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 Class 12 Biology Revision Notes Chapter 5 Principles of Inheritance and Variation

Genetics is the study of principles and mechanism of heredity and variation. Gregor Johann Mendel is known as ‘father of Genetics’.

• Inheritance is the process by which characters are passed on from parent to progeny. It is the basis of heredity.
• Variation is the degree by which progeny differ from their parents. Variation may be in terms of morphology, physiology, cytology and behavioristic traits of individual belonging to same species.
• Variation arise due to
  • Reshuffling of gene/chromosomes.
  • Crossing over or recombination
  • Mutation and effect of environment.

Mendel’s Law of Inheritance: Mendel conducted hybridization experiments on garden pea (Pisum sativum) for seven years and proposed the law of inheritance in living organisms.

Selection of pea plant: The main reasons for adopting garden pea (Pisum sativum) for experiments by Mendel were –

• Pea has many distinct contrasting characters.
• Life span of pea plant is short.
• Flowers show self-pollination, reproductive whorls being enclosed by corolla.
• It is easy to artificially cross-pollinate the pea flowers. The hybrids thus produced were fertile.

Working method: Mendel’s success was also due to his meticulous planning and method of work –

• He studied only one character at a time.
• He used all available techniques to avoid cross-pollination by undesirable pollen grains.
• He applied mathematics and statistics to analyse the results obtained by him.
• Mendel selected 7 contrasting characters of garden pea for his hybridization experimentsContrasting Characters Studied by Mendel in Pea
  CharacterContrasting character (Dominant/Recessive)Stem heightTall/DwarfFlower colourViolet/WhiteFlower positionAxial/TerminalPod shapeInflated/ConstrictedPod colourGreen/YellowSeed shapeRound/wrinkledSeed colourYellow/Green
• Mendel conducted artificial hybridization/cross pollination using true breeding pea lines. True breeding lines are those that undergo continuous self-pollination and shows stable trait inheritance.
• Hybridization experiment includes emasculation (removal of anther) and transfer of pollen (pollination).

Inheritance of one gene (Monohybrid cross)

Mendel crossed tall and dwarf pea plant and collected all the seeds obtained from this cross. He grew all the seeds to generate plants of first hybrid generation called F1 generation. He observed that all the plants are tall. Similar observation was also found in other pair of traits.

Mendel self-pollinated the F1 plants and found that in F2 generation some plants are also dwarf. The proportion of dwarf plants is 1/4th and tall plants of 3/4th.

• Mendel called the ‘factors’ that passes through gametes from one generation to next generation. Now a day it is called as genes (unit of inheritance).
• Genes that code for a pair of contrasting traits are known as alleles.
• Alphabetical symbols are used to represent each gene, capital letter (TT) for gene expressed in F1 generation and small letter (tt) for other gene.
• Mendel also proposed that in true breeding tall and dwarf variety allelic pair of genes for height is homozygous (TT or tt). TT, Tt or tt are called genotype and tall and dwarf are called phenotype.
• The hybrids which contain alleles which express contrasting traits are called heterozygous (Tt).
• The monohybrid ratio of F2 hybrid is 3:1(phenotypic) and 1:2:1(genotypic).

Test cross is the cross between an individual with dominant trait and a recessive organism in order to know whether the dominant trait is homozygous or heterozygous.

Principle or Law of Inheritance

Based on observations of monohybrid cross, Mendel proposed two law of inheritance-

1. Law of dominance– states that –

a. Characters are controlled by discrete units called factors.
b. Factors always occur in pair.
c. In a dissimilar pair of factors one member of pair dominate the other.

	Dominance	Recessive
(i)	When a factor (allele) expresses itself in the presence or absence of its dominant factor called dominance.	It can only express itself in the absence of or its recessive factor allele.
(ii)	It forms a complete functional enzyme that perfectly express it.	It forms a incomplete defective enzyme which fails to express itself when present with its dominant allele, i.e., in heterozygous condition.

2. Law of Segregation- alleles do not blends and both the characters are recovered during gametes formation as in F2 generation. During gametes formation traits segregate (separate) from each other and passes to different gametes. Homozygous produce similar kinds of gametes but heterozygous produce to different kinds of gametes with different traits.

Incomplete dominance

• It is a post Mendelian discovery. Incomplete dominance is the phenomenon of neither of the two alleles being dominant so that expression in the hybrid is a fine mixture or intermediate between the expressions of two alleles.
• In snapdragon (Mirabilis jalapa), there are two types of pure breeding plants, red flowered and white flowered. On crossing the two, F1 plants possess pink flowers. On selfing them, F2 generation has 1red: 2 pink: 1white. The pink flower is due to incomplete dominance.

Co-dominance

• It is the phenomenon of two alleles lacking dominance-recessive relationship and both expressing themselves in the organism.
• Human beings, ABO blood grouping are controlled by gene I. The gene has three alleles I^A, I^B and i. Any person contains any two of three allele I^A, I^B are dominant over i.
• The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the kind of sugar is controlled by the gene.
• When I^A and I^B are present together, both express their own types of sugars because of co-dominance.

Incomplete Dominance	Co-Dominance
1.	Effect of one of the two alleles is more conspicuous.	1.	Effect of both the alleles are equally conspicuous.
2.	It produces a mixture of the expression of two alleles.	2.	There is no mixing of the effect of the two alleles.
3.	The F1 does not resemble either of the parents.	3.	The F1 resembles both the parents.
	E.g.: Flower colour in dog flower.		E.g.: ABO blood grouping in humans,

Multiple Alleles

They are multiple forms of a medelian factor or gene which occur on the same gene locus distributed in different organisms in the gene pool with an organism carrying only two alleles and a gamete only one allele. ABO blood grouping also provides a good example of multiple alleles.

Inheritance of Two genes (Dihybrid Cross)

A cross made to study simultaneous inheritance of two pairs of mendelian factors of genes.

Law of independent Assortment – The law states that ‘when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters’.In Dihybrid cross two new combinations, round green & wrinkled yellow are formed due to independent assortment of traits for seed shape i.e round, wrinkled and seed color i.e , yellow and green.

The ratio of 9:3:3:1 can be derived as a combination series of 3 yellow: 1 green, with 3 round : 1 wrinkled. This derivation can be written as follows: (3 Round : 1 Wrinkled) (3 Yellow : 1 Green) = 9 Round, Yellow : 3 Wrinkled, Yellow: 3 Round, Green : 1 Wrinkled, Green

Chromosomal Theory of Inheritance

• Chromosome as well as gene both occurs in pair. The two alleles of a gene pair are located on the same locus on homologous chromosomes.
• Sutton and Boveri argued that the pairing and separation of a pair of chromosomes would lead to segregation of a pair of factors (gene) they carried.
• Sutton united the knowledge of chromosomal segregation with mendelian principles and called it the chromosomal theory of inheritance.

Linkage and Recombination

• When two genes in a Dihybrid cross were situated on same chromosome, the proportion of parental gene combination was much higher than the non-parental type. Morgan attributed this due to the physical association or the linkage of the two genes and coined the linkage to describe the physical association of genes on same chromosome.
• The generation of non-parental gene combination during Dihybrid cross is called recombination. When genes are located on same chromosome, they are tightly linked and show very low recombination.Difference between crossing over and linkage
  Crossing overLinkage1. It leads to separation of linked genes1. keeps the genes together2. It involves exchange of segments between non-sister chromatics of homologous chromosomes.2. It involves individual chromosomes.3. The frequency of crossing over can never exceed 50%.3. The number of linkage group can never be more than haploid Chromosome number.4. It increases variability by forming new gene combinations.4. It reduces variability.

Sex Determination

• Henking in 1891 observed a trace of specific nuclear structure in few insects. He also observed that this specific nuclear structure is located on 50% of sperms only. He called this x body. He was not able to explain its significance.
• Latter it was observed that the ovum that receive the sperms with x body become female and those not becomes males, so this x body was called as sex chromosome and other chromosomes are called autosomes.
• In humans and other organisms XY types of sex determination is seen but in some insects like Drosophila XO type of sex determination is present.
• In both types of sex determination, male produce two different types of gametes either with or without X chromosome or some with X chromosome and some with Y chromosomes. Such types of sex determination are called male heterogamety.
• In birds ZW type of sex determination is present., two different types of gametes are produced by females in terms of sex chromosomes; this type of sex determination is called female heterogamety.
• Sex determination in human beings XY type. Out of 23 pairs of chromosomes, 22 pairs are exactly same in male and female called autosomes. A pair of X chromosome is present in female and XY in male. During spermatogenesis, male produce two type of gametes (sperms), 50% carries Y chromosome and remaining 50% contain X chromosome. Female, produce only one kind of gamete (ovum) having X chromosomes only.
• When sperm having Y chromosome the sex of baby is male and when sperm carrying X chromosome fertilse the egg, the sex of baby is female.

Mutationis a phenomenon which results in alternation of DNA sequence and consequently results in the change in the genotype and phenotype of an organism. The mutations that arise due to due to change in single base pair of DNA are called point mutation e.g Sickle cell anaemia.

Pedigree Analysis

• The analysis of traits in several of generation of a family is called the pedigree analysis. The inheritance of a particular trait is represented in family tree over several generations. It is used to trace the inheritance of particular trait, abnormality and disease.

Genetic Disorders

Broadly, genetic disorders may be grouped into two categories – Mendelian disorders and
Chromosomal disorders.

They are transmitted as the affected individual is sterile.This is always dominant in nature.

Mendelian Disorders	Chromosomal disorders
These are due to alteration in a single gene.	These are caused due to absence or excess of one or more chromosomes or abnormal arrangement of one/more chromosomes.
They are transmitted into generations through Mendelian principles of inheritance.	They may be recessive or dominant in nature.
Examples: Colour blindness Pheffykenonia.	Examples: Downs syndrome, Turner’s syndrome

Medelian disorder includes-

a. Haemophilia- sex linked recessive disease in which, in an infected individual, a minor cut leads to non-stop bleeding. Heterozygous female (carrier) can transmit the disease to their son. The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic (unviable in the later stage of life).

b. Sickle cell anemia- an autosome linked recessive trait in which mutant haemoglobin molecules undergo polymerization under low oxygen tension causing change in shape of the RBC from biconvex disc to elongated sickle like structure. The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule. The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG

c. Phenylketonuria- inborn error of metabolism inherited as autosomal recessive trait. The affected individual lacks an enzyme that converts the amino acids phenylalanine to tyrosine . . As a result of this phenylalanine is accumulated and converted into phenylpyruvic acid and other derivatives that results into mental retardation.

Chromosomal Disorders-Failure of segregation of chromatids during cell division results in loss or gain of chromosome called aneuploidy. The failure of cytokinesis leads to two sets of chromosome called polyploidy.

a. Down’s Syndrome– is due to presence of additional copy of the chromosome number 21. The affected individual is short statured with small rounded head, furrowed tongue and partially opened mouth. Mental development is retarded.

b. Klinefleter’s Syndrome– due to presence of an additional copy of X-chromosome (XXY). Such persons have overall masculine development however, the feminine development (development of breast, i.e., Gynaecomastia) is also expressed. They are sterile.

c. Turner’s Syndrome– caused due to the absence of one of the X chromosome. 45 with XO, such females are sterile as ovaries are rudimentary. They lack secondary sexual characters.

Reproductive Health Notes Class 12 Biology Chapter 4

→ According to World Health Organisation (WHO), reproductive health means total well-being in all aspects of reproduction. It includes physical, emotional, behavioral, and social health. A reproductively healthy society has people with normal emotional and behavioral interactions as well as physically and functionally normal reproductive organs.

India has greater proportions of young individuals who belong to different age groups such as adolescents, early childhood, and puberty. Health and education of the younger generation, age of marriage, and childbearing capacity of women are some important areas of concern for the overall reproductive health of the human population.

Reports have revealed that enrolments for secondary school education are low especially for girls, complications during pregnancy, childbirth, and abortions are major reasons for female deaths, the chances of infection of sexually transmitted diseases are maximum between 15 – 24 years.

→ In the world, India was the first country to start action plans and programs to attain total reproductive health at the national level. These programs are called family planning and were started in 1951. Reproductive and Child Health Care (RCH) programs are creating awareness about various reproduction-related areas, providing facilities and support for building a reproductively healthy society.

→ The health centers provide information, guidance, and assistance to mothers before and after delivery. Pregnant women need more nutritious food especially calcium, iron, and vitamins. They should avoid the use of alcohol, drugs, and tobacco because they may cause abnormalities in the developing baby. Women should avoid taking medicines as some may be teratogenic (abnormality causing).

→ These centers also provide safe delivery of the infant and postnatal care. Delivery by untrained midwives may be dangerous so women should prefer delivery in hospitals with trained physicians.

