UPSC Biology Reproduction in Animals Reproduction


Category : UPSC







Reproduction is the process by which all living organism give rise to new organisms similar to themselves. It is essential for the survival of the species since all the living beings have a similar life span. Organism reproduces by two modes asexual and sexual reproduction.


Asexual Reproduction

Asexual reproduction produces offspring that are genetically identical to the parent because the offspring are all clones. The main process of asexual reproduction is mitosis. This type of reproduction is common among same single cell organisms for example, amoeba, etc. Many plants also reproduce asexually.


Sexual Reproduction

Sexual reproduction is a biological process that creates a new organism by combining the genetic material of two organisms in a process that starts with meiosis, a specialized type of cell division.


Difference between asexual and sexual reproduction



Asexual reproduction

Sexual reproduction


It occurs only in invertebrates and lower chordates.

It occurs almost in all types of animals.


It is always uniparental.

It is usually biparental.


Gametes are not formed.

Two types of gametes are formed.


It involves only mitosis.

It involves both meiosis and mitosis. ­­


Daughter organisms are genetically identical to the parent.

Daughter organisms genetically differ from their parents.


Since there is no variation, so it does not contribute to evolution of the species.

Because of variations, it contributes to the evolution of species.


Occurs by fission, budding or fragmentation.

Occurs by the formation of haploid gametes which fuse to form a diploid zygote.


It is a quick method of multiplication.

It is a slower method of multiplication.





In plants, asexual reproduction is of 3 types - agamospermy, spore formation and vegetative reproduction.


Vegetative Propagation

Vegetative propagation or vegetative reproduction is the process of multiplication in which a portion of fragment of the plant body functions as propagules and develop into a new individual.


Artificial Vegetative Propagation

  • Cutting - e.g. - sugarcane
  • Grafting - e.g. - grafted margo, roses, orange, seedless

      grapes guava, apple and pear.


Underground stem

  • Rhizome - Ginger, banana, turmeric, Lotus, Musa, etc.
  • Conn - Gladiolus, colocasia, crocus, Alocasia, etc.
  • Bulbs - Onion, garlic and lilies.
  • Tubers - Potato, Helianthus tuberosus etc.
  • Suckers - Mint and chrysanthemum.


Creeper stem

  • Runners - Cyndon, oxalis and centealla
  • Stolen- Fragaria, vallisneria
  • offset - Pistia, Eichkomia, etc.
  • Aerial stem - Opuntia.

Leaves - ex- Bryophyllum, Begonia, streptocarpus, saint paulia



Sexual reproduction is the process of development of new organisms through the formation and fusion of gametes. In flowering plants, stamens are male reproductive organs while carpels are female reproductive organs. Sexual reproduction can be summarised as:





Male Reproduction Unit

It includes

  • Stamen - unit of male gamete, consists anther, connective and filament.
  • Microsporangium - sporangium containing micropores.
  • Microsporogenesis - Formation of micropores or pollen grains
  • Pollen-grains - it consists male reproductive bodies of flower.

Female Reproduction Unit

It includes

  • Gynoecium/Pistil -Female reproductive part and carpet is a unit of gynoecium. Carpel consists three parts-stigma, style and ovary.
  • Megasporangium (Ovule) - The integumented nucellus or megasporangium
  • Megasporogenesis - The process of formation of megaspore mother cell.
  • Embryo sac - Female gametophyte




Sexual Reproduction Cycle




The process of transfer of pollen grains form an anther to the stigma of the some flower or different flower is called pollination.





Post Fertilization Events

It involves development of endosperm, embryo, ovules and seeds

Endosperm - Endosperm is the nutritive tissue which provides nourishment to the embryo in seed plant. It also protects the embryo from mechanical injury. It may be completely consumed by developing embryo before it matures (e.g. beans and peas) or it may persist in the mature seed and used up during seed germination, e.g., coconut.

Embryo - The process of development of mature embryo from zygote or oospore is called embryogeny. Zygote starts dividing to produce embryo, together with the development of endosperm.

Seed - Seed is a fertilized ovule. It is the final product of Fertilization in angiosperm and acts as a main propagative unit in plants. Ovules mature into seed and simultaneously ovary develops into a fruit.

  • Transformation of various units of ovary during seed formation are.


(i) Ovary wall      

Fruit wall

(ii) Ovary  


(iii) Integuments

Seed coats

(iv) Outer


(v) Inner


(vi) Ovule



Handy Facts

  • Apomixes is the production of seed without fertilization.
  • The normal process of cell cycle involving meiosis and fertilization is called amphimixis.
  • Polyembryony is the state of occurrence of more than one embryo in a seed, e.g. onion and groundnut.


Handy Facts

  • Emasculation – It is the process of removal of another from the flower bud before the another dehiscens
  • Artificial hybridisation – It is the process in which the desired ae taken out by emasculation and then pollination.



