Table At Glance

Points To Remember

REPRODUCTION IN ORGANISMS

Reproduction:

defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself.

Asexual reproduction:

  • Offsprings produced by single parents.
  • Without involvement of gamete formation
  • Offsprings are genetically identical to their parents.

Methods of asexual reproduction:

  • Cell division as a method of asexual reproduction as in Protista and monera.
  • Binary fission e.g. Amoeba, Paramecium.
  • Budding: e.g. yeast.
  • Asexual reproductive structures:
    • Zoospores: aquatic fungi, Chlamydomonas.
    • Conidia: Penicillium.
    • Bud:Hydra
    • Gemmules: sponges.
  • Vegetative propagation units in plant: (Vegetative propagules)
    • Runner, rhizome, sucker, tuber, offset, bulb.

Sexual reproduction:

  • Involvement of single or two individual.
  • Production of male and female gametes ( haploid)
  • Gametes fused to form a diploid zygote.
  • Zygotes developed into new organism.
  • The offsprings are not genetically identical with their parents.

Features of sexual reproduction:

  • Period between birth and sexual maturity is called juvenile phase. It is known as vegetative phase in plant.
  • Bamboo species flower only once in their life time generally after 50-100 yr.
  • Strobilanthus kunthiana (neelakranji) flowers once in 12 years.
  • Oestrus cycle: cyclical changes during reproduction in non-primate mammal like cows, sheep, rats, deers, dogs, tiger etc.
  • Menstrual cycle: cyclical changes during reproduction in primate mammals like monkeys, ape, and humans.
  • Seasonal breeders: reproductive cycle takes place in favourable seasons as in wild animals.
  • Continuous breeders: reproductively active throughout their reproductive phase.

Pre-fertilization events:

  • Process of gamete formation is gametogenesis.
  • Two gametes are similar in appearance are called homogametes(isogametes).
  • Gametes produced are of two morphologically distinct types called heterogametes.
  • Male gamete is called antherozoids or sperm and the female gamete is called ovum or egg.

Sexuality in organism:

  • Plant having both male and female sex organ called homothallic or monoecious.
  • Plants having only one sex organ is called heterothallic or dioecious.
  • In flowering plants, the unisexual male flower is staminate, i.e. bearing staments, while the female is pistillate or bearing pistils.
  • Animal having one type of reproductive system, called unisexual.
  • Animal having both male and female reproductive system, called hermaphrodite or bisexual.

Cell division during gamete formation:

  • Gametes in all heterogametic species two types namely male and female.
  • Gametes are always haploid irrespective of parent’s ploidy.
  • A haploid parent produces gametes by mitotic division.
  • Diploid parent produces gametes by meiotic division.
  • In diploid organisms specialized cells called meiocytes (gamete mother cell) undergo meiosis to produce haploid gametes.

Gamete transfer:

  • Male and female gamete must be physically brought together to facilitate fusion called fertilization.
  • In most cases male gametes are motile, female gametes are non-motile.
  • In case of few fungi and algae, both male and female gametes are motile.
  • In most cases water is the medium for gamete transfer.
  • Male gametes are produced in several thousand times the number of female gametes produced to compensate the loss during transfer.

Fertilization:

  • Fusion of male and female gamete is called fertilization or syngamy.
  • The female gamete undergoes development to form new organism without fertilization. This phenomenon is calledparthenogenesis.
  • Gametic fusion takes place outside the body i.e. water is called external fertilization.
  • Their must be synchrony of gamete release, large number of gametes released to enhance the chance of fertilization.
  • Enable the individual to produce large number of offsprings.
  • A major disadvantage is that the offsprings are extremely vulnerable to predators.
  • Fertilization takes place inside the body is called internal fertilization.

Zygote:

  • Formation of zygote after fertilization is universal in all sexually reproducing organisms.
  • Zygote is formed usually in water in case of external fertilization.
  • Zygote is formed inside the body of the organism in internal fertilization.
  • Zygote of fungi and algae develops a thick wall that is resistant to dessication and damage.
  • Organism with haplontic life cycle, zygote undergoes meiosis to produce haploid spores.

Embryogenesis:

  • Development of zygote into an embryo is called embryogenesis.
  • Zygote undergoes cell division (mitosis) and cell differentiation.
  • Oviparous animal which lays eggs and development takes place inside egg.
  • Viviparous animal gives birth to the young. The development takes place inside the body of the female.
  • In plants:
    • Zygote developed into embryo.
    • Ovule developed into seed
    • Integument of the ovule developed into seed coat.
    • Ovary developed into fruit.
    • Ovary wall developed into pericarp.

SEXUAL REPRODUCTION IN FLOWERING PLANTS
Pre fertilization: structure and events:
  • Hormonal and structural changes in plants leads to development of flower,
  • Androecium consists of a whorl of stamens represents male sex organ.
  • Gynoecium represents the female reproductive organ.

Stamen, Microsporangium and Pollen grain:

  • Typical stamen consists of two parts, long and slender stalk called filament and terminal bilobed structure calledanther.
  • Atypical angiosperm anther is bilobed.
  • Each lobe have two theca i.e. dithecous.
  • Each anther contains four microsporangia located at the corners, two in each lobe.
  • Microsporangia become pollen sacs and are packed with pollen grains.

