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By going through these CBSE Class 12 Biology Notes Chapter 7 Evolution, students can recall all the concepts quickly.

Evolution Notes Class 12 Biology Chapter 7

→ The study of the history of life forms on earth is called Evolutionary Biology.

→ The origin of life on earth can be understood only against the background of the origin of the universe especially earth.

→ The universe is vast. The earth is almost a speck. The universe is about 20 billion years old. The universe comprises huge clusters of galaxies.

→ The Big Bang theory explains to us the origin of the universe. It states that a singular huge explosion laid the foundation of the universe.

→ Most scientists believe that the formation of biomolecules preceded the appearance of the first cellular forms of life.

→ Conventional religious literature tells us that the theory of creation has connotations.

• One, that all living organisms that we see today, were created as such.
• Two, the diversity was always the same since creation and will be the same in the future also.
• Three, that the earth is about 4000 years old.

→ Charles Darwin concluded that existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago.

→ According to Darwin, fitness refers ultimately and only to reproduce fitness. Thus, those who are a better fit in an environment, leave more progeny than others. There therefore will survive more and hence are selected by nature. He called it natural selection and implied it as a mechanism of evolution.

→ Comparative anatomy and morphology show similarities and differences between organisms of today and those that existed millions of years ago. Such similarities can be interpreted to understand common ancestors were shared or not.

→ The diversity of life forms on earth has been changing over millions of years.

→ It is believed that variations in a population either due to meiotic recombination during gametogenesis or germ live mutations result in variable fitness in learning fertile progeny.

→ Branching descent and natural selection are the two key concepts o.f the Darwinian Theory of Evolution.

→ Hardy-Weinberg Principle states that allele frequencies in a population are stable and constant from generation to generation. The gene pool remains a constant.

→ Homology is accounted for by the idea of branching descent; study of comparative anatomy, fossils comparative, biochemistry provide evidence for evolution.

→ The story of the evolution of modern man among the stories of the evolution of individual species is most interesting. It appears to parallel the evolution of the human brain and language.

→ Evolutionary Biology: Study of history of life forms on earth.

→ Big Bang Theory: Theory that explains the origin of the universe.

→ Fossils: Remains of hard parts of life forms found in rocks.

→ Divergent evolution: In animals, the same structure developed in different directions due to adaptations to different needs.

→ Homology: It indicates common ancestry.

→ Adaptive Radiation: The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography.

By going through these CBSE Class 12 Biology Notes Chapter 6 Molecular Basis of Inheritance, students can recall all the concepts quickly.

Molecular Basis of Inheritance Notes Class 12 Biology Chapter 6

→ Gene is a macromolecule attached to an undifferentiated protein thread (chromonema) that can pass from one cell to another and can be transmitted from one generation to another without being changed at all.

→ Gene is a unit of heredity and responsible for inheritance.

→ Gene is a part of DNA and is made up of nucleotides. It can grow, reproduce and mutate. Gene is the unit of recombination. Genetic information is conveyed from DNA to mRNA.

→ Genes mainly act by producing proteins or enzymes which are required at various levels of metabolism. Proteins are made up of polypeptides which are formed from amino acids. Genes determine the physical and physiological characteristics of living beings.

→ DNA and RNA are two types of nucleic acids, which are polymers of nucleotides. DNA is the genetic material in most organisms. RNA is found only in some viruses as genetic material, it acts as a messenger to transfer the genetic information from DNA to proteins. It also functions as an adapter, structural and catalytic molecule.

→ DNA (deoxyribonucleic acid) is the polymer of deoxyribonucleotides. The haploid content of human DNA is 3.3 × 10⁹ bp. DNA is chemically and structurally more stable than RNA.

→ Nucleic acids were first isolated by Friedrich Miescher (1869) from pus cells. These were named nuclein. Due to their acidic nature, they were named nucleic acid, and Altmann (1899) named them nucleic acids. Fisher (1880s) discovered the presence of purine and pyrimidine bases. Levene (1910) found deoxyribose nucleic acid contains phosphoric acid and deoxyribose sugar. He characterized four types of nucleotides.

Chargaff (1950) found that purines are equal to pyrimidines in DNA, and adenine = thymine, and guanine = cytosine. W.T. Astbury discovered through X-ray diffraction that DNA is a polynucleotide with nucleotides arranged perpendicular to the long axis of the molecule and are 0.34nm away from one another.

