NCERT Solutions Class 12 Biology Chapter 1
NCERT Solutions Class 12 Biology Chapter 1: Reproduction in Organisms
The NCERT Solutions Class 12 Biology Chapter 1 is about reproduction in all living organisms. Reproduction is a natural process of producing offspring by conjoining chromosomes. Pre-existing living beings perform this practice to balance the stability of life. NCERT Solutions Class 12 Biology Chapter 1 deals with the process of birth among animals and plants that ensures species generation. In contrast, every species has to experience ageing and eventually die at a certain age.
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Key Topics Covered In NCERT Solutions Class 12 Biology Chapter 1
Life span is the period which begins from birth and ends with the natural death of an organism. Reproduction is an essential biological process by which an organism will give birth to another similar organism.
Some basic facts about reproduction are given below.
- Reproduction is the procedure that ensures the continuation of species from generation to generation. It leads to the evolution of genetic variation.
- The variation in genetics is inherited during reproduction.
- Asexual reproduction is defined as the form of reproduction in which only one parent is involved.
- Sexual reproduction is the reproduction in which two parents of the opposite sex are involved in fusing male and female gametes.
- In asexual reproduction, only one parent participates in producing the youngsters. Correspondingly, the babies produced are identical to each other and the parents.
- Asexual reproduction is commonly seen in unicellular organisms, animals, and plants with relatively simple organisms. Additionally, it can also be seen in multicellular organisms.
Asexual Reproduction in Animals:
The commonly seen modes of asexual reproduction in case of animals are as follows:
- Fission, generally known as binary fission, occurs in prokaryotic microorganisms and a few multicellular organisms.
- After the development phase, the organisms are split into independent organisms. Few single-celled eukaryotes go through binary division via mitosis.
- In various organisms, part of an individual is separated, and a second individual is formed.
- For example, in many asteroid echinoderms, this process occurs when the central disk separates.
- Some of the sea anemones and a few polyps will also reproduce via division.
- In a few cases, it is seen that the nucleus divides multiple times by amitotic divisions. This leads to the formation of many new copies of nuclei. Cytoplasmic division does not happen during this time. However, the Cytoplasm will accumulate around each nucleus.
- Consequently, many unicellular and seedless offspring will be formed from a single cell. This particular method of propagation is known as multiple fission. For example, Amoeba and Paramecium.
Differences Between Binary and Multiple Fission:
|S. No.||Characteristics||Binary Fission||Multiple Fission|
|1||Numbers of daughters created.||Parents separate into two daughters.||Parents divide into several daughters.|
|2||Time of Formation||During supportive
|During unfavourable conditions.|
|3||Fate of Parent||Nothing is left with parents.||Residual Cytoplasm is left.|
- The budding is a kind of asexual reproduction that happens from the advancement of part of a cell or a particular area of the body that leads to the separation of the original organism into two individuals.
- The budding process is ordinary in some invertebrates, such as corals and hydras.
- In hydras, a bud is produced that grows up and detaches from the main body. While in sprouting corals, the bud does not fall off and reproduces as part of a new colony.
- Sporulation or Spore Formation:
- Sporulation is also called sporogenesis. It is a shape of asexual reproduction that includes spores. Spores, is derived from “sporā.”, which means “seed”. And “genesis means ‘birth’ or ‘origin. Spores are dormant reproductive cells that are identical to seeds in that, where they serve as units of multiplication.
- As spores are distinct from the seeds, they lack the embryo created by the fusion of male and female gametes.
- Spores have thick walls and are contrary to various adverse conditions such as high temperatures and low humidity.
- When the conditions are favourable, they will germinate to give birth to fresh individuals. Spores are built in some plants and fungi.
- Fragmentation indicates the breaking up of the parent organism into fragments, and each particle is capable of becoming a new organism. This is noticed in fungi, for example, yeasts and lichens, moulds, cyanobacteria, vascular and non-vascular plants, and animals.
- This form of asexual reproduction in animals may be unintentional. Human activity, predation, and other environmental elements can cause them to break up into fragments.
Asexual Reproduction in Plants:
The modes of asexual reproduction that are seen commonly in plants are:
Fission is known to be the simplest of all asexual methods. It is generally established in fungi and algae. Single-cell stem cells split mitotically to form two identical daughter cells and the mother. Every daughter cell eventually becomes an independent organism.