Structure of microsporangium:

  • Each microsporangium surrounded by four wall layers
    • Epidermis
    • Endothecium
    • Middle layer.
    • Tapetum.
  • The innermost layer is tapetum which is multinucleated, with dense cytoplasm; it nourishes the developing pollen grain.
  • The centers of each microsporangium contain homogenous cells called sporogenous tissues.

Microsporogenesis:

  • The process of formation of microspores from pollen mother cell through meiosis is called microsporogenesis.
  • The sporogenous tissue of microsporangium differentiated into microspore mother cell or pollen mother cell.
  • Each microspore mother cell undergoes meiosis and gives rise to haploid microspore tetrad.
  • On dehydration microspore tetrad dissociated to form four microspores.
  • Each microspore developed into a pollen grain.

Pollen grain:

  • Pollen grain represents the male gametophytes.
  • It is spherical and measuring about 25-50 micrometer in diameter.
  • It is covered by two layers.
  • The hard outer layer called the exine is made up of sporopollenin, which is one of the most resistant organic materials known. It can withstand high temperature and strong acids and alkali. No enzyme can degrades sporopollenin is so far known.
  • The exine has prominent apertures called germ pore where sporopollenin is absent.
  • The inner wall of pollen grain is called intine. It is thin and continuous layer made of cellulose and pectin.
  • On maturity the pollen grain contains two cells, the vegetative cell and generative cell.
  • The vegetative cell is bigger, has abundant food reserve and a large irregularly shaped nucleus.
  • The generative cell is small and floats in the cytoplasm of vegetative cell.
  • In 60% of angiosperms, pollen grains are shed at this 2-celled stage.
  • In others the generative cell divides mitotically to form two male gametes before pollen grain are shed (3-celled stage).

Economic importance of pollen grain:

  • Pollen grain may cause severe allergies and bronchial afflictions.
  • It may cause chronic respiratory disorders – asthma, bronchitis, etc.
  • Pollen grain of Parthenium or carrot grass causes pollen allergy.
  • Pollen grains are rich in nutrients hence used as pollen tablets for food supplements.
  • Pollen consumptions increase performance of athletes and race horses.
  • After shedding the viability depends on temperature and humidity.
  • In wheat and rice the pollen grain lose viability within 30 min. of their release.
  • In Rosaceae, Leguminoseae and Solanaceae they remain viable for months.
  • Pollen grain can be preserved for years in liquid nitrogen (-196oC).

The Pistil, Megasporangium (ovule) and Embryo Sac:

  • The Gynoecium represents the female reproductive part of the flower.
  • The Gynoecium may contain single pistil (monocarpellary) or may have more than one pistil (multicarpellary).
  • Fused pistils are called syncarpous and free pistils are called apocarpous.
  • Each pistil has three parts the stigma, style and ovary.
  • Inside the ovary is the ovarian cavity (locule).
  • The placenta located inside the ovarian cavity.
  • Megasporongia or ovules arise from the placenta.
  • The number of ovule inside the ovary may be single or many.

The Megasporangium (Ovule):

  • Ovule is a small structure attached to the placenta of locule with a stalk called funicle.
  • The body of the ovule fused with the funicle in the region called hilum.
  • Hilum is the junction between the funicle and ovule.
  • Each ovule has one or two protective envelops called integuments.
  • Integument covered the ovule except an opening at the top called micropyle.
  • Opposite of the micropylar end, is the chalaza, representing the basal part of the ovule?

Megasporogenesis:

  • The process of formation of megaspores from the megaspore mother cell is called Megasporogenesis.
  • In the centre of the ovule there is a mass of tissue called nucellus.
  • Cells of nucellus have abundant reserve food materials.
  • One cell of the nucellus towards micropylar end differentiated into megaspore mother cell (MMC).
  • It is a large diploid cell, dense cytoplasm with prominent nucleus.
  • The MMC undergo meiotic division resulting four haploid megaspores.

HUMAN REPRODUCTION
THE MALE REPRODUCTIVE SYSTEM.
  • Located in the pelvis region.
  • Male reproductive system includes
    • A pair of testes.
    • Accessory ducts.
    • Accessory glands.
    • External genitalia

Testes:

  • Located outside the abdominal cavity within a pouch called scrotum.
  • Scrotum provides low temperature required for spermatogenesis.
  • Each testis is about 4 to 5 cm length and 2 to 3 cm width.
  • Each testis has about 250 compartments called testicular lobules.
  • Each lobule contains one to three seminiferous tubules.
  • Seminiferous tubules lined by male germ cells and Sertoli cells.
  • Male germ cell undergoes meiosis and produce sperm.
  • Sertoli cells provide nutrition to the germ cell and the sperm.
  • In between the seminiferous tubule there is interstitial cell or Leydig cell.
  • Leydig cells produce testicular hormones called androgen(testosterone).

Accessory ducts:

  • Includes rete testis, vasa efferentia, epididymis and vas deferens.
  • Seminiferous tubules open into vasa efferentia through rete testis.
  • The vasa efferentia leaves the testis and open into epididymis.
  • The epididymis leads to vas deferens that ascends to the abdomen through inguinal canal and loops over the urinary bladder.
  • Vas deferens receives a duct from seminal vesicle and opens into the urethra as the ejaculatory duct.
  • Urethra originates from the urinary bladder and extends through the penis to its external opening called urethral meatus.

