How Do Organisms Reproduce

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Introduction

• Reproduction is the most basic level of making copies of the similar ones.
• Inside the nucleus there is chromosome and inside the chromosome contains the genetic material known as DNA( Deoxyribo-nucleic acid ).
• DNA has the information for making proteins.
• If the proteins are changed , the information will be altered and hence change in the body designs.
• If the proteins are changed , the information will be altered and hence change in the body designs.
• Reproduction is essential for the stability of population of species.
• Variation can be defined as any difference between the individuals in a species or groups of organisms of any species.

Reproduction

Asexual Reproduction

• Fission:

1. Fission involves division of unicellular organism/cell into two daughter cells.
2. This division can take place at any plane of axis.
3. Eg – protozoa , amoeba , bacteria.
4. This kind of reproduction is oriented in leishmania which causes kala-zaar.
5. Leishmania has a whip-like structure.
6. Plasmodium which causes malaria undergoes multiple fission.
7. Yeast reproduce by putting out small buds, that separate out from the parent body to become new individuals.

Binary fission in leishmania

• Budding :

1. This kind of reproduction is most prominently seen in hydra.
2. Here a bud develops as an outgrowth due to repeated cell division at one site.
3. These buds grows into tiny individuals.
4. These buds gets detached from the parent when become mature.

Diagram showing budding in hydra

• Fragmentation :

1. Fragmentation involves breaking up of an organism into smaller fragments and then these fragments grow to become new individuals.
2. Eg – Spirogyra

• Regeneration :

1. In this method if the individual is cut into pieces then each piece turns to become a new individual.
2. Eg- Planaria, hydra.
3. Regeneration is carried out by specialized cells.
4. These cells divide, proliferate, and make large number of cells.

• Vegetative Reproduction

1. This mode of reproduction is prominently seen in plants.
2. It involves processes such as layering and grafting.
3. Eg – Plants such as sugarcane, roses, and grapes.
4. It can be seen in plants which have lost the capacity to produce seeds such as banana , rose, orange and jasmine.
5. Another advantage of vegetative propagation is that all plants produced are genetically similar enough to the parent plant to have all its characteristics.
6. Another prominent example is buds produced on the margins of the Bryophyllum leaf, when these buds get detached from the plant body it falls on the soil to develop into new plants.

• Spore Formation

1. Most often bread is invaded by the fungi.
2. The thread-like structure which is scattered over any food material is the hyphae of fungi.
3. The aerial hyphae are known as sporangium, which is a stick-like structure with tiny blob on the stick.
4. These blob-like structure contains spores.
5. When these spores are released into the air current gets scattered and germinates into a new individual.
6. During unfavorable conditions these spores are covered by thick walls.
7. When the favorable conditions are back the thick walls are ruptured to release these spores.

Sexual Reproduction

• This process involves two parents ie. both male and female , and fusion of their gametes to produce a zygote (unicellular) and then a developed organism.

• Variations occurs among individuals due to sexual mode of reproduction.

• DNA gets combined from both the parents & gets accumulated in the offspring.

• Gamete cells/reproductive cells undergo meiotic division , in this kind of division the chromosome number gets halved, so that when each parent cell gets fused the diploidy is maintained.

• Male germ cells are generally motile.

• Female germ cell is static and large.

Sexual Reproduction In Plants

• Unisexual flower : Flowers which contain either the male reproductive part (stamen) or the female reproductive part (pistil). Eg- Papaya, watermelon.

• Bisexual flower : Flowers which contain both male and female reproductive parts (ie. both stamen and pistil). Eg- Hibiscus, mustard.

• Stamen is the reproductive part of the male ,it consists of 2 prominent parts:

1. A long filamentous structure known as filament.
2. A bilobed structure known as anther, it has pollen grains inside.
3. Pollen grains are the male gametes. ( Gametes are reproductive cells ).

• Pistil is the reproductive part of female ,it consists of 3 prominent parts:

1. An exposed part known as stigma(sticky), which acts as landing platform for pollen grains.
2. A long slender part known as style, which transports pollen grain to the ovule, for fertilization.
3. The basal part swollen part known as ovary inside which ovule is placed.
4. After fertilization ovule turns into seed and ovary into fruit.

Image of pistil

Image of stamen

Self – pollination	Cross – pollination
Transfer of pollen grains from anther to the stigma of the same flower.	Transfer of pollen grains from anther of a flower to stigma of another flower.
It doesn’t include any agents to transfer pollen grains. Self pollinated flowers are generally not colorful or attractive.	It includes agents like wind, water and insect to transfer the pollen grains. Cross pollinated flowers are generally colorful and attractive.