Wilkins and Franklin (1953) through X-ray photographs found that DNA was a helix with 2.0nm width. One turn of the helix was 3.4 nm with 10 layers of bases stacked in it. Through these photographs, Watson and Crick (1 953) built a three-dimensional model of DNA. They were awarded Nobel Prize in 1962. They purposed that DNA consists of a double helix with two chains having sugar-phosphate as the backbone and nitrogen bases on the inner sides.

The nitrogen bases of two chains form complementary pairs with purines of one and pyrimidine of the other held together by hydrogen bonds. The two chains are antiparallel with 5′ → 3′ orientation and 3′ → 5′ orientation. The two chains are twisted helically as a rope ladder with rigid steps twisted into a spiral. Each turn contains 10 nucleotides. In Vitro, DNA synthesis was carried out by Komberg (l 959). DNA has got an implicit mechanism for replication and copying.

→ A nucleotide is made up of three components: a nitrogenous base, a pentose sugar (ribose in RNA, deoxyribose in DNA), and a phosphate group. Nitrogenous bases are of two types: purines and pyrimidines. Purines are Adenine and Granite and pyrimidines are Cytosine, Uracil, and Thymine. Thymine is present in DNA. Thymine is replaced by Uracil in RNA.

→ A nucleoside is formed by a nitrogenous base linked to pentose sugar by an N-glycosidic bond, e.g. deoxyadenosine or adenosine, deoxycytidine, or cytidine.

Structure of DNA.

A. Chemical Structure and bonding of different constituents of DNA in the two chains.
B. sequence of nucleotides in a part of the double helix of DNA. C. coiling in double helix or duplex of DNA.

→ Two nucleotides are bound to each other through a phosphodiester bond. The phosphate group provides acidity to the nucleic acids. In Bacteria nucleotide, the DNA is covalently closed at its two ends. It’s called circular DNA. Its also present in mitochondria, plastids, and some viruses. Eukaryotic cells have free linear DNA. Both types of DNA are coiled and supercoiled to get into small space.

→ DNA replication is autocatalytic, it occurs during the S-phase of the cell cycle. Watson and Crick proposed a semiconservative model of replication for DNA. During which one strand of the daughter strand is derived from the parental duplex and the other strand is formed a new. Taylor et al (1957) worked with Broad Bean root tips, using

The experiment of Mcselson and Stahi (i958) to prove semi-conservative replication of DNA

Semi-conservative replication of DNA showing Zipper duplication

radiolabelled thymine and showed DNA replication is semi-conservative. In 1958 Nesselson and Stahl proved the semi-conservative mode of replication. They worked with E.Coli, using a heavy isotope of nitrogen, N¹⁵. E.Coli was grown with N¹⁵ for several generations till the bacteria became completely labeled with N¹⁵. They were then shifted to medium with normal N¹⁴ nitrogen.

The sample was taken after every generation and tested for the presence of N¹⁵ and N¹⁴ using density gradient centrifugation with CsCl. The first generation was found to be a hybrid between N1¹⁵ and N¹⁴. The second-generation contained two types of DNA, 50% light (N¹⁴) and 50% intermediate. This is only possible if two strands separate during replication and act as a template for the synthesis of new complementary strands. Thus proving a semiconservative mode of replication.

→ The process of replication starts at a particular spot known as the origin of replication. The deoxyribonucleotides are first phosphorylated and activated. Energy and phosphorylase enzymes are required for activation. Enzymes’ topoisomerases are specialized to break and reseal the DNA strands. Enzyme helicases unwind the DNA helix and separate the two strands. DNA binding proteins bind on the separated strands. The whole of DNA does not open up for replication, the point of separation proceeds from one end to another. The replication fork appears Y- Y-shaped during the process of replication.


Replication of DNA continuous over one strand and discontinuous over other strands

DNA polymerase enzyme requires an RNA primer to initiate the process/ RAN primer is synthesized at the 5′ end of new DNA strand by enzyme primase. The two separated strands act as templates. The new nucleotides are added according to the law of base pairing i.e. A pairs with T and G pairs with C.

Energy is utilized in forming hydrogen bonds between the free nucleotides and nitrogen bases of templates. Elongation of the DNA chain requires enzyme DNA polymerase III in the presence of Mg²⁺ and ATP. The adjacent nucleotides attach to one another by phosphodiester bonds. As replication proceeds, the strands unwind and at the end, the RNA primer is removed and the gap is filled with the help of DNA polymerase 1. This is also called Zipper duplication.