Accessory glands:

  • Includes
    • Paired seminal vesicle
    • A prostate gland
    • Paired bulbourethral gland.
  • Secretion of these glands constitutes the seminal plasma.
  • Seminal plasma rich in fructose, calcium, and certain enzyme.
  • Secretion of bulbo-urethral glands helps in lubrication of penis.

External genitalia:

  • Penis is the external genitalia.
  • It is made of special tissue that helps in erection of the penis to facilitate insemination.
  • The enlarged end of penis is called glans penis.
  • Glans penis is covered by a loose fold of skin called foreskin.

THE FEMALE REPRODUCTIVE SYSTEM

  • Located in the pelvic region of the female.
  • The female reproductive system includes:
    • A pair of ovaries
    • A pair of oviduct.
    • Uterus
    • Cervix
    • Vagina
    • External genitalia.
    • A pair of mammary gland.

Ovaries:

  • It is the primary female sex organs that produce the female gamete (ovum).
  • It also produces several steroid hormones.
  • The ovaries located in the lower abdomen.
  • Each ovary is about 2-4 cm in length.
  • Connected to the pelvic wall and uterus by ligaments.
  • Each ovary is covered by thin epithelium which encloses the ovarian stroma
  • The ovarian stroma has two zones
    • A peripheral cortex.
    • An inner medulla.

Oviduct:

  • Oviducts, uterus and vagina constitute the female accessory ducts.
  • Each fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the uterus.
  • Close to the ovary the oviduct has a funnel shaped structure called infundibulum?
  • The edges of the infundibulum possess finger-like projections called fimbriae, which helps in collection of the ovum after ovulation.
  • The infundibulum leads to a wider part of the oviduct called ampulla.
  • The last part of the oviduct is called isthmus which joined to uterus.

REPRODUCTION IN ORGANISMS

Reproduction:

defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself.

Asexual reproduction:

  • Offsprings produced by single parents.
  • Without involvement of gamete formation
  • Offsprings are genetically identical to their parents.

Methods of asexual reproduction:

  • Cell division as a method of asexual reproduction as in Protista and monera.
  • Binary fission e.g. Amoeba, Paramecium.
  • Budding: e.g. yeast.
  • Asexual reproductive structures:
    • Zoospores: aquatic fungi, Chlamydomonas.
    • Conidia: Penicillium.
    • Bud:Hydra
    • Gemmules: sponges.
  • Vegetative propagation units in plant: (Vegetative propagules)
    • Runner, rhizome, sucker, tuber, offset, bulb.

Sexual reproduction:

  • Involvement of single or two individual.
  • Production of male and female gametes ( haploid)
  • Gametes fused to form a diploid zygote.
  • Zygotes developed into new organism.
  • The offsprings are not genetically identical with their parents.

Features of sexual reproduction:

  • Period between birth and sexual maturity is called juvenile phase. It is known as vegetative phase in plant.
  • Bamboo species flower only once in their life time generally after 50-100 yr.
  • Strobilanthus kunthiana (neelakranji) flowers once in 12 years.
  • Oestrus cycle: cyclical changes during reproduction in non-primate mammal like cows, sheep, rats, deers, dogs, tiger etc.
  • Menstrual cycle: cyclical changes during reproduction in primate mammals like monkeys, ape, and humans.
  • Seasonal breeders: reproductive cycle takes place in favourable seasons as in wild animals.
  • Continuous breeders: reproductively active throughout their reproductive phase.

Pre-fertilization events:

  • Process of gamete formation is gametogenesis.
  • Two gametes are similar in appearance are called homogametes(isogametes).
  • Gametes produced are of two morphologically distinct types called heterogametes.
  • Male gamete is called antherozoids or sperm and the female gamete is called ovum or egg.

Sexuality in organism:

  • Plant having both male and female sex organ called homothallic or monoecious.
  • Plants having only one sex organ is called heterothallic or dioecious.
  • In flowering plants, the unisexual male flower is staminate, i.e. bearing staments, while the female is pistillate or bearing pistils.
  • Animal having one type of reproductive system, called unisexual.
  • Animal having both male and female reproductive system, called hermaphrodite or bisexual.

Cell division during gamete formation:

  • Gametes in all heterogametic species two types namely male and female.
  • Gametes are always haploid irrespective of parent’s ploidy.
  • A haploid parent produces gametes by mitotic division.
  • Diploid parent produces gametes by meiotic division.
  • In diploid organisms specialized cells called meiocytes (gamete mother cell) undergo meiosis to produce haploid gametes.

Gamete transfer:

  • Male and female gamete must be physically brought together to facilitate fusion called fertilization.
  • In most cases male gametes are motile, female gametes are non-motile.
  • In case of few fungi and algae, both male and female gametes are motile.
  • In most cases water is the medium for gamete transfer.
  • Male gametes are produced in several thousand times the number of female gametes produced to compensate the loss during transfer.

Fertilization:

  • Fusion of male and female gamete is called fertilization or syngamy.
  • The female gamete undergoes development to form new organism without fertilization. This phenomenon is calledparthenogenesis.
  • Gametic fusion takes place outside the body i.e. water is called external fertilization.
  • Their must be synchrony of gamete release, large number of gametes released to enhance the chance of fertilization.
  • Enable the individual to produce large number of offsprings.
  • A major disadvantage is that the offsprings are extremely vulnerable to predators.
  • Fertilization takes place inside the body is called internal fertilization.

