Reproduction In Organisms

Reproduction is essential for the organism because-

1) It enables the continuity of species on the earth.

2) It helps in the transfer of gene characteristics from one generation to another.

In Sexual reproduction new individuals produced after cell division exhibit variation. Variations increase the adaptability of an organism to its changing environmental conditions whereas asexual reproduction does not bring about variations in offspring, therefore sexual reproduction is better mode of reproduction.

Offspring formed by asexual reproduction are always morphologically and genetically identical because they have the same gene as their parent, therefore referred to as clone.

Yes, this statement is always true.

Explanation: Offspring formed due to sexual reproduction have better chances of survival because sexual reproduction exhibit variations and these variations are important for survival of species. Offspring which do not exhibit variations and are exact copies of their parent (as in asexual reproduction) occupy the same niche or place in the ecosystem. The populations tends to get wiped out if this area gets altered due to natural or manmade causes. However under such conditions individuals with variations can colonise other habitats and survive.

The progeny formed from asexual reproduction is always morphologically and genetically identical or clone to their parents since they possess exact copies of DNA of their parent whereas in sexual reproduction DNA copying is accompanied by creation of new cellular apparatus. The cell divides and produces new cells, which exhibits variations. So, differences are found in morphological and physiological features of progeny as DNA copies generated during sexual reproduction are similar but not identical.

Vegetative reproduction is also considered as asexual reproduction because in this type of reproduction also new plants are formed from vegetative cells and it does not involve fusion of gametes. The new plants can be formed from root, stem or leaves.

Vegetative propagation is formation of new plant from vegetative parts or propagules of the parent .e.g.

1. Stem tubers develop new plants in the region of eyes. e.g. potato

2. Tap root branches develop adventitious buds and form new plants. E.g. Guava

Juvenile phase- also called vegetative phase. It is the period of growth in an organism after its birth and before it reaches reproductive maturity. This phase is of different duration in different organisms.

Reproductive phase- also known as maturity phaseor puberty, as reproductive structures mature during this phase. It is a period when an organism reproduces sexually.

Senescent phase-This is the last phase of life span and ultimately leads to death. It is the period when an organism loses the ability to reproduce and grows old.

Higher organisms have resorted to sexual reproduction in spite of its complexity because sexual reproduction exhibits variations and these variations lead to evolution of better organisms and thus provides better chances of survival.

Meiosis is also known as reduction division as the amount of genetic material is reduced to half in this division. Formation of gametes involves meiosis as gametes produced by organisms are haploid i.e. having only one set of chromosomes, and formation of gametes is called gametogenesis. Therefore, meiosis and gametogenesis are always interlinked.

(a) Ovary —diploid (2 n)

(b) Anther —diploid (2n)

(c) Egg —haploid ( n)

(d) Pollen —haploid ( n)

(e) Male gamete —haploid (n)

(f) Zygote —diploid (2n)

Explanation: Since ovary & anther undergoes only mitotic divisions during their development in which chromosome number remains the same, so these structures are diploid. The zygote is formed by the fusion of both male and female gametes (haploid structures) .So, when two haploid structures fuse the resultant is a diploid structure i.e.zygote.

Egg, pollen, male gamete undergoes meiosis during their development, which reduces the chromosome number to half , hence these are haploid structures.

External fertilization is the process in which fusion of male and female gametes takes place in external medium i.e. outside the female body. It mainly occurs in water animals for e.g. Frog, fish etc.

Disadvantages of external fertilization- External fertilization leads to wastage of large number of eggs , so eggs has less chance of fertilization.

In post- fertilization changes the zygote divides many times and forms an embryo within the embryo. The ovule gets converted into seed and develops a tough coat. Ovary ripens as fruit and embryo develops into a seedling during germination.

Plants having both male and female reproductive organs in the same flower are called bisexual flowers.

E.g. Hibiscus –Rosa sinensis

Mustard- Brassica campestris

Sunflower-Helianthus annus

Lily- Lilium candidum

Pea- Pisum sativum

A staminate flower is a male flower as it bears only stamens whereas a pistillate flower is a female flower as it bears only pistils.


Staminate flower Pistillate flower

E.g. Of plants bearing unisexual flowers- Papaya, cucumber, watermelon, maize etc.

Oviparous animals lay eggs outside the body so they are under continuous threat of various environmental conditions and predators whereas in viviparous animals development of young ones takes place inside the body where they're protected and have constant nutrition avaliable to them. Therefore, offspring of oviparous animals are at a greater risk as compared to viviparous animals.