DNA polymerase can act only in the 5′ → 3′ direction so replication is continuous on the strand (3′ → 5′) known as the leading strand. The other strand called lagging strand 1 (5′ → 3′) replicates itself in small stretches called Okazaki fragments. These fragments are joined by the DNA ligase enzyme. Any mismatch or mutation if occurs during replication can be corrected by proofreading and DNA repair mechanisms

→ Frederick Griffith (1928) by doing transforming experiments on mice with Streptococcus pneumonia found out the transfer of genetic material from a heat-killed infectious stain to the normal non-infectious stain.

→ Earlier the genetic material was thought to be protein. In 1933 – 44 Oswald Avery, Colin Macleod, and Maclyn McCarty discovered that the transforming biochemical in Griffith’s experiments was DNA.

→ Alfred Hershey and Martha Chase (1952) proved that DNA is the hereditary material. They worked with bacteriophage T, which infects E.Coli.

→ Francis Crick proposed the central dogma in molecular biology which explains the flow of genetic information
i.e. DNA → RNA → Protein.

→ The formation of RNA over a DNA template is called transcription. Transcription is meant for taking the coded information from DNA to the site where it is required for protein synthesis. Only one DNA strand transcribes RNA, it is called a sense strand. Transcription requires enzyme RNA polymerase. Prokaryotes have only one RNA polymerase. Eukaryotes have three RNA polymerases.

RNA polymerase 1 synthesizes rRNA, 28S, 18S, and 5.8S, RNA polymerase II synthesizes hnRNA, mRNA, and snRNAs, and RNA polymerase III synthesizes tRNA, 5SRNA, and siRNAs. A transcription unit consists of a promoter, the structural gene, and a terminator.

Schematic Structure of a Transcription Unit

→ In eukaryotes, the primary transcript contains exons and introns so it is non-functional. Exons are coding sequences whereas introns are intervening sequences. These introns are removed by splicing. It is followed by capping, methyl guanosine triphosphate addition to 5′ end and of hnRNA and tailing around 200 – 300 adenyl residues are added at 3′ end. The fully processed hnRNA is called mRNA and is transported out of the nucleus.

→ The relationship between the sequence of amino acids in a polypeptide and nucleotides sequence of DNA or mRNA is called genetic code.

→ George Gamow proposed that the genetic code is a triplet in nature. Marshall and Nirenberg’s method for cell-free protein synthesis helped to decipher the code. The chemical method developed by Har Gobind Khorana helped in synthesizing RNA molecules with defined base combinations. Severo Ochoa’s enzyme polynucleotide phosphorylase helped to polymerize RNA with defined sequences. All these methods helped in deciphering the genetic code.

→ The translation is the process of polymerization of amino acids to form a polypeptide. mRNA sequence decides the sequence of amino acids. Amino acids are joined through peptide bonds. Ribosomes are considered as the protein-synthesizing cellular factory. It requires amino acids, mRNA, tRNA, aminoacyl tRNA synthetase, and various enzymes along with ribosomes to complete the process of protein synthesis.

The process of translation occurs in the cytoplasm. The process takes place in several steps like activation of amino acids, initiation, elongation, and termination. Polyribosomes or polysomes help to produce a number of copies of the same polypeptide. In it, different ribosomes are held together by a strand of messenger RNA. These ribosomes usually form rosette or helical groups during active protein synthesis and are known as polyribosomes.

Ribosomes as a protein factory. A relationship between the various components. B. synthesis of the polypeptide on ribosome connected with the endoplasmic reticulum.

Cistron is a segment of DNA consisting of a stretch of base sequences that codes for one polypeptide chain, one transfer RNA (tRNA), ribosomal RNA tRNA) a molecule or performs any other specific function in connection with transcription, including controlling the functioning of other cistrons (operon model of gene action).

Regulation of gene expression may occur at various steps like

1. transcriptional level,
2. processing level (splicing),
3. transport of mRNA from the nucleus to the cytoplasm.
4. translational level.

An operon is a part of genetic material (or DNA) which acts a: a single regulated unit having one or more structural genes, an operator gene, a promoter gene, a regulator gene, a repressor, and an inducer or corepressor (from outside). Operons are of two types, inducible and repressive.

Lac operon is an example of an inducible operon system. In E.Col; the enzyme beta-galactosidase catalyzes the hydrolysis of lactose into glucose and galactose, which is used as a source of energy. If the bacteria do not have lactose in the medium they won’t need beta-galactosidase enzyme. Thus the production of an enzyme (protein) is regulated by the presence of lactose (inducer).