Zygote:

  • Formation of zygote after fertilization is universal in all sexually reproducing organisms.
  • Zygote is formed usually in water in case of external fertilization.
  • Zygote is formed inside the body of the organism in internal fertilization.
  • Zygote of fungi and algae develops a thick wall that is resistant to dessication and damage.
  • Organism with haplontic life cycle, zygote undergoes meiosis to produce haploid spores.

Embryogenesis:

  • Development of zygote into an embryo is called embryogenesis.
  • Zygote undergoes cell division (mitosis) and cell differentiation.
  • Oviparous animal which lays eggs and development takes place inside egg.
  • Viviparous animal gives birth to the young. The development takes place inside the body of the female.
  • In plants:
    • Zygote developed into embryo.
    • Ovule developed into seed
    • Integument of the ovule developed into seed coat.
    • Ovary developed into fruit.
    • Ovary wall developed into pericarp.

REPRODUCTIVE HEALTH
REPRODUCTIVE HEALTH – PROBLEM AND STRATERIES:
  • The programme “family planning” initiated in 1951.
  • Reproductive and child health care (ACH)
  • Sexually transmitted diseases (STD).
  • Amniocentesis: A fetal sex determination test based on the chromosomal pattern in the amniotic fluid surrounding the developing embryo.
  • ‘Saheli’ an oral contraceptive for female, developed by CDRI.

POPULATION EXPLOSION AND BIRTH CONTROL:

  • Increased health facilities, better living conditions are the cause of population explosion.
  • Out of 6 billion world population 1 billion are Indians.
  • Rapid decline in death rate, maternal mortalility rate (MMR) and infant mortality rate (IMR) are major cause of population growth.
  • Indian population growth rate is around 1.7 percent.

Characteristics of ideal contraceptive.

  • User friendly.
  • Easily available.
  • Effective
  • Nor or least side – effects.
  • No way interferes with sexual drive.

BIRTH CONTROL METHODS:

Natural methods:

work on the principle of avoiding chances of ovum and sperms meeting.

Periodic abstinence:

  • Avoid or abstain from coitus form day 10 to 17 of the menstrual cycle when ovulation could be expected.
  • Chance of fertilization is very high in this period.
  • It is called fertile period.

Withdrawal or coitus interruption:

  • The male partner withdraws his penis from the vagina just before ejaculation, so as to avoid insemination into the vagina.

Lactational amenorrhea:

  • No menstruation during lactation period.
  • Chance of fertilization is nil.
  • It is effective upto six month.

 Barrier methods:

  • Principle of working: prevents physical meeting of sperm and ovum.
  • Such methods available both for male and female.

Condoms:

  • Barriers made of thin rubber/latex sheath.
  • Used to cover the penis in male or vagina and cervix in the female.
  • Used just before coitus so that semen not entered into the female reproductive tract.
  • Male and female condoms are disposable.
  • Prevents AIDS and STDs.

Diaphragm, cervical caps and vaults:

  • Barriers made of rubber.
  • Inserted into the female reproductive tract to cover the cervix.
  • Prevents conception by blocking the entry of sperm through cervix.
  • They are reusable.

Intra Uterine Devices:

  • These devices are only used by female.
  • Inserted by doctor or by expert nurses in the uterus through vagina.
  • Non-medicated IUDs e.g. Lippes loop.
  • Copper releasing IUDs (CuT, Cu7, Multiload 375)
  • Hormone releasing IUDs (Progestasert, LNG-20)

Principle of working:

  • Increase phagocytosis of sperm within the uterus.
  • Cu ion released suppresses sperm motility and fertilizing capacity of sperm.
  • Hormone releasing IUDs make the uterus unsuitable for implantation and the cervix hostile to the sperm.

Oral contraceptives:

  • This methods used by female only.
  • Used in the form of tablets hence popularly called pills.
  • Pills contain progestogens or progestogen-estrogen combination.
  • Pills have to be taken daily for a period of 21 days.
  • Started within first five days of menstruation.
  • Pills are very effective with lesser side effect.
  • Saheli- a non steroidal preparation used as oral contraceptive pills.

Principle of working:

  • Inhibit ovulation.
  • Inhibit implantation.
  • Alter the quality of cervical mucus to prevent/retard entry of sperms.

Injections or implants:

  • Progestogens alone or in combination with estrogen used as injections or implants under the skin by female.
  • Mode of action is similar as in pills
  • It is very effective for long periods.

Emergency contraceptives:

  • These methods are used within 72 hours of coitus, rape or casual unprotected intercourse.
  • Administration of progestogens or progestogen-estrogen combination.
  • Use of IUDs.

Surgical methods:

  • It is also called as sterilization method.
  • Advised to both male and female partner.
  • Permanent or terminal method to prevent pregnancy.
  • Sterilization process in male is called ‘vasectomy,
  • Sterilization process in female is called ‘Tubectomy’
  • In vasectomy, a small part of the vas deferens is removed or tied up.
  • In Tubectomy a small part of the fallopian tube is removed.
  • Reversibility is very poor.

PRINCIPLES OF INHERITANCE AND VARIATION
PRINCIPLES OF INHERITANCE AND VARIATION
  • Genetics: deals with the inheritance, as well as the variation of characters from parents to offsprings.
  • Inheritance: is the process by which characters are passed on from parent to progeny.
  • Variation: is the degree by which progeny differ from their parents.

