HOW DO ORGANISMS REPRODUCE
Reproduction is biological process in which an organism produces young one of the same kind. Reproduction is not necessary to maintain the life of an organism like other life processes. Reproduction requires lot of energy to be spent then why does organism reproduce?
Different organisms have different life span. After certain time organism dies, to maintain life on earth, reproduction is required. Reproduction may be sexual when both male and female are involved and if single parent is sufficient to produce an organism of same species is asexual. Sexual reproduction introduces variation, useful variations are essential for evolution and adaptation. Reproduction also maintains population of young, adult and aged. Thus reproduction is also one of the fundamental features of living organism for continuity of species.
VARIATION AND ITS IMPORTANCE
Reproduction is the production of new organism of its own kind. Reproduction is required to continue life of an organism of a particular species in a population.
Individual produced during reproduction are always not similar to parents and also different among themselves. Difference in progeny is termed as variation. Why does this variation occur? Answer to question is during the process of reproduction DNA copying mechanism occurs. One cell divides into two. If DNA copying is highly accurate there will be no variations. Since, biological processes are always not accurate. There is some inaccuracy in DNA copying mechanism.
It will cause variation, but if changes are drastic cellular apparatus will not work and the new cell will not survive. Variation helps an individual to survive over the period of time, even if there are some changes in temperature, PH and availability of water. Thus variation is linked with stability of population of a species. It allow an organism to use a particular niche (microhabitat).
MODE OF REPRODUCTION
Organism can reproduce in two ways: →
- When only single parent is involved in reproduction is termed as asexual reproduction.
- When both (Male + Female) parents are involved in reproduction is called sexual reproduction.
ASEXUAL MODE OF REPRODUCTION
- It does not involve fusion of gametes.
- Only single parent can undergo this mode of reproduction.
- New individual produced by this reproduction are genetically identical.
- This is rapid and cheap mode of replication.
- Asexual reproduction occurs by simple fission or mitosis cell division.
- Most common types of asexual reproduction are of following:
1. FISSION: fully grown organism simply splits into two or many. If splits into two known as binary fission. Example → Amoeba, bacteria, Leishmania, paramecium, euglena. Binary fission occur in a definite orientation for eg.. Longitudinal or transverse.
If single fully grown individual give rise to many individuals known as multiple fission. Example → Plasmodium
REGENERATION: formation of a new individual from their body parts. They can also repair their lost body organs. Example → Planaria, hydra, wall lizard.
2. FRAGMENTATION: a small fragment of body can give to the development of new individual. Example → sponges, spirogyra.
3. SPORE FORMATION: in many plant species specific structures are formed called sporangia(singular – sporangium), which are not reproductive parts, but produces spore .Which are covered by a thick wall, when a mature sporangium burst spores are librated they germinate in the presence of moisture and form a new plant. Example: Rhizopus, penicillium
4. BUDDING: An out growth is formed on the surface of body due to cell division called bud. When this bud gets mature and gets de- attached from parent and form new individual in favorable condition. Example: Hydra and yeast.
5. VEGETATIVE PROPAGATION: It is a common mode of plant propagation but not known in animals. Vegetative part such as root, shoot or leaves are used to form a new plant. It is of two different type Natural and Artificial.
NATURAL METHODS OF VEGETATIVE PROPAGATION:-
- BY STEM – Example: Potato, ginger, onion, turmeric
- BY ROOT – Example: Sweet potato, Dahlia
- BY LEAF BUD – Example: Bryophyllum
ARTIFICIAL METHODS VEGETATIVE PROPOGATION
- Cutting – Example: sugarcane, roses, grapes.
- Grafting – example: rose, mango
- Layering –example :orange, jasmine
6. TISSUE CULTURE: It is known as micro propagation. A part of plant is removed from the tip; these cells are placed in a medium containing nutrient and hormones. Cells divide and re-divides form a heap of cells called callus. Callus is then transferred to another medium containing nutrients and hormones where it grows and differentiate into a plantlet and then transferred to the field. This technique is used for ornamental plants. Disease free plants can be obtained by this technique.
SEXUAL REPRODUCTION
- In sexual reproduction, gametic fusion takes place that results into a zygote formation.
- Gametes are formed by meiosis cell division. During which DNA copying mechanism occur.
- Since, DNA copying is not very accurate it brings variation in next progeny.
- Variation may be useful or harmful.
- Zygote develop into embryo which takes forms an individual.
- Gametes are always half number of chromosome. After fusion of gametes, zygote becomes diploid (two sets of chromosome).
Structure of a flower - Flower represents reproductive part of a plant.
- Flower can be bisexual, when both androecium and gynoecium are present. E.g. → Hibiscus, mustard, pea, etc… Flower can be a unisexual flower if it has only Androecium (male), or only gynoecium (female). E.g. → papaya and cueurbit.
- Outer most part of flower is called calyx which is a group of sepals.
- 2nd (whorl) outer most is corolta, which is the group of petals.
- Stamen (androecium) represent male part of flower made up of Anther and filament.
- Carpel (gynoecium) represent female part of plant. It is made up of stigma, long style and swollen ovary.
- Male germ cell (pollen) are produced in Anther.
- Female germ cell (ovum) is produced in ovule which is present inside ovary.
- Stigma is the landing platform for pollen grains
- Transfer of pollen grains from anther to stigma is called pollination.