→ The health centers also take care of infant immunization and prophylaxis against anemia and deficiency of vitamins. They should be provided with the following vaccines:

Table: National Immunisation Schedule

Age	Vaccination
3 – 12 Months	DPT – 3 doses at intervals of 4-6 weeks. Polio (oral) – 3 doses at intervals of 4-6 weeks. BCG (intradermal).
9 – 15 Months	The measles vaccine – one dose.
18 – 24 Months	DPT – booster dose. Polio (oral) – booster dose.
5 – 6 Years	DT (bivalent vaccine) against diphtheria and tetanus – booster dose. Typhoid vaccine – 2 doses at an interval of 1-2 months.
10 Years	Tetanus toxoid – booster dose. Typhoid vaccine – booster dose.
16 Years	Tetanus toxoid – booster dose. Typhoid vaccine – booster dose.
Mother during pregnancy	(a) Previously immunized One booster dose of tetanus toxoid 4 weeks before the expected delivery date.(b) Nonimmunised Two doses of tetanus toxoid:  1st between 16-24 weeks and 2nd between 24-32 weeks of pregnancy.

→ These centers train midwives to handle the safe delivery of infants. They also arrange for milk feeding programs. The infants do not have antibodies of their own, they get it from the mother’s milk. Such infants are less prone to allergies than bottle-fed ones.

→ The health centers educate the couples about the importance of small families and proper spacing between successive birth. Too young women are likely to produce underweight and weak babies. To start with pregnancy the reproductive system should be fully mature, physically and functionally as well.

→ Government and non-governmental agencies are working together, using various audio-visual aids to aware people about various programs, infrastructure facilities and to find out new improved methods and to implement them properly.

→ Increased health facilities and better living conditions have increased the population at an alarming level. A rapid decline in death rate, the maternal mortality rate (MMR) and infant mortality rate (IMR), and an increase in the number of people in reproducible age are the main reasons for this. This could lead to a scarcity of basic amenities so serious efforts to check this population growth rate are required.

→ One step to control the population rate is to control the birth rate of the population. To educate and motivate the fertile couples to have smaller families.

→ The regulation of conception by preventive methods or devices to limit the number of off-springs is called birth control. A variety of methods are used for birth control.

→ The birth control methods which prevent fertilization are known as contraception. A contraceptive should be user-friendly, easily available, effective, and reversible with no side effects.

These contraceptive methods are of two main types:
1. Temporary methods: As clear from the name these are temporary measures that are effective for a limited period.
(a) Safe period or Rhythm method: Generally one week before and one week after the menstrual cycle is considered a safe period. This is also called natural family planning. In it, the couples avoid coitus from 10 to 17 days of the menstrual cycle.

It is termed Periodic abstinence. It is based on the observations that ovulation occurs on about the 14th day of the menstrual cycle. An ovum survives for about 1-2 days, sperms remain active for about 3 days. This method reduces the chances of fertilization to 80%.

(b) Coitus Interruptus: This is the oldest method of birth control. It involves the withdrawal of the penis from the vagina by the male before ejaculation so as to avoid insemination. The drawbacks of this method are that the male produces some lubricating fluid from Cowper’s glands which contains many sperms. A lapse of timing may result in late withdrawal and therefore pregnancy.

(c) Lactational Amenorrhea: This means the absence of menstruation. It is based on the fact that ovulation does not occur during intense lactation after parturition, so there is no menstrual! cycle. The chances of conception are nil. This method does not have any side effects. It can only be effective for a maximum of six months after parturition.

(d) Chemical methods: These include jellies, foam tablets, pastes, or creams that contain spermicides (agents to kill sperms) such as lactic acid, boric acid, citric acid, zinc sulfate, or potassium permanganate. Before intercourse, if these are introduced into the vagina, they adhere to the mucous membrane and kill the sperms.

(e) Mechanical means: These are barrier methods that prevent the sperms and ovum to come closer.

They are of three types:
1. Condom (Nirodh) is made up of a thin rubber/latex sheath meant to cover the penis so that semen would not enter into the female reproductive system. The female condom covers the vagina and cervix, just before coitus. These should be discarded after a single-use. Their use is simple and has no side effects. These are very useful against STDs and AIDS.

2. Diaphragm and cervical cap: These are the rubber plastic covers that are fitted on the cervix in a female’s vagina and blocks the entry of sperms through the cervix. These are reusable and must be kept fit for at least six hours after intercourse. Every time these are smeared with spermicidal jelly, creams, or foams to increase their contraceptive efficiency.

3. Intrauterine Devices (IUDs): These are metal or plastic objects inserted inside the uterus of the female. These may be non-medicated lUD’s such as Lippes Loop, Copper releasing IUDs e.g. CuT, Cu7, Multiload 375, and the hormone-releasing ones e.g. Progestasert. LNG-20.

They prevent the fertilization of egg or embryo implantation. IUDs increase phagocytosis of sperms within the uterus, Cu²⁺ ions released by some of them suppress sperm motility and their fertilizing capacity. The hormone-releasing IUDs make the uterus unsuitable for implantation and cervix, hostile to the sperms. These should be used with the help of a physician. Their presence may act as a minor irritant.

Their drawbacks are spontaneous expulsion, occasional hemorrhage, perforation of the uterus, or tubal pregnancy.
1. Physiological (Oral) devices: These are birth control pills that check ovulation by inhibiting the secretion of follicle-stimulating hormone and luteinizing hormone. A combined pill is widely used, it contains progesterone and estrogen in high doses to prevent ovulation.

→ Pill Mala D is taken daily, and pill Saheli is taken weekly, it contains a non-steroidal preparation called ‘Centchroman’. These have side effects like nausea, breast tenderness, weight gain, slight bleeding, and high blood pressure. They also reduce certain types of cancer.

→ Progestagen along with estrogen is used by females as injections or implants under the skin. Their action is similar to pills and is for a longer duration (3 to 4 years).

→ Progestagens if taken within 72 hours of coitus are very effective and can avoid pregnancy due to some accidents.

2. Permanent Method: These are surgical methods or sterilization, which provides a permanent or terminal method for birth control. In males, it is called vasectomy and in females, it is called tubectomy. Surgical methods block gamete transport and thus prevent pregnancy. In a vasectomy, a small part of the vas deferens is removed or tied up by a small incision on the scrotum.

In tubectomy, a small part of the fallopian tube is removed or tied up through a small incision in the abdomen or through the vagina. This is done under local anesthesia and does not affect the normal sex life. These techniques are highly effective and widely used but they have poor reversibility.

→ Laparoscopy: A small laparoscope (telescopic instrument) is used in tubal ligation. It blocks the fallopian tubes. Thus the eggs fail to pass the fallopian tube and sperms fail to reach the eggs.

→ Sterilization is the most effective measure for birth control. All these methods should be used under the guidance of a medical practitioner.

→ Voluntary Termination of Pregnancy or Medical Termination of Pregnancy (MTP) is known as abortion. The pregnancy is terminated before the fetus becomes viable. It is a method of fertility control used all over the world. Certain pills induce menstruation which acts as abortions and checks the implantation of a zygote or detaches the implanted egg. MTPs if done during the first 12 weeks of pregnancy is safe. It becomes riskier during the second trimester. Only a certified practitioner should be contacted for MTP.

Contraception methods

→ RU – 486 is an analog of progesterone that terminates pregnancy within the first few weeks. It acts by blocking the receptors in the uterus thus preventing progesterone from maintaining pregnancy.

→ Infections or diseases that transmit through unsafe sexual intercourse are called sexually transmitted diseases (STDs) or reproductive tract infections (RTI) or Venereal diseases (VD) Gonorrhoea and syphilis are the most common. Another is AIDS. Adolescents are more vulnerable to these because of a lack of proper knowledge.

Table: Common STDs and their causative agents

Infection/Disease	Causative agent
Gonorrhea	Neisseria gonorrhoeae
Syphilis	Treponema pallidum
Chlamydiosis	Chiarnydia trachomatis
Genital Herpes	Herpes Simplex Virus. Human Papilloma Virus
Hepatitis-B	Hepatitis Virus
HIV-AIDS	Human Immunodeficiency virus
Trichomoniasis	Trichomonas vaginal is/Protozoan

→ To avoid these one should avoid having sex with unknown partners or multiple partners, always use condoms during coitus and seek medical help as soon as possible.

→ Early symptoms of most of these infections are minor. It includes slight itching, fluid discharge, slight pain or swelling in the genital region. If not paid proper attention these may become complicated ones as pelvic inflammatory disease (PID), abortions, ectopic pregnancy, stillbirth, infertility, or even cancer of the reproductive tract.

→ Infertility is the condition when couples are unable to produce children in spite of unprotected sexual cohabitation. Infertility may be physical, congenital, diseases, drugs, immunological, or even psychological. These problems can be cured by assisted reproductive technologies (ART). In vitro fertilization (IVF) is done followed by Embryo transfer (ET)is one of such practices done to cure infertility.

In IVF, ova from the donor female and sperms from the donor male are collected and induced to form a zygote, which is then transferred into the fallopian tube known as ZIFT-zygote intrafallopian transfer. For ZIFT the embryos are up to 8 blastomeres. Embryos with more than 8 blastomeres are transferred into the uterus called JUT (intrauterine transfer) for further complete development.

GIFT: gamete intrafallopian transfer, is the transfer of ovum from a donor to the receiver female who cannot produce one. Intracytoplasmic sperm injection (ICSI) is a product where embryos are produced in the laboratory. The artificial insemination (AI) technique is used in case of male’s sperm count is low. In IUT: intrauterine insemination, semen is collected from donors and artificially introduced into the vagina or uterus.

→ Polyovulation: Discharge of several ova in one ovulatory cycle.

→ Hygienist: A person well versed in the principles of hygiene.

→ Laparoscopy: Examination of the peritoneal cavity through an incision in the abdominal wall.

→ Abortion: Giving birth to an embryo or fetus prior to the stage of viability at about 20 weeks of gestation.

→ Premature birth: Birth after the age of fetal viability but before full term.

→ Fetus: Developing young one from the end of the eight weeks to the moment of birth.

→ Foeticide: Destruction of embryo or fetus in the uterus.

→ RCH programs: Reproductive and Child Health Care program.

→ IUDs: Intra-Uterine Devices.

→ MTP: Medical termination of pregnancy.

→ VD: Venereal diseases.

→ RTI: Reproductive tract infections.

→ PID: Pelvic inflammatory diseases.

→ ART: Assisted reproductive technologies.

→ IVF: Invitro fertilization.

→ ET: Embryo transfer.

→ ZIFT: Zygote intrafallopian transfer.

→ IUT: Intra uterine transfer. .

→ GIFT: Gamete intrafallopian transfer.

→ ICSI: Intracytoplasmic sperm injection.

→ AI: Artificial insemination.

→ IUI: Intra-uterine insemination.

Class 12 Biology Revision Notes Chapter 3 Human Reproduction

Humans are sexually reproducing and viviparous. The reproductive events in humans include formation of gametes (gametogenesis), i.e., sperms in males and ovum in females, transfer of sperms into the female genital tract (insemination) and fusion of male and female gametes (fertilisation) leading to formation of zygote. This is followed by formation and development of blastocyst and its attachment to the uterine wall (implantation), embryonic development (gestation) and delivery of the baby (parturition)

The Male Reproductive System: It cChapteronsists of:

a) Primary sex organs i.e. a pair of testes suspended in a scrotum.

b) Secondary sex organs i.e. a pair of ducts each differentiated into rete testis, vasa efferentia, epididymis and vas deferens, ejaculatory duct and the associated glands

c)  External genitalia

• The testes are situated outside the abdominal cavity in a pouch called scrotum, which help in maintaining the low temperature of testes necessary for spermatogenesis.
• Each testes has about 250 testicular lobules and each lobule contain highly coiled seminiferous tubules in which sperms are produced. Each seminiferous tubules is lined by two types of cells, spermatogonia ( male germ cell) and Sertoli cells.
• Leydig cells or interstitial cells present around the seminiferous tubules synthesize and secrete androgen hormone.

• Ejaculatory duct store and transport the sperm from testes to outside through urethra which originate from urinary bladder and extend through penis to its external opening urethral meatus.
• The penis is male external genitalia. The enlarged end of penis is called the glans penis is covered by a loose fold of skin called foreskin.
• Male accessary glands include paired seminal vesicles, prostrate and paired bulbourethral glands. Secretion of these glands forms the seminal plasma which contains fructose, calcium and enzymes. The secretion of bulbourethral glands also helps in lubrication of the penis.