MENDEL’S LAWS OF INHERITANCE:

  • Gregor Mendel. Conducted hybridization experiments on garden peas for seven years (1856 – 1863) and proposed laws of inheritance.
  • Mendel conducted artificial pollination/cross pollination experiments using several true-breeding pea lines.
  • A true breeding line is one that, having undergone continuous self-pollination for several generations.
  • Mendel selected 14 true-breeding peas’ plant varieties, as pair’s which were similar except for one character with contrasting traits.
    • True breed selected by Mendel
    • Stem height- Tall / dwarf
    • Flower color- Violet/white
    • Flower position – Axial / terminal
    • Pod shape- Inflated / beaded or constricted
    • Pod color- Green / yellow
    • Seed  color- Yellow/ green
    • Seed shape – round / wrinkled

INHERITANCE OF ONE GENE:

  • Mendel crossed tall and dwarf pea plants to study the inheritance of one gene.
  • He collected the seeds produced as a result of this cross and grew them to generate plants of the first hybrid generation. This generation is called filial progeny or the F1.
  • Mendel observed that all the F1 progeny plants ere tall, like one of its parents; none were dwarf.
  • He made similar observations for the other pairs of traits – he found that the F1 always resembled either one of the parents, and that the trait of the other parent was not seen in them.
  • Mendel then self – pollinated the tall F1 plants and to his surprise found that in the F2 generation some of the offsprings were ‘dwarf; the character that was not seen in the F1 generation was now expressed.
  • The proportion of plants that were dwarf was 1/4th of the F2 plants while 3/4th of the F2 plants were tall.
  • The tall and dwarf traits were identical to their parental type and did not show any blending, that is all the offsprings were either tall or dwarf, none were of in between height.
  • Similar results were obtained with the other traits that he studied: only one of the parental traits was expressed in the F1 generation while at the F2 stage both the traits were expressed in the proportion of 3:1.
  • The contrasting traits did not show any blending at either F1 or F2 stage.

 Mendel’s proposition:

  • Mendel proposed that something was being stably passed down, unchanged, from parent to offspring through the gametes, over successive generations. He called these things as ‘factors’.
  • Now a day we call them as genes.
  • Gene is therefore are the units of inheritance.
  • Genes which codes of a pair of contrasting traits are known as alleles, i.e. they are slightly different forms of the same gene.

Alphabets used:

  • Capital letters used for the trait expressed at the F1 stage.
  • Small alphabet for the other trait.
  • ‘T’ is used for Tall and‘t’ is used for dwarf.
  • ‘T’ and‘t’ are alleles of each other.
  • Hence in plants the pair of alleles for height would be TT. Tt. or tt.
  • In a true breeding tall or dwarf pea variety the allelic pair of genes for height are identical or homozygous, TT and ttrespectively.
  • TT and tt are called the genotype.
  • Tt plant is heterozygous for genes controlling one character (height).
  • Descriptive terms tall and dwarf are the phenotype.

Test cross:

  • When F1 hybrid is crossed back with the recessive parent, it is known as test cross.
  • It is used to know the genotype of the given plant/animal.

Law of Dominance:

  • Characters are controlled by discrete units called factors.
  • Factors occur in pairs.
  • In a dissimilar pair of factors one member of the pair dominates (dominant) the other (recessive).

Law of Segregation:

  • The alleles do not show any blending and that both the characters are recovered as such in the F2 generation though one of these is not seen at the F1 stage.
  • The parents contain two alleles during gamete formation; the factors or alleles of a pair segregate or separate from each other such that a gamete receives only one of the two factors.
  • Homozygous parent produces all gametes that are similar i.e contain same type of allele.
  • Heterozygous parents’ produces two kinds of gametes each having one allele with equal proportion.

EVOLUTION
ORIGIN OF LIFE:
  • Stellar distances are measured in light years.
  • The universe is very old – almost 20 billion years old.
  • The Big Bang theory attempts to explain to us the origin of universe.

The Big Bang theory:

  • A singular huge explosion unimaginable in physical term.
  • The universe expanded and hence the temperature came down.
  • Hydrogen and Helium formed sometime later.
  • The gases condensed under gravitation and formed the galaxies of the present day universe.
  • In the solar system of the Milky Way galaxy, earth was supposed to have been formed about 4.5 billion years back.

Condition of early earth:

  • Earth formed 4.5 billion years back.
  • There was no atmosphere on early earth.
  • Water vapor, methane, carbon dioxide and ammonia released from molten mass covered the surface.
  • The UV rays from the sun broke up water into Hydrogen and oxygen and lighter H2 escaped.
  • Oxygen combined with ammonia and methane to form water, CO2 and others.
  • The ozone layer was formed.
  • As it cooled, the water vapor fell as rain, to fill all the depressions and form oceans.
  • Life appeared 500 Million years after the formation of earth.

Origin of life:

  • Early Greek thinkers thought units of life called spores were transferred to different planets including earth.
  • ‘Panspermia’ is still a favorite idea for some astronomers.
  • For a long time it was also believed that life came out of decaying and rotting matter like straw, mud etc.This was thetheory of spontaneous generation.

