Reproduction is a very important process in all organisms. Animals produce offspring through asexual and sexual reproduction. Asexual reproduction produces offspring that are genetically identical to the parents because the offspring are all clones of the original parents. The genetic diversity of sexually produced offspring is thought to give species a better chance of survival in unpredictable or changing environments. Sexually reproducing species must maintain two types of individuals, male and female, which can limit their ability to colonise new habitats because both sexes must be present.
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Key Terms: Reproduction, Asexual Reproduction, Vegetative Reproduction, Sexual Reproduction, Variations, Evolution
What is Reproduction?
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Reproduction is an important biological method wherein offspring produced are similar to their parents concerning different features. This special phenomenon is important in the continuity of all species in the biosphere, generation after generation.
Generally, reproduction is seen in all living organisms from single-celled ones such as amoeba to multicellular ones, such as whales and human beings. Reproduction is carried out in two methods, depending upon the involvement of one or both parents.
Reproduction In Organisms
Necessity Of Reproduction
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Here are the most important necessities of Reproduction-
- Reproduction is necessary to the mechanism of the continuity of all species, and as a consequence, maintains a dynamic balance in all ecosystems to various biotic components proportionately.
- Without the process of reproduction, species that are ruling the world now may become extinct.
- Reproduction is the major channel for organic evolution due to variations created from the reproduction mechanism through the intermixing of genes in species (only in sexual reproduction).
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| Other Important Links Related To This Topic | ||
|---|---|---|
| Double Fertilization in Angiosperms | Pollination | Parthenocarpy |
| Flower Structure | Reproduction in Plants | Pollen Grains |
| Sporulation | Internal Fertilization | Gametogenesis |
Types of Reproduction
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There are two types of reproductions in organisms -
- Sextual Reproduction
- Asexual Reproduction
Types Of Reproduction
Asexual Reproduction
In this kind of asexual reproduction, many new offspring of a similar kind are produced by the involvement of single parents only. The asexually produced offsprings are not only identical to each other but are also the exact copies of their maternal parents because in this method a single mother organism divides mitotically to reproduce its daughter offspring.
The different modes of asexual reproduction in living organisms are as follows:
Asexual Reproduction
Asexual reproduction is seen in:
- Single-celled organisms like Amoeba, Bacteria, Hydra, Saccharomyces, etc. In which, Amoeba and Bacteria show binary fission, Hydra, Saccharomyces (yeast cells) reproduce by budding.
- Some vegetatively propagated plants like Ginger, turmeric potato, sweet potato, sugarcane, Bryophyllum, etc. can reproduce through vegetative propagation, a kind of asexual reproduction.
- Some animal species like starfish, earthworms, etc. reproduce through fragmentation.
Merits of Asexual Reproduction:
Here are the merits of asexual reproductions-
- As it is carried out by a single individual, it does not require a mate for reproduction
- The process of asexual reproduction is faster when compared to that of sexual reproduction
- Here very less amount of energy is required comparatively
- The process of asexual reproduction is less complicated as it involves only a single parent
- It can take place in different climatic conditions and environments
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Sexual Reproduction
In this kind of reproduction, a new daughter offspring is produced due to the involvement of two parents of the opposite sexes. This type of reproduction is mostly seen in all multicellular organisms including worms, insects, Mollusca, birds, reptiles, dogs, cats, cattle, elephants, whales, etc. The complete mechanism of sexual reproduction consists of a series of events, including
- Pre-fertilization changes
- Fertilization
- Post-fertilization
Sexual Reproduction
Demerits of Sexual Reproduction:
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The involvement of two parents (male and female) results in the intermixing of genes resulting in the formation of a new male or female offspring
- Genetically different offsprings are produced
- Variations in successive offsprings and generations increase the chances of survival and evolution.
Things to Remember
- Reproduction is an important biological method which is important in the continuity of all species.
- In asexual reproduction, many new offspring of a similar kind are produced by the involvement of a single parent.
- The different modes of asexual reproduction in living organisms are Budding,
- In Sexual reproduction, a new daughter's offspring is produced due to the involvement of two parents.
- Both asexual and sexual methods of reproduction have both merits and demerits.
Important PYQs Related To This Chapter
- Meiosis takes place in…(NEET 2013)
- The sexual reproduction is absent in….(NEET 1995)
- For union between stock and scion in grafting which one is the first to occur…(NEET 1990)
- A clone is ... [KCET 2011]
- Animals which possess cleidoic eggs exhibit…(KCET 2011)
- Which among these is not a post fertilization event ?...(KCET 2016)
- Type of asexual reproduction found in Hydra is..(KEAM)
- Which of the following is having longitudinal binary fission ?…(KEAM)
- In grafting, the stock and scion should be joined…
- Bananas are vegetatively propagated by… (AMUEEE 2012)
- Vegetative propagation by leaves is seen in… (JKCET 2010)
- Vegetative propagation in water hyacinth takes place by…(AMUEEE 2013)
- A slender, prostrate subaerial branch of the stem which creeps along….