The Female Reproductive System: It consists of :

a)The primary sex organ that is a pair of ovaries

b)Secondary sex organs- the duct system consisting of a pair of fallopian tube , a uterus , cervix and vagina

c)External genitalia

d)Mammary glands

• Ovaries are primary female sex organ that produce the female gamete and several steroid hormones. Each ovary is covered by thin epithelium which encloses the ovarian stroma, which is divided into a peripheral cortex and an inner medulla.
• Fallopian tube extends from periphery of ovary to the uterus. The part closer to ovary is a funnel shaped structure called infundibulum having finger like projection called fimbriae.
• Infundibulum leads to ampulla and join with uterus with isthmus. Uterus is pear shaped structure also called womb.
• Uterus open vagina through a narrow cervix. The cavity of cervix (cervical canal) along with vagina forms the birth canal.
• The wall of uterus has three layers of tissue:

I. Perimetrium- external membrane.

II. Myometrium – middle thick layer of smooth muscles which exhibit strong contraction during delivery of baby.

III. Endometrium – line the uterine wall and undergo cyclic changes during menstrual cycle.

Female external genitalia includes

• Mons pubis – cushion of fatty tissues covered by skin and pubic hair.
• Labia majora- fleshy fold that surround the vaginal opening.
• Labia manora – paired fold of tissue under labia majora.
• The opening of vagina is often partially covered by a membrane called hymen. The tiny finger like projection present at the upper junction of two labia manora above the urethral opening is called clitoris.

Mammary glands are paired structures that contain glandular tissues and variable fats. Each glandular tissue contains 15-20 mammary lobes containing alveoli that secrete milk. Mammary ducts join to form mammary ampulla.

Gametogenesis: The process of formation of male and female gametes in testes and ovary respectively is called gametogenesis.It is of two types:
1. Spermatogenesis in males
2. Oogenesis in females

Spermatogenesis- in testes immature, male germ cells (spermatogonia) produce sperm by spermatogenesis that begin at puberty.

• The spermatogonia present at the inner side of seminiferous tubules multiply by mitotic division and increase in number. Each spematogonium contain 46 chromosomes.
• Spermatogonia forms spermatocyte that undergo meiotic division to reproduce secondary spermatocytes having 23 chromosomes.
• The spermatids are transformed into spermatozoa by the process called spermiogenesis. The sperm heads remain embedded in sertoli cells and are released from seminiferous tubules by the process of spermiation.

Hormonal control of spermatogenesis

• Spermatogenesis initiated due to increase in secretion of gonadotropin releasing hormone by hypothalamus
• Increase in GnRH act on anterior pituitary and stimulate secretion of two gonadotropins, LH and FSH
• LH acts on Leydig cells and stimulates them to secrete androgens.
• FSH acts on Sertoli cells, stimulates secretion of some factors which help in spermiogenesis

Structure of sperm- sperm is a microscopic structure composed of a head, neck, a middle piece and a tail. The sperm head contain elongated haploid nucleus, anterior portion of which is covered by cap like structure acrosome.

Human male ejaculates about 200-300 million sperms during a coitus. The seminal plasma along with the sperms constitutes the semen. The function of male sex secondary ducts and glands are maintained by androgen hormones.

Oogenesis : The process of formation of mature female gametes is called oogenesis. It started during embryonic development stage when millions of ogonia (gamete mother cells) are formed in each fetal ovary.

• The gametes mother cells start division and enter into prophase-I of meiotic division and get temporally arrested at that stage called primary oocytes.
• Each primary oocyteget surrounded by a layer of granulosa cell than it is called the primary follicle.
• At puberty, about 60,000- 80,000 primary follicles are left in each ovary.

• Primary follicle gets surrounded by more layers of granulosa cells called secondary follicle that transform into tertiary follicle that contain fluid filled cavity called antrum.

• The tertiary follicles further changes into the mature follicle called Graafian follicle, which rapture to release secondary oocytes (ovum) from the ovary by the process of ovulation.

Menstrual cycle: The reproductive cycles in female primates is called menstrual cycle. It start at puberty and is called menarche.

Phases of Menstrual Cycle

The menstrual cycle consists of following four phases:

(1) Menstrual Phase:

(i) In a 28 days menstrual cycle,the menses  takes place on cycle days 3-5.

(ii) The production of LH from the anterior lobe of the pituitary gland is reduced.

(iii) The withdrawal of  this hormone causes degeneration of the corpus luteum and, therefore progestrone production is reduced.

(iv) Production of oestrogen is also reduced in this phase.

(v) The endometrium of uterus breaks down & menstruation begins.

(vi) The cells of endometrium secretions, blood & unfertilised ovum constitutes the menstrual flow.

(2) Follicular Phase:

(i) This phase usually includes cycle days 6-13 or 14 in a 28 days cycle.

(ii) The follicle stimulating hormone (FSH) secreted by the anterior lobe of the pituitary gland stimulates the ovarian follicle to secrete oestrogens.

(iii) Oestrogen stimulates the proliferation of the endometrium of the uterine wall.

(iv) The endometrium becomes thicker by rapid cell multiplication and this is accompanied by an increase in uterine glands & blood vessels.

(3) Ovulatory Phase:

(i) Both LH & FSH attain a peak level in the middle of cycle (about 14^th day).

(ii) Oestrogen concentration in blood increases.

(iii) Rapid secretion of LH induces rupturing of graffian follicle and thereby the release of ovum.

(iv) In fact LH causes ovulation.

(4) Luteal Phase:

(i) Includes cycle days 15 to 28.

(ii) Corpus luteum secretes progestrone.

(iii) Endometrium thickens.

(iv) Uterine glands become secretory.

Hormonal Control of MC

(i) FSH stimulates the ovarian follicles to produce oestrogens.

(ii) LH stimulates corpus luteum to secrete progestrone.

(iii) Menstrual phase is caused by the increased production of oestrogens.

(iv) LH causes ovulation

(v) Proliferative phase is caused by the increased production of oestrogens.

(vi) Secretory phase is caused by increased production of progestrone.

Fertilisation and Implantation

The process of fusion of sperm with ovum is called fertilisation.

• During coitus (copulation) semen is released into vagina. The motile sperms swim rapidly to reach the junction of isthmus and ampulla of fallopian tube. The ovum also reaches there and fusion of gametes takes place in at ampullary-isthmic junction.
• In this acrosome of sperm undergoes acrosomal reaction and releases certain sperm lysins which dissolve the egg envelopes locally and make the path for the penetration of sperm.
• These sperm lysins contain a lysing enzyme hyaluronidase which dissolves the hyaluronic acid polymers in the intercellular spaces which holds the granulosa cells of corona radiata together; corona penetrating enzyme (that dissolves the corona radiata) and acrosin (which dissolves the zona pellucida). Then it dissolves the zona pellucida.

Cortical reaction:

(a) Immediately after the entry of a sperm into the egg, the later shows a cortical reaction to check the entry of more sperms.

(b) In this reaction, the cortical granules present beneath the egg’s plasma membrane release chemical substance between the ooplasm and the plasma membrane (vitelline membrane).

(c) These substances raise the vitelline membrane above the egg surface. The elevated vitelline membrane is called fertilization membrane.

(d) The increased space between the ooplasm and the fertilization membrane and the chemical present in it effectively check the entry of other sperm.

(e) If polyspermy occurs, that is more than one sperm enter the secondary oocyte, the resulting cell has too much genetic material to develop normally

• The haploid gametes fuse together to form diploid zygote. As the zygote moves towards the uterus, the mitotic division starts and form cleavage to change into 2, 4,8,16 celled blastomeres.
• The blastomeres with 8 to 16 cells are called morula. Morula divide to change into blastocysts .The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called the inner cell mass.The outer layer of blastocyst is called trophoblast that attach with endometrium of uterus, called implantation that leads to pregnancy.

Pregnancy and embryonic development

The finger-like projections on trophoblaste after implantation called is called chronic villi that along with uterine wall forms functional unit between developing embryo and maternal body called placenta. Placenta is attached with fetus with an umbilical cord that transport food and oxygen to embryo.

• Hormones hCG (human chorionic gonadotropin), hPL (human placental lactogen) and relaxin are produced in woman only during pregnancy by placenta.
• After implantation, the inner cell mass (embryo) differentiates into an outer layer called ectoderm and an inner layer called endoderm. A mesoderm soon appears between the ectoderm and the endoderm. These three layers give rise to all tissues (organs) in adults. It is important to note that the inner cell mass contains certain cells called stem cells which have the potency to give rise to all the tissues and organs
• In human, after one month of pregnancy the embryo’s heart is formed. By the end of 2^nd month limbs and digits are formed. By the end of 12 months, major organs and external genital organs are well developed. The first movement of foetus is observed in 5 months. By the end of 24 weeks body is covered with fine hair, eye lids and eyeless are formed. At the end of 9 months fetus is fully developed.

PARTURITION AND LACTATION

Parturition-the process of delivery of fully developed foetus is called parturition.

• Signals for parturition originate from the fully developed fetus and placenta inducing mild uterine contractions called Foetal ejection reflex
• It triggers the release of oxytocin from maternal pituitary

The mammary glands of female, start producing milk, to the end of pregnancy by the process of lactation. The milk produced during the initial few days of lactation is called colostrum, which contain several antibodies.

Class 12 Notes For Sexual Reproduction in Flowering Plants

Reproduction ensures continuity of species generation after generations as the older individuals undergo senescence and die. Flowering plants shows sexual mode of reproduction and bears complex reproductive units as male and female reproductive units along with accessary structures.

Flower is a modified stem which functions as a reproductive organ and produces ova and/or pollen. A typical angiospermic flower consists of four whorls of floral appendages attached on the receptacle: calyx, corolla, androecium (male reproductive organ consisting of stamens) and gynoecium (composed of ovary, style and stigma) .

Pre-fertilisation: Structures and Events

• Several structural and hormonal changes lead to formation and development of the floral primordium. Inflorescence is formed that bears floral buds and then flower.

• In flowers, male (androecium) and female (gynoecium) differentiate and develops in which male and female gametes are produced.

Stamen, Microsporangium and Pollen Grain :

• Stamen consists of long and slender stalk called filament and generally bilobed anthers. Each lobe contains two theca (dithecious).

• The anther is four-sided structure consisting of four microsporangia, two in each lobes.

• Microsporangia develop further and become pollen sacs which contain pollen grains.

• Microsporangium is generally surrounded by four layered walls- the epidermis, endothecium, middle layer and tapetum. Innermost layer tapetum nourishes the developing pollen grains.

• Sporogenous tissues- It is compactly arranged homogenous cells which are present at centre of each microsporangium when the anther is young..

Microsporogenesis- The process of the formation and differentiation of microspores (pollen grains) from microspore mother cells (MMC) by reductional division is called microsporogenesis.

• The cells of sporogenous tissues undergo meiotic division to form microspore tetrad. As the anther mature and dehydrate, the microspore dissociate and develops into pollen grains.

Pollen grain represents the male gametophytes. Pollen grains are made of 2 layered Wall,

1. Exine :- Made of sporopollenin- most resistant organic matter known.It can withstand high temperatures and strong acids and alkali. No enzyme can degrade sporopollenin

2. Intine :-
-Thin and continuous layer
– Made of cellulose and pectin

3. Germ pores
– apertures on exine where sporopollenin is absent
– forms pollen tube.

4. A plasma membrane surrounds cytoplasm of pollen grain.

MATURE POLLEN
— A mature pollen consist of 2 cells with nucleus (Vegetative and Generative)

VEGETATIVE CELL

• Bigger
• Abundant food reserve
• Large irregular nucleus
• Responsible for the development of pollen grain

GENERATIVE CELL

• Small
• Involves in syngamy (fuse with an egg)
• Dense cytoplasm and nucleus

• Pollen grains of many species e.g Parthenium cause severe allergies and bronchial diseases in some people and leads to chronic respiratory disorders– asthma, bronchitis, etc.

• Pollen grains are rich in nutrients and are used as pollen tablets as food supplements.

• Viability of pollen grain varies with species to species and should land on stigma before this period to germinate. Pollen grains of large number of species are stored in liquid nitrogen at temperature – 196⁰, called pollen bank.

The Pistil, Megasporangium (Ovule) and Embryo sac

• Gynoecium may consists of single pistil (monocarpellary) or more than one pistil (polycarpellary) which may be fused (syncarpous) or free (apocarpous).

e.g Multicarpellary and syncarpous pistil- Papaver

Multicarpellary and apocarpous pistil- Michelia

• Each pistil has three parts the stigma, style and ovary. Inside the ovary is ovarian cavity (locule). The placenta is located inside the ovarian cavity. Megasporangia (ovules) arise from placenta.