Louis Pasteur experiment:

  • Careful experimentation demonstrated that life comes only from pre-existing life.
  • He showed that in pre-sterilized flasks, life did not come from killed yeast while in another flask open to air, new living organism arose from ‘killed yeast’.
  • This disproved the theory of spontaneous generation.

Oparin – Haldane theory of origin of life:

  • Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre- existing non-living organic molecule (e.g. RNA, protein etc.).
  • Formation of life was preceded by chemical evolution i.e. formation of diverse organic molecule from inorganic constituents.

 Urey and Miller experiment:

  • The conditions on earth were –
    • High temperature.
    • Volcanic storms.
    • Reducing atmosphere containing CH4, NH3 etc.
  • In 1953, S.L.  Miller an American Scientist created similar conditions in a laboratory scale.
    • He created electric discharge in a closed flask to raise temperature upto 800oC as it was in primitive earth.
    • Used CH4 H2, NH3 and water vapor inside the flask.
    • He observed the formation of amino acids.
  • Acceptance of chemical evolution theory: (evidences)

    • Miller observed the synthesis of amino acids from simple inorganic chemicals in simulated condition in the laboratory.
    • In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats.
    • Analysis of meteorite content also revealed similar compounds indicating that similar processes are occurring elsewhere in space.

    Theory of biogenesis:

    • The first non-cellular forms of life could have originated 3 billion years back.
    • They would have been giant molecules (RNA, proteins, Polysaccharides, etc).
    • These capsules reproduced their molecules perhaps, named as coaservates.
    • The first cellular form of life did not possibly originate till about 2000 millions years ago.
    • The first cellular forms of life were probably unicellular.
    • All life forms were in water environment only.
    • This theory of biogenesis from non-living molecules was accepted by majority.

    EVOLUTION OF LIFE FORMS – A THEORY:

    • Conventional religious literature tells us about the theory of special creation.
    • The theory of special creation has three connotations:-
      • All the living organisms (species types) that we see today were created as such.
      • The diversity was always the same since creation and will be same in future.
      • Earth is about 4000 years old.

    Challenge to special creation theory:

    • Observation made during a sea voyage in a sail ship called H.M.S. Beagle round the world. Charles Darwin concluded that existing life forms share similarities to varying degrees not only among themselves but also with life forms that millions of years ago.
    • Many such life forms exist any more. There had been extinctions of different life forms in the years gone by just as new forms of life arose at different periods of history of earth.
    • There has been gradual evolution of life forms.
    • Any population has built in variation in characteristics.
    • Those characteristics which enable some to survive better in natural conditions (climate, food, physical factors, etc) would outbreed others that are less-endowed to survive under such natural condition.
    • Survival of the fittest. The fitness according to Darwin refers ultimately and only leaves more progeny than others.
    • These, therefore, will survive more and hence are selected by nature. He called it as natural selection.
    • Alfred Wallace, a naturalist who worked in Malay Archipelago had also come to similar conclusions around the same time.
    • The geological history of earth closely correlates with the biological history of earth.

    STRATEGIES FOR ENHANCEMENT IN FOOD PRODUCTION
    ANIMAL HUSBANDRY:
    • The agricultural practice of breeding and raising livestock.
    • Deals with care and breeding of livestock like buffaloes, cows, pigs, horses, cattle, sheep, camels, goats etc.
    • Extended form includes poultry farming and fisheries.
    • Fisheries include rearing, catching selling etc. of fish, mollusks (shell fish) and crustaceans (prawns, crabs etc.)

    Diary farm management:

    • Dairying is the management of animals for milk and its products.
    • Use of improved breed of cow such as Jersey.
    • Well housed.
    • Should have adequate water
    • Maintained disease free
    • Feeding should be scientific manner.
    • Quantity and quality of fodder
    • Stringent cleanliness and hygiene.
    • Regular visit by a veterinary doctor would be mandatory.

    Poultry farm management:

    • Poultry is the class of domesticated fowl (birds) used for food and eggs.
    • Selection of disease free and suitable breeds.
    • The improved breed of poultry is Leghorn.
    • Proper and safe farm conditions
    • Proper feed and water
    • Hygiene and health care.

    Animal breeding:

    • A group of animals related by descent and similar in most characters like general appearance, features size, configuration, etc, are said to be a breed.
    • Inbreeding: crosses between same breed.
    • Outbreeding: crosses between different breeds.

    Inbreeding:

    • Mating of more closely related individuals within the same breed for 4-6 generations.
    • Superior male and female is identified and mated in pairs.
    • Progeny obtained are evaluated and superior males and females among them are identified for further mating.
    • More milk per lactation is the criteria for superior female for cow and buffalo. Superior male which gives rise tosuperior progeny.
    • Inbreeding increases homozygosity.
    • Inbreeding is necessary to create pure line in any animal.
    • Inbreeding exposes harmful recessive gens that are eliminated by selection.
    • Helpful in accumulation of superior genes.
    • Continuous inbreeding reduces fertility and even productivity. This is called inbreeding depression.

    Outbreeding:

    • Out-breeding is the breeding of unrelated animals.

    Out-crossing:

    • Mating of animals within the same breed but having no common ancestor on either side of their pedigree upto 4-6 generations.
    • Offsprings of such mating is called out-cross.
    • A single outcross often helps to overcome inbreeding depression.

