how do organism reproduce, sexual reproduction, class 10, chapter 8

 

Sexual Reproduction:  The mode of reproduction that takes place with the involvement of two individuals of two different sexes i.e. male and female.

During sexual reproduction, male organism having male sex organs produces male gametes i.e. sperms which are small and motile and the female organism having female sex organs produces ova which are generally large and store food. Male and female gametes fuse to form a zygote that grows into a new organism.

Significance of Sexual Reproduction :

·         Since gametes are derived from two different organisms, it results in a new combination of genes which increases the chances of genetic variations.

·         Sexual reproduction involves division in the sex organs that reduces the DNA matter to half so that the zygote formed after fusion has the same amount of DNA as the parents it maintains DNA in a species.

Limitation of Sexual Reproduction: Sexual reproduction involves the process of combining DNA from two different organisms which may bring some undesirable features also.

Sexual reproduction in flowering plants

The reproductive parts are present in the flower.

·         The parts of the flower are sepals, petals, stamens and carpels.

·         Sepals are green structures that protect the inner parts when the flower is in bud stage.

·         Petals are colourful and attract the insects for pollination.

·         Stamens are male reproductive parts and produce pollen grains that contain male gametes. Each stamen has two parts—

·         Filament i.e. stalk and Anther i.e. swollen top part which has large number of pollen grains.

The carpel is the female reproductive part and produces ovules that contain female gametes. It has three parts—Stigma which is top sticky part and receives pollen grains during pollination.

Style which is the middle long part and ovary which is the swollen part and contains ovules. Each ovule has an egg cell i.e. female gamete.

·         The flowers may be bisexual i.e. having both stamens and carpels for example; Mustard China Rose (Hibiscus).

·         The flower may be unisexual i.e. paving either stamens or carpels for example; Papaya, Watermelon.

Pollination: The process of transfer of pollen grains from an anther to the stigma of the flower is pollination. Two types of pollination are:

(i) Self-pollination: The transfer of pollen grains from the anther to the stigma of the same flower or another flower of the same plant.

(ii) Cross-pollination: The transfer of pollen grains from the anther to the stigma of another flower or another flower of a different plant of the same species. It generally takes place with the help of some agents like insects, birds, wind and water.

Fertilization: Fertilization is the process of fusion of male and female gamete to form a zygote during sexual reproduction. Pollination is followed by fertilisation in plants. The events are

·         Pollen grains land on the stigma of the ovary.

·         Pollen tubes grow out of the pollen grains, travel through the style and reach the ovary, through micro pyle.

·         Pollen tube has two male germ cells. Each ovule has two polar nuclei and a female germ cell (egg).

·         Pollen tube releases two male germ cells inside the ovule, one of them fuses with female germ cell and forms a zygote which grows into the baby plant i.e. embryo, the fusion is known as syngamy. The other male germ cell fuses with two polar nuclei, the process is known as triple fusion. So in flowering plants two fusions take place during fertilisation. It is called double fertilisation.

Post-fertilisation changes: After fertilisation the following changes takes place in the flower.

·         Zygote divides several times and forms an embryo inside the ovule.

·         The ovule develops a tough coat and changes into the seed.

·         The ovary grows rapidly and ripens to form a fruit.

·         Petals, sepals, stamens, style and stigma shrivel and fall off.

Seed and its parts: The advantage of seed is that it protects the future plant i.e. embryo.

Seed has two parts: Cotyledons and Embryo Cotyledons store food for the future plant.

Embryo has two parts: plumule and radicle. Plumule develops into shoot and radicle develops into root.

The process of development of a seedling from the embryo under appropriate conditions is known as germination.

Sexual Reproduction in Human beings

o    Sexual reproduction is the only mode of reproduction

o    Puberty/ Adolescence is the period during adolescence when the rate of general body growth begins to slow down and reproductive tissues begin to mature.

o    A human male reaches puberty at 13-14 years, whereas a female reaches the same around 11-13 years

Following changes are observed during Puberty:

Male

o    Thick hair growth under armpits & genital area

o    Facial hair

o    Change in voice

o    Occasional Penis enlargement

o    Skin becomes oily and pimples may appear on the face

Female

o    Start of menstruation cycle

o    Breast enlargement

o    Hair growth under armpits & genital area

o    Skin becomes oily and pimples may appear on the face

Human Male Reproductive system

 Human male reproductive system consists of the following parts:

1. Testes

o    Occur in pairs

o    Produce sperms

o    Produce male hormone, testosterone

 

2.Scrotum

o    Extension of abdominal cavity containing testes

o    Protects testes

o    Maintains a temperature lower than body temperature

 

3.Epididymis

Attached to each testis is a highly coiled tube called epididymis. The sperms are stored here and they mature in the epididymis. Each epididymis leads into the sperm duct or the vas-deferens. 

 

4.Vas deferens

o    Tube like structure emerging from lower part of epididymus

o    Opens to the ejaculatory duct

o     It is meant for the passage of the sperms in the male body.

 

5.Penis It is the organ which is used to introduce semen into the female body. It is richly supplied with blood vessels.