Fertilization

1. Pollen grains are released from the anther and then lands on the stigma.
2. Stigma shows receptivity to pollen grains belonging to same species, and rejecting pollen grains of other species.
3. Then germination of pollen grains occurs, a pollen tube is produced thus providing a pathway for transferring the pollen grains to the ovule.
4. Fusion of male(pollen grains) and female(ovule) gametes to produce a zygote is known as fertilization.
5. After fertilization, ovule turns into seed, and ovary into fruit.
6. After fertilization, the petals, sepals, stamens, style and stigma may shrivel and fall off.

Sexual Reproduction In Animals

• Puberty is the time in life when a boy or girl becomes sexually mature. It is a process that usually happens between ages 10 and 14 for girls and ages 12 and 16 for boys. It causes physical changes, and affects boys and girls differently.

• In girls:

1. The first sign of puberty is usually breast development.
2. Then hair grows in the pubic area and armpits.
3. Menstruation (or a period) usually happens last.

• In boys:

1. Puberty usually begins with the enlargement of testicles and penis.
2. Then hair grows in the pubic area and armpits.
3. Muscles grow, the voice deepens, and facial hair develops as puberty continues.

• Male reproductive system:

1. Testes are the primary reproductive organs outside the abdominal cavity which is enveloped inside a sac-like structure known as scrotum.
2. Testis produce the male germ/reproductive cells/gametes known as sperm.
3. Testis also produce the male hormone known as testosterone.
4. Sperms produced are delivered to the urethra through vas deferens.
5. Vas deferens unites with tube coming from urinary bladder.
6. Urethra acts as common passage for both urine and sperms.
7. Fluid from seminal vesicle, prostate and bulbourethral glands constitutes the seminal fluid.
8. This seminal fluid when mixed with sperm becomes semen.

• Female reproductive system:

1. The primary reproductive organ in females is ovary which produces ovum.
2. Ovum are female reproductive cells/gamete cells.
3. During the birth, females contain thousands of immature eggs.
4. During puberty, eggs starts maturing.
5. One egg is released each month alternatively from either of the ovaries.
6. Egg /ovum is carried out from ovaries to the womb/uterus through the fallopian tube also known as oviduct.
7. Uterus is an elastic bag-like structure, which opens into vagina through cervix.

Sexual Reproduction In Animals

• The sperms enter through the vaginal passage during sexual intercourse. They travel upwards and reach the oviduct where they may encounter the egg. The fertilized egg (zygote) starts dividing and form a ball of cells or embryo. The embryo is implanted in the lining of the uterus where they continue to grow and develop organs to become foetus. We have seen in earlier sections that the mother’s body is designed to undertake the development of the child.

• Hence the uterus prepares itself every month to receive and nurture the growing embryo. The lining thickens and is richly supplied with blood to nourish the growing embryo.

• The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. This is a disc which is embedded in the uterine wall.

• It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo.

• The developing embryo will also generate waste materials which can be removed by transferring them into the mother’s blood through the placenta.

• The development of the child inside the mother’s body takes approximately nine months. The child is born as a result of rhythmic contractions of the muscles in the uterus.

Reproductive Health

Birth Control Methods

• Condoms are physical barriers which prevents any kind of sexually transmitted diseases.

• Condoms actually acts as barrier preventing sperm and ovum physically meeting.

• These can be worn both on the penis and inside the vagina.

• There are some other contraceptives which alter the hormonal balance of the body thus eggs are not released from the ovaries and hence no fertilization will take place.

• Other contraceptive devices such as the loop or the copper-T are placed in the uterus to prevent pregnancy.

• Two kinds of surgical methods :

1. Vasectomy : surgical removal of a part of vas deferens.
2. Tubectomy :surgical removal of a part of fallopian tube/ oviduct.

Vasectomy

Tubectomy

• Prenatal sex determination has been prohibited to prevent the increasing case of female feticides and to maintain a proper child sex ratio.

• Condoms are physical barriers which prevents any kind of sexually transmitted diseases.

• Condoms actually acts as barrier preventing sperm and ovum physically meeting.

• These can be worn both on the penis and in the vagina.

• There are some other contraceptives which alter the hormonal balance of the body thus eggs are not released from the ovaries and hence no fertilization will take place.

• Other contraceptive devices such as the Lippes loop or the copper-T are placed in the uterus to prevent pregnancy.