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.’

Sexual Reproduction in Flowering Plants

• 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.

Reproduction in Human Beings

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

Male Reproductive System

• 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.

Female Reproductive System

• 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.