Reproduction in Organism | Notes | Class 12th

A biological process called reproduction involves creating new organisms from an already existing one. Without it, species cannot exist for very long. Reproduction supports the survival of the species through successive generations as older individuals experience senescence and eventually pass away.

or in otherwords.

Reproduction (or procreation or breeding) is the biological process by which new individual organisms – “offspring” – are produced from their “parent” or parents.


-Life span – • An organism’s life span is defined as the time from conception to natural death. From a few days (Butterfly 1 to 2 weeks) to thousands of years, an organism’s life span can vary (Banyan tree).


Based on whether one or two organisms are involved in the reproduction process, there are various types of reproduction.

Types of Reproduction


when a single parent gives birth to a child, whether or not a gamete is involved.


When the reproductive process comprises two parents of opposing sex and also includes the

The process of fusing male and female gametes is known as Sexual reproduction.


Asexual reproduction 

is the term for this type of reproduction.

‣ Unmarried Procreation

  1. Usually, creatures with very simple organizational structures follow.
  2. children born to single parents.
  3. with or without the participation of gamete formation.
  4. The resulting offspring are morphologically and genetically similar to the parent and each other.

‣ Being clones of their parent.

  • The parent cells divide into two in Protista and Monera to produce new individuals.

NOTE – Cell division is hence the primary means of reproduction in these species.

Types of Asexual Reproduction

  • Binary fission: a cell divides into two parts and develops into an adult quickly using this asexual reproduction technique. Former amoeba and paramecium


  • Budding: This process results in the production of tiny buds, which at first remain joined to their parents but separate as they mature. as in yeast.


  • Special reproductive structures, including zoospores (a motile structure), conidia (a penicillium), buds (a hydra), and gemmules (found in algae), are used by fungi and basic plants to reproduce (sponges).


  • Vegetative propagules such as the runner, rhizome, sucker, tuber, offset, and bulb are used in vegetative reproduction in plants.
  • Some plants only bloom during a specific season, while others bloom all year round.

Other plants, such as several types of bamboo, flower only once in their lives (after 50 to 100 years), and Strobilanthus kunthiana (neelakuranji), which blooms every 12 years.

H2O HYACINTH (Terror of Bengal)

  • One of the worst plants for invasion
  • Whenever there is standing water, it thrives.
  • oxygen from the water, which causes fish to die.
  • introduced in India due to its lovely flowers and leaf shape
  • Vegetative growth occurs at an astonishing rate.


When conditions are not favorable, sexual Reproduction takes over from asexual reproduction, which is the more prevalent mode of reproduction in organisms with simpler bodies like algae and fungus.

It involves the development of male and female gametes by two people of the opposite sex.

offspring produced by the fusion of male and female gametes that are not genetically similar to the parents or to each other.

The pattern of reproduction is the same in all sexually reproducing organisms.

  • When male and female gametes fuse during sexual reproduction, kids are produced that are not genetically identical to either parent.



Juvenile phase – Juvenile phase refers to the time between birth and sexual maturity. It is referred to as the vegetative phase in plants. The juvenile/vegetative phase ends and the reproductive phase begins.

  1. The gestational phase
  • During the reproductive period, the female placental animals show cyclic changes in the functions of their ovaries, accessory glands, and hormones.

Periodic period

It affects humans, apes, and monkeys.

  • The menstrual, proliferative, and secretory phases make up the cycle.
  • During the final few days of the cycle, blood flows. The endometrium that has ruptured is expelled during menstruation.
  • When their cycles are menstruating, females forbid copulation.

Oestrous cycle

  • Non-primate animals like cows, sheep, rodents, deer, dogs, tigers, etc. go through this cycle.
  • It comprises of a brief oestrous or heat period. In a cow, it lasts between 12 and 24 hours before an oestrous, or the inactive period.
  • During this cycle, blood does not circulate. Endometrium that has broken is reabsorbed.

Females only allow copulation throughout the oestrous cycle. Hormones control the changeover between various stages of the life cycle in both plants and animals. The reproductive processes are regulated by the interactions of hormones and environmental factors.