- Pollination can occur by itself if pollen grain lands on the stigma of same flower. Cross pollination occurs if pollen grains land on the stigma of other flower of same species.
- Pollen grains germinate on stigma and form a long pollen tube to reach female germ cell, which is present in ovule of ovary.
- Fusion of male and female germ cell form zygote. The process is known as fertilization. (In angiosperm, there is double fertilization and triple fusion)
After fertilization different parts of followers shows following features
- Sepals →shrivel or falls off.
Petals → shrivel or falls off.
Stamens → shrivel or falls off.
Stigma → shrivel or falls off.
Style → shrivel or falls off.
- Zygote → embryo
- Ovule → seed Ovary → fruit
Seed is covered by a tough seed coat outer testa and inner tegmen. It contain embryo inside which on germination forms a plant plumule of embryo develop into shoot and radical on germination develop root. Seed germination requires optimum temperature and moisture.
REPRODUCTION IN HUMAN BEINGS
- Human being shows only sexual mode of reproduction.
- Sexual maturity in human starts in early teenage years.
- Sexual maturity involves proportional changes in the body, new sensations and new features.
- In boys, their hair growth in new body parts (armpits and genital area) , skin becomes oily, voice begin to crack, etc..
- Girls begin to menstruate along with other secondary sexual characters.
- These entire changes takes place slowly over a period years and this period is known as adolescence.
- When an adolescent reach sexual maturity and become capable of reproduction is said to be puberty.
- Sexual maturation is required at this age in order to create a germ cell and to participate in sexual reproduction.
MALE REPRODUCTIVE SYSTEM
- Human reproductive system is made up of a pair of testis. The testes are located in scrotum outside the abdominal cavity.
- Testes has about 20C less temperature than the body, which is required for the formation male germ cell(sperm)
- Testes perform two important roles (a) formation of male germ cell cells. (b) Secretion of testosterone that brings secondary sexual traits in boys at the time of puberty.
- Sperm formed inside testes are transported by vas deferens till urethra.
- Urethra is a common passage for sperm and urine. Urethra receives secretion of prostate gland, seminal vesicle and bulbourethal gland.
- Secretion of accessory glands provides nutrition, motility and easy path to reach female genital track.
- Urethra runs through the penis and open outside as male genital pore.
- Sperms are tiny cells with (half number of chromosome) genetic material. It has a long tail and a head.
- Tail helps sperm to reach towards female germ cell.
FEMALE REPRODUCTIVE SYSTEM
- Female reproductive system is a system has a pair of ovary as primary sex organs.
- Each ovary lies near the kidney of its side, ovary is almond shaped.
- Function of ovaries is to:
1. secrete estrogen and progesterone hormone
2. production of female germ cell(egg)
- Each ovary already contains thousands of immature eggs prior to birth of a female. At puberty egg starts maturing in a definite way.
- One egg is mature in 28 days in one of the ovary.
- Fusion of egg (ovum) and sperm occurs at fallopian tube (oviduct).
- Two oviduct (fallopian tube) units to form a sac like elastic structure called uterus.
- Fertilized egg is also called zygote, it divides and re-divides to form embryo
- Embryo is in the form of a ball of cells. Embryo gets attached to the inner lining of uterus. This process is called implantation.
- Implanted embryo gradually changes into foetus by the process of organ formation.
- An intimate association between maternal uterine wall and foetus is called placenta.
- Placenta is a disc like structure contains villi from embryo side and blood space from maternal side.
- Placenta provides nutrition and oxygen to foetus and In return waste material and carbon dioxide to maternal uterine wall.
- Development of foetus takes about 38 to 40 weeks. Child is born due to contraction of uterine muscles in a rhythm.
- Uterus opens into vagina through cervix.
- Vagina is called birth canal and it is also the passage for menstrual flow.
- What happens if the egg is not fertilized? It remains alive for about a day. At the same time uterus also prepares itself to receive fertilized egg (zygote) every month.
- Inner lining of uterus gets thick to provide nutrition to embryo.
- If no fertilization occurs, spongy and thick lining of uterus is not required, thus it slowly breaks and comes out through vagina, called menstrual flow, it has blood and mucous.
- Menstruation lasts for about 3 to 5 days. It repeats after every 28 days.
REPRODUCTIVE HEALTH
According to WHO reproductive health means well being in all aspects of reproduction, i.e.., physical, emotional, social and behavioral.
- It is very significant to maintain good reproductive health. It can achieve by having knowledge of STD.
- STD refers to sexually transmitted diseases, all STD are not transmitted by sexual contact such as gonorrhea and syphilis is bacterial, whereas wort is viral.
- AIDS is transmitted by transfer by HIV virus from while unprotected sexual act.
- If female is physically and mentally not ready for pregnancy then there are many ways to avoid it by various contraceptive methods such as:
1. Mechanical method – e.g. Condoms
2. Intrauterine devices(IUCD) – e.g. Cu – T
3. Oral contraceptive pills – e.g. (tablets of hormones) Saheli
4. Surgical method – Male → vasectomy
Female → Tubectomy
- Contraceptive also causes side effects such as Cu – T some time causes irritation in uterus, oral pills causes nausea, abdominal pain.
- Surgical methods are permanent with no side effect, but they are not reversible.
- There should be no illegal sex selective abortion (MTP) as for a healthy society there is a need of proper male and female sex ratio.
- Contraceptive methods should be used to control population not for female foeticide.
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