Biology - Sexual Reproduction

Introduction

The sexual mode of reproduction comprises the process of combining DNA from two different individuals.
There are two germ-cells (responsible for producing a new organism); one is large and contains the food-stores whereas the other one is smaller and likely to be motile.
The motile germ-cell, normally, is known as the ‘male gamete’ and the germ-cell containing the stored food is known as the ‘female gamete.’

As shown in the image given below, flowers have different parts, such as sepals, petals, stamens, and carpels. Among these, stamens and carpels are the reproductive parts and contain the germ-cells.

Stamen is the male reproductive part, which produces pollen grains (yellowish substance).
Carpel, which is present in the center of a flower, is the female reproductive part.
Carpel is made of three parts.
The bottom part, which is swollen, is the ovary; the middle part, which is elongated, is known as the style; and the terminal part, which may be sticky, is known as the stigma.

The ovary contains ovules and each ovule has an egg cell.
The male germ-cell that produced by the pollen grain fuses with the female gamete present in the ovule.
The fusion of the germ-cells or fertilization produces zygote, which is capable of growing into a new plant.
The flower, which contains either stamens or carpels, is known as unisexual, such as papaya, watermelon, etc.
The flower, which contains both stamens and carpels, is known as bisexual, such as Hibiscus, mustard, etc.

Human beings have typical sexual reproduction process where mature male and female mate to produce a new baby.

The male reproductive system produces the germ-cells; further, other part of the reproductive system delivers the produced germ-cells to the site of fertilization.
The formation of sperms or germ-cells takes place in the testes.
The formation of sperm typically requires a lower temperature than the normal body temperature.
The testes secrete hormone, namely testosterone that brings changes in the appearance of boys at the time of their puberty.
The formed sperms are then delivered through the vas deferens, which unites with a tube coming from the urinary bladder.
The urethra, likewise, acts as a common passage for both the sperms and urine.
The sperms are fluids that consist of mainly genetic material; it has a long tail that helps to move towards the female germ-cell.

The female germ-cells or eggs are produced in the ovaries.
The egg is transported from the ovary to the womb through a thin oviduct known as fallopian tube.
The two oviducts unite and form an elastic bag-like structure known as the uterus, which opens into the vagina through the cervix.
During the sexual intercourse, most likely, the egg and the sperm (zygote) get fertilized and implanted in the lining of the uterus.
The thickened lining (of the uterus) and richly supplied blood nourish the growing embryo (in the uterus).
The embryo receives nutrition from the mother’s blood with the help of a special tissue known as placenta.
Likewise, the development of a child inside the mother’s body, takes about nine months.