Megasporangium (ovule)

• Ovule is a small structure attached to placenta.
• Funicle – stalk by which ovule is attached to placenta
• Hilum- junction between ovule and funicle
• Integuments- protective envelops
• Micropyle- small opening at the tip of ovule into where pollen tube enters
• Chalaza- basal part of ovule
• Nucellus (2n)-mass of cells enclosed in integuments. Has abundant food reserve.

Megasporogenesis- The process of formation of megaspore from megaspore mother cell by meiotic division is known as megasporogenesis. This process takes place in ovule

Ovule differentiates a single megaspore mother cell (MMC) in the micropylar region of nucellus. MMC undergoes meiotic division that results into the production of four megaspores.

• In most of the flowering plants three megaspores degenerate. 1megaspore develops into female gametophyte (embryo sac).

• The nucleus of functional megaspore divides mitotically to form two nuclei which move to opposite poles to form 2-nucleate embryo sac. Two more sequential mitotic division results into 8-nucleate embryo sac.

• Six of the eight nuclei surrounded by cell wall and remaining two nuclei (polar nuclei) are situated below the egg apparatus.

• Three cells are grouped at micropylar end to constitute egg apparatus and three cells at chalazal end forms antipodal cells. At maturity ,embryosac is 8-nucleate and 7 celled.

Pollination – transfer of pollen grains from anther to stigma.

a) Autogamy– transfer of pollen grain from anther to stigma of same flower.

i. Cleistogamous – flower which do not open. cleistogamous flowers are autogamous as there is no chance of cross-pollen landing on the stigma. Cleistogamous flowers produce assured seed-set even in the absence of pollinators. e.g Viola (common pansy), Oxalis, and Commelina.

ii. Chasmogamous– exposed anther and stigma.

b) Geitonogamy – transfer of pollen grains from anther to stigma of different flower of same plant. Geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plant

c) Xenogamy– transfer of pollen grain from anther to stigma of different plant’s flower of same species.

Agents of pollination includes abiotic (water, wind) and biotic (insects, butterfly, honey bee etc. large number of pollen grains are produced by plants using abiotic mode of pollination as most of pollen grains are wasted during transfer.

Adaptations in flowers for Pollination

I. Wind Pollination

• pollen grains :– light, non- sticky, winged
• anther :- well exposed
• stigma :- large and feathery
• flower :- one ovule, arranged as inflorescence

Ex : corn cob, cotton, date palm

II. Water Pollination
– Bryophytes, Pteridophytes, Algae

• pollen grains : protected by mucilaginous covering

Ex : Fresh water plants- Vallisneria, Hydrilla
Sea grass- Zostera

Main features of wind and water pollinated plants
– produce pollen grains in large no.
– do not produce nectar

III. Insect Pollination
– Flowers : large, colourful, fragrant, rich in nectar
– Pollen grains : sticky
– Stigma : sticky

Certain rewards to pollinators:

• nectar and (edible) pollen grains as foods
• provide safe place for laying eggs

Ex : Amorphophallus, Yucca

Outbreeding Devices– the various mechanisms take discourage self-pollination and encourage cross pollination as continued self-pollination leads to inbreeding depression. It includes

• Pollen release and stigma receptivity not synchronized.

• Anther and stigma are placed at different position.

• Inhibiting pollen germination in pistil.

• Production of unisexual flowers.

Pollen pistil interaction – the pistil has ability to recognize the compatible pollen to initiate post pollination events that leads to fertilisation. Pollen grain produce pollen tube through germ pores to facilitate transfer of male gametes to embryo sac.

Artificial Hybridization

• Crossing diff varieties of species- hybrid individual- with desirable characters of the parent plants
• desired pollen grains for pollination- stigma protected from contamination
• Emasculation : removal of anther
• Bagging : flower covered- bag made up of butter-prevent contamination of stigma from unwanted pollen

Bagged flower- attains receptivity- mature pollen grains- dusted on the stigma – rebagged- fruits allowed to develop

Double Fertilisation- after entering the one of the synergids, each pollen grain releases two male gametes. One male gametes fuse with egg (Syngamy) and other male gametes fuse with two polar nuclei (triple fusion) to produce triploid primary endosperm nucleus (PEN). Since two types of fusion takes place in an embryo sac the phenomenon is called double fertilisation. The PEN develops into the endosperm and zygote develops into embryo.

Post fertilisation events include endosperm and embryo development, maturation of ovules into seeds and ovary into fruits.

Endosperm– the primary endosperm cell divides many time to forms triploid endosperm tissue having reserve food materials.

Two types of endosperm development :
(i) Free nuclear type (common method)
(ii) Cellular type

(a) Non-albuminous- endosperm completely utilized- before maturation of seeds. e.g pea, groundnut

(b) Albuminous- a portion of endosperm remain in mature seeds. e.g wheat, maize, castor

Embryo- Embryo develops at the micropylar end of the embryo sac where the zygote is located.

Embryogeny – early stages of embryo development.The zygote gives rise to the proembryo and subsequently to the globular, heart-shaped and mature embryo.

Embryo consists of:
– embryonal axis
– cotyledons
– plumule
– radicle

Monocotyledonous Seed
– Scutellem = Cotyledon
– Coleorrhiza: undifferentiated sheath covering radical & root cap
– Coleoptile: sheath covering plumule

Seed
– Fertilized and mature ovule develops into seed.

Seed consists of:
– cotyledon(s)
– embryonal axis
– Seed coat- double layered- formed by integuments

• Testa (outer coat)
• Tegmen (inner coat)

– Micropyle:- small opening on seed coat, it facilitates entry of H2O & O2 into seeds (for germination)
– Hilum:- scar on seed coat
– Seed – Albuminous / Non-Albuminous
– Perisperm : remnants of nucellus that is persistent. Ex: Black pepper
– Dormancy: state of inactivity

• The wall of ovary develops into wall of fruit called pericarp. In true fruits only ovary contributes in fruit formation by in false fruit thalamus also contributes in fruit formation.

Apomixis
– Form of asexual reproduction- mimics sexual reproduction- seed formed without fertilisation
– Formation of apomictic seeds :
• diploid cell (formed without meiosis)- develop into embryo without fertilization
• cells of nucellus (2n) surrounding embryo sac- protrude into embryo sac- develop into embryos. Ex. Citrus and Mango.

Polyembryony
– Occurrence of more than one embryo in a seed
– Often associated with apomixes. Ex: Citrus, groundnut     

Class 12 Biology Revision Notes

Reproduction is a biological process of formation of new offsprings from the pre-existing organism. Reproduction becomes a vital process without which species cannot survive for long It ensures continuity of species generation after generations as older individuals undergo senescence and ultimately they die.

Life span – • The period from birth to the natural death of an organism represents its life span. Life span of organisms varies from few days (Butterfly-1to 2 weeks) to thousands of years (Banyan tree).

Types of Reproduction:
Based on whether there is one or two organisms taking part in the process of reproduction

• ASEXUAL REPRODUCTION
• SEXUAL REPRODUCTION

When the offspring is produced by single parents with or without the involvement of gamete formation, the reproduction is called asexual reproduction.

When two parents (opposite sex) participates in reproduction process and also involves the fusion of male and female gametes, it is called sexual reproduction.

Asexual Reproduction

1. Usually followed by organisms with relatively simpler organizations.
2. Offsprings produced by single parent.
3. With/without involvement of gamete formation.
4. Offsprings produced are genetically and morphologically similar to each other and to the parent, i.e. they are clones.

• In Protista and Monera, the parent cells divides into two to give rise to new individuals. Thus, in these organisms cell division is the mode of reproduction itself.

• Binary fission– in this method of asexual reproduction, a cell divides into two halves and rapidly grows into an adult. Ex- amoeba, paramecium.

• Budding– small buds are produced that remain attached initially with parents and get separated on maturation. Ex. Yeast.

• Fungi and simple plants like algae reproduce through special reproductive structures like zoospores (motile structure), conidia (penicillium), buds (hydra) and gemmules (sponges).

• In plants, vegetative reproduction occurs by vegetative propagules like runner, rhizome, sucker, tuber, offset and bulb.

WATER HYACINTH (Terror of Bengal)

• One of the most invasive weeds
• Grows wherever there is standing water
• Drains oxygen from water- leads to death of fishes.
• Introduced in India because of its pretty flowers & shape of leaves
• Vegetative propagation occurs at a phenomenal rate

Asexual reproduction is the most common method of reproduction in organisms having simpler body like in algae and fungi but during unfavorable condition they shift to sexual reproduction.

SEXUAL REPRODUCTION:

• Involves formation of male and female gamete by two individuals of the opposite sex.
• Offspring produced by fusion of male and female gametes not identical to each other or to the parents.
• All sexually reproducing organisms share a similar pattern of reproduction.

• In sexual reproduction, fusion of male and female gametes results in offspring that are not identical to parents.

DIFFERENT PHASES IN SEXUAL REPRODUCTION:

a. Juvenile phase – The period between birth and sexual maturity is called juvenile phase. In plants it is known as vegetative phase.The end of juvenile/vegetative phase marks the beginning of the reproductive phase.

b. Reproductive phase-

• Some plants show flowering in particular season and some other flowers in all seasons. Some other plants like bamboo species flowers once in life time (after 50-100 years), Strobilanthus kunthiana (neelakuranji),flowers once in 12 years.

• The female placental animals exhibit cyclic change in activities ovaries and accessary glands as well as hormone during the reproductive phase.

Menstrual cycle
• It occurs in monkeys, apes and human beings.
• Cycle consists of 3 phases-menstrual, proliferative and secretory phase.
• Blood flows in the last few days of the cycle. The broken endometrium is passed out during menstruation.
• Female does not permit copulation during menstrual phase of the cycle.

Oestrous cycle
• It occurs in non primates like cow, sheep, rat, deer, dog, tiger etc.
• It consists of a short period of oestrous or heat. it is 12-24 hours in cow followed by anoestrous or passive period.
• Blood does not flow in this cycle. The broken endometrium is reabsorbed.
• Female permits copulation only during oestrous period.
• Both in plants and animals, hormones are responsible for the transition between different phases of life cycle. Interaction between hormones and environmental factors regulate the reproductive processes.

c. Senescent phase –

• It is the end of reproductive phase.
• Old age ultimately leads to death

Events in Sexual Reproduction : Pre-fertilisation, Fertilisation, Post-fertilisation

Pre-fertilisation– all the events prior to fusion of gametes are included in it. It includes gametogenesis and gamete transfer.

a. Gametogenesis is the process of formation of male and female gametes. Gametes are haploid cells which may be similar or dissimilar in structure. In algae, both gametes are similar in structure called homogametes (isogametes). In higher organism that reproduces sexually, two morphologically distinct gametes are formed called heterogametes, male gametes are called antherozoid or sperm and female gametes are called ovum or egg.

Isogametes. heterogametes

In fungi and plants, homothallic and monoecious terms are used to denote the bisexual condition and heterothallic and dioecious are used for unisexual condition. In flowering plants, the unisexual male flower is staminate, i.e., bearing stamens, while the female is pistillate or bearing pistils.

• In animals, species which possess both male and female reproductive organs in same individual are called bisexual or hermaphrodites (earthworm, sponges, tapeworm etc.) and both having either male or female reproductive organs are called unisexual (cockroach, human).

• Gametes are always haploid( having half set of chromosome ), although organisms may be haploid and diploid. Diploid organisms form gametes by meiotic division. The organisms belonging to algae, fungi, and bryophytes have haploid plant body and pteridophytes, gymnosperms, angiosperms and most of animals are diploid ( having double set of chromosome )

• In diploid organisms, gamete mother cell (meiocyte) undergoes meiosis in which one set of chromosome is present in gametes.

b. Gamete Transfer – in majority of organisms, male gametes are motile and females gametes are non-motile, except in fungi and algae in which both gametes are motile.

• In simple plants like algae, fungi, bryophytes and pteridophytes water is the medium through which male and female gametes moves. The number of male gametes are much more than number of female gametes as most of male gametes fail to reach the female gametes.

• In higher plants pollen grains are carrier of male gametes and ovule has eggs. Pollen grains must be transferred from anther to stigma to facilitate fertilisation. The transfer of pollen grains from anther to stigma is called pollination. Pollination may be self (anther to stigma of same flower) or cross (anther to stigma of different flower).

• Pollen grains germinate on stigma to produce pollen tube that delivers the male gametes near the ovule.

c. Fertilisation – The fusion of male and female gamete is called fertilization or syngamy. It results in the formation of diploid zygote.

• The process of development of new organisms without fertilisation of female gametes is called parthenogenesis. For example honey bee, rotifers, and lizards

EXTERNAL FERTILIZATION	INTERNAL FERTILIZATION
Syngamy occurs outside the body of the organism Large numbers of gametes are released in the surrounding medium. Ex. Bony fishes and Amphibians.	Syngamy occurs inside the body of the organism Numbers of ova produced are less, but large numbers of male gametes are released and they travel towards the ovum. Ex. Birds and Mammals.

d. Post Fertilisation Events- events in the sexual reproduction after formation of zygote.