- Some algae bear branches of Advent, like in the case of Dictyota, Fucus, buds like in Protosiphon Yeast, and mushrooms produce sprouts.
- These compositions result from uneven division and hold fast to the mother cell. Eventually, they divide and mature into a new organism.
- The process of fragmentation is very familiar in plants. It is a very traditional way of plant vegetative reproduction.
- The fragmentation process materialises when rooting branches are torn or detached from the leading group due to mechanical pressure or other reasons.
- Different plants have divergent mechanisms.
- Spore formation:
- Asexual reproduction in plants arises from a wide variety of motile and non-motile spores, also known as conidia.
- Ciliated motile asexual spores, called zoospores, are created by algae and fungi. The zoospores swim in water for some metres with the assistance of flagella connected to them. In the later stage, they directly progress into new independent individuals under good conditions. Examples are Oedogonium and Ulothrix.
- Few of the fungi are terrestrial too. These have non-flagellated and non-motile spores or conidia. These spores are therefore transparent in weight and dry. They have a strong coat and are well altered for dispersal by wind. For example, Penicillium, and Aspergillus.
- The constituent which bears the actual spores is defined as the sporangium. The sporangium exists on a sporophyte. It guides the sporophyte, which multiplies rapidly in an asexual manner to give rise to vast numbers of spores. Few ferns, for example, Nephrolepis, bear spores are multiplied asexually by them. Those plants are homosporous, meaning they own only one type of spore throughout their lifetime.
- Gymnosperms and Selaginella (pteridophyte) are heterosporous because they bear two types of spores.
It is a process in which new plants are obtained without producing sexual structures, i.e. spores or seeds. It necessitates the propagation of plants through various vegetative parts such as the rhizome, sucker, bulb, tuber, etc. In this, a fusion of the female and the male gamete does not come about and requires only one parent. This is grouped into natural and artificial.
- Natural Methods:
With natural propagation methods, the maturing of a new plant from an organ of the mother plant transpires under suitable environmental conditions. These altered organs can enlarge from the stem, leaf, root, or flower.
- By roots: Asparagus, sweet potatoes, and dahlias.
- Through the leaves: The shoots flourish on the leaf edges with this process. These buds aid in generating new plants, as in Bryophyllum.
- Through flower buds: In plants such as oxalis and agave, flowers.
- Buds generate new plants, and in Dioscorea, axillary buds do so.
- Through the stem: Corridors noticed in the grass, dislocations formed in Pistia, runners in Nephrolepis, and runners in mint plants.
- Artificial Methods:
In this Class of methods, only a tiny part of the plant organ is used for obtaining a complete fresh plant. The most standard methods used are cutting, layering, and grafting.
In cutting, a tiny piece of root is cut, and when planted in moist soil, it will lead to the artificial inducement and expansion of adventitious roots, for example, in lemon.
Rose, hibiscus, sugarcane, and chrysanthemum plants are refined by cuttings that entail stem pieces with nodes. The tiny cuttings are planted in moist soil to grow new plants. Underground parts of the stem lead to the development of adventitious roots, whereas buds develop and blossom on the aerial parts of stems. The new plants are in a normal state known as cutting. Later, these cuttings are transplanted in various prepared places.
This method is used for growing rose, grape, lemon, jasmine and hibiscus. The lowest branches of these plants are bent slightly and shielded with soil in such a manner that the tip of the branch protrudes from the ground, and the middle part of the plant is inside the earth. It will then flourish adventurous roots from this buried area of the plant’s stem. This branch is cut off and excluded from the mother plant, whereby a new plant is obtained.
Grafting is carried out on plants with trouble forming roots or by those that generally have a frail root system.
- This method involves connecting two plants of the same or non-identical species. This is achieved by joining the tissues of the two plants directly. When brought into contact, the meristematic tissue of two plants divides and multiplies. As a result, the cells of each plant fuse.
- The rooted plant is known as the stem plant. While the plant that is grafted onto it is called the sprout. A plant is chosen as the “scion” with superior and desirable properties. The stock is generally challenging, robust, and resilient. Mango, pear, apple, citrus, guava, lychee and many other fruit plants are collected and kept.