→ Anticodon: A triplet of bases present on tRN A complementing with mRNA codon is called the anticodon.

→ A-site: It’s the site where the second and next amino-acyl-tRNA enters the ribosome.

→ Codon: Triplet of bases on mRNA, which codes for one amino acid.

→ Central dogma: Unidirectional flow of information from DNA to RNA to protein.

→ Cistron: A segment of DNA that determines a single polypeptide chain.

→ DNA polymerase: The enzyme playing a pivotal role in adding the building blocks to the primer in a sequence as guided by the DNA template. It can polymerize nucleotides only in the 5’ → ‘3’ direction.

→ Frameshift mutation: The mutations which are caused by shifting the entire reading frame by addition or deletion on the segment of DNA.

→ Genetic code: The genetic presentation of codon through which the information in RNA is decoded in a polypeptide chain.

→ Glycosylation: The addition of sugar residues by modification of certain proteins, which are released in the lumen and are trapped in Golgi vesicles.

→ Hydrogen bond: The bond between nitrogenous bases of DNA binding two nucleotide chains. It is a weak bond.

→ Inducer: An effector molecule responsible for the induction of enzyme synthesis at recognition sites, to prevent self-cleavage by a modified enzyme that recognizes the sites and methylates specific nucleotides at each site.

→ Jumping genes: These are genes that shuffle from one location to another.

→ Phosphodiester bond: The bond between two adjacent nucleotides of two adjacent sugar moieties at 3’ and 5’ positions with phosphoric acid.

→ Phenocopy: When a normal gene under a different set of environmental conditions copies down the phenotypic characters of a mutant.

→ Restriction enzyme: An endonuclease that recognizes specific nucleotide sequences in DNA and makes a double-strand cleavage of DNA molecule.

→ Regulatory gene: Any gene which regulates or modifies the activity of other genes.

→ Repression: The phenomenon in which the synthesis of a set of enzymes leading to a product is shut down if the product is present in plentiful amounts.

→ Rho-factor: The factor which is required for termination of RNA synthesis at some sites.

→ Structural gene: A gene that codes for a polypeptide.

→ Silent mutation: This kind of mutation does not cause any change in the protein.

→ Thalassemia: Haemoglobin-based genetic disorder which involves frameshift mutation in β-chain of hemoglobin.

→ Transformation: The process in which the cell takes up the segment of the naked DNA from its surroundings and incorporates it in its hereditary material and ultimately expresses the character specified by incoming DNA.

→ Wobble position: The position on the codon where mutation occurs at 3rd base of triplet which still permits the normal interaction with anticodon.

By going through these CBSE Class 12 Biology Notes Chapter 5 Principles of Inheritance and Variation, students can recall all the concepts quickly.

Principles of Inheritance and Variation Notes Class 12 Biology Chapter 5

→ Genetics is a branch of biology which deals with principles of inheritance arid is practices. Progeny resembling the parents in morphological and physiological features has attracted the attention of many biologists.

→ During the mid-nineteenth century, Gregor Mendel conducted hybridization experiments on garden peas and proposed the laws of inheritance in living organisms.

→ Mendel proposed the principles of inheritance, which today are referred to as Mendel’s Law of inheritance. He proposed that the factors (genes) regulating the characters are found in pairs known as alleles. The expression of the characters in the offspring follows a definite pattern in first-generation (F₁), second-generation (F₂), and so on.

→ The dominant characters are expressed when the factors are in heterozygous conditions (Law of Dominance). The recessive characters are only expressed in homozygous conditions. The characters never blend in heterozygous conditions. A recessive character that was not expressed in heterozygous condition may be expressed again when becomes homozygous. Due to this reason, characters segregate while the formation of gametes (Law of Segregation).

→ Among all characters, some show incomplete dominance while some show co-dominance.

→ Mendel found that the factors independently assort and combine in all permutation and combination (Law of Independent Assortment.)

→ Different combinations of gametes are theoretically represented in a square tabular form known as ‘Punnett Square’.

→ The factors on chromosomes regulating the characters are called the genotype. The physical expression of characters is called the phenotype.

→ Later the Mendel’s Law was extended in the form of the ‘Chromosomal Theory of Inheritance’. However, later on, Mendel’s law of independent assortment does not hold true for the genes that were located on the same chromosomes. These genes were called ‘linked genes’.