Zygote is the vital link that ensures continuity of species between organisms of one generation and the next. Every sexually reproducing organism, including human beings, begin life as a single cell–the zygote.

• In the organisms, having external fertilisation, zygote is formed in external medium (water) and those having internal fertilisation zygote is formed inside the body of female.

• In algae and fungi, zygote develops a thick wall resistant to desiccation and damage. This germinates after a period of rest.

• In the organisms having haplontic life cycle, zygote divides to form haploid spores that germinate to form haploid individual.

Embryogenesis – the process of development of embryo from the zygote. During this, zygote undergoes mitotic division and cell differentiation. Cell division increase the number and cell differentiation help information of new group of cells and organs.

Oviparous	Viviparous
Development of zygote takes place outside the body of organisms and lay fertilized of unfertilized eggs.Ex – Reptiles and birds.	Development of zygote takes place inside the body of organisms and produces young ones.Ex- Human, dog, horse etc.

• In flowering plants, zygote is formed inside the ovule. After fertilisation, sepals, petals and stamens of flower fall off. The zygote develops into embryo and ovules into seeds. The ovary develops into fruits which develop a thick wall called pericarp, protective in function.

• After dispersal, seeds germinate under favorable condition to produce new plants.

A few kinds of fruit showing seeds (S) and protective pericarp (P)      

Class 12 Chemistry Revision Notes Chapter 16 Chemistry in Everyday Life

• Drugs:  Drugs are low molecular mass substances which interact with targets in the body and produce a biological response.
• Medicines: Medicines are chemicals that are useful in the diagnosis, prevention, and treatment of diseases
• Therapeutic effect: Desirable or beneficial effect of a drug like the treatment of symptoms and cure of a disease on a living body is known as therapeutic effect
• Enzymes: Proteins which perform the role of biological catalysts in the body are called enzymes
• Functions of enzymes:
  (i) The first function of an enzyme is to hold the substrate for a chemical reaction. Active sites of enzymes hold the substrate molecule in a suitable position so that it can be attacked by the reagent effectively.
  (ii) The second function of an enzyme is to provide functional groups that will attack the substrate and carry out chemical reaction.
• Role of drugs: Main role of drugs is to either increase or decrease role of enzyme catalysed reactions. Inhibition of enzymes is a common role of drug action.
• Enzyme inhibitor: Enzyme inhibitor is drug which inhibits catalytic activity of enzymes or blocks the binding site of the enzyme and eventually prevents the binding of substrate with enzyme.
• Drug can inhibit attachment of substrate on active site of enzymes in following ways:
  

1. Competitive Inhibition: Competitive Inhibitors are the drugs that compete with the natural substrate for their attachment on the active sites of enzymes.
2. Non-Competitive Inhibition: Some drugs do not bind to the enzyme’s active site, instead bind to a different site of enzyme called allosteric site. This binding of inhibitor at allosteric site changes the shape of the active site in such a way that substrate cannot recognise it. If the bond formed between an enzyme and an inhibitor is a strong covalent bond and cannot be broken easily, then the enzyme is blocked permanently. The body then degrades the enzyme-inhibitor complex and synthesizes the new enzyme.
   

• Receptors: Proteins which are vital for communication system in the body are called receptors. Receptors show selectivity for one chemical messenger over the other because their binding sites have different shape, structure, and amino acid composition.
• Receptors as Drug Targets: In the body, message between two neurons and that between neurons to muscles is communicated through chemical messengers. They are received at the binding sites of receptor proteins. To accommodate a messenger, shape of the receptor site changes which brings about the transfer of message into the cell. Chemical messenger gives message to the cell without entering the cell. 
• Antagonists and Agonists: Drugs that bind to the receptor site and inhibit its natural function are called antagonists. These are useful when blocking of message is required. Drugs that mimic the natural messenger by switching on the receptor are called agonists. These are useful when there is lack of natural chemical messenger.
• Therapeutic action of different classes of drugs:
  (i) Antacid: Chemical substances which neutralize excess acid in the gastric juices and give relief from acid indigestion, acidity, heart burns and gastric ulcers. Examples: Eno, gelusil, digene etc.
  (ii) Antihistamines: Chemical substances which diminish or abolish the effects of histamine released in body and hence prevent allergic reactions. Examples: Brompheniramine (Dimetapp) and terfenadine (Seldane).
  (iii) Neurologically Active Drugs: Drugs which have a neurological effect i.e. affects the message transfer mechanism from nerve to receptor.
• Tranquilizers: Chemical substances used for the treatment of stress and mild or severe mental diseases. Examples: Derivatives of barbituric acids like veronal, amytal, Nembutal, luminal, seconal.
• Analgesics: Chemical substances used to relieve pain without causing any disturbances in the nervous system like impairment of consciousness, mental confusion, in coordination or paralysis etc.
• Classification of Analgesics:
  (a) Non-narcotic analgesics: They are non-addictive drugs. Examples: Aspirin, Ibuprofen, Naproxen, Dichlofenac Sodium.
  (b) Narcotic analgesics: When administered in medicinal doses, these drugs relieve pain and produce sleep. Examples: Morphine and its derivatives) Anti-microbials: Drugs that tends to destroy/prevent development or inhibit the pathogenic action of microbes such as bacteria (antibacterial drugs), fungi (anti-fungal agents), virus (antiviral agents), or other parasites (anti-parasitic drugs) selectively.
  v) Anti-fertility Drugs: Chemical substances used to prevent conception or fertilization are called anti-fertility drugs. Examples – Norethindrone, ethynylestradiol (novestrol).
• Types of antimicrobial drugs :
  (a) Antibiotics: Chemical substances produced by microorganisms that kill or prevent the growth of other microbes.

Classification of antimicrobial drugs based on the mode of control of microbial diseases:

1. Bactericidal drugs – Drugs that kills organisms in the body. Examples – Penicillin, Aminoglycosides, Ofloxacin.
2. Bacteriostatic drugs – Drugs that inhibits growth of organisms. Examples – Erythromycin, Tetracycline, Chloramphenicol.

Classification of antimicrobial drugs based on its spectrum of action:

1. Broad-spectrum antibiotics – Antibiotics which kill or inhibit a wide range of Gram-positive and Gram-negative bacteria are called broad-spectrum antibiotics. Examples – Ampicillin and Amoxycillin.
2. Narrow spectrum antibiotics – Antibiotics which are effective mainly against Gram-positive or Gram-negative bacteria are called narrow-spectrum antibiotics. Examples- Penicillin G.
3. Limited spectrum antibiotics  -Antibiotics effective against a single organism or disease

(b) Antiseptics: Chemical substances that kill or prevent growth of microorganisms and can be applied on living tissues such as cuts, wounds etc., are called anti-spetics. Examples – Soframicine, dettoletc.

(c) Disinfectants: Chemical substances that kill microorganisms but cannot be applied on living tissues such as cuts, wounds etc., are called disinfectants. Examples – Chlorine (Cl2), bithional, iodoform etc.

• Food additives: Food additives are the substances added to food to preserve its flavor or improve its taste and appearance.
• Different types of food additives:

1. Artificial Sweetening Agents: Chemical compounds which gives sweetening effect to the food and enhance its flavour. Examples – Aspartame, Sucrolose and Alitame.
2. Food preservatives: Chemical substances which are added to food material to prevent their spoilage due to microbial growth. Examples – Sugar, Salts, Sodium benzoate
3. Food colours: Substances added to food to increase the acceptability and attractiveness of the food product. Examples – Allura Red AC, Tartrazine
4. Nutritional supplements: Substances added to food to improve the nutritional value. Examples -Vitamins, minerals etc.
5. Fat emulsifiers and stabilizing agents: Substances added to food products to give texture and desired consistency. Examples – Egg yolk (where the main emulsifying chemical is Lecithin)
6. Antioxidants: Substances added to food to prevent oxidation of food materials. Examples – ButylatedHydroxy Toluene (BHT), ButylatedHydroxy Anisole (BHA).

• Soaps: It is a sodium or potassium salts of long chain fatty acids like stearic, oleic and palmitic acid.

This reaction is known as saponification.

• Types of soaps:

1. Toilet soaps are prepared by using better grades of fats and oil sand care is taken to remove excess alkali. Colour and perfumes are added to make these more attractive.
2. Transparent soaps are made by dissolving the soap in ethanol and then evaporating the excess solvent.
3. In medicated soaps, substances of medicinal value are added. In some soaps, deodorants are added.
4. Shaving soaps contain glycerol to prevent rapid drying. A gum called, rosin is added while making them. It forms sodium rosinate which lathers well.
5. Laundry soaps contain fillers like sodium rosinate, sodium silicate, borax, and sodium carbonate.
6. Soaps that float in water are made by beating tiny air bubbles before their hardening.
7. Soap chips are made by running a thin sheet of melted soap ontoa cool cylinder and scraping off the soaps in small broken pieces.
8. Soap granules are dried miniature soap bubbles.
9. Soap powders and scouring soaps contain some soap, a scouring agent (abrasive) such as powdered pumice or finely divided sand, and builders like sodium carbonate and trisodium phosphate.

• Advantages of using soaps: Soap is a good cleansing agent and is 100% biodegradable i.e. micro- organisms present in sewage water can completely oxidize soap. Therefore, soaps do not cause any pollution problems.
• Disadvantages of using soaps: Soaps cannot be used in hard water because hard water contains metal ions like Ca2+ and Mg2+ which react with soap to form a white precipitate of calcium and magnesium salts

These precipitates stick to the fibers of the cloth as gummy mass and block the ability of soaps to remove oil and grease from fabrics. Therefore, it interferes with the cleansing ability of the soap and makes the cleansing process difficult.

In acidic medium, the acid present in solution precipitate the insoluble free fatty acids which adhere to the fabrics and hence block the ability of soaps to remove oil and grease from the fabrics. Hence soaps cannot be used in acidic medium

• Detergents: Detergents are sodium salts of long chain of alkyl benzene sulphonic acids or sodium salts of long chain of alkyl hydrogen sulphates.

• Classification of detergents:

(a)Anionic detergents: Anionic detergents are sodium salts of sulphonated long chain alcohols or hydrocarbons. Alkyl hydrogen sulphates formed by treating long chain alcohols with concentrated sulphuric acid are neutralised with alkali to form anionic detergents. Similarly alkyl benzene sulphonates are obtained by neutralising alkyl benzene sulphonic acids with alkali. Anionic detergents are termed so because a large part of molecule is an anion.

They are used in household cleaning like dishwasher liquids, laundry liquid detergents, laundry powdered detergents etc. They are effective in slightly acidic solutions where soaps do not work efficiently.

(b)Cationic detergents: Cationic detergents are quarternary ammonium salts of mine with acetates, chlorides or bromides as anions. Cationic parts possess a long hydrocarbon chain and a positive charge on nitrogen atom. Cationic detergents are termed so because a large part of molecule is a cation. Since they possess germicidal properties, they are used as germicides. They has strong germicidal action, but are expensive.

(c) Non- ionic detergents: They do not contain any ion in their constitution. They are like esters of high molecular mass.

Example: Detergent formed by condensation reaction between stearic acid reacts and poly ethyl eneglycol.

It is used in Making liquid washing detergents. They have effective H- bonding groups at one end of the alkyl chain which make them freely water soluble.

• Biodegradable detergents: Detergents having straight hydrocarbon chains that are easily decomposed by microorganisms. Example: Sodium lauryl sulphate

• Non-Biodegradable detergents: Detergents having branched hydrocarbon chains that are not easily decomposed by microorganisms.

Class 12 Chemistry Revision Notes Chapter 15 Polymers

• Polymers: Polymers are high molecular mass substance consisting of large number of repeating structural units. As polymers are single, giant molecules i.e. big size molecules, they are also called macromolecules
• Monomers: The simple molecules which combine to form polymers by forming single or multiple bonds are called monomers.
• Polymerization: The process of formation of polymers from respective monomers is called polymerization
• Classification of Polymers:

1. Based on source of availability, it is classified into
   1. Natural polymers: Polymers obtained from nature, mostly plants and animals. Examples – Cellulose, starch, etc.
   2. Synthetic polymers: Polymers prepared in laboratory. Examples – Teflon, Nylon 6,6 , Synthetic rubber (Buna – S) etc.
   3. Semi synthetic polymers: Polymers derived from naturally occurring polymers by carrying out chemical modifications. Examples – Rayon (cellulose acetate), cellulose nitrate, etc.
2. Based on the structure of polymer, it is classified into
   1. Linear polymers: Polymer consists of long and straight chains. Examples – High density polythene, polyvinyl chloride, etc.
   2. Branched chain polymers: Polymers contains linear chains having some branches. Examples – Low density polythene
   3. Cross linked or network polymers: Polymers in which monomer units are cross linked together to form a 3 dimensional network polymers. Examples – Bakelite, melamine, etc.
3. Based on the mode of polymerisation, it is classified into
   I. Addition polymers: Polymers are formed by the repeated addition of monomers with double and triple bonds. It is further classified into,
   Homopolymers:Polymers formed by the polymerisation of a single monomeric species. Examples – Polythene, Polystyrene.
   Copolymers:Polymers formed by addition polymerisation of two different monomers. Examples – Buna-S, Buna –N.
   II. Condensation polymers: Polymers formed by repeated condensation reaction between two different bi-functional or tri-functional monomeric units with elimination of simple molecules. Examples – Nylon 6, 6, Nylon 6.