The reproductive phase comes to an end during the senescent period.

*Death inevitably results from old age.


Gametogenesis – is the process through which male and female gametes are created. Haplotype cells, or gametes, can have a similar or different structure. Both gametes in algae are homogametes, which are similar in structure (isogametes). Two physically distinct gametes called heterogametes are created in higher organisms that reproduce sexually; the male gametes are known as antherozoids or sperm and the female gametes are known as ovum or eggs.

Homothallic and Monoecious terminology are used to describe the Bisexual condition in fungi and plants, while Heterothallic and Dioecious terms are used to describe the Unisexual situation. The female flower of a flowering plant is pistillate, or bearing pistils, whereas the unisexual male bloom is staminate, or bearing stamens.


  • In animals, species with either male or female reproductive organs are referred to as unisexual (cockroach, human), while species with both male and female reproductive organs in the same individual are referred to as bisexual or hermaphrodites (earthworm, sponge, tapeworm, etc.).


  • Despite the fact that organisms can be both Haploid and Diploid, gametes are always Haploid (containing half set of chromosomes). Meiotic division produces gametes in diploid organisms. Algae, fungi, and bryophyte organisms have haploid plant bodies, whereas pteridophytes, gymnosperms, angiosperms, and the majority of animal species are diploid (having two sets of chromosomes).


  • Gamete mother cells (meiocytes) in diploid organisms go through meiosis, which results in gametes having only one set of chromosomes.


  • Male and female gametes travel through water in simple plants including algae, fungus, bryophytes, and pteridophytes. Due to the fact that the majority of male gametes do not reach the female gametes, there are significantly more male gametes than female gametes.


  • In higher plants, ovules contain eggs and pollen grains carry male gametes. To enable fertilisation, pollen grains must be moved from one stigma to another. Pollination is the process of moving pollen grains from an anther to the stigma. Self-pollination is an alternative to stigma.

Gamete Transfer – The majority of species have non-motile female gametes and motile male gametes, with the exception of fungi and algae, which have both gametes that can move.

Pollen tubes that convey the male gametes close to the ovule are created when pollen grains germinate on stigmas.

  1. Fertilization, also known as syngamy, is the joining of the male and female gametes.

It causes the development of diploid zygotes.

  • Parthenogenesis is the process of developing new creatures without the fertilization of female gametes. For instance, rotifers, lizards, and honey bees.

Pre-fertilization, Fertilization, and Post-fertilization are Sexual Reproduction Events.

‣ Pre-fertilization includes all of the activities that take place before the fusing of the gametes. Gamete transfer and gametogenesis are included.


difference between internal and external fertilization. reproduction

‣  Post Fertilization Events: Sexual reproduction-related activities that occur after zygote development.


The zygote is a crucial connection that maintains species continuity between organisms of one generation and the following. The zygote is the single cell that all sexually reproducing organisms, including humans, are born from.


  • In species with external fertilization, the zygote develops in an external medium (water), whereas in organisms with internal fertilization, the zygote develops within the body of the female.
  • In fungus and algae, the zygote forms a strong wall that is resistant to injury and desiccation. After some relaxation, this begins to grow.
  • The zygote divides to produce haploid spores, which then germinate to produce a haploid individual in organisms with a haplontic life cycle.


Embryogenesis is the process through which an embryo develops from a zygote. The zygote goes through cell differentiation and mitosis at this time. Cell differentiation aids in the creation of new cell groupings and organs, while cell division increases the number of cells.


Oviparous Viviparous
Outside of the body of the organism, zygotes develop and lay fertile or unfertilized eggs.

Ex: Birds and reptiles.

Zygote development occurs inside the bodies of creatures, giving rise to offspring.

Ex-human, canine, equine, etc.

  • In plants that produce flowers, the zygote develops inside the ovule. Flowers lose their sepals, petals, and stamens after fertilisation. The zygote transforms into ovules, which then become seeds. The ovary transforms into fruits with a thick, protective wall called a pericarp.


  • Following dispersal, seeds germinate favorably to create new plants.


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