→ Different genes were linked to sexes also. These are called sex-linked genes. Both males and females have a set of chromosomes. One set was common while the other set was different. The chromosomes that were different in the two sexes were named as sex chromosomes and the remaining set was named autosomes. In human beings, a normal male has 22 pairs of autosomes and a pair of sex chromosomes as XY. A female has 22 pairs of autosomes and a pair of sex chromosomes XX.

→ An analysis of traits in several generations of a family is called pedigree analysis. In the pedigree analysis, the inheritance of a particular trait is represented in the family tree over generations.

→ Genetic disorders may be grouped into two categories: Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in a single gene. The pattern of inheritance of Mendelian disorders can be traced in a family by the pedigree analysis. Some examples of Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle cell anemia, Colour blindness, Phenylketonuria, Thalassemia, etc.

Chromosomal disorders are caused due to absence or excess or abnormal arrangement of one or more chromosomes. Some common examples of chromosomal disorders are Down’s syndrome, Turner’s syndrome, Klinefelter’s syndrome, etc.

→ Hybridization: Mating between two (or more) individuals differing ¡n genotype.

→ Mutation: It is a sudden and heritable change in a character of an organism.

→ Heterozygous: Hybrids that contain alleles that express contrasting traits.

→ Punnett square: A graphical representation to calculate the probability of all possible genotypes öf offspring in a genetic cross.

→ Law of dominance: It explains the expression of only one of the parental characters in a monohybrid cross in the F₁ and the expression of both in the F₂.

→ Law of segregation: It ¡s based on the fact that the alleles do not show a blending and that both the characters are recovered as such in the F₂ generation though one of there is not seen at the F₁ stage.

→ Incomplete dominance: When the F₁ has a phenotype that does. not resemble either of the two parents and is in between the two it is incomplete dominance.

→ Aneuploidy: Failure of segregation of chromatin during cell division results in the gain or loss of a chromosome(s) is called aneupLoidy.

→ Pedigree traits: An analysis of traits in several generations of a family.

→ Mendelian disorders: Disorders mainly determined by alteration or mutation in a single gene.

→ Chromosomal disorders: Disorders caused due to the absence or excess or abnormal arrangement of one or more chromosomes.

By going through these CBSE Class 12 Biology Notes Chapter 4 Reproductive Health, students can recall all the concepts quickly.

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.

By going through these CBSE Class 12 Biology Notes Chapter 3 Human Reproduction, students can recall all the concepts quickly.

Human Reproduction Notes Class 12 Biology Chapter 3

→ Humans are sexually reproducing and viviparous. The reproductive events in humans induce the formation of gametes (gametogenesis) i.e.; sperms in. males and ovum in females, the transfer of sperms into the female genital tract (insemination), and the fusion of males and females garnets (fertilization) leading to the formation of zygote.

→ After the formation and development of the blastocyst and its attachment to the uterine wall (implantation), embryonic development (gestation), and delivery of the baby (parturition).

→ The male reproductive system is located in the pelvis region. It includes the pain of the testes along with accessory ducts, glands, and the external genitalia.

→ The female reproductive system consists of a pair of ovaries along with a pair of oviducts, uterus, cervix, vagina, and the external genitalia located in the pelvic region. The female reproductive also has a pair of memory glands that are integrated structurally and functionally to support the processes of ovulation, fertilization, pregnancy, birth, and child care.

→ The primary sex organs: the testis in the males and the ovaries in the females produce gametes i.e.; sperms and ovum, respectively, by the process called gametogenesis.

→ In testis, the immature male cells (spermatogonia) produce sperms by spermatogenesis that begins at puberty.

→ After the process of spermiogenesis, sperm heads become embedded in the Sertoli cells. There are finally released from the seminiferous tubules by the process called spermiation.

→ Sperm is composed of a head, neck, middle piece, and tail. A plasma membrane envelops the whole body of sperm.

→ The process of formation of a mature female gamete is called oogenesis which is markedly different from spermatogenesis. Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary, no more oogonia are formed and added after birth.

→ The reproductive cycle in the female primates (e.g. monkeys, apes, and human beings) is called the menstrual cycle. The first menstruation begins at puberty and is called menarche. In human females, menstruation is repeated at an average interval of 28/29 days, and the cycle of events starting from one menstruation till the next one is called the menstrual cycle.

→ Rapid secretion of L, H leading to its maximum level during mid-cycle called LH surge induces rupture of Graafian follicle and thereby the release of an ovum (ovulation). The ovulation (ovulatory phase) is followed by the luteal phase during which the remaining parts of the Graafian foil ice transform as the corpus luteum.

