SEXUAL REPRODUCTION
Sexual reproduction involves two individuals for producing a
new individual.
The process of fusion of two gametes is called fertilization.
After fertilization, a zygote is formed which develops into a new organism.
Sexual
reproduction in Plants :
The flowering plants or angiosperms bear special reproductive
parts located in the flower. Various parts of flower are; sepals, petals,
stamens and pistil.
Most flowers have both male and female reproductive organs.
The flower may be unisexual (papaya, watermelon) when it contains either
stamen or pistil or bisexual (Hibiscus, Mustard) when it contains both
stamens and pistils.
male reproductive part of flower called stamen.
female reproductive part of flower called pistil.
Pistil is made of three parts. The swollen bottom
part is the ovary, middle elongated part is the style and the
terminal part which may be sticky is the stigma. The ovary contains ovules
and each ovule has an egg cell.
Each stamen consists of stalk called filament,
and a flattened fertile top called anther. The anthers produce the pollen grains.
The pollen grains produce male gametes which fuse with female
gamete (egg celI) present in the ovule. This fusion of the germ-cells or
fertilization gives zygote which grows into a new plant.
Pollination: It
is the process of transfer of pollen grains from the anther to the stigma of
flower.
Self-pollination: If transfer of pollen
occurs in the same flower, it is referred to as self-pollination.
Cross-pollination: If the pollen is transferred
from one flower to another, it is known as cross-pollination.
The transfer of pollen grains carried out by different
agencies like wind, water, insects or animals.
Fertilization : A tube grows
out of pollen grain and travels through the style to reach the female
germ-cells present in ovule in the ovary.
Out of two male gametes present in pollen tube one fuses with
egg to form zygote. This fusion is called fertilization.
After fertilization, the zygote divides several times to form
an embryo within the ovule. The ovule develops a tough coat and
gradually turns into a seed. The ovary grows rapidly and ripens to form
a fruit. Meanwhile the petals, sepals, stamens, style and stigma may
shrivel and fall off.
Reproduction in
human beings :
The reproductive organs of human beings are called gonads.
These are testes in male and ovaries in female. The male gonad
produces sperms and female gonad produces ova (eggs) at the age
of puberty (after attainment of sexual maturity). Various changes occur
in girls and boys at this age.
Male
Reproductive System consists of the following organs:
Testes: A pair of testes are situated in scrotum that lie outside the abdominal cavity and behind the penis. Testes produce sperms and Testosterone hormone. Testosterone brings about changes in appearance of boys at the time of puberty.
VAS deferens: From each
testis, a duct arises which is known as vas deferens which unites with a tube
coming from urinary bladder. It brings sperms from testis.
Urethra: Vas deferens tube opens into a common tube called
urethra. It runs through a muscular organ called Penis. Penis is male
copulatory organ.
Accessory Glands: Glands like
prostate and seminal vesicles and Cowper’s gland add their secretions which
make transport of sperms easier and this fluid also provides nutrition.
Female Reproductive System :
It consists of the following organs:
Ovaries: Paired ovaries are located in the abdominal cavity near
the kidney. Ovaries produce female gamete (ovum or egg) and secrete female
hormones (estrogen and progesterone). One egg is produced every month
alternately by one of the ovaries.
Fallopian Tube: The egg is carried from the ovary to womb/uterus through a thin oviduct or fallopian tube.
Uterus: The two oviducts unite into an elastic bag like structure known as the uterus.
Vagina : Uterus opens into vagina. It is female copulatory organ.
Sexual Cycle in
female:
After puberty, only one egg is produced alternately from one
ovary after a period of 28 days.
Egg in fallopian tube encounter sperms which enter
through the vaginal passage during sexual intercourse.
This fertilized egg (zygote) gets implanted in the lining of
uterus which later forms embryo.
Embryo gets nutrition from the mother’s blood with the help
of special tissue called placenta.
If the egg is not fertilized, if lives for about one day
since the ovary releases one egg every month, the uterus prepares itself every
month to receive the fertilized egg. Thus, its lining becomes thick and spongy.
If it does not get zygote, the developed lining slowly breaks down and comes
out through vagina as blood and mucus. This cycle takes place
roughly every month and is known as menstruation. It usually lasts for
about 2-5 days.
Reproductive Health
:
Reproductive organs need a lot of care and hygiene. Otherwise
they are susceptible to many infections or diseases.
The diseases which spread through sexual routes are known as sexually
transmitted diseases e.g., bacterial infections like syphilis, gonorrhea
and viral infections such as warts and HIV- AIDS.
Condom helps to prevent transmission of many of these
infections to some extent.
BIRTH CONTROL:
Contraceptive methods are adopted to prevent unwanted
pregnancy and to have sufficient gap between successive births.
Frequent pregnancy causes many health problems and also adds to an already exploding population. Many ways have been devised to avoid pregnancy. Contraception can be achieved by:
• Mechanical barrier method (use of condoms).
To prevent union of sperm and egg.
Use of condoms, cervical caps and diaphragm.
• Chemical methods (use of pills).
Use of oral pills.
These change hormonal balance of body so that eggs are not
released.
May have side effects.
• Use of contraceptive devices (copper-T).
Intrauterine contraceptive device (IUCD).
Copper-T or loop is placed in uterus to prevent pregnancy.
• Surgical methods (vasectomy in males and tubectomy in females)
In males, the vas deference is blocked to prevent
sperm transfer called vasectomy.
In females, the fallopian tube is blocked to prevent egg
transfer called tubectomy.