Based on Molecular forces, it is classified into

Step 1: Chain initiating step: Organic peroxides undergo homolytic fission to form free radicals which acts as initiator. Initiator adds to C-C double bond of an alkene molecule to form a new free radical

Step 2: Chain propagating step: Free radicals formed by homolytic cleavage adds to a double bond of monomer to form a larger free radical. Radical formed adds to another alkene molecule to form a larger free radical. This process continues until the radical is destroyed. These steps are called propagation steps.

Step 3: Chain terminating step: For termination of the long chain, free radicals combine in different ways to form polythene. One mode of termination of chain is shown as under:

a). Low density polythene (LDP) is a polymer of ethene.

It is used in the insulation of electricity carrying wires and manufacture of squeeze bottles, toys and flexible pipes

b). High density polythene(HDP) is a polymer of ethene.

It is used for manufacturing buckets, dustbins, bottles, pipes, etc.

c). Polytetrafluoroethene (is a polymer of Teflon)

It is used in making oil seals and gaskets and also used for non – stick surface coated utensils

d). Polyacrylonitrile is a polymer of acrylonitrile.

It is used as a substitute for wool in making commercial fibres such as orlon or acrilan.

1. Polyamides: Polymers possess amide linkage (-CONH-) in chain. Thesepolymers are popularly known as nylons. Examples:
(a) Nylon 6, 6: It is prepared by the condensation polymerisation of hexamethylenediamine with adipic acid under high pressure and at high temperature. 
It is used in making sheets, bristles for brushes and in textile industry.

(b) Nylon 6: It is obtained by heating caprolactum with water at a high temperature 
It is used for the manufacture of tyre cords, fabrics and ropes.

2. Polyesters: These are the polycondensation products of dicarboxylic acids and diols Example: Terylene or Dacron

It is used to create resistance in polymerised product and is used in blending with cotton and wool fibres and also as glass reinforcing materials in safety helmets, etc.

3. Phenol – formaldehyde polymer (Bakelite and related polymers)

a). Bakelite: These are obtained by the condensation reaction of phenol with formaldehyde in the presence of either an acid or a base catalyst. The initial product could be a linear product – Novolac used in paints.

b). Novolac on heating with formaldehyde forms Bakelite

It is used for making combs, phonograph records, electrical switches and handles of various utensils

4. Melamine – formaldehyde polymer: Melamine formaldehyde polymer isformed by the condensation polymerisation of melamine and formaldehyde

It is used in the manufacture of unbreakable crockery.

a). Natural rubber: Natural rubber is a linear polymer of isoprene (2-methyl-1, 3-butadiene) and is also called as cis – 1, 4 – polyisoprene.

b). Synthetic rubber: Synthetic rubbers are either homopolymers of 1, 3 – butadiene derivatives or copolymers of 1, 3 – butadiene or its derivatives with another unsaturated monomer.

A) Neoprene or polychloroprene

It is used for manufacturing conveyor belts, gaskets and hoses

B) Buna – N

It is used in making oil seals, tank lining, etc. because it is resistant to the action of petrol, lubricating oil and organic solvents

C) Buna – S

a). Poly – -hydroxybutyrate – co--hydroxyvalerate (PHBV):
It is obtained by the copolymerisation of 3-hydroxybutanoic acid and 3 – hydroxypentanoic acid

It is used in speciality packaging, orthopaedic devices and in controlled release of drugs.

b). Nylon 2–nylon 6: It is an alternating polyamide copolymer of glycine(H2N–CH2–COOH) and amino caproic acid (H2N (CH2)5 COOH)

Name of Polymer	Monomer	Structure	Uses
Polypropene	Propene		Manufacture of ropes, toys, pipes, fibres, etc.
Glyptal	(a) Ethylene glycol Manufacture of(b) Phthalic acid		Manufacture of paints and lacquers
Polystyrene	Styrene		As insulator, wrapping material, manufacture of toys, radio and television cabinets
Polyvinyl chloride (PVC)	Vinyl chloride		Manufacture of rain coats, hand bags, vinyl flooring, water pipes

1. Elastomers: Polymer chains are held together by weakest intermolecular forces. Polymers are rubber – like solids with elastic properties. Examples – Buna – S, Buna – N, Neoprene.
2. Fibre: Polymers have strong intermolecular force like hydrogen bonding. Fibres are the thread forming solids which possess high tensile strength and high modulus. Examples – Nylon 6, 6, Polyesters.
3. Thermoplastic polymers: Polymers are held by intermolecular forces which are in between those of elastomers and fibres. These polymers are capable of repeated softening on heating and hardening on cooling. Examples – Polythene, Polystyrene.
4. Thermosetting polymers: Polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and eventually undergo a permanent change. Examples – Bakelite, Urea-formaldelyde resins
5. Addition Polymerisation or Chain Growth Polymerisation: Addition polymerisation is called chain growth polymerisation because it takes place through stages leading to increase in chain length and each stage produces reactive intermediates for use in next stage of the growth of chain. Most common mechanism for addition polymerisation reactions is free radical mechanism

Important Addition Polymers:

Condensation Polymerisation or Step Growth polymerization: Polymerisation generally involves a repetitive condensation reaction between two bi-functional monomers. In condensation reactions, the product of each step is again a bi-functional species and the sequence of condensation goes on. Since, each step produces a distinct functionalized species and is independent of each other, this process is also called as step growth polymerisation.

Condensation Polymers:

Terylene or Dacron: It is manufactured by heating a mixture of ethylene glycol and terephthalic acid at 420 to 460 K in the presence of zinc acetate-antimony trioxide catalyst.

Vulcanisation of rubber: The process of heating a mixture of raw rubber with sulphur and an appropriate additive in a temperature range between 373 K to 415 K to improve upon physical properties like elasticity, strength etc.

Examples of synthetic rubber:

Biodegradable Polymers: Polymers which are degraded by microorganisms within a suitable period so that biodegradable polymers and their degraded products do not cause any serious effects on environment.

Examples of biodegradable polymer:

Commercially important polymers along with their structures and uses

Class 12 Quick Revision Notes for Chapter 14 Biomolecules Chemistry

• Carbohydrates: Polyhydroxy aldehydes or polyhydroxy ketones or compounds on hydrolysis give carbohydrates.
• Classification of carbohydrates:
  Monosaccharides
  (a) Simplest carbohydrates
  (b) It cannot be hydrolysed into simpler compounds
  (c) Examples – Glucose, mannose
  Oligosaccharides
  (a) Carbohydrates which gives 2 to 10 monosaccharide units on hydrolysis
  (b) Examples – Sucrose, Lactose, Maltose
  Polysaccharides
  (a) Carbohydrates which on hydrolysis give large number of monosaccharide units.
  (b) Examples – Cellulose, starch
• Anomers: Pair of optical isomers which differ in configuration only around C1 atom are called anomers. Examples – -D-glucopyranose and -D-glucopyranose.
• Epimers: Pair of optical isomers which differ in configuration around any other C atom other than C1 atom are called epimers. E.g. D-glucose and D- mannose are C2epimers.
  

Preparation of glucose (also called dextrose, grape sugar):

• From starch

• Structure of glucose

• Structure elucidation of glucose:

a) D – glucose with HI

b) D – glucose with HCN

c) D – glucose with NH₂OH

d) D- glucose with Fehling’s reagent

e) D – glucose with Tollen’s reagent

f) D – glucose with nitric acid

g) D – glucose with (CH₃CO)₂O and ZnCl₂

h) D – glucose with bromine water

i) Glucose with phenylhydrazine to form osazone

Glucose and fructose gives the same osazone because the reaction takes place at C1 and C2 only.

• Other Reactions of Glucose (Presence of ring structure)

Glucose does not give Schiff’s test and does not react with sodium bisulphite and NH3. Pentaacetyl glucose does not react with hydroxyl amine. This shows the absence of –CHO group and hence the presence of ring structure.

• Cyclic structure of glucose:

• Haworth representation of glucose:

• Cyclic structure of fructose:

• Haworth representation of fructose

• Glycosidic linkage: The oxide linkage formed by the loss of a water molecule when two monosaccharides are joined together through oxygen atom is called glycosidic linkage.
• Sucrose (invert sugar):

a) Sucrose is a non-reducing sugar because the two monosaccharide units are held together by a glycosidic linkage between C1 of -glucose and C2 of – fructose. Since the reducing groups of glucose and fructose are involved in glycosidic bond formation, sucrose is a non-reducing sugar.

b) Sucrose is dextrorotatory but on hydrolysis it gives dextrorotatory & laevorotatory and the mixture is laevorotatory.

• Haworth Projection of Sucrose:

• Maltose:

1. Maltose is composed of two α-D-glucose units in which C1 of one glucose (I) is linked to C4 of another glucose unit (II).
2. The free aldehyde group can be produced at C1 of second glucose in solution and it shows reducing properties so it is a reducing sugar.
   

• Haworth projection of maltose:
  
• Lactose (Milk sugar):It is composed of β-D-galactose and β-D-glucose. The linkage is between C1 of galactose and C4 of glucose. Hence it is also a reducing sugar.
  
• Haworth projection of lactose:

• Starch: It is a polymer of -glucose and consists of two components — Amylose and Amylopectin.
• Amylose:

1. It is a water soluble component
2. It is a long unbranched chain polymer
3. It contains 200 – 1000 -D-(+)- glucose units held by – glycosidic linkages involving C1 – C4glycosidic linkage
4. It constitutes about 15-20% of starch

• Amylopectin

1. It is a water insoluble component
2. It is branched chain polymer
3. It forms chain by C1 – C4glycosidic linkage whereas branching occurs by C1 – C6glycosidic linkage
4. It constitutes about 80-85% of starch

• Cellulose:

1. It occurs exclusively in plants.
2. It is a straight chain polysaccharide composed only of -D-glucose units which are joined by glycosidic linkage between C1 of one glucose unit and C4 of the next glucose unit.

• Glycogen:

1. The carbohydrates are stored in animal body as glycogen.
2. It is also known as animal starch because its structure is similar to Amylopectin.
3. It is present in liver, muscles and brain.
4. When the body needs glucose, enzymes break the glycogen down to glucose.

• Amino acids:

Amino acids contain amino (–NH2) and carboxyl (–COOH) functional groups.

Where R – Any side chain
Most naturally occurring amino acids have L – Config.

• Types of amino acids:

a). Essential amino acids: The amino acids which cannot be synthesised in the body and must be obtained through diet, are known as essential amino acids. Examples: Valine, Leucine

b). Non-essential amino acids: The amino acids, which can be synthesised in the body, are known as non-essential amino acids. Examples: Glycine, Alanine

• Zwitterion form of amino acids:

1. Amino acids behave like salts rather than simple amines or carboxylic acids. This behaviour is due to the presence of both acidic (carboxyl group) and basic (amino group) groups in the same molecule. In aqueous solution, the carboxyl group can lose a proton and amino group can accept a proton, giving rise to a dipolar ion known as zwitter ion. This is neutral but contains both positive and negative charges.
2. In zwitterionic form, amino acids show amphoteric behaviour as they react both with acids and bases.

• Isoelectronic point: The pH at which the dipolar ion exists as neutral ion and does not migrate to either electrode cathode or anode is called isoelectronic point.
• Proteins: Proteins are the polymers of -amino acids and they are connected to each other by peptide bond or peptide linkage. A polypeptide with more than hundred amino acid residues, having molecular mass higher than 10,000u is called a protein.
• Peptide linkage: Peptide linkage is an amide linkage formed by condensation reaction between –COOH group of one amino acid and –NH2 group of another amino acid.