→ The corpus luteum secretes large amounts of progesterone which is essential for the maintenance of the endometrium. During pregnancy, all events of the menstrual cycle stop and therefore there is no menstruation.

→ In human beings, menstrual cycles cases around 50 years of age. This is termed menopause. Cyclic mensuration is an indicator of normal reproductive life between menarche to menopause.

→ Fertilization is the process of fusion of a sperm. During this process, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane that block the entry of additional sperms. This ensures that only one sperm can fertilize an ovum.

→ The mitotic division starts as the zygote moves through the isthmus of the. oviduct towards the uterus and forms 2, 4, 8, 16 daughter cells called blastomeres. The embryo with 8 to 16 blastomeres is called a morula.

→ The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cells divide and cover the blastocyst. As a result, the blastocyte becomes embedded in the endometrium of the uterus. This is implantation and it leads to pregnancy.

→ The average duration of human pregnancy is about 9.5 months which is called the gestation period. Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the fetus. The process of delivery of the fetus is called parturition.

→ The mammary glands of the female undergo differentiation during pregnancy and start producing milk towards the end of pregnancy by the process called lactation. The milk produced during the initial few days of lactation is called colostrum.

→ Leydig cells: Cells that synthesize and secrete testicular hormones called androgens.

→ Bulboureth rai glands: G Lands which help in the lubrication of the penis.

→ Clitoris: Tiny finger-like structure which lies at the upper junction of the two labia minora above the urethral opening.

→ Lactiferous duct: Duct through which milk is sucked out.

→ Spermiation: A process by which Sertoli cells are released from the seminiferous tubules.

→ Acrosome: Cap-like structure found ¡n sperm that help fertilization of the ovum.

→ Oogenesis: The process of formation of a mature female gamete.

→ Primary oocytes: The stage when cells start dividing and enter into prophase-l of the meiotic division and get temporarily arrested.

→ Menarche: The first menstruation begins at puberty and is called men arc he.

→ Menstrual cycle: In human females, menstruation is repeated at an average interval of about 28/29 days, and the cycle of events starting from one menstruation till the next is called the menstrual cycle.

→ Menopause: Menstrual cycles cease around 50 years of age. that is termed menopause.

→ Fertilization: The process of fusion of a sperm with an ovum is called fertilization.

→ Implantation: When the blastocysts become embedded in the endometrium of the uterus, it is called implantation.

→ Relaxin: A hormone secreted by the ovary in the late part of pregnancy.

→ Parturition: The process of delivery of the fetus is called parturition.

→ Colostrum: The milk produced during the initial days of lactation is called colostrum.

By going through these CBSE Class 12 Biology Notes Chapter 2 Sexual Reproduction in Flowering Plants, students can recall all the concepts quickly.

Sexual Reproduction in Flowering Plants Notes Class 12 Biology Chapter 2

→ Reproduction is the process of continuous production of offsprings. It is an important way of multiplication and perpetuation of species.

→ Modes of reproduction in plants can be broadly classified into two groups:

1. asexual reproduction,
2. sexual reproduction.

→ Asexual reproduction or Apomixis only takes place with a single parent. It does not involve the formation of sex organs, meiosis and fusion of gametes.

→ Regeneration of a whole new plant from vegetative parts of the plant is called vegetative reproduction. Its unique features of plants and can be natural or induced.

→ Runners, rhizomes, bulbs, corns and tubers are means of propagation.

→ Cutting, layering, grafting and micropropagation are artificial means of vegetative propagation. These are used for commer¬cially important plants.

→ A population of genetically identical plants derived from an individual is called a clone.

→ Plants that have lost the capacity to produce seeds e.g. banana, reproduce vegetatively.

→ Grafting is the technique used to improve the varieties of plants.

→ The flower and floral parts are the organs of sexual reproduction in angiosperms.

→ Sexual reproduction involves meiosis and the fusion of gametes.

→ The flower is a modified shoot with whorls of reproductive leaves – sepals, petals, stamens and carpels. Stamen and carpel are essential floral parts; sepals and petals are non-essential floral parts.

→ The calyx is the whorl of sepals. It is green in colour and protects the other parts of the bud. It prevents rapid transpiration.

→ Corolla is the whorl of petals. It is generally coloured, attractive and fragrant. It helps in pollination by attracting pollinators.

→ The androecium is the whorl of stamens. Stamen is made up of filament and anther. Anthers are bilobed and contain microsporangia (pollensac). Microsporangia produce a large number of pollen grains.

→ Gynoecium or pistil is the whorl of carpels. It consists of ovary, style and stigma.

