- Reproduction is a process by which living organisms produce new individuals of their own and maintain their existence generation after generation.
- Asexual modes of reproduction involve a single parent and no involvement of gametes. It is common in unicellular organisms, is also seen in lower multicellular plants and animals as well as in some higher plants.
- Modes of asexual reproduction are fission, fragmentation, regeneration, budding, spore formation and vegetative fragmentation.
- Sexual reproduction : It involves two parents, male and female. A new individual is produced by the fusion of male and female gametes/germ cells.
- Fertilisation : It is the fusion of male and female gametes and the product of this fusion is called zygote which develops into a new organism.
- Significance of sexual reproduction : It results in combining DNA from two different individuals leading to creation of and new combination of variants and it forms the basis of evolution.
- Sexual reproduction in plants : Flower is the reproductive organ of flowering plants (Angiosperms).
a) Unisexual flowers : When a flower has either stamens or carpels, e.g., papaya and watermelon.
b) Bisexual flowers : When a flower has both stamens and carpels, e.g., mustard, Hibiscus.
- Parts of a flower : 4 whorls, i.e., sepals, petals, stamens and carpels/pistils. Sepals and petals are accessory whorls. Stamens and carpels/pistil are reproductive parts.
i) Stamens : Male reproductive part produces pollen grains; each pollen grain produces two male germ cells.
ii) Carpels or Pistil : Female part consists of ovary , style and stigma. Ovary contains ovules, each ovule contains an egg.
- Pollination : Transfer of pollen from another to stigma.
i) Self-pollination : Pollen is transferred from another to stigma of same flower.
ii) Cross-pollination : Pollen of one flower is transferred to another flower by wind, water or animals.
- Fertilisation : After pollination, pollen grains present on stigma germinate to produce a pollen tube carrying two male germ cells. It finds its way to ovule due to chemotropism. Finally, pollen tube fuses with ovule. Male and female germ cells fuse to form zygote.
Sexual Reproduction in Human
- Puberty : The stage/age when reproductive organs become functions. 10-12 years, in females and 13-14 years in males. It is accompanied by some physical changes in the body, e.g., cracking of voice, facial hair (beard) in makes and development of breast and onset of menstruation in females. These are the aspects of sexual maturity of the body. They are collectively known as secondary sexual characters.
- Male reproductive system in human being : It consists of testes, vas deferens, seminal vesicles, prostrate glands, urethra and penis.
- Female reproductive system in human beings : It consists of ovaries, fallopian tubes, uterus and vagina.
- Placenta : A special tissue through which the developing embryo/foetus gets nutrition from mother’s blood. It also transports wastes of the embryo into mother’s blood.
- Gestation period : Total period of embryonic development from the time of fertilization till birth is 40 weeks (280 days or 9 months 7 days).
- Menstrual cycle : It is sexual or reproductive cycle in human females. Its onset at puberty is called Menarche. It ends at the age of 50-55 years. It is called Menopause. It repeats itself every 28-30 days.
- Important events in sexual cycle of females:
a) Menstruation : Degeneration and removal of inner thickened lining of uterus along with blood after every 28 days, through the vaginal canal. Both these events stop if pregnancy occurs and are resumed after the childbirth. If fertilization does not occur, both the processes keep occurring periodically every month.
b) Ovulation : Release of mature from the ovary.
- Reproductive health:
i) It is important to have awareness about how to control population as well as prevention of sexually transmitted diseases (STDs) to maintain reproductive health.
ii) Some common STDs are gonorrhoea, syphilis (Bacterial infection) and HIV-AIDS, warts (viral infection).
- Contraceptive methods to avoid pregnancy:
i) Mechanical/barrier method : Use of condoms and IUCD (Intrauterine Contraceptive Devices) like Copper-T.
ii) Changing the hormonal balance by chemical method : Oral pills (Oral contraceptives) to prevent release of ovum.
iii) Surgical methods :
a) Vasectomy : Blocking/cutting a part of each vas deferens.
b) Tubectomy : Blocking/cutting a part of each fallopian tube.
- Sexually transmitted disease can be prevented by maintaining sexual hygiene, not participating in sexual act with multiple partners and using barrier methods of contraception.