 

6.Urethra  

        Tube like structure

o    Common passage for both semen & urine from the body to. the outside

Reproductive glands: They produce different secretions which provide nutrition as well as medium for locomotion to the sperms.
The secretions of the three glands along with the sperms is known as semen.

o    Prostate gland: produce the fluid that nourishes and also preventing sperm coagulation.

o    Seminal vesicles: Produce viscous fluid which help in sperm mobility in female

o    Cowper’s gland : Secretes mucous to lubricate female passage

 

Spermatogenesis :

Spermatogenesis is the process of production of sperm in testies.

 

Human Female reproductive system

Female reproductive system consists of the following parts:

A pair of Ovaries : Each ovary is almond shaped and present inside the abdominal cavity. Only one ovum is produced by one ovary in one month and each ovary releases an ovum in alternate months. The release of an ovum from the ovary into the abdominal cavity is known as ovulation.

Oogenesis: the process of the formation of a mature ovum from ovary.

Functions of ovary

·         To produce and release ova

·         To produce female reproductive hormones: estrogen and progesterone.

o    Fallopian tube : There are two fallopian tubes. The two fallopian tubes attach ovary to uterus.

o    transfer ovum from ovary

o    fertilization take place hear.

 

Uterus

• Pear-shaped muscular hollow structure
• Foetus develops here
• Cervix
• Narrow lower part of uterus and uterus opening.
• Vagina
• Tube like structure
• Sperm discharge occurs here
• Acts as birth canal

 

Fertilization in Human beings

Fertilization is internal in human beings

1.    Ovulation – It is the release of ovum from the ovary into the fallopian tube. With the ovulation, thickening of uterine wall takes place. Ovulation occurs every month in female after attaining puberty (i.e. after the age of 13).

2.    Copulation – During intercourse, sperm of the male is injected into the female’s vaginal tract. In one secretion there are a million sperms but only one sperm is capable of fusing with the ovum. All others are degenerated.

3.    Fertilization – The fusion of sperm & egg is called fertilization & it takes place in the fallopian tube. As a result diploid zygote is formed.

4.    Implantation– Zygote undergoes repeated divisions and fixing of the zygote into the uterine wall is called implantation. This takes place after few days of fertilization. This is now called as Embryo. Embryo in advanced stages of development is termed as Foetus.

5.    Placenta- It is the temporary formed tissue that provides nutrition to the growing embryo or developing zygote. Embryo in the uterus receives nutrients from the mother’s body through the Umbilical cord which in turn is connected to the uterine wall of mother through Placenta.

6.    Gestation period– It is the period of development of zygote into full grown foetus. In humans it is of 9 month.

7.    Parturition – Expelling a fully grown baby from mother’s body is known as parturition.

Sexual cycle in Females: Menstruation

• An egg is released from either of the ovaries every 28 days. The unfertilized egg is alive for 24 hours after ovulation. Uterus prepares itself to receive the foetus. As a result, the Endometrium thickens.
• If fertilization doesn’t take place, then no zygote is formed. Therefore, endometrium breaks which results in bleeding through vagina.
• Process of bleeding though vagina due to breakage of endometrium is termed as ‘Menstruation’. This bleeding lasts for 2-6 days. This occurs approx. 14 days after ovulation.
• Since Menstruation occurs every 28 days; this is also referred as Menstrual cycle
• • Menstrual cycle in a woman continues till 45-55 years of age, post which ovary becomes dormant. No ovulation, no menstruation occurs after this. This is termed as “Menopause”

  Reproductive Health

  Reproductive Health is a state of complete physical, mental and social well-being in all aspects of reproduction.

  o    Family planning

  Family planning is necessary to limit this huge increase in population.

  Overpopulation can give rise to serious problems like lack of food, employment and education which in turn would affect the economy and also the survival of population.

• There are several means to avoid unwanted pregnancy or maintain proper gap between children. Some of the ways are as follows:

  1.    Mechanical barrier method: sperm does not reach the egg.

  ·         Condoms: Balloon like elastic covering that tightly fits over the penis and Collects ejaculated sperms during intercourse

  ·         Copper-T: the loop or the copper-T are placed in the uterus to prevent pregnancy. Again, they can cause side effects due to irritation of the uterus.

   

  2.        Oral/ Chemical method” : Oral contraceptive pills these Does not allow ovulation to occur. they change hormonal balances, they can cause side-effects too.

  3.        Surgical method: 

  ·         Vasectomy: It involves cutting and ligating the vas deferens in males.

  ·         Tubectomy: It involves cutting and ligating Reproductive organs the fallopian tubes in females.

  ·         surgery itself can cause infections and other problems if not performed properly. Surgery can also be used for removal of unwanted pregnancies

• 

For a healthy society, the female-male sex ratio must be maintained. Because of reckless female foeticides, child sex ratio is declining at an alarming rate in some sections of our society, although prenatal sex determination has been prohibited by law.

Sexually Transmitted Diseases (STDs)

There exists many communicable diseases which spread by sexual contact during intercourse.

Bacterial infections such as gonorrhoea and syphilis,

Viral infections such as warts and HIV-AIDS.

o    HIV AIDS

o    Caused by the HIV virus which destroys the immune system of the body. There is no cure for AIDS till date. The person suffering from AIDS eventually dies due to infection.

 

To prevent STDs, ensure the following:

o    Use of condoms during intercourse

Confirm that a new partner is HIV tested before intercourse