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Reproduction In Plants And Animals


Reproduction is the process of formation of new individuals of a species from the pre-existing ones. A simple cell duplicates its genetic material and passes it on from one generation to another.

Living organisms reproduce mainly by two methods:

  1. asexual reproduction and
  2. sexual reproduction.

In asexual reproduction, the offspring arises from a single individual parent. Sexual reproduction basically involves two individuals of different sexes, namely a male sex and a female sex.

Reproduction in Plants

Plants also reproduce sexually and asexually.

Asexual Reproduction in Plants
Lower plants such as bacteria, algae, yeast, moulds and other fungi reproduce asexually as well as sexually. Asexual reproduction takes place by the method of binary fission or by budding.

  • In binary fission, the cell divides into two daughter cells by a transverse wall when the conditions are favourable, e.g. bacteria.
  • Vegetative reproduction occurs either by cell division or by fragmentation, e.g. Spirogyra.
  • Others such as ferns produce spores (asexually) on the underside of leaves.

Vegetative Reproduction It is the simplest method of reproduction occurring in plants. The vegetative parts of a plant body, such as root, stem, leaf, etc., produce new members of the plant. Vegetative propagation is common in plants such as orchids, ornamental plants and grasses.

  1. Role of Roots in Vegetative Propagation:
  • In addition to their normal functions of fixation, absorption and conduction of water and minerals from the soil, both tap roots and adventitious roots are modified in various ways for food storage for perennation.
  • The tuberous roots of sweet potato and mint bear adventitious buds. When such bud-bearing roots are planted in the soil, new plants are produced.
  1. Role of Stems in Vegetative Propagation:
  • The common grass and mint grow their stems horizontally parallel to the ground. New roots and shoots develop at their nodes. These roots grow downward into the soil and the shoot upward to form new plants.
  • Ginger is a modified stem with nodes, internodes and scaly leaves. Axillary bud growing out from the nodes develops into a new plant (Figure).



Rhizome of Ginger


  1. Role of Leaves in Vegetative Propagation: Leaves of some plants, such as Bryophyllum, produce buds in the notches in the margin (Figure). When such leaves fall in the moist soil, their buds in the margin begin to grow as young tiny plants.


Leaf of Bryophyllum


The art of joining the parts of two different plants such that they grow as one plant is called grafting. This is a characteristic unique to plants. Grafting is generally done between related varieties and species. It is usually used for the propagation of rubber, apple, pear, citrus, mango and guava.

 is the raising of new plants from a small plant tissue with the help of tissue culture. A group of genetically similar individuals obtained through micropropagation is called a clone.

  • Tissue culture is based on totipotent nature of plant cells or concept of totipotency, i.e. each and every plant cell has the inherent capacity to develop into a complete plant. Steward first developed a full plant from a single cell of wild carrot root.
  1. Parthenogenesis: In parthenogenesis, the unfertilised egg is stimulated to undergo development. The organism produced by parthenogenesis is generally haploid, i.e. it contains only one set of chromosomes, or half the number of chromosomes.
    Sexual Reproduction in Plants Most of the plants are bisexual, i.e. the male and the female reproductive parts are present in the same plant. The reproductive part of higher plants is the flower.

The various parts of a flower are Calyx (sepals), corolla (petals), androecium (stamens) and gynoecium (carpels) (see Figure).

  1. Sepals are generally green and are the outermost part of the flower.
  2. Petals form the second inner whorl next to sepals. They are bright in colour.
  3. Stamens are the third inner whorl. It is the male reproductive part. It is formed of a long, narrow filament and a broad sac-like anther at its tip. Pollen grains are formed inside the anther. The formation of microspores or pollens is called microsporogenesis. Each microspore mother cell gives rise to four haploid microspores or pollen grains.
  4. Gynoecium or pistil is the female reproductive part and carpel is the unit of gynoecium. Carpel is distinguished into three parts, namely ovary, style and stigma. Ovary is the swollen basal part of the carpel that bears one or several ovules. The ovary maybe one or many-chambered. Inside the ovary, the ovules develop from a special tissue called the placenta. The manner in which the placentae are distributed in the ovary is known as placentation.