Peptide link age

• Primary structure of proteins: The sequence of amino acids is said to be the primary structure of a protein.
• Secondary structure of proteins: It refers to the shape in which long polypeptide chain can exist. Two different types of structures:

– Helix:

1. It was given by Linus Pauling in 1951
2. It exists when R- group is large.
3. Right handed screw with the NH group of each amino acid residue H – bonded to – C = O of adjacent turn of the helix.
4. Also known as 3.613 helix since each turn of the helix hasapproximately 3.6 amino acids and a 13 – membered ring is formed by H – bonding.
5. C = O and N – H group of the peptide bonds are trans to each other.
6. Ramchandran angles (and) – angle which makes with N – H and angle which makes with C = O.

– pleated sheet:

1. It exists when R group is small.
2. In this conformation, all peptide chains are stretched out to nearly maximum extension and then laid side by side which are held together by hydrogen bonds.

• Tertiary structure of proteins: It represents the overall folding of the polypeptide chain i.e., further folding of the 2° structure.
• Types of bonding which stabilize the 3° structure:

1. Disulphide bridge (-S – S-)
2. H – bonding – (C = O … H – N)
3. Salt bridge (COO– … + )
4. Hydrophobic interactions
5. van der Waals forces

• Two shapes of proteins:

Fibrous proteins
a) When the polypeptide chains run parallel and are held together by hydrogen and disulphide bonds, then fibre– like structure is formed.
b) These proteins are generally insoluble in water
c) Examples: keratin (present in hair, wool, silk) and myosin (present in muscles), etc

Globular proteins
a) This structure results when the chains of polypeptides coil around to give a spherical shape.
b) These are usually soluble in water.
c) Examples: Insulin and albumins

• Quaternary structure of proteins:

1. Some of the proteins are composedof two or more polypeptide chains referred to as sub-units.
2. The spatial arrangement of these subunits with respect to each other is known as quaternary structure of proteins.

• Denaturation of proteins:

1. The loss of biological activity of proteins when a protein in its native form, is subjected to physical change like change in temperature or chemical change like change in pH. This is called denaturation of protein.
2. Example: coagulation of egg white on boiling, curdling of milk.

• Nucleoside:

1. Base + sugar

• Nucleotide:

1. Base + sugar + phosphate group

• Nucleic acids (or polynucletides):

1. Long chain polymers ofnucleotides.
2. Nucleotides are joined by phosphodiester linkage between 5’ and 3’ C atoms of a pentose sugar.

• Two types of nucleic acids:DNA

1. It has a double stranded -helix structure in which two strands are coiled spirally in opposite directions.
2. Sugar present is –D–2-deoxyribose
3. Bases:
   i) Purine bases: Adenine (A) and Guanine (G)
   ii) Pyrimidine bases: Thymine (T) and cytosine (C)
4. It occurs mainly in the nucleus of the cell.
5. It is responsible for transmission for heredity character.RNA

1. It has a single stranded -helix structure.
2. Sugar present is –D–ribose
3. Bases:
   i) Purine bases: Adenine (A) and Guanine (G)
   ii) Pyrimidine bases: Uracil (U) and cytosine (C)
4. It occurs mainly in the cytoplasm of the cell.
5. It helps in protein synthesis.

Double helix structure of DNA:

1. It is composed of two right handed helical polynucleotide chains coiled spirally in opposite directions around the same central axis.
2. Two strands are anti-parallel i.e., their phosphodiester linkage runs in opposite directions.
3. Bases are stacked inside the helix in planes to the helical axis.
4. Two strands are held together by H – bonds (A = T, G C).
5. The two strands are complementary to each other because the hydrogen bonds are formed between specific pairs of bases.
6. Adenine forms hydrogen bonds with thymine whereas cytosine forms hydrogen bonds with guanine.
7. Diameter of double helix is 2 nm.
8. Double helix repeats at intervals of 3.4 nm. (One complete turn)
9. Total amount of purine (A + G) = Total amount of pyramidine (C + T)

• Vitamins: Vitamins are organic compounds required in the diet in small amounts to perform specific biological functions for normal maintenance of optimum growth and health of the organism.
• Classification of vitamins: Vitamins are classified into two groups depending upon their solubility in water or fat.

1. Water soluble vitamins i) These vitamins are soluble in water.
   ii) Water soluble vitamins must be supplied regularly in diet because they are readily excreted in urine and cannot be stored (except vitamin B12) in our body.
   iii) Example: Vitamin C, B group vitamins.
2. Fat soluble vitamins
   i) These vitamins are soluble in fat and oils but insoluble in water.
   ii) They are stored in liver and adipose (fat storing) tissues.
   iii) Example: Vitamin A, D, E and K

Important vitamins, their sources and their deficiency diseases:

Name of vitamins	Sources	Deficiency diseases
Vitamin A	Fish liver oil, carrots, butter and milk	xerophthalmia (hardening of cornea of eye) Night blindness
Vitamin B1 (Thiamine)	Yeast, milk, green vegetables and cereals	Beriberi (loss of appetite, retarded growth)
Vitamin B2 (Riboflavin)	Milk, egg white, liver, kidney	Cheilosis (fissuring at corners of mouth and lips), digestive disorders and burning sensation of the skin.
Vitamin B6 (Pyridoxine)	Yeast, milk, egg yolk, cereals and grams	Convulsions
Vitamin B12	Meat, fish, egg and curd	Pernicious anaemia (RBC deficient in haemoglobin)
Vitamin C (Ascorbic acid)	Citrus fruits, amla and green leafy vegetables	Scurvy (bleeding gums)
Vitamin D	Exposure to sunlight, fish and egg yolk	Rickets (bone deformities in children) and osteomalacia (soft bones and joint pain in adults)
Vitamin E	Vegetable oils like wheat germ oil, sunflower oil, etc.	Increased fragility of RBCs and muscular weakness
Vitamin K	Green leafy vegetables	Increased blood clotting time

Class 12 Chemistry Revision Notes Chapter 13 Amines

• Amines: Amines are regarded as derivatives of ammonia in which one, two or all three hydrogen atoms are replaced by alkyl or aryl group.
• Classification of amines:

• Preparation of amines:

(i) By reduction of nitro compounds: Nitro compounds can be catalytically reduced by passing hydrogen gas in presence of Raney Ni, finely divided Pt or Pd as catalyst at room temperature.

a) 

b) 

Nitro compounds can also be reduced with active metals such as Fe, Sn, Zn etc. with conc. HCl.

a) 

b) 

(ii) By Hoffmann’s method (Ammonolysis of alkyl halides): Reaction of alkyl halides with an ethanolic solution of ammonia in a sealed tube at 373 K forms a mixture of primary, secondary and tertiary amine and finally quarternary ammonium salt. Process of cleavage of C-X bond by ammonia is called ammonolysis.

• The free amine can be obtained from the ammonium salt by treatment with a strong base:
  a) 
  b) 
  c) 
• Order of reactivity of halides is: RI>RBr>RCl
• Larger the size of halogen atom easier is the cleavage of R-X bond
• Limitations of Hoffmann’s method: Method gives mixture of amines which are difficult to separate in a laboratory.
• Methods to get only one product by Hoffmann’s method:

(i) When ammonia is taken in excess primary amine is formed as main product

(ii) When alkyl halide is used in excess quarternary ammonium salt is formed as main product.
Method is not suitable for preparation of aryl amines because aryl amines are relatively less reactive than alkyl halides towards nucleophilic substitution reactions.

(iii) By reduction of nitriles: Nitriles can be reduced to amines using H₂ / Ni , LiAlH₄ or Na(Hg) / C₂H₅ OH

(iv) By reduction of amides: Amides are reduced to corresponding amines by LiAlH4

(v) By Gabriel phthalimide synthesis: Gabriel synthesis is used for the preparation of primary amines. When phthalimide is treated with ethanolic potassium hydroxide, it forms potassium salt of phthalimide which on heating further with alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine.

Aromatic primary amines cannot be prepared by this method because aryl halides do not undergo nucleophilic substitution with potassium phthalimide.

(vi) By Hoffmann bromamide degradation reaction: Primary amines can be prepared from amides by treatment with Br₂ and KOH. Amine contains one carbon atom less than the parent amide.

• Physical properties of amines:

(i) Solubility: Lower aliphatic amine is soluble in water because they can form hydrogen bonding with water. Solubility decreases with increases in molar mass of amines due to increase in size of hydrophobic group

(ii) Boiling points: Among the isomeric amines primary and secondary amines have high boiling point because they can form hydrogen bonding. Tertiary amine cannot form hydrogen bonding due to the absence of hydrogen atom available for hydrogen bond formation. Hence order of boiling of isomeric amines is Primary>Secondary> Tertiary

• Chemical properties of amines:

(a) Basic character of amines: Amines have an unshared pair of electrons on nitrogen atom due to which they behave as Lewis base. Basic character of amines can be better understood in terms of their K_b and pK_b values

Or 

Greater K_b value or smaller pK_b indicates base is strong.

(b) Comparison of basic strength of aliphatic amines and ammonia: Aliphatic amines are stronger bases than ammonia due to +I effect of alkyl groups leading to high electron density on the nitrogen atom.

(c) Comparison of basic strength of primary, secondary and tertiary amines

(i) The order of basicity of amines in the gaseous phase follows the expected order on the basis of +I effect: tertiary amine > secondary amine > primary amine > NH₃

(ii) In aqueous solution it is observed that tertiary amines are less basic than either primary or secondary amines. This can be explained on basis of following factors:

a) Solvation effect: Greater is the stability of the substituted ammonium cation formed, stronger is the corresponding amine as a base. Tertiary ammonium ion is less hydrated than secondary ammonium ion which is less hydrated than primary amine. Thus tertiary amines have fewer tendencies to form ammonium ion and consequently are least basic.
On the basis of solvation effect order of basicity of aliphatic amines should be primary amine>secondary amine>tertiary amine.

b) Steric factor: As the crowding of alkyl group increases from primary to tertiary amine hinderance to hydrogen bonding increases which eventually decreases the basic strength. Thus there is a subtle interplay of the inductive effect, solvation effect and steric hinderance of the alkyl group which decides the basic strength of alkyl amines in the aqueous state.
When the alkyl group is small like CH₃ there is no steric hindrance to hydrogen bonding. In this case order of basicity in aqueous medium is

When alkyl group is ethyl group order of basicity in aqueous medium is

c) Comparison of basic strength of aryl amines and alkylamines: Generally aryl amines are considerably less basic than alkyl amines .Taking an example of aniline and ethylamine it is observed that ethyl amine is more basic than aniline. In aniline –NH2 group is directly attached to benzene ring. Hence unshared pair of electron on nitrogen is less available for protonation because of resonance. Below mentioned are resonating structures of aniline.

In the above resonating structures there is a positive charge on nitrogen atom making the lone pair less available for protonation. Hence aniline is less basic than ethyl amine which has no resonating structures. Less basicity of aniline can also be explained by comparing the relative stability of aniline and anilinium ion obtained by accepting a proton. Greater the number of resonating structures, greater is the stability of that species.
Aniline is resonance hybrid of five resonating structures whereas anilinium ion has only two resonating structures.

Thus aniline has less tendency to accept a proton to form anilinium ion.

d) Effect of substituent on basic character of amines: Electron donating or electron releasing group/groups (EDG) increases basic strength while electron withdrawing (EWG) decreases basic strength.

• Reactions of amines:

a) Acylation Reaction: Aliphatic and aromatic primary and secondary amines (which contain replaceable hydrogen atoms) react with acid chlorides, anhydrides and esters to form substituted amide. Process of introducing an acyl group (R-CO-) into the molecule is called acylation. The reaction is carried out in the presence of a stronger base than the amine, like pyridine, which removes HCl formed and shifts the equilibrium to the product side.

Since tertiary amine do not contain replaceable hydrogen atom they do not undergo acylation reaction.

b) Carbylamine reaction: Only aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium hydroxide form isocyanides or carbylamines.

Secondary and tertiary amines do not give the above test.

c) Reaction of primary amine with nitrous acid:
(i) Primary aliphatic amine on reaction with nitrous acid (HNO₂) forms aliphatic diazoniumsalt which decomposes to form alcohol and evolve nitrogen.

(ii) Primary aromatic amines react with nitrous acid (HNO2) in cold (273-278 K) to form diazonium salt.

d) Reaction with benzene sulphonyl chloride: Hinsberg’s reagent-Benzenesulphonyl chloride (C6H5SO2Cl) reacts with primary and secondary amines to form sulphonamides.

The hydrogen attached to nitrogen in sulphonamide formed by primary amine is strongly acidic due to the presence of strong electron withdrawing sulphonyl group. Hence, it is soluble in alkali.

Since sulphonamide formed by secondary amine does not contain any hydrogen atom attached to nitrogen atom, so it is not acidic. Hence it is insoluble in alkali.

• Ring substitution in aromatic amine: Aniline is more reactive than benzeneand undergoes electrophilic substitution reaction preferably at ortho and para position.

