12th Biology, Chapter 1

 Chapter: 1    REPRODUCTION IN ORGANISM  

a) It helps in continuity of species generation after generation.

b) It helps in transferring of genetic characters.

c) It helps in increasing the no. of species.

d) It helps in leading to evolution.

Sexual reproduction is a better mode of reproduction. Because it results in genetic variation, evolution and more chance of survival.

Because they are morphologically and genetically similar.

Yes this statement is always true. Because it shows genetic variation thus more chance of survival advantages.

Progeny formed from asexual reproduction

Progeny formed from sexual reproduction

Individuals are genetically identical

Individuals show genetic variation

Only mitotic divisions takes place

Both meiotic and mitotic divisions takes place

Formed from single parent

Formed by two parents of opposite sex 

Asexual reproduction

Sexual reproduction

Uniparental

Biparental

No fusion and formation of gametes

Fusion and formation of gametes

Only mitotic divisions takes place

Both meiotic and mitotic divisions takes place

Individuals are morphologically and genetically identical

Individuals show genetic variations.

Vegetative reproduction is also considered as a type of asexual reproduction because it involves a single parent and does not involve the formation and fusion of gametes.

New plants are regenerated from a small portion of any vegetative part of the plant.

E.g. Runners of oxalis, stem cutting of sugarcane.

Juvenile phase: It is the period in the life of an organism from birth till attaining sexual maturity. 

Reproductive phase: it is the period of reproductive maturity till the ability to reproduce.

Senescent phase: It is the period between end of reproductive phase and death of an organism.

Sexual reproduction results in variation there by resulting evolution of new species that is why higher organisms have resorted to sexual reproduction in spite of its complexity.

Meiosis occurs during gametogenesis as a result of which haploid gametes are formed.

Ovary: 2n (diploid)

Anther: 2n (diploid)

Egg: n (haploid)

Pollen: n (haploid)

Male gamete: n (haploid)

Zygote: 2n (diploid)

External fertilisation: Fusion of gametes takes place outside the body of the organism particularly in surrounding water.

 Disadvantage: 

(a) The life of offspring formed is always under threat of predators until they reach adulthood. 

(b) They are also exposed to harsh environmental conditions.

Zoospore

Zygote

An asexually motile reproductive structure.

Formed by fusion of male and female gametes and non-motile.

Germinate immediately without dormancy.

Undergoes a period of dormancy.

Formed under favourable condition.

Formed towards the end of favourable conditions.

Gametogenesis: Process by which gametes are formed, it involves meiosis.

Embryogenesis: Process by which zygote develops into an embryo, it involves mitosis.

After fertilisation, the primary endosperm nucleus forms the endosperm.

Zygote forms an embryo.

Ovule develops into seed.

The stamens, style, stigma, sepal, petals, usually fall off. In some case the sepals become persistent on the fruit as in brinjal.

The ovary wall becomes fruit wall called pericarp. 

A flower bearing both male and female reproductive organs is called bisexual flower. E.g. pea, mustard, petunia, tomato, brinjal etc.

Papaya, Cucumber, bitter guard etc.

Offspring of oviparous animals are:

Extremely Vulnerable to predators up to adulthood.

Exposed to harsh environment.

             Offspring of viviparous animals are:

Highly protected from unfavourable condition.

Nourished and nurtured by parent.

Under parental care.