- The graft can be of different kinds. Namely, bud graft, tongue graft and lateral graft, wedge graft, and crown graft, depending on the joining of the two parts.
Significance of Vegetative Reproduction:
- Vegetative reproduction is a perfect reproduction method in plants in which we want to preserve parental characteristics.
- It is suitable for plants that are less efficient sexually, have poor seed viability, tiny seeds, long seed dormancy, etc.
- They can also be easily expanded by this method.
- Vegetative propagation is ideal for obtaining disease-free plants.
- The needed characters can be brought together from two varieties by using Grafting.
- Sexual reproduction includes the origination of male and female gametes, either by the same individual or by different individuals of the opposite sex.
- The initiated gametes fuse to form the zygote, which grows into a new organism. It is an arduous and slow process compared to asexual reproduction.
- Since this process is the fusion of male and female gametes, the children are not exactly identical to the parents. .
- Even with different external morphology, physiology and anatomy, sexual reproduction in plants, animals, and fungi patterns are similar. All organisms go through general development before reproductive growth. Only when they are reproductively mature can they breed sexually. General growth is called the juvenile phase and the vegetative phase in the case of plants.
- The processes and procedures of sexual reproduction are fundamentally similar in all organisms. The systems which are associated with sexual reproduction are pretty different.
- In every case, sexual reproduction is characterised by the fusion of the male and female gametes of the species.
For clarity, these sequential events can be examined as three different stages: pre-fertilisation, fertilisation, and post-fertilization.
- Gametogenesis is explained as the procedure of the formation of gametes. There are two kinds of gametes; male and female gametes extracted from male and female parents. Gametes are the haploid (n) in nature.
- Gametes that are identical in appearance are called isogametes or homogametic. They are morphologically and physiologically alike. For example, Cladophora and Ulothrix.
- Most sexually reproducing organisms have morphologically and physiologically distinct kinds of gametes called heterogametes or isogametes. The male gametes are tiny and more active. On the other hand, the female gametes are larger and sluggish. The male gametes are sperm or antherozoid, and the female gamete is called ovum or egg.
- Gametes are haploids all the time. The parent might be either haploid or diploid. A haploid parent creates gametes which are haploid by mitotic division.
- Various fungi organisms, Monera, algae, Bryophyta, gymnosperms, angiosperms, and most animals are diploid. This is where meiosis turns out to produce haploid gametes.
- In diploid organisms, when meiocytes, i.e. gamete stem cell and diploid 2n, undergo meiosis, one set of chromosomes is assembled into each gamete.
- Gamete transfer:
After their emergence, the male and female gametes must come into contact for fertilisation. The male gamete is commonly mobile, and the female gamete is generally stationary. Gamete transfer requires an appropriate medium transfer.
- Many male gametes do not reach female gametes, so male gametes are consolidated in huge numbers correlated with female gametes.
- In angiosperms, pollen grains move the male gametes. The ovule consists of the ovules. Pollen grains are generated on the anthers and transferred to the stigma. This phenomenon is called pollination. Pollination demands the involvement of external agents such as insects, wind, animals, and water.
- The pollen grains sprout in the stigma, and the pollen tubes that move the male gametes reach the ovule and eject two gametes near the ovule.
- In bisexual animals, the organism has to grow a unique mechanism for the transmission of gametes since male and female gametes are formed in different individuals, which is essential for fertilisation.
- The fusion of both gametes, i.e. male and female, is called syngamy. In this, a diploid zygote is formed. This method is known as fertilisation.
- In most fish, algae, and amphibians, syngamy occurs outside the body of organisms. This category of gamete fusion is called external fertilisation. This is seen in frogs and bony fish, where many offspring are produced. They are highly vulnerable to predators, which threatens their survival.
- Syngamy develops in the organism’s body in plants, i.e. fungi, pteridophytes and mosses; birds, reptiles, and mammals. Hence the process is called internal fertilisation. The mobile male gametes reach the egg and fuse with it, which occurs inside the female body.
- In seed plants, the motionless male gametes are carried to the female gametes through pollen tubes.
- The shaping of the zygote is standard in sexual reproduction. It is diploid. With external fertilisation, the zygote is developed in the external environment (water), while with internal fertilisation, the zygote is shaped in the body by organisms
- The further growth of the zygote depends on the organism’s life cycle and the conditions to which it is sensitive. In organisms such as fungi and algae, the zygote builds a thick wall resistant to desiccation and damage and usually goes between a dormant phase before germination.
