Chapter 8 How do Organism Reproduce?

Reproduction is a process by which every living organism makes a copy like itself as seen in parents to their children. This is only done because of replication of DNA (deoxyribonucleic acid) by transferring the genetic information from the parents to their offsprings or simply we can say that passing their physical or mental character genetically to main the chromosome number of species.

Variations are beneficial to the species than individual because during certain environmental conditions their is so drastic change that their survival  of species becomes difficult. For example, if their is sudden rise in temperature of water, then most of the bacteria living in that water would die. So only few variants that can resistant to heat would be able to survive. However, if these few variants were not there, then the entire species of bacteria would have  destroyed. Thus, these variants help in the survival of the species.So all variations are not necessarily beneficial for the individual organisms.

Asexual reproduction occurs in different ways in different organisms. So, binary fission and multiple fission both are the types of asexual reproduction.

Binary fission:- It is the division of parent cell into two small daughter nucelii. Mainly three types of binary fission shown in some organisms- Irregular, longitudinal, transverse. Like in protozoan protists, the replicated chromosome separated by intranuclear mitosis and starts dividing. Then, the cytoplasm constricts between two separating nuclei and forms two equal sized daughter nuclei with a nucleus (eg. Amoeba shows irregular fission, Euglena shows longitudinal fission and Paramecium shows transverse binary fission). Or like in Planarians also, they are divided by transverse binary fission with the equal sized daughter individuals.

Multiple fission:- Unlike binary fission, the division of parent cell will be into many small daughter nuclei. And it can be shown in mainly two organisms- Plasmodium or Amoeba. Plasmodium is a malarial parasite, when multiple fission takes place in adults or in its encysted zygote (called sporogony) and their daughter individuals are then called merozoites.

Spores are produced from sporangium, they do not require any medium for the dispersal and are light in weight, so can easily be transferred for germination. Spores can be remain alive but not actively growing till their favourable condition comes, they help organisms to survive or to get over the stress phase. Many spores can transferred at once, so reproduction is very quick, that’s why organisms are benifitted if they reproduces through spores. Major advantage is that spores are large in number, so population will also increases and survival chances are also high.

Regeneration is the process of renewal, restoration and growth of tissues to the organisms itself that makes organisms or ecosystem resillience to the natural fluctuation that is done by the disturbance. And in complex organisms, different tissues and organs have their different structures. So, the rengeneration process is unable to give rise to new individuals from complex organisms.

Vegetative propagation occurs without seeds. The lower plants reproduce vegetatively through budding, fission, fragmentation, buds, spores etc. Every part of the plant such as roots, stems, leaves and buds takes part in vegetative propagation and can give rise to same new plants. Plants which have superior traits are vegetatively propagated cause they can give rise to identical plants. Vegetative propagation is of two types:-

1. Natural vegetative propagation

2. Artificial vegetative propagation 

Vegetative propagation is the only method of reproduction in those plants who lost their capacity to produce seeds, eg. Banana, oranges, rose etc. Vegetative propagation can be done by plant tissue culture for the production of disease free plants.

DNA is a genetic material which carries information from the parents to their offspring by the process DNA replication in which complementary strand is made from the template strand of DNA with the help of various enzymes. If any error or mutation occurs in copying DNA, then there may be possibility of abnormality occurance in the offsprings from their parents. That’s why copying of DNA without an error is an essential process of reproduction.

Pollination:- Transfer of pollen grain from the anther (male part of the flower) of stamen to the stigma (female part of the flower) of carpel is known as pollination. It is of two types:-

1. Self pollination:- It involves the transfer of pollen grains from the anther to the stigma of the same flower or genetically similar flower.

2. Cross pollination:- It involves the transfer of pollen grains from the flower of one plant to the stigma of the flower of another plant.

Transfer of pollen grains can be occur through many agents like anemophily (wind pollination), hydrophily (water pollination), entomophily (insect pollination), ornithophily (pollination by birds) and chiropterophily (bat pollination). 

Fertilisation:- Fusion of haploid male gamete (spermatozoan) and a haploid female gamete (ovum) and they together forms a diploid cell, i.e, zygote is known as fertilisation.

Seminal vesicles and prostate gland both are the accessory sex glands in male reproduction system.seminal vesicle secrete fluid that consist of nutrientsthat support sperm until fertilisation occurs.

Seminal vesicles contains hormone called prostaglandins, which stimulate contraction in the female reproductive system for the transportation of sperms to the oviduct with ovum.

Prostate gland secretes thin, milky and acidic fluid which is discharged into the part of urethra. It also contains sperms nutrient and some anticoagulant enzymes. Their secretion activates the sperms to swim fluently.

At the time of puberty, many changes can be seen in girls. Hormonal changes can be seen, girl’s body increase in size like hips become rounded in shape and they get more curvy waist, voice become thin. Vagina, breast size and nipples size get increases or we can say they begin to develop. And at the time of puberty menstruation occurs.