  • Most fruits develop only from the ovary are called true fruits.g. cucumber, tomato, coconut. Now a days many seedless grapes, oranges and water melones are being developed by horticulturists. These are seedless fruits that are formed without fertilization, e.g., banana.
  • When floral parts other than ovary, particularly thalamus contributes to fruit formation, such fruits are called false fruits,g. apple, strawberry, cashew etc.


Some common fruits with their edible part.

Fruits can also be classified on the macro level:

  • Simple fruit: It results from the ripening of simple or compound ovary. E.g., Mustard, Mango, Lemon.
  • Aggregate fruit: It results from several corpets derived from the same flower. E.g., Raspberry, Strawberry.
  • Composite fruit: It develops from an inflorescence rather than from a single flower. E.g., Jackfruit, Mulberry







It is the process used to create an exact copy of a cell tissue or a complete organism. It was performed by lan Wilmut and his colleagues at Roslin institute edinburg, Scotland. They cloned sheep named “Dolly”, she was born on 5th July 1996 and was the 1st mammal cloned from adult somatic cell. She died on 14th feb. 2003 due to lung disease.



  • In this process Two parents are involved and Gametes formation occurs.
  • The daughter individuals are genetically different from both the parents.
  • The parental individuals may be unisexual (dioecious) or bisexual/ hermaphrodite (monoecious) e.g. Paramecium, Plasmodium, Hydra, tape worm and earthworm.


Reproduction in Human

In human beings reproduction is much the same as for mammals specialized reproductive organs are located in their lower abdomen.

  • Male consists glands called testes that make microscopic, tadpole - shaped sperm cell
  • The female has glands called ovaries that make pin point - sized egg cell.
  • Humans are sexually reproducing and viviparous.
  • Rate of reproduction is slower in sexual reproduction.
  • Human are unisexual. The reproductive system of each sex consists of many organs. The latter are distinguishable into primary and secondary sex organs. Besides these, there are some accessory sex characters.

Puberty is the name for the time when your body beings to develop and change as your move them kid to adult. Usually, puberty starts between ages 8 and 13 in girls and ages 9 and 15 boys.

Male Reproductive System

  • Its Accessory or external sexual character are low pitch voice, beard, broad shoulder, Moustaches, Narrow lips, breathing by means of diaphragm


Female Reproductive System

  • Accessory or external sex characters of female are high pitched voice, smooth face, narrow shoulder, broad hips, sternal breathing



  • According to the World Health Organisation (WHO), reproductive health means a total well-being in all aspects of reproduction, i.e., physical, emotional, behavioural and social.

 Table: Method of Birth control


S. No.





Penis is withdrawn before ejaculation.


Tubectomy / Tubal ligation

Woman's fallopian tubes are cut and tied, permanently blocking sperm release.


Lactational amenorrhea

As long as mother breast feeds the cild, chances of conception is nil



Man?s vasa deferentia are cut and tied permanently blocking sperm passage.



a small part of the fallopian tube is removed or tied up through a small incision in the abdomen or through vagina.


Intrauterine device (IUD) non-medicated IUDs (e.g., Lippes loop), copper releasing lUDs (CuT, Cu7, Multiload 375) and the hormone releasing lUDs (Progestasert, LNG-20).

Small plastic or metal device placed in the uterus to -^-prevent implantation. Some contain copper, other release hormones.


Oral contraceptive e.g. - saheli. MalaD. etc.

Synthetic estrogens and progesterones prevent normal menstrural cycle; primarily prevent ovulation.


Male condom

Thin rubber sheath on erect penis collects ejaculated semen.


Female condom

Plastic pouch inserted into vagina catches semen.



Soft rubber cup covers entrance to uterus, prevents sperm from reaching egg and holds spermicide.


Cervical cap

Miniature diaphragm covers cervix closely, prevents sperm from reaching egg and holds spermicide.


  • MTP is used to get rid of unwanted pregnancies and where continuation of the pregnancy could be harmful or even fatal either to mother or to the foetus or both.



  • Diseases which are transmitted through sexual intercourse are collectively called sexually transmitted diseases (STD) or venereal diseases (VD) or reproductive tract infections (RTI).
  • These disease are caused by a wide range of bacterial, viral, protozoan, fungal agents and ectoparasites.


Table: Some STDs and their pathogens







Treponema pallidum



Neisseria gonormoeae



Haemophilus ducreyi



Gardnerella vaginalis



Chlamydia trachomatis



Herpes genitalis

HSV-2 (DNA) virus


Condyloma acuminatum

Papova (DNA) virus


Molluscum contagiosum

Pox (DNA) virus




Trichomonas Vaginalis




  • Inability to conceive or produce children even after 2 years of unprotected sexual cohabitation is called infertility.
  • Various methods are now available to help such couples.

The main Art-Techniques i.e. (Assisted reproductive technology)

The main ART-techniques includes:

In vitro fertilization (IVF)

Zygote intra fallopian transfer (ZIFT)

Intra cytoplasmic sperm injection (ICST).

Gamete intra fallopian transfer (GIFT).

Surrogacy or surrogate motherhood.

Other Topics

Notes - Reproduction

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