(i) Bromination: Aniline reacts with bromine water at room temperature to give a white precipitate of 2, 4, 6-tribromoaniline

In order to stop reaction at monosubstitution activating effect of –NH2 group is reduced by acetylation. This prevents di and tri substituted products. Acetyl group is removed by hydrolysis.

(ii) Nitration:
(a) Under strongly acidic medium aniline gets protonated to form anilinium ion, which is deactivating group and is meta directing. Hence minitroaniline is also formed in 47% along with ortho and para products.

Aromatic amines cannot be nitrated directly because HNO3 being a strong oxidising agent oxidises it forming black mass.

(b) Nitration by protecting the –NH₂ group by acetylation reaction with acetic anhydride:

iii) Sulphonation: Aniline reacts with conc. H₂SO₄ to form aniliniumhydrogensulphate which on heating with sulphuric acid at 453-473K produces p-aminobenzenesulphonic acid, commonly known as sulphanilic acid, as the major product.

• Reactions of benzene diazonium chloride:
  a) Reactions involving displacement of nitrogen:
  
  b) Reactions involving retention of diazo group, coupling reactions: Diazonium ion acts as an electrophile because there is a positive charge on terminal nitrogen. Therefore benzene diazonium chloride couples with electron rich compounds like phenol and aniline to give azo compounds. Azo compounds contain –N=N- bond and reaction is coupling reaction.
  

Class 12 Chemistry Revision Notes Chapter 12 Aldehydes, Ketones and Carboxylic acid

Aldehydes: Aldehydes are the organic compounds in which carbonyl group is attached to one hydrogen atom and one alkyl or aryl group.

Where R can be an alkyl or aryl group

Preparation of aldehydes:

a) By oxidation of alcohols: Oxidation of primary alcohols in presence of oxidizing agent like K2Cr2O7/H2SO4, KMnO4,CrO3 gives aldehydes.

b) By dehydrogenation of alcohols: When the vapours of primary alcohol passed through heated copper at 573 K, it forms aldehyde.

c) By hydration of alkynes: Ethyne on hydration with  at 333 K forms acetaldehyde.

d) By Rosenmund reduction: Hydrogenation of acyl chloride over palladium on barium sulphate gives aldehyde.

e) By reduction of nitriles:
i) Stephen Reaction: Reduction of nitriles in presence of stannous chloride in presence of HCl gives imine which on hydrolysis gives corresponding aldehyde.

ii) Nitriles are selectively reduced by DIBAL-H (Diisobutylaluminium hydride) to aldehydes.

f) By reduction of ester: Esters are reduced to aldehydes in presence of DIBAL-H (Diisobutylaluminium hydride)

g) From Hydrocarbons:

(i) By oxidation of methyl benzene: Etard Reaction: Chromyl chloride oxidizes methyl group to a chromium complex, which on hydrolysis gives corresponding benzaldehyde.

Using chromium oxide: Toluene or substituted toluene is converted to benzaldehyde in presence of chromic oxide in acetic anhydride.

(ii) By side chain chlorination followed by hydrolysis:Halogenation of toluene: Side chain halogenation of toluene gives benzal chloride which on hydrolysis gives Benzaldehyde.

(iii) Gatterman –Koch reaction: Benzene or its derivatives on treatment with carbon monoxide and HCl in presence of anhydrous aluminium chloride or cuprous chloride (CuCl) gives benzaldehyde or substituted benzaldehydes.

• Ketones: Ketones are the organic compounds in which carbonyl group is attached to two alkyl group or aryl group or both alkyl and aryl group.
  
  Where R, R’ may be alkyl or aryl.
• Preparation of ketones:
  a) By oxidation of alcohols: Oxidation of secondary alcohols in presence of oxidizing agent like ,  gives ketones.
  
  b) By dehydrogenation of alcohols: When the vapours of a secondary alcohol are passed over heated copper at 573 K, dehydrogenation takes place and a ketone is formed.
  
  c) By hydration of alkynes: Alkynes on hydration with  at 333 K form ketones.
  
  d) From acyl chloride: Acyl chloride on treatment with dialkyl cadmium (prepared by reaction of cadmium chloride with Grignard reagent) gives ketone.

e) From nitriles: Nitriles on treatment with Grignard reagent followed by hydrolysis give ketones.

f) By Friedel Crafts acylation reaction: Benzene or substituted benzene on treatment with acid chloride in presence of anhydrous aluminium chloride forms ketone.

g) Preparation of aldehydes and ketones by ozonolysis of alkenes:

• Reactions of aldehydes and ketones:

1. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons (or inductive effect).
2. Electronic Effect: Relative reactivities of aldehydes and ketones in nucleophilic addition reactions is due the positive charge on carbonyl carbon. Greater positive charge means greater reactivity. Electron releasing power of two alkyl groups in ketones is more than one in aldehyde. Therefore positive charge is reduced in ketones as compared to aldehydes. Thus ketones are less reactive than aldehydes.
3. Stearic Effect: As the number and size of alkyl group increase, the hindrance to the attack of nucleophile also increases and reactivity decreases. In aldehydes there is one alkyl group and one hydrogen atom, whereas in ketones there are two alkyl groups (same or different).

• Nucleophilic addition reactions of aldehydes and ketones:

(a) Addition of hydrogen cyanide (HCN) to form cyanohydrins

(b) Addition of sodium hydrogensulphiteto form bisulphate addition compound

(c) Addition of Grignard reagent (RMgX) to form alcohol

(d) Addition of alcohol:

(i) Aldehydes on addition of monohydric alcohol in presence of dry HCl forms hemiacetal and acetal.

(ii) Ketones do not react with monohydric alcohols. Ketones react with ethylene glycol under similar conditions to form cyclic products known as ethylene glycol ketals.

(e) Addition of ammonia and its derivatives:

• Reduction of aldehydes and ketones:

(a) Reduction to alcohols:

Aldehydes and ketones on catalytic hydrogenation in presence of Ni, Pt or Pd by using lithium aluminium hydride  or sodium borohydride  forms primary and secondary alcohols respectively.

(b) Reduction to hydrocarbons:

(i) Clemmensen reduction: Carbonyl group of aldehydes and ketones is reduced to  group on treatment with zinc amalgam and concentrated hydrochloric acid.

(ii) Wolff-Kishner reduction: Carbonyl group of aldehydes and ketones is reduced to  group on treatment with hydrazine followed by heating with sodium or potassium hydroxide in high boiling solvent such as ethylene glycol.

(iii)

• Oxidation of aldehydes and ketones:

(i) Aldehydes are oxidized to acids in presence of mild oxidising agents HNO3, K2Cr2O7, KMnO4.

(ii) Ketones are oxidized under drastic conditions i.e. with powerful oxidising agents like  at higher temperature.

In case of unsymmetrical ketones cleavage occurs in such a way that keto group stays with smaller alkyl group. This is known as Popoff’s rule.

(iii)Haloform reaction: Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom i.e. methyl ketones are oxidised by sodium hypohalite to sodium salts of corresponding carboxylic acids having one carbon atom less than that of carbonyl compound. The methyl group is converted to haloform.

• Reactions of aldehydes and ketones due to  -hydrogen:

(i) Aldol condensation: Aldehydes and ketones having at least one  -hydrogen undergo a self condensation in the presence of dilute alkali as catalyst to form  -hydroxy aldehydes (aldol) or  -hydroxy ketones (ketol), respectively.

(ii) Cross aldol condensation: Aldol condensation between two different aldehydes and ketones is called aldol condensation. If both of them contain  -hydrogen atoms, it gives a mixture of four products.

• Canizzaro reaction: Aldehydes which do not have an  -hydrogen atom undergo self-oxidation and reduction (disproportionation) reaction on treatment with concentrated alkali to form alcohol and salt of acid.

• Test to distinguish aldehydes and ketones:

1. Tollen’s test: When an aldehyde is heated with Tollen’s reagent it forms silver mirror. Tollen’s reagent is ammoniacal solution of  
   Ketones do not form silver mirror and hence do not give this test.
2. Fehling’s test: When an aldehyde is heated with Fehling’s reagent it formsreddish brown precipitates of cuprous oxide.Fehling’s reagent: Fehling solution A (aqueous solution of ) + Fehling solution B (alkaline solution of sodium potassium tartarate)
   
   Ketones do not give this test.

• Carboxylic Acids:Carboxylic acids are the compounds containing the carboxylfunctional group (-COOH).

• Preparation of carboxylic acid:

(i) From alcohols: Primary alcohols are readily oxidised to carboxylic acids with common oxidising agents such as potassium permanganate  in neutral, acidic or alkaline media or by potassium dichromate (K2Cr2O7) and chromium trioxide  in acidic media.

a) 

b) 

(ii) From aldehydes: Oxidation of aldehydes in presence of mild oxidizing agents like Tollen’s reagent (ammoniacal solution of ) or Fehling reagent (Fehling solution A (aqueous solution of ) + Fehling solution B (aqueous solution of sodium potassium tartarate)) forms carboxylic acids.

1. 
2. 

(iii) From alkylbenzenes: Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzenes with chromic acid or acidic or alkaline potassium permanganate.

(iv) From alkenes: Suitably substituted alkenes are oxidised to carboxylic acids on oxidation with acidic potassium permanganate or acidic potassium dichromate.

1. 
2. 

(v) From Nitriles: Nitriles on hydrolysis in presence of dilute acids or bases forms amide which on further hydrolysis gives carboxylic acid.

(vi) From Grignard reagent: Grignard reagents react with carbon dioxide (dry ice) to form salts of carboxylic acids which on hydrolysis forms carboxylic acids.

(vii) From acyl halides and anhydrides: Acid chlorides when hydrolysed with water give carboxylic acids .On basic hydrolysis carboxylate ions are formed which on further acidification forms corresponding carboxylic acids. Anhydrides on hydrolysis forms corresponding acid(s)

(viii) From esters: Acidic hydrolysis of esters gives directly carboxylic acids while basic hydrolysis gives carboxylates, which on acidification give corresponding carboxylic acids.

• Physical properties of carboxylic acids:

(i) Solubility: As the size of alky group increases solubility of carboxylic acid decreases because non-polar part of the acid increases

(ii) Boiling points: Carboxylic acids are higher boiling liquids than aldehydes, ketones and even alcohols of comparable molecular masses. This is due to extensive association of carboxylic acid molecules through intermolecular hydrogen bonding.

• Acidity of carboxylic acids:

Carboxylic acids are more acidic than phenols. The strength of acid depends on extent of ionization which in turn depends on stability of anion formed.

(i) Effect of electron donating substituents on the acidity of carboxylic acids: Electron donating substituent decreases stability of carboxylate ion by intensifying the negative charge and hence decreases acidity of carboxylic acids.

(ii) Effect of electron withdrawing substituent on the acidity of carboxylic acids: Electron withdrawing group increases the stability of carboxylate ion by delocalizing negative charge and hence, increases acidity of carboxylic acid. The effect of the following groups in increasing acidity order is Ph< I < Br <cl< f=””>2 < CF₃</cl<>

(a) Effect of number of electron withdrawing groups: As the number of electron withdrawing groups increases –I effect increases, increasing the acid strength

(b) Effect of position of electron withdrawing group: As the distance between electron withdrawing group and carboxylic group increases, electron withdrawing influence decreases.

• Reaction of carboxylic acids:

Reactions involving cleavage of C-OH bond:

Carboxylic acids on heating with mineral acids such as  or with  give corresponding anhydride.

(i) Anhydride formation:

(ii) Esterification: Carboxylic acids are esterified with alcohols in the presence of a mineral acid such as concentrated  or HCl gas as a catalyst.

(iii) Carboxylic acids react with PCl5, PCl3 and SOCl2 to form acyl chlorides.

1. 
2. 
3. 

(iv) Reaction with ammonia (NH3): Carboxylic acids react with ammonia to give ammonium salt which on further heating at high temperature gives amides.

i)

ii)

Reactions involving COOH group:

(i) Reduction: Carboxylic acids are reduced to alcohols in presence of LiAlH4 or B2H6.

(ii) Decarboxylation : Sodium or potassium salts of carboxylic acids on heating with soda lime (NaOH + CaO in ratio of 3:1) gives hydrocarbons which contain one carbon less than the parent acid.

(c) Reactions involving substitution reaction in hydrocarbon part:

(i) Hell-Volhard-Zelinsky reaction: Carboxylic acids having an -hydrogen are halogenated at the -position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give -halocarboxylic acids)

(ii) Ring substitution in aromatic acids: Aromatic carboxylic acids undergo electrophilic substitution reactions. Carboxyl group in benzoic acid is electron withdrawing group and is meta directing.

i)

ii)