Section of a Flower

  • The transfer of pollen grains from the anther to the stigma is called pollination. It is of two types, namely self-pollination and cross-pollination.
  • The transfer of pollen grains within the same or genetically similar flower is called self-pollination. Self-pollination is of two types, namely autogamy and geitonogamy. Autogamy is the transfer of pollen grains from the anther to the stigma of the same flower. Geitonogamy is the transfer of pollen grains from the anther to the stigma of a flower present in the same inflorescence or in the same plant.
  • Cross-pollination or alogamy is the process when pollens are transferred from the anther to the stigma of different flowers on different plants. Cross-pollination within a species is called xenogamy.
  • Pollination is a characteristic of angiosperms. Cross-pollination is advantageous because it results in the formation of better progeny. For cross-pollination, agent is a must. Agents may be abiotic (wind, water) or biotic (birds, insects, bats, snails, etc).
  • Accordingly pollination may be classified as follows:
  1. Anemophily: Pollination by wind, e.g. palm, maize.
  2. Hydrophily: Pollination by water, e.g. Vallisneria.
  • Biotic agents:
  1. Ornithophily: Pollination by birds, e.g. Bombax.
  2. Entomophily: Pollination by insects, e.g. AristolochiaFicus.
  3. Chiropteriphily: Pollination by bats, e.g. Cadamba.
  4. Malacophily: Pollination by snails and slugs, e.g. aroids.
  • Insect-pollinated flowers usually possess sticky pollens with rough surface and the flowers are large, colourful and scented. Honey bees are the chief pollinators of agri-horticultural crops.
  • Emasculation is the removal of stamens of a plant to prevent self-pollination.
  • In angiosperms meiosis occurs when pollen grains are formed. The fusion of nuclei of male and female gametes is called fertilisation.
  • Fertilisation in which male gametes are carried through pollen tube is called siphonogamy.
  • Inside the embryo sac, when one male gamete fuses with egg to form the diploid zygote, the process is called syngamy, and when the second male gamete fuses with two polar nuclei, the process is called triple fusion. The occurrence of syngamy and triple fusion simultaneously in angiosperms is called double fertilisation.
  • As a result of fertilisation, a diploid zygote is formed. The triploid endosperm develops from the fertilised definitive nucleus.
  • The zygote divides further to form the embryo, while the endosperm nucleus forms the endosperm of the seed. The ovary enlarges to form the fruit and the ovary wall forms the fruit wall (pericarp). The ovules become the seeds.
  • A fruit may contain one or more seeds. When the fruit is ripe, the seeds contained within the fruit are released by one of the various methods of dispersal and grow into new plants under suitable conditions.

Reproduction in Animals


Animals also reproduce by sexual and asexual methods.

Asexual Reproduction in Animals

  • Fission (binary fission or multiple fission):
    This is the most common method of reproduction in lower forms of animals. It results in the division of the parent amoeba into two daughter amoebae. First, the nucleus divides into two, followed by the division of the body.
  • Budding:
    Some multicellular animals such as Hydra produce small buds which grow in size and get separated.
  • Regeneration:
    Animals such as Hydra and starfish have great power of regrowing the missing part. This process is called regeneration.

Sexual Reproduction in Animals Most animals reproduce sexually. In a majority of animals, like in human beings, male and female sex organs are in different individuals. Such organisms are called unisexual. In certain animals such as earthworm, a single individual has both male and female sex organs. Such organisms are called bisexualor hermaphrodite.

  • Gonads are the primary sex organs. The gonads produce gametes by meiotic division. Testis are the male gonad that produces sperms and ovary is the female gonad that produces eggs or ova.
  • In fishes and amphibians, fertilisation usually takes place outside the body. It is called external fertilisation.
  • Internal fertilisation takes place in reptiles, birds and mammals. In such cases, the male gamete (sperm) is transported from the testis into the body of female where fertilisation takes place. This transfer occurs at the time of mating or copulation. Structures associated with mating are called copulatory organs or accessory sex organs.
  • Human reproduction employs internal fertilisation and depends on the integrated action of hormones, the nervous system and the reproductive system.

Male Reproductive System Male reproductive system consists of a pair of testes, a paired duct system consisting of epididymus, vasa efferentia, vas deferens, ejaculatory duct and urethra. Secondary sex organs are seminal vesicles, Cowper’s glands, prostate glands and penis.