Sample Questions
Ques. 1. Name any alga that can reproduce by zoospores. Why are they called zoospores? (2 Marks)
Ans. Asexual reproduction through zoospore takes place in an alga called Chlamydomonas. They are called zoospores because they are motile due to the presence of whiplike flagella.
Ques. 2. Give an example of a fungus which reproduces by processes like (i) budding and (ii) conidia. (2 Marks)
Ans. Budding is seen in the unicellular fungus called Yeast (Saccharomyces). The conidial formation is seen in an ascomycetes fungus called Penicillium.
Ques. 3. Name the vegetatively propagated structures in the following kind of plants : (i) Agave and (ii) Bryophyllum (2 Marks)
Ans. (i) Vegetatively propagated structures in Agave are called Bulbils (ii) Vegetative structures in Bryophyllum are Leaf buds or adventitious buds
Ques. 4. Name the vegetatively propagated structures in the following plants (i) Potato, and (ii) Pistia. (2 Marks)
Ans. (i) Axillary buds are called eye buds that are the vegetative structures in potatoes (ii) Offsets are the vegetative structures in Pistia.
Ques. 5. Which of the following statements is true for Hydra that lives in water?
(i) It can produce asexual gemmules.
(ii) It can produce unicellular buds.
(iii) It can produce multicellular buds. (2 Marks)
Ans. Statement (iii) is correct. Hydra is a multicellular animal. It can reproduce asexually by multicellular buds on the body. Both asexual gemmules and unicellular buds are absent in hydra.
Ques. 6. Name the units of vegetative propagation in the Eichornia (Water Hyacinth) plant. Explain why it has become the most invasive aquatic weed in India? (2 Marks)
Ans. Eichornia (Water hyacinth) most commonly reproduces vegetatively by offsets. It propagates at a very fast rate in water bodies. Hence, it spreads all over the water body within a short period of time anywhere in the country. So, it has become the most invasive aquatic weed all over India.
Ques. 7. Plants like potatoes and sugarcane do not produce seeds for generating new plants in fields. Then how do they produce new plants in agriculture? Give two other examples where new plants are generated in the same way as above. (3 Marks)
Ans. Plants like potatoes and sugarcane do not produce seeds for generating new plants because they do not produce functional and viable seeds. New plants generally arise from the nodes present on the modified underground stems of these special plants.
In potatoes, botanically, the modified underground stem is called a tuber. It has eyes on nodes that give rise to daughter plants. In sugarcane, stem cuttings of a certain size are planted in soil. When the nodes or eyes come in contact with moist soil produce roots and new shoots.
Other plants that produce vegetatively are strawberries and grapes.
Ques.8. Why is meiosis (cell division) an essential event in the sexual life cycle of any organism? Give 2 reasons. (3 Marks)
Ans. Meiosis is a very important stage in the sexual cycle of any organism because :
- It maintains the fixed number of chromosomes for generations (2n). Haploid gametes (n) are formed as a result of meiotic or reduction division. The diploid (2n) stage has been restored after fertilization of the gametes through the zygote formation.
- It will increase the chances of genetic diversity and variation in the regional population due to crossing over during meiosis between the homologous chromosomes and their random separation during prophase I.
Ques. 9. Why is a moss plant (bryophyte) unable to complete its life cycle in a dry condition or environment? 2 reasons. (3 Marks)
Ans. A moss plant (belonging to Bryophyta) can not complete its life cycle in dry environmental conditions because of the following 2 important reasons:
- The moss plant generally requires a thin sheet of water or moist humid conditions for the imbibition and dehiscence of the antheridial wall (male sex organ) and the opening of the neck canal cells in the archegonium (female sex organ).
- Water is required for hundreds of the flagellated antherozoids (male gametes) to swim toward the female gamete (egg or ovum) for the sake of fertilisation. It is due to chemotactic movements under the influence of a chemical substance called maleic acid.
Ques.10. What are the differences between sexual and asexual reproduction in living organisms? (5 Marks)
Ans. Here are the basic differences between asexual and sexual reproduction-
| Asexual Reproduction | Sexual Reproduction |
|---|---|
| Offspring are generated without the union of two sexual games from two different organisms of the same species | The offspring are produced by the union of two gametes from two different organisms of the same species |
| It is of many types like binary fission, fragmentation, budding, spore formation, etc.. | Sexual reproduction is by syngamy and conjugation. |
| Uniparental, that is only one parent is involved. | Bi-parental, that is two parents have involved |
| Cells divide by mitosis only. | Cells divide by both mitosis and meiosis |
| Only somatic or vegetative cells are involved. | Germ cells or reproductive cells are involved. |
| It is generally seen in less advanced unicellular animals and lower invertebrates with simple body structures. | It occurs in advanced plants and animals. |
| There is no union or fusion of gametes in the process of asexual reproduction. | There is the union or fusion of gametes in the process |
| The cells or organisms multiply very rapidly in a shorter period of time. | The cells or organisms multiply very slowly over a comparatively long period of time. |
| Here no fertilization takes place in the process. | Here, fertilization takes place in the process. |
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