→ Flowers that contain both stamen and pistil are called bisexual or hermaphrodite.

→ Stigma receives pollen grains, style provides the way to the ovary, the ovary is basal swollen part of gynoecium which contains ovules.

→ The ovule is an integument megasporangium where meiosis occurs and a megaspore is formed. It develops into an 8 nuclei embryosac.

→ Placentation is the manner in which the placenta is distributed. In the placenta, ovules are suspended.

→ The 8 nuclei of the monosporic embryo sac (e.g.Polygonum) are arranged such that a mature female gametophyte or embryosac contains: Two synergids, a single egg, a single secondary nucleus(2n) and three antipodals.,

→ Mature pollen grains are liberated from dehisced anthers. They are at a two-celled stage. The exine of pollen grains is made up of sporopollenin.

→ Pollination is the transfer of pollen grains to the stigma of the flower.

→ When the pollen grains are transferred from another to the stigma of the same flower it is called self-pollination. It occurs by autogamy and geitonogamy.

→ When pollen grains are transferred from the anther to the stigma of the flower of another plant it is termed cross-pollination. It takes place by the wind, water, insects, animals, bats and birds.

→ Allogamy represents cross-pollination where genetic recombination is ensured.

→ The pollen grains deposited on the stigma, after mutual recognition, absorb water and germinate and form a pollen tube.

→ Pollen tube traverses through stigma and style and reaches the ovary. It enters the ovule through micropyle, enters into embryo sac and releases two male gametes.

→ Siphonogamy is the carrying of male gametes to the egg through a pollen tube. It occurs in angiosperms.

→ Angiosperms exhibit double fertilization.

→ During fertilization, one male gamete fuses with the egg to form a diploid zygote in embryosac.

→ Second male gamete fuses with two polar nuclei to give rise to triploid primary endosperm nucleus inside embryosac.

→ After the process of fertilization, the ovule develops into a seed. The diploid zygote develops an embryo and the triploid primary endosperm nucleus forms an endosperm.

→ The ovary matures into a fruit.

→ The size, shape and colours of fruits and seeds vary enormously.

→ In a mature seed, the reserve food material is stored for embryo development and sustenance. In non-endospermic seeds, seeds are stored in cotyledons and in endospermic seeds, seeds are stored in endosperm.

→ The integuments of the ovule are transformed into seed coats.

→ All seeds have certain common features: an embryo, stored food and protective coverings.

→ Seeds are the principal means of the perpetuation of the species.

→ The embryo is differentiated into radicle, plumule and cotyledons. Dicot embryos have two cotyledons and monocot embryos have single terminal cotyledon.

→ A true fruit derived from the ovary consists of seeds and a pericarp. The pericarp is three layered-epicarp, mesocarp and endocarp.

→ Seed may remain dormant for some time before germination and growing into a new plant.

→ Amphimixis: The normal sexual reproduction is called

→ amphimixis. It involves meiosis and the fusion of haploid gametes.

→ Apomixis: It is the substitution of usual sexual reproduction which does not involve meiosis and syngamy.

→ Autogamy: Autõgamy results when a flower is pollinated by its own pollen.

→ Apogamy: It is the phenomenon in which an embryo is formed from any cell of embryosac (except egg) without fertilization.

→ Automixis: It is the fusion of nuclei derived both from the same zygote and from the same meiosis.

→ Aleurone layer: It is a layer of aleurone grains (protein grains) present on the outer surface of seeds and of maizë etc.

→ Coleoptile: The covering sheath of plumule in monocots.

→ Coleorhiza: The protective sheath of radicle in monocots.

→ Callus: The mass of undifferentiated cells formed in a culture medium.

→ Gootee: The process of air layering practised in lichi, promo- gran dates.

→ Grafting: Process of combining characters -of two related plants having vascular cambium.

→ Monogamy: The process of entry of pollen tube into ovule through integuments for fertilization.

→ Non-recurrent apomixis: The kind of apomixis in which the haploid egg or any other cell of haploid embryo sac develops an embryo without fertilization.

→ Polliniurn: Pollen grains contained in a pollen sac remain united in a single grain mass called pollinium.

→ Placentation: Arrangement and distribution of placenta within the ovary.

→ ParthenogeneSis: The kind of uniparental sexual reproduction in which an embryo is formed from an unfertilized egg.

→ PolyembryoflY: The phenomenon of formation of more than one embryo per ovule.

→ Pseudogamy: The phenomenon where pollination is needed for the development of apomictic embryò.