  • Testes are the primary sex organs and they produce male sex hormone called testosterone. Testes are masses of coiled seminiferous tubulesSperms are produced in the seminiferous tubules. Spermatozoa are nourished during their development by sertoli cells. Mature sperms are stored in epididymus. Vas deferens transports the sperms from the epididymus to urethra. Movement of the sperm through the duct is by the peristaltic contractions of its muscular coat. Ejaculatory duct eject the sperms into the urethra just prior to ejaculation. Ejaculation is the discharge of semen due to powerful rhythmic contractions of urethra. Each ejaculate of a man contains about 200 million sperms.
    In some mammals such as lion, bull and man, the testes remain permanently in the scrotum and keep functioning throughout the year. In certain seasonally breeding mammals such as bat, the testes enlarge, become functional and descend into scrotum in the breeding season. In a few cases such as elephant and whale, the testes remain permanently in the abdomen.
  • Scrotum is the sac of skin situated outside the body cavity and allows sperms to develop at the optimum temperature which is slightly lower than the body temperature.
  • The testis is attached to the scrotum by a band of connective tissue called gubernaculum. Testis and the scrotum communicate with the abdominal cavity through inguinal canal. Failure of testis to descend into scrotum from abdominal cavity is called cryptorchidism.
  • Function of the Accessory Glands
  1. Seminal vesicle provides the energy source for the sperms. The alkaline nature of the fluid helps to neutralise the acid in the female tract, which, if not neutralised, would kill and inactivate the sperms.
  2. Prostate gland: The prostatic secretion contributes to sperm motility and viability.
  3. Cowper’s gland: Secretes mucus which lubricates the end of the penis during sexual intercourse.

Female Reproductive System The female reproductive system consists of ovaries, fallopian tubes, uterus, vagina, accessory glands and external genital organs.

  • Ovaries are the primary sex organs and they produce female sex hormones namely estrogen, progesterone, and female gametes or ova.
  • Follicles are specialised structure where oocyte growth and meiosis I occur. These follicles are initially formed during embryonic development but start maturing once a month after puberty only. Mature follicles are called Graafian follicles.
  • When a mature egg leaves the ovary, it enters the oviduct. Fertilisation takes place in the oviduct.
  • Uterus protects and nourishes the developing embryo. Cervical mucous supplements the energy requirements of the sperms.
  • In female mammal, insemination occurs in vagina.
  • The FSH hormone is responsible for inducing spermatogenesis and oogenesis. Rupturing of follicles and discharge of ova is called ovulation.
  • Fertilizins are the substances secreted from mature egg.
  • During the period of ovulation in female, LH is present in greatest concentration.
  • In a 28-day human menstrual cycle, ovulation occurs on 14th day. The menstrual cycle in mammals is controlled with the help of progesterone and estrogen. Menstruation is triggered by an abrupt decline in the amount of progesterone.
  • The fertilisation cone, which pulls the sperms into the egg, is from the plasma membrane of the egg. After a sperm has penetrated on ovum during fertilisation, a fertilisation membrane is formed to prevent the entry of further sperms.
  • During pregnancy, the production of ova in ovary is prevented by progesterone. The fertilised eggs in human females get implantation in the uterus after about 7 days of fertilisation.
  • Placenta is the region where foetus receives maternal blood and nutrition. Placenta in human is haemochorial.
  • Gestation period is the duration between fertilisation and parturition.
  • The expulsion of completely developed foetus from the uterus is called parturition. Soon after the delivery, the mammary glands of human females secrete colostrum.
  • Frequent pregnancy causes many health problems and also adds to an already exploding population. A number of methods have been clinically devised to control childbirth. There are barriers, chemical and surgical methods of birth control.
  • In barrier methods, physical devices such as condom, diaphragm and cervical caps are used. They prevent the entry of sperm in the female genital tract during copulation.
  • The chemical methods are the use of specific drugs by females. There are two types of drugs, such as oral pills and vaginal pills. Oral pills are mainly hormonal preparations, and are called oral contraceptives. The oral contraceptive is purely a hormonal preparation that inhibits the production of gametes by the action on hypothalamus, pituitary and ovaries.
  • The intrauterine contraceptive device is a small, T-shaped device with a copper wire. This prevents implantation of blastocyst.
  • In women, ligature of the fallopian tube can be done (tubectomy) to prevent the passage of ova down the fallopian tube.
  • The communicable diseases occurring due to sexual contact are called sexually transmitted diseases (STDs). These are gonorrhoea, syphilis and AIDS.

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