Embryo gets nourishment inside the mother’s body through the placenta. Placenta is an organ which forms in uterus during the pregnancy and is less than 1kg in weight. It helps to bring the foetus and the maternal blood close enough for the exchange of oxygen and nutrition and it also removes the waste product from the baby’s blood. And, it also has the umbilical cord (naval string) which is attached near the centre of placenta to the foetus.

Copper- T cannot help in protecting a woman from sexually transmitted diseases. An Intrauterine device is present which contains copper in female’s body. It is used for the birth control and as a contraceptive method.

Yeast

Yeast is a unicellular fungi and reproduces asexually by the formation of spores. During the process of budding, the parent cell produces a small bud which grows in size. Then, the parent cell nucleus divides and the daughter nuclei goes in the bud. And then the bud gets detached and grow separately like a new individual on the substratum.

Vas deferens

Vas deferens is a tiny muscular tube found in male reproductive system, which carries sperms from epididymis to the ejaculatory ducts.

(d) Pollen grains

Anther is the male part of the flower. It consists of pollen grains and they carried to the stigma (female part of the flower) through various agents like butterflies, wind, water for the process of reproduction.

Reproduction is a process to produce a young one similar to their parents genetically or morphologically. There are two modes of reproduction:- asexual or sexual reproduction.

Sexual reproduction is the process of forming a diploid cell zygote from one haploid male gamete or one haploid female gamete. In this two parents are involved, and when a offspring is formed than variation occurs and variation is the key factor of the evolution. If there is no variation, population cannot respond to the changing environment and may face an risk of being extinct from the environment. 

Asexual reproduction is the process of making two or more daughter cells from one parent cell, i.e, only one parent is involved. So, there is no variation occurs as in sexual reproduction occurs. It is dynamic, static where no evolution occurs in their morphological characters, where each offspring is genetically or morphologically identical to each other.

The long term survival period happens in sexual reproduction than asexual because of the variation. When genetic variation occurs, it helps the organism to survive in the drastic environmental changes.

Testis are the primary sex organs in male reproductive system. It helps in maintaining the health of male body. sperm  produces  in seminiferous tubules, and also produces a hormone like androgen  called testosterone and secrets inhibin protein. Testosterone is the male sex hormone helps in developing the male reproductive tissues like testis or prostate or in the growth of body muscles and hair.

Menstruation occurs at the time of puberty in females. Menstruation occurs to prevent the pregnancy phase. It releases the tissues which supports the foetus to grow during the pregnancy. Menstruation is the bleeding phase, where an egg released by female does not get fertilized or attached to the uterine wall then uterine lining dies due to deficiency of hormone (progesterone), and the lining of fallopian tube breaks down and then the blood oozes out from the ruptured vessels through the vaginal opening.

There are various birth control methods which prevent fertilization (meeting of a sperm to ovum to form a zygote) is known as contraception. There are mainly three major types of contraception:-

1. Temporary methods

2. Permanent method

3. Medical termination of pregnancy

• Temporary methods:- they contain natural, barrier or physiological methods of the birth control. In natural, Lactation amenorrhea (absence of menstruation) method is used, where there is intense lactation occurs during the absence of periods in females which prevents from the birth control. In barrier methods- condoms, cervical caps, vaults and Intrauterine devices are used for the contraception. Or, in physiological devices oral pills or injections can be taken for the birth control which confirms the ovulation occurance in females by secreting the FSH (follicle stimulating hormone) or LH (Luteinizing hormone). 

• Permanent method:- it is a surgical method for the birth control. In man it is known as Vasectomy or in females it is known as tubectomy. Vasectomy is the process of removal of short segment of each vas deferens and tying up of the remaining ends tightly with the surgical thread. And tubectomy is the process of removal of fallopian tube and the remaining ends are tied up tightly with the surgical thread.

• Medical termination of pregnancy:- also called induced abortion. It is the voluntary termination of a pregnancy before the foetus making. It is done to get rid of unwanted pregnancy, rapes etc.

 In unicellular organisms, asexual reproduction occurs where there is only one parent is involved and no gamete production or parthenogenesis occurs, where one parent cell gets divided into two or multiple daughter cells by binary or multiple fission (eg. Binary fission shown in bacteria, amoeba, planarians and multiple fission shown in plasmodium).

In multicellular organisms, sexual reproduction occurs where two parents are involved to form a zygote or parthenogenesis occurs. All mammals human beings, apes etc. show sexual reproduction process where mother shows viviparity, i.e, gives birth directly to the young ones.

Organisms survive only to reproduce. Reproduction is very important for the stability to populations of species by extending their genernation or the population of same species from the existing generation. It also helps in the study of evolution by recording the data of their ancestors to the new generation of same species.

There can be many reasons for adopting contraceptive methods:-

1. The main reason for adopting the contraceptive methods is birth control or the population control.

2. Condoms are the safeguard against the infection of AIDS (acquired immune deficiency syndrome) or STD (sexually transmitted diseases)

3. The induced abortion method of contraception is used to get rid of unwanted pregnancy by the unprotected intercourse, when women get raped by someone, or where mother’s life or foetus is in danger and when women is not able to conceive the baby due to the weak immune system of the baby.