- Some unicellular animals form the zygote nucleus. This type of sexual reproduction is known as conjugation.
- The zygote is the essential link that ensures the continuity of species between organisms from one generation to the next.
- Embryogenesis indicates the method of embryo development from the zygote. The zygote undergoes cell differentiation and cell division (mitosis) during embryogenesis.
- Cell divisions will lead to a rise in the number of cells in the developing embryo. In contrast, cell differentiation assists the group of cells undergoing certain modifications to form specialised tissues and organs to shape organisms.
- In animals, if the zygote’s growth happens in the female parent’s body, it is known as viviparous.
- In egg-laying animals such as birds and reptiles, fertilised eggs covered by a hard calcareous shell are deposited in a safe place. After an incubation period, the babies hatch.
- Besides, the zygote evolves into a cub that emerges from the mother’s body in viviparous animals such as mammals, including humans. The probability of survival of the offspring is higher with live-bearing organisms due to adequate embryonic care and safety.
NCERT Solutions Class 12 Biology Chapter 1: Exercises and Answer Solutions
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Q.1 Why is reproduction essential for organisms?
Reproduction is a biological process in which an organism gives rise to young ones (offspring) similar to itself. The young one grows, matures and again reproduces. This continuous process ensures that a species is maintained for long and does not become extinct. Organisms spend a lot of energy in the process of reproduction to ensure that their genes are passed on to the next generation. The best-fit organisms in nature are those who produce the most offspring and are best adapted to the environment. This way the continuity of life is maintained.
Q.2 Which is a better mode of reproduction sexual or asexual? Why?
Sexual mode of reproduction is better than asexual reproduction.
Sexual reproduction involves gametes (eggs or sperms) produced by the same or different individuals which fuse to form a zygote. The zygote then grows and develops into an adult individual. The offspring inherits half of its genes from one parent and the other half from the other parent. Also, the gametes are produced by meiotic division where recombination introduces variation. Thus, the offspring has a different combination of genes than either parent. Such variations are very important and advantageous to the species under changing environmental conditions because the offspring might be better adapted to the new environment than either of the parents, resulting in better survival.
In the asexual mode of reproduction, offspring are produced by a single parent without the involvement of gametes. Only one parent is involved and the offspring have the same phenotype and genotype as that of the parent without any variations. As long as the environment remains the same, this mode of reproduction is beneficial but under changing environmental conditions, this might be very disadvantageous as the lack of variations may affect the adaptability and the offspring may not be able to survive.
Q.3 Why is the offspring formed by asexual reproduction referred to as clone?
The term clone refers to the organisms or cells, which are genetically identical. In the asexual mode of reproduction, a single individual (parent) produces offspring. The offspring that are produced are not only identical to one another but are exact copies of their parent, therefore they are called ‘clones’. These clones are formed by the process of mitosis, thus they are phenotypically and genetically identical to their parent.
For example; in Protists and Monerans, the organism or the parent cell divides into two to give rise to new individuals. Amoeba reproduces by binary fission where the cell simply divides into two halves and each rapidly grows into two adults. Yeast reproduces by budding.
Q.4 Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
Offspring formed due to sexual reproduction have better chances of survival under changing environmental conditions due to variability introduced in their genotype. This occurs due to the recombination of genes during meiosis. The fusion of the two gametes from two different parents results in genotypically and phenotypically different offspring which might have better survival or adaptability to the changing environment. This does not hold true in case of the asexual mode of reproduction.
However, there might be cases where the genetic makeup of the new offspring is at certain disadvantages or results in offspring that are not suited to the environment. For such cases, this form of reproduction may turn out to be disadvantageous. Thus, the given statement does not always hold true.