    Cross-breeding:

    • Superior male of one breed are mated with superior female of another breed.
    • It allows the desirable qualities of two different breeds to be combined.
    • Hisardaleis a new breed of sheep developed in Punjab by crossing Bikaneri ewes and Marino rams.

    Interspecific hybridization:

    • Male and female of two different species are mated.
    • The progeny may combine desirable features of both the parents.(mule)

    Artificial insemination:

    • Controlled breeding experiments are carried out using artificial insemination.
    • The semen is collected from the male and injected into the reproductive tract of the selected female by the breeder.
    • The semen collected may be used immediately or can be frozen for later use. The semen can be transported in a frozen form to where the female is housed.

    Multiple Ovulation Embryo Transfer Technology:

    • It is used to improve chances of successful production of hybrids.
    • Cow is administered hormones with FSH-like activity
    • induce follicular maturation and super ovulation
    • Production of 6-8 eggs instead of one egg per cycle.
    • The female is either mated with an elite bull or artificially inseminated.
    • Non-surgical recovery of fertilized eggs at 8-32 cells stages.
    • Each one transferred to surrogate mother.
    • The genetic mother is available for another round of super ovulation.
    • This technology is used to increase herd size in a short time.

    Bee – keeping:

    • Bee-keeping is called apiculture.
    • It includes maintenance of hives of honeybees for production of honey.
    • Honey is a food of high nutritive values and also used as medicine.
    • Honey bees also produce beeswax which has many used in industry, like preparation of cosmetics and polishes of various kinds.
    • Bee-keeping practiced in area with sufficient bee pastures of some wild shrubs, fruit orchards and cultivated crops.
    • Apis indica is most common species used in apiculture.

     

    • The following points are important for successful bee-keeping:
      • Knowledge of the nature and habits of bees.
      • Selection of suitable location for keeping the beehives.
      • Catching and hiving of swarms (group of bees)
      • Management of beehives during different seasons.
      • Handling and collection of honey and of beeswax.
      • Bees are the pollinator for many plants, hence keeping beehives in crop fields during flowering period, increases pollination and improve honey yield.

    MICROBES IN HUMAN WELFARE
    MICROBES IN HUMAN WELFARE
    • Microbes are diverse – protozoa, bacteria, fungi and microscopic plants viruses, viroids and also prions (proteinocious infectious agents)
    • Microbes like bacteria and fungi can be grown in nutrient media to form colonies and can be seen in naked eyes.
    • Some microbes’ causes diseases and some are useful for human being.

    MICROBES IN HOUSEHOLD PRODUCTS:

            Lactic acid Bacteria:

    • Lactic acid Bacteria (LAB) grow in milk and convert it to curd.
    • LAB produces acids that coagulate and partially digest milk proteins.
    • A small amount of curd added to fresh milk as inoculums or starter.
    • LAB improves nutritional quality of milk by increasing vitamin B12
    • LAB plays very important role in checking disease causing microbes.
    • Dough, used to make dosa and idli is also fermented by bacteria.
    • The puffed-up appearance of dough is due to the production of CO2.
    • Baker’s yeast (Saccharomyces cervisiae) is used to making bread.
    • ‘Toddy’ a traditional drink is made by fermentation of sap from palms.
    • Large holes in ‘Swiss cheese’ are due to production of large amount of CO2 by a bacterium namedPropionibacterium sharmanii.
    • The ‘Roquefort cheese’ is ripened by specific fungi, which gives specific flavor.

    MICROBES IN INDUSTRIAL PRODUCTS:

    • Microbes are used in industry to synthesize a number of products
    • Beverages and antibiotics are some examples.
    • Microbes are grown in very large vessels called fomenters.

    Fermented Beverages:

    • Yeasts are used for production of beverages like wine, beer, whisky, brandy or rum.
    • Saccharomyces cervisiae commonly called ‘brewer’s yeast used for fermenting malted cereals and fruit juices to produce ethanol.
    • The type of raw material used for fermentation and the processing, different types of alcoholic drinks are produced.
    • Wine and beer are produced without distillation.
    • Whisky, brandy and rum are produced by distillation of the fermented brooth.

    Antibiotics:

    • Antibiotics are the chemical substances which are produced by some microbes and can kill or retard the growth of other microbes.
    • The first antibiotic discovered is the penicillin, from a mould (fungus) Penicillium notatum.
    • Antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough. Diphtheria and leprosy.

    Chemicals, Enzymes and other Bioactive Molecules:

    • Aspegillus niger (a fungus) produces citric acid.
    • Acetobacter aceti (a bacterium) produce acetic acid.
    • Clostridium butylicum (a bacterium) produce butyric acid.
    • Lactobacillus(a bacterium) produces lactic acid.
    • Saccharomyces cerevisiae (yeast) used for production of ethanol.
    • Lipases are used in detergent produced by microbes.
    • Pectinase, proteases and cellulase, make bottled fruit juices clearer.
    • Streptokinase produced by Streptococcus used as a ‘clot buster’, for removing clots from the blood vessels.
    • Cyclosporin-A produced by a fungus called Trichoderma polysporum used as immunosuppressive agent in organ transplantation.
    • Statins produced by Monascus purpureus used as blood cholesterol lowering agents. It acts as competitive inhibitor for the enzyme responsible for synthesis of cholesterol.

