colourful and attract the insects for pollination.
Stamens are male reproductive parts and produce pollen grains that contain male gametes. Each stamen has two parts—
Filament i.e. stalk and Anther i.e. swollen top part which has large number of pollen grains.
Pollination: The process of transfer of pollen grains from an anther to the stigma of the flower is pollination. Two types of pollination are:
(i) Self-pollination: The transfer of pollen grains from the anther to the stigma of the same flower or another flower of the same plant.
(ii) Cross-pollination: The transfer of pollen grains from the anther to the stigma of another flower or another flower of a different plant of the same species. It generally takes place with the help of some agents like insects, birds, wind and water.
Fertilization. The fusion between the pollen grain and female egg cell. It occurs inside the ovary. The zygote is produced in this process.
The zygote divides several times to form an embryo within the ovule. The ovule develops a rough coat and is converted into a seed.
Ovary grows rapidly and ripens to form fruit, while the seed contains the future plant or embryo which develops into a seedling under suitable conditions. This process is known as Germination.
Reproduction in Human Beings:
Humans use a sexual mode of reproduction.
It needs sexual maturation which includes the creation of the germ cells, i.e., egg (ova) in the female and sperm in the male partner and this period of sexual maturation is called Puberty.
Human beings have a well-developed male and female reproductive system.
The formation of the male germ cell (sperms) takes place in the testes (male reproductive organ). Actually, a pair of testes are located inside the scrotum situated outside the abdominal cavity. It is meant to keep a relatively low temperature needed for the production of sperms by testes. Testes release a male sex hormone called testosterone whose function is to:
regulate the production of sperms;
brings about changes in appearance seen in boys at the time of puberty; and
The sperms along with the secretion of the prostate gland and seminal vesicle, together constitute semen, which is released and made to enter into the female genital tract during Copulation.
Female Reproductive System:
Ovaries: Paired ovaries are located in the abdominal cavity near the kidney. Ovaries produce female gamete (ovum or egg) and secrete female hormones (estrogen and progesterone). One egg is produced every month alternately by one of the ovaries.
Fallopian Tube: The egg is carried from the ovary to the womb/uterus through a thin oviduct or fallopian tube.
Uterus: The two oviducts unite into an elastic bag-like structure known as the uterus.
Vagina: Uterus opens into the vagina. It is a female copulatory organ.
The female germ cells or eggs are made in the ovaries, a pair of which is located in both sides of the abdomen.
When a girl is born, the ovaries already contain thousands of immature eggs. At the time of puberty, some of these eggs start maturing. One egg is produced every month by one of the ovaries.
The egg is carried from the ovary to the womb through a fallopian tube. These two fallopian tubes unite into an elastic bag-like structure known as the uterus.
The uterus opens into the vagina through the cervix.
Fertilization occurs in the fallopian tube of the female genital tract.
The fertilized egg also called zygote gets implanted in the lining of the uterus, and starts dividing. The uterus is richly supplied with blood to nourish the growing embryo.
If the zygote is not formed, the inner wall of the uterus breaks which causes bleeding through vagina. This process is called Menstruation. It occurs at a regular interval of 28 days.
The embryo gets nutrition from the mother’s blood with the help of a special tissue called Placenta.
Placenta provides a large surface area for glucose and oxygen to pass from the mother to the embryo. Similarly the wastes from developing embryos are removed to mother’s blood through placenta.
The child is born as a result of rhythmic contractions of the muscles in the uterus after nine months (36 weeks) of development inside the mother’s womb, called Gestation Period.
The sexual cycle in a woman continues upto the age of 45 to 50 years. After that the ovaries do not release eggs. This stage is called Menopause. It also marks the end of menstruation in women.
16. Male Reproductive System consists of the following organs:
Testes: A pair of testes are situated in scrotum that lie outside the abdominal cavity and behind the penis. Testes produce sperms and hormone, Testosterone hormone. Testosterone brings about changes in appearance of boys at the time of puberty.
VAS deferens: From each testis, a duct arises which is known as vas deferens which unites with a tube coming from urinary bladder. It brings sperms from testis.
Urethra: Vas deferens tube opens into a common tube called urethra. It runs through a muscular organ called Penis. Penis is male copulatory organ.
Accessory Glands: Glands like prostate and seminal vesicles and Cowper’s gland add their secretions which make transport of sperms easier and this fluid also provides nutrition.
Epididymis: Attached to each testis is a highly coiled tube called epididymis. The sperms are stored here and they mature in the epididymis.
The secretions of the seminal plasma, along with the sperms is known as semen,also called seminal fluid
Significance of Sexual Reproduction :
Sexual reproduction involves DNA as well as cellular apparatus of two different organisms which promotes diversity of characters in the offspring.
Since gametes are derived from two different organisms, it results in a new combination of genes which increases the chances of genetic variations.
Sexual reproduction results in the origin of. new species.
Sexual reproduction involves division in the sex organs that reduces the DNA matter to half so that the zygote formed after fusion has the same amount of DNA as the parents it maintains DNA in a species.
Reproductive Health: Reproductive health means total well-being in all aspects of reproduction, z.e., physical, emotional, social and behavioural.
Contraception: It is the avoidance of pregnancy through different methods—Natural methods, Barrier method, Oral contraceptives, Surgical methods.
Advantages of contraception: Help in birth control, prevent sexually transmitted diseases, prevent unwanted pregnancies, keep population explosion in check.
Surgical methods
Vasectomy: It involves cutting and ligating the vas deferens in males.
Tubectomy: It involves cutting and ligating Reproductive organs the fallopian tubes in females.
Medical termination of pregnancy (MTP) or abortions is carried out to eliminate the developing embryo. This practice can, however, be misused to carry out female foeticide which involves the killing of the female foetus. It should be avoided at all cost as it disturbs the male-female ratio in a population.
Chemical methods
Use of spermicides: These are strong sperm-killing chemicals available in the form of creams, jellies etc. which are injected into the vagina just before copulation.
Oral contraceptive pills: These are hormonal pills which prevent ovulation but do not stop menstruation.
Mechanical methods: These are used to prevent the passage of semen to the follopian tube :
Use of condoms: Condoms are thin rubber tubes worn over the penis before sexual intercourse. The semen gets collected in this and is not discharged into the vagina.
Diaphragm: It is a thin rubber fixed over a flexible metal ring which is fitted over the cervix in a woman’s body by a doctor.
IntraUterine Contraceptive Device (IUCD) or loop: It is inserted in the uterus and its insertion causes certain secretion which prevents the implantation of the embryo in the uterine wall.
Both methods (ii) and (iii) cause side effects.