Q.5 How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
The differences between the progeny formed from asexual reproduction and sexual reproduction are as follows:
|Progeny from asexual reproduction||Progeny from sexual reproduction|
|1. Progeny is phenotypically and genetically identical to the parent as only one parent is involved in the asexual mode of reproduction.||1. Progeny is phenotypically and genetically different from the parent as this mode of reproduction involves the fusion of two different gametes from two parents.|
|2. At least two or more progeny are formed.||2. At least one or more progeny are formed.|
|3. Lack of variation makes progeny less suitable under changing environmental conditions, thus chances of survival are less.||3. Variation from the parent as well as among themselves makes progeny more suitable to the changing environmental conditions, thus chances of survival are more.|
Q.6 Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
The difference between asexual and sexual reproduction is as follows:
|Asexual Reproduction||Sexual Reproduction|
|1. A single parent is involved.||1. Two parents are involved.|
|2. It does not involve the fusion of male and female gametes.||2. It involves the fusion of male and female gametes.|
|3. There is no genotypic or phenotypic variation introduced in the asexual mode of reproduction. Identical individuals are produced (clones).||3. Genotypic and phenotypic variations are introduced in the sexual mode of reproduction. Individuals produced are not identical among themselves or with their parents.|
|4. It is a fast process and is not energy-intensive.||4. It is a slow process and is energy-intensive.|
|5. It is commonly seen in simpler single-celled organisms like yeast and fungi.||5. It is usually seen in higher animals and plants.|
|6. It is an advantageous mode of reproduction if the environment is constant.||6. It is an advantageous mode of reproduction if the environment is not constant.|
Vegetative reproduction is a term commonly used for an asexual mode of reproduction in plants where new plants are obtained without the involvement of seeds or spores. The units of vegetative propagation, such as runner, rhizome, sucker, tuber, offset, bulb etc. (called vegetative propagules), give rise to new individual offspring on their own. Since only one parent is involved in the process, it is a type of asexual reproduction. The offspring produced is phenotypically and genetically identical to the parent.
Q.7 What is vegetative propagation? Give two suitable examples.
Vegetative propagation is a term commonly used for an asexual mode of reproduction in plants. The units of vegetative propagation, such as runner, rhizome, sucker, tuber, offset, bulb etc. (called vegetative propagules), are well-equipped to give rise to a new individual on their own. Only one parent is involved in the process. The offspring produced is phenotypically and genetically identical to the parent thus, advantageous traits are preserved. No special mechanism, such as pollination, is required as only one parent is involved in the reproduction. This is a faster mode of reproduction which saves time and energy. Vegetative propagules also help the plants to survive unfavourable weather conditions. Special characteristics or features of the plant are maintained but no variation is introduced.
(a) Some plants, such as Canada thistle and most bamboos, send out long underground stems that produce new plants, often at considerable distances from the original plant. Such plants can form enormous colonies of new plants within relatively few years.
(b) Plants, like potato, sugarcane, banana and ginger, give rise to new plants through vegetative propagation. Small plants emerge from the buds of potato tuber, and the rhizome of banana and ginger.
(a) Juvenile phase,
(b) Reproductive phase,
(c) Senescent phase.
(a) Juvenile phase: The period of growth from birth until an organism reaches a certain stage of maturity in life before it can reproduce sexually.
(b) Reproductive phase: The phase of life in an animal or a plant when it is matured enough to reproduce.
(c) Senescent phase: The phase of life when the body metabolism slows down and the plant or animal cannot propagate further or reproduce.
Q.9 Higher organisms have resorted to sexual reproduction in spite of its complexity? Why?
Higher organisms have resorted to sexual reproduction in spite of its complexity because in sexual reproduction the offspring, although similar to their parents, are not identical to them due to recombination of genes received from the mother and father. This recombination of genes produces genetic variations in the offspring. In this way, sexual reproduction leads to a greater variety of population. This means that a species (animal or plant) can adapt more quickly to the environmental changes. Sexual reproduction, therefore, accords diversity to the species by providing genetic variation. This helps in the evolution of the species.
Q.10 Explain why meiosis and gametogenesis are always interlinked?
Meiosis is a special type of nuclear division which segregates one copy of each homologous chromosome into each daughter cell. It reduces the number of chromosomes to half forming haploid daughter cells. It also introduces genetic variation in the daughter cells due to the process of recombination. The process of formation of haploid gametes involved in the sexual mode of reproduction is called the gametogenesis and it takes place through meiosis. The genetic variations due to recombination during meiosis ensure better chances of survival of the offspring under different environmental conditions. Thus, the process of meiosis and gametogenesis are always interlinked.