    MICROBES IN SEWAGE TREATMENT:

    • The waste water generated in cities and town containing human excreta. This municipal water-water is called sewage.
    • Before disposal to the natural body sewage is treated in sewage treatment plants (STPs) to make it less polluting.
    • Treatment is done by heterotrophic microbes naturally present in sewage.

    Primary treatment:

    • Involves the physical removal of particles – large and small from sewage through filtration and sedimentation.
    • Initially floating debris is removed by sequential filtration.
    • The grit (soil and small pebbles) are removed by sedimentation.
    • All solids that settle form the primary sludge, and the supernatant forms the effluents.
    • The effluents are from the primary settling tank taken for secondary treatment.

    BIOTECHNOLOGY: PRINCIPLES AND PROCESSES
    BIOTECHNOLOGY: PRINCIPLES AND PROCESSES
    • Two core techniques that enabled birth of modern biotechnology:
      • Genetic engineering: Techniques to alter the chemistry of genetic material (DNA and RNA) to introduce into host organisms and thus change the phenotype of the host organism.
      • Maintenance of sterile (microbial contamination-free) ambient chemical engineering processes to enable growth of only the desired microbe/eukaryotic cell in large quantities.

    Conceptual development of the principle of genetic engineering:

    • Asexual reproduction preserves the genetic identity of species.
    • Sexual reproduction creates variation and creates unique combinations of genetic makeup.
    • Traditional hybridization procedures used in plant and animal breeding lead to inclusion of undesirable genes along with desired genes.
    • The techniques of genetic engineering which includes creation of recombinant DNA, use of gene cloning and gene transfer, overcome this limitation and allows us to isolate and introduce only one or a set of desirable genes without introducing undesirable genes into target organism
    • Three basic steps in genetically modifying an organism –
      • Identification of DNA with desirable gene
      • Introduction of the identified DNA into the host.
      • Maintenance of introduced DNA in the host and transfer of the DNA to its progeny.

    TOOLS OF RECOMBINANT DNA TECHNOLOGY:
    Restriction Enzymes:

    • In the year 1963 two enzymes discovered from Escherichia coli which restrict the growth of bacteriophage in it.
      • One of these added methyl groups to DNA.
      • Other cut the phage DNA. (restriction endonuclease)
  • The first restriction endonuclease discovered is Hind II.
  • Hind II always cut DNA molecule at particular point by recognizing a specific sequence of six base pairs. This is calledrecognition sequence for Hind II.
  • Till date around 900 restriction enzymes isolated from 200 strains of bacteria each of which recognize different recognition sequences.
  • Restriction enzyme belongs to nucleases.
  • There are two kind of nucleases:
    • Exonuclease
    • Endonuclease
  • Exonuclease removes nucleotides from the free ends of the DNA.
  • Endonucleases make cuts at specific positions within the DNA.
  • Each restriction endonuclease recognizes a specific palindromic nucleotide sequences in the DNA.
  • Palindromes are the group of letters that read same both forward and backward, e.g. “MALAYALAM”.
  • The palindrome in DNA is a sequence of base pairs that reads same on the two strands when orientation of reading is kept same. 
  • The restriction enzyme cut the strand of DNA little away from the centre of the palindrome sites, but between the same two bases on the opposite strand. This leaves single stranded portions at the ends. There are overhanging stretches called sticky ends on each strand.
  • This stickiness of the ends facilitates the action of the enzyme DNA ligases.
  • The foreign DNA and the host DNA cut by the same restrictionendonuclease, the resultant DNA fragments have the same kind of ‘sticky-ends’ and these can be joined together using DNA ligases.
  • Convention for naming restriction endonuclease:

    • The first letter of the name comes from the genus.
    • Second two letters come from the species of the prokaryotic cell from which the enzyme isolated
    • The fourth letter is in capital form derived from the Strain of microbes.
    • The Roman letter followed is the order of discovery
    • Best example: EcoRI comes from Escherichia coli RY 13

    Separation and isolation of DNA fragments:

    • The cutting of DNA by restriction endonucleases results in the fragments of DNA.
    • These fragments are separated by a technique called gel electrophoresis.
    • Since the DNA fragments are negatively charged, they can be separated by forcing them to move towards anodeunder an electric field through a medium/matrix.
    • Most commonly used matrix is agarose, a natural polymer extracted from sea weed.
    • DNA fragments separate according to their size through sieving effect provided by the agarose gel. Hence the smaller the fragment size, farther it moves.
    • The separated fragments are visualized by staining them with Ethidium bromide followed by exposure to UV radiation.
    • The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. This step is calledelution.

    Cloning vectors:

    • The plasmid and bacteriophages have the ability to replicate within bacterial cells independent of the control of chromosomal DNA.
    • Alien DNA linked with the vector multiply its number equal to the copy number of the plasmid or bacteriophage.

    Features of cloning vector:

    Origin of replication:

    • This is the sequence where the replication starts called ori gene.
    • The alien DNA linked with vector also replicates.
    • Controls the copy number of the linked DNA.

    Selectable marker:

    • It is required to identify recombinant from the non-recombinant.
    • Helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.
    • Transformation is a procedure through which a piece of foreign DNA is introduced in a host bacterium.
    • Normally, the gene coding resistance to antibiotics such as ampicilin. Tetracycline, chloramphenicol or kanamycins etc are considered as useful selectable markers for E.coli.
    • Thr normal E.coli cells do not carry resistance against any of antibiotics.

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