Online Notes on Chapter=8 ( How do Organisms Reproduce) Part 2

This is Online Notes on Chapter=8 (How do Organisms Reproduce)  Part 2 for preparation of CBSE BOARD Examination, NTSE etc.

Sexual Reproduction:

When reproduction takes place as a result of the fusion of male and female
gametes is called sexual reproduction.
Fusion of gametes is called fertilization which results in variation.

Sexual Reproduction in Plants:

• Flowers are the reproductive organs of plants.
• A typical flower consists of four main whorls namely sepals, petals,
stamen and pistil.

Types of Flowers:

• Bisexual flower : Both male and female reproductive parts are present.
E.g., Hibiscus, mustard.

• Unisexual flower : Either male or female reproductive part is present.
E.g., Papaya, watermelon.

Structure of Flower :

Process of Seed Formation:

• Pollen grains, produced in the anther, are transferred to the stigma of
same flower (self pollination) or stigma of another flower (cross
pollination) through agents like air, water or animals.

• Pollen grains germinate and form pollen tubes which pass through style
to reach upto the ovules present in ovary.

• The fusion of male and female gametes is called fertilization. Zygote is
produced inside the ovary.

• Zygote divides to form embryo. Ovule develops thick coat and changes
into seed gradually.

• Ovary changes into fruit and other parts of flower fall off.

• The seed germinates to form a plant under suitable conditions such as air,
moisture etc.

Reproduction in Human Beings:

• Humans use sexual mode of reproduction.

• Sexual maturation : The period of life when production of germ cells
i.e., ova (female) and sperm (male) start in the body. This period of

sexual maturation is called puberty.

Changes at Puberty:

(a) Common in male and female

• Thick hair growth in armpits and genital area.
• Skin becomes oily, may result in pimples.

(b) In girls

• Breast size begin to increase.
• Girls begin to menstruate.

(c) In boys

• Thick hair growth on face.
• Voice begin to crack.

These changes signals that sexual maturity is taking place.

Male Reproductive System:

(a) Testes : A pair of testes are located inside scrotum which is present
outside the abdominal cavity. Scrotum has a relatively lower temperature needed
for the production of sperms.
• Male germ cell i.e., sperms are formed here.
• Testes release male sex hormone (testosterone). Its function is :

(i) Regulate production of sperms.
(ii) Bring changes at puberty.

(b) Vas deferens : It passes sperms from testes upto urethera.

(c) Urethera : It is a common passage for both sperms and urine. Its outer
covering is called penis.

(d) Associated glands : Seminal vesicles and prostate gland add their
secretion to the sperms. This fluid provide nourishment to sperms and make their
transport easy.

Sperm alongwith secretion of glands form semen.

Female Reproductive System:

(a) Ovary : A pair of ovary is located in both sides of abdomen.

• Female germ cells i.e., eggs are produced here.
• At the time of birth of a girl, thousands of immature eggs are present
in the ovary.
• At the onset of puberty, some of these eggs start maturing.
• One egg is produced every month by one of the ovaries.

(b) Oviduct or Fallopian tube:

• Receives the egg produced by the ovary and transfer it to the uterus.
• Fertilisation i.e., fusion of gametes takes place here.

(c) Uterus : It is a bag-like structure where development of the baby takes
place.

• Uterus opens into vagina through cervix.

When egg is fertilised :

• The fertilized egg called zygote is planted in uterus and develops into an
embryo.

• 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 the
exchange of glucose, oxygen and waste material.

• The time period from fertilization upto the birth of the baby is called
gestation period. It is about 9 months.

When egg is not fertilised :

• The uterus prepares itself every month to receive fertilized egg.

• The lining of the uterus becomes thick and spongy, required to support
the embryo.

• When fertilisation had not taken place, this lining is not needed any
longer.

• This lining breaks and comes out through vagina as blood and mucus.
This cycle takes around 28 days every month and called menstruation.

Reproductive Health:

Reproductive health means a total well-being in all aspects of reproduction
i.e., physical, emotional, social and behavioural.

Sexually Transmitted Diseases (STDs):

• Many diseases can be sexually transmitted such as :
Bacterial : Gonorrhoea and syphilis.

Viral : Warts and HIV-AIDS
• Use of condom prevents these infections to some extent.

Contraception:

It is the avoidance of pregnancy, can be achieved by preventing the
fertilisation of ova.

Methods of contraception:

(a) Physical barrier:

• To prevent union of egg and sperm.
• Use of condoms, cervical caps and diaphragm.

(b) Chemical methods:

• Use of oral pills
• These change hormonal balance of body so that eggs are not released.
• May have side effects.

(c) Intrauterine contraceptive device (IUCD):

• Copper-T or loop is placed in uterus to prevent pregnancy

(d) Surgical methods:

• In males the vas deferens is blocked to prevent sperm transfer called
vasectomy.

• In females, the fallopian tube is blocked to prevent egg transfer called
tubectomy.

Female Foeticide:

• The practice of killing a female child inside the womb is called female
foeticide.

• For a healthy society, a balanced sex ratio is needed that can be achieved
by educating people to avoid malpractices like female foeticide and
prenatal sex determination.

• Prenatal sex determination is a legal offence in our country so as to
maintain a balanced sex ratio.

Share this

AEI Online Tutor