Q.11 Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
(a) Ovary __________
(b) Anther __________
(c) Egg __________
(d) Pollen __________
(e) Male gamete __________
(f) Zygote __________
|Part of the Plant||Haploid (n)/ Diploid (2n)|
|(a) Ovary||Diploid (2n)|
|(b) Anther||Diploid (2n)|
|(c) Egg||Haploid (n)|
|(d) Pollen||Haploid (n)|
|(e) Male gamete||Haploid (n)|
|(f) Zygote||Diploid (2n)|
Q.12 Define external fertilisation. Mention its disadvantages.
External fertilisation is the process in which the fusion of male and female gametes resulting in the formation of a diploid zygote occurs in the external medium (water), i.e. outside the body of the organism.
Disadvantages of external fertilisation are:
- Wastage of resources as a large number of gametes are to be produced and released in the external medium by parents to increase the chances of fusion of gametes.
- Offspring are extremely prone to predators; thus threatening their survival up to adulthood.
Q.13 Differentiate between a zoospore and a zygote.
The differences between a zoospore and a zygote are as follows:
|1. A zoospore is the most common asexual structure (microscopic motile structure) formed in several algae and fungi.||1. A zygote is the result of the fusion of male and female gametes.|
|2. It is a motile structure that uses flagella for its movement.||2. It is a non-motile structure.|
|3. It is produced by a single organism and is the result of the asexual mode of reproduction.||3. It is a result of the sexual mode of reproduction and is formed by two organisms.|
|4. It is haploid (n).||4. It is diploid (2n).|
Q.14 Differentiate between gametogenesis from embroyogenesis.
Gametogenesis is the formation of haploid male and female gametes from diploid meiocytes through the process of meiosis. The two gametes produced can be similar in appearance, like in some algae but usually, they are morphologically different, like in most sexually reproducing organisms.
Embryogenesis is the process of development of an embryo from the zygote. The zygote undergoes repeated mitotic cell divisions increasing the cell number and cell differentiation resulting in the generation of specialised cells (followed by tissues and organs) to carry out specific cellular functions.
Q.15 Describe the post-fertilisation changes in a flower.
The post-fertilisation events are the events in sexual reproduction that take place after the formation of zygote. In flowering plants, the zygote is formed inside the ovule. As soon as the fertilisation takes place, the sepals, petals and stamens of the flower wither and fall-off. The pistil, which is the female reproductive organ of the plant, remains attached to the plant. The zygote develops into an embryo and the ovules develop into the seeds. The ovary develops into fruit which develops a thick wall called pericarp. This works as a protective covering of the fruit.
Q.16 What is a bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
A bisexual flower is a flower that has both the essential whorls i.e., androecium and gynoecium (male and female reproductive units). They are also called as perfect flowers. Such flowers usually have numerous stamens.
The given table shows the common names and scientific names of some bisexual flowers.
|Examples of bisexual flower||Scientific name|
|Sweet Pea||Lathyrus odoratus|
|China rose||Hibiscus rosa-sinensis|
Q.17 Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?
Cucurbits are usually climbing or trailing plants such as squash, pumpkin, cucumber, gourd, watermelon, etc. They have distinct, male and female flowers. Male (staminate) and female (pistillate) flowers, also called unisexual flowers, are found on a single plant (monoecious). These flowers have five fused petals with five stamens (male) or an inferior ovary (female). The male flowers tend to open first, followed by the female flowers. Pollination occurs only when both the male and female flowers open. The female flower opens for only one day.
Other examples of plants bearing unisexual flowers are:
Papaya, watermelon, muskmelon, castor, maize
Q.18 Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Animals are classified into oviparous and viviparous based on whether the development of the zygote after fertilization takes place outside or inside the body of the female partner. Oviparous animals lay fertilised or unfertilised eggs and viviparous animals give birth to young ones.
The fertilised eggs of oviparous animals (like reptiles and birds), covered by the hard calcareous shell, are laid outside the body and after a period of incubation, young ones are hatched out. They are too young to protect themselves from predators or other environmental conditions. Thus, their chances of survival are less.
However, in the case of viviparous animals, (like most mammals, including humans) the zygote develops into a young one inside the body of the mother under perfect conditions. They come out of the mother’s body only after they have attained a certain developmental stage. Since they get better embryonic care and protection, the chances of survival are more in the offspring of viviparous animals.
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