When reproduction takes place as a result of the fusion of two gametes, one from each parent, it is called sexual reproduction.
- The process of fusion of male and female gametes is called fertilization.
- The formation of gametes involves the exchange of chromosomal (genetic)fragments between homologous chromosomes causing genetic recombination which leads to variation.
Sexual Reproduction in Plants
It occurs mostly in flowering plants. In fact, flowers are the reproductive organ of plants.
- A typical flower consists of four main whorls namely calyx (sepals), Corolla (Petals), Androecium (Stamens) and Gynoecium (Carpels).
- Pollen grains of a flower, transfer to the stigma of the carpel of the same flower (Self-Pollination)or to the stigma of carpel of another flower (Cross-Pollination).
- This transfer of pollens is achieved by the agent like wind, water or animals.
- After Pollination, a pollen tube grows out of pollen grains, through which male germ cell reaches the ovary and fuses with the female germ cell.
- Fertilization: The fusion of male and female gamete is called fertilization. It occurs inside the ovary. A zygote is produced in this process.
OVARY->OVULE->EGG CELL AND POLAR NUCLEI.
- The zygote divides several times to form an embryo within the ovule. The ovule develops a rough coat and is converted into a seed.
- Ovary grows rapidly and ripens to forms a fruit, while the seed contains the future plant or embryo which develops into a seedling under a suitable condition. This process is known as Germination.
- Flowers can also be unisexual (contain either stamen or carpel) or bisexual (contains both stamen and carpel).
- Unisexual flowers: PAPAYA, WATERMELON.
- Bisexual flowers: HIBISCUS, MUSTARD.
Reproduction in Human Beings
- Humans use a Sexual Mode of reproduction.
- It needs sexual maturation which includes the creation of the germ cells ie, egg (ova) in the female and sperm in the male partner & this period of sexual maturation is called Puberty.
Male Reproductive System
- The formation of male germ cell (sperms) takes place in the testes(male reproductive organ)
- A pair of the testis is located inside scrotum which is present outside the abdominal cavity. Scrotum has a relatively low temperature needed for the production of sperms by testes.
- Testes release a male sex hormone called testosterone and its function is to:
- Regulate the production of sperm
- Bring about changes in appearance seen in boys at the time of puberty.
- The sperms along with the secretion of the prostate gland and seminal vesicle, together constitute semen, which is released and made to enter into the female genital tract during Copulation.
Female Reproductive System
- The female germ cells or eggs are produced in the ovaries. (located in both side of the abdomen).
- When a girl is born, the ovaries already contain thousands of immature eggs.
- At puberty, some of these eggs start maturing. One egg is produced every month by one of the ovaries.
The Egg is carried from the ovary to the womb through a fallopian tube. These two fallopian tubes unite into an elastic bag like structure known as the uterus. The Uterus opens into the vagina through the cervix.
Fertilization occurs in the fallopian tube of the female genital tract.
- The fertilized egg also called zygote (2n) gets implanted in the lining of the uterus, and start dividing. Actually, uterus is richly supplied with blood to nourish the growing embryo. If a zygote is not formed, the inner wall of uterus breaks which causes bleeding through the vagina. This process is called MENSTRUATION. It occurs at a regular interval of 28 days.
- The Embryo gets nutrition from the mother’s blood with the help of a special tissue called PLACENTA. It provides a large surface area for glucose and oxygen to pass from the mother to the embryo. Similarly, the wastes from developing embryo are removed to mother’s blood through the placenta.
- The time period from fertilization up to the birth of the baby is called Gestation Period. In humans, it is about nine months (36 weeks).
- The sexual cycle (Menstruation) in a woman continues up to the age of 45-50 years. After that, the ovaries do not release the egg. This stage is called Menopause. It also marks the end of the reproductive life of a woman.
- Female sex hormones are oestrogen and progesterone which are produced by the ovary.
- Reproductive Health means a total well-being in all aspects of reproductive, i.e., physical emotional, social and behavioural.
- Contraception: It is the avoidance of pregnancy. It can be achieved
A healthy society needs a balanced sex ratio that can be achieved by educating people to avoid malpractices like female foeticide & prenatal sex determination.