Sexual Reproduction

Category : 7th Class

*       Sexual Reproduction

 

A sexual reproduction requires two individual of opposite sexes (male and female). An egg or ovum is called female gamete and a sperm is called male gamete. In sexual reproduction,' a male gamete fuses with a female gamete, which results in the development of new organism.  

 

*           Sexual Reproduction in Flowering Plants

A sexual reproduction requires two opposite sex cells male gamete and female gamete. When a flowering plant is mature to produce new plants sexually, it produces flowers, which contain the sex organs of the plant. There are some flowers, which contain only one sex organ (either male sex organ or female sex organ), called unisexual flower. And some flowers contain both type of sex organ, called bisexual flower. In the plants, the male sex organ is called stamen and the female sex organ is called carpel. Upper part of the stamen (male sex organ) is anther, which is joined with filament. Another contains pollen grains and pollen grains contain male gametes. Upper part of the carpel is stigma and lower part of the carpel is ovary. Ovary contains the ovule and ovule contains female gametes, called ova or eggs. Stigma receives the pollen grain from the anther and transfer it to the ovule, where fertilization takes place. This fertilized eggs grow into seeds, which develop into new plants after germination.

 

 

 

*           Sexual Reproduction in Animals

Animals are unicellular or in other word male sex cells and female sex cells are contained by two different bodies. Male contains male sex cells and female contains female sex cells. Male sex cells or male gametes are called sperm and female sex cells or female gametes are called ovum (plural ova) or egg. Male gamete fuses with the female gamete. Meeting of the male sex cell with the female sex cell is termed as fertilization. In some animals like human being, fertilization takes place inside the body, known as internal fertilization. And in some animals like frog, fertilization takes place outside the body, known as external fertilization. During the fertilization, nucleus of female sex cell fuses with the nucleus of male sex cell forming a single cell called zygote. This zygote goes on mitosis division. As the embryo goes on development, structural feature of the organism becomes clear. After 8 to 9 weeks of fertilization features of the organism can be recognized clearly. At this stage the embryo is known as foetus. The foetus grows and develops into a new baby.

 

What actually happens during the fertilization

 

We know that the nucleus of the human body cells contains 46 chromosomes. Whereas sex cells, i.e. sperm and. ova contains only 23 chromosomes and therefore they are called haploids. During the fertilization, nucleus of the two haploids (egg and sperm) fuses to form a single cell. Thus number of chromosomes in the nucleus of the fertilized cell becomes 46. Therefore, fertilization is the process in which two haploid cells (egg and sperm) fuses to form a diploid cell.

Thus we see, in the sexual reproduction, development of a new organism begins from a single cell called zygote. Zygote forms after the fusion of two haploids (sex cells), which come from two different sexes. Zygote is a single cell, which goes on more and more mitosis division forming a new organism.

 

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       Which one of the following parts of flower contains female sex cell?

(a) Ovules

(b) Stigma

(c) Filament

(d) Anther

(e) None of these

 

Answer: (a)

 

 

      How many chromosomes a human female sex cell contains?

(a) 23

(b) 46

(c) 44

(d) 52

(e) None of these

 

Answer: (a)

 

 

summary.jpg

Reproduction is the process by which an organism produce its new young ones

There are two types of reproduction, asexual and sexual.

Asexual reproduction does not require two opposite sexes, new young one is produced from a single parent.

Fission, budding, fragmentation, spore formation, vegetative propagation are the methods of asexual reproduction.

Sexual reproduction require two opposite sexes, new young one is produced after fertilization of egg cell.

Fusion of male sex cell with the female sex cell is called fertilization.

There are two types of fertilization, internal fertilization and external..



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