→ Scutellum: Single cotyledon of maize grain.

→ Siphonogamy: The process of carrying male gametes in the vicinity of female gamete by pollen tube.

→ Tapetum: The nutritive layer of cells around pollen sacs in anther.

→ Vivipary: The germination of seed within fruit while still attached to parent wall.

→ Viability: The ability of seeds to retain the power of germination.

By going through these CBSE Class 12 Biology Notes Chapter 1 Reproduction in Organisms, students can recall all the concepts quickly.

Reproduction in Organisms Notes Class 12 Biology Chapter 1

→ Reproduction is an important characteristic of the life cycle of living organisms. It involves producing offsprings from the existing (parent) organism. It occurs by asexual and sexual means.

→ Asexual reproduction generally takes place in protozoans, lower chordates, and lower invertebrates. It involves no formation and fusion of gametes. It occurs by various methods like budding, fission, fragmentation, plasmogamy, etc. Budding may be external (e.g. Hydra) or internal (e.g. Spongilla). Fission may be binary fission (e.g. Amoeba, Paramecium) or multiple fission (e.g. Amoeba, Plasmodium). Plasmotomy as in Opalina and fragmentation as in coelenterate colony and sponges.

→ Asexual reproduction is uniparental and does not produce variations in the next generation. The off-springs are identical to their parent and can be called clones.

→ Sexual reproduction takes place by the formation and fusion of gametes.
It involves various processes

1. gametogenesis i.e. formation of sex cells called the gametes. Gametes are produced by both male (male gamete) and female (female gamete) of the same species,
2. fertilization is the fusion of spermatozoa (male gamete) with the ovum (female gamete) to form a zygote,
3. development is the formation of a completely new individual from the zygote by repeated mitotic divisions.

→ Sexual reproduction involves the fusion of gametes called syngamy. It may be isogamous (e.g. Monocystis) or anisogamous (e.g. human beings). If the fusing gametes are similar (isogametes) .it is isogamous and if the fusing gametes are \ dissimilar, (heterogametes or isogametes) its anisogamy. In human beings, the sperm is microscopic, motile, and flagellated while the ovum is large, non-motile, spherical, and laden with food.

→ Syngamy may be exogamy if the fusing gametes are from two parents and endogamy if the fusing gametes are from the same parent.

→ Sperms and ova are produced by meiosis from spermatogonia and oogonia found in the testes of males and ovaries of females.

→ Sexual reproduction is biparental and introduces variations in the – offsprings. Sexual reproduction involving the fusion of male and female pronuclei is called conjugation e.g. ciliates.

→ Parthenogenesis is the process of the development of an egg into an offspring without fertilization. It may be natural (e.g. Apisindica) or artificial (Echinus). ,

→ Organisms may be unisexual or dioecious (e.g. human beings) or bisexual or monoecious (e.g. earthworm).

→ In sexually reproducing organisms the reproductive system consists of three types of organs:

1. primary sex organs, ‘viz. testes and ovaries, which produce haploid gametes by meiosis;
2. secondary sex organs, such as prostate and seminal vesicles in males and fallopian tubes, uterus, and vagina in the female, which are ducts to convey appropriate site for fertilization to the gametes and glands to provide useful secretions;
3. accessory sex organs, viz. facial hair, broad larynx, etc. in males and breasts in females, to distinguish between the two sexes by appearance.

→ The male reproductive system consists of a pair of testes suspended in the scrotal sac; a pair of ducts, each differentiated into an epididymis to store the sperms, a vas deferent for conduction of sperms and penis as an intermittent organ. A male urethra passing through an erectile penis, and 3 types of glands, viz., a pair of seminal vesicles, a prostate gland, and a pair of Cowper’s glands. The secretion of glands mix with sperms to form semen.

→ Testes consist of numerous coiled seminiferous tubules (crypts). Each is lined by germinal epithelium formed of germ cells and Sertoli (nurse) cells. Germ cells produce spermatozoa which obtain nutrition from the Sertoli cells. The interstitial cells (Leydig’s cells) of testes produce the male sex hormone, testosterone. Secondary sex glands of males include a prostrate, two seminal vesicles, and two Cowper’s glands. The secretion of these glands along with the sperms from the semen.

→ The female reproductive system is comprised of a pair of ovaries, two fallopian tubes (oviducts), a uterus, and a vagina. Each ovary is lined by the germinal epithelium of germ cells which form primary follicles. A primary follicle changes into Graafian follicles under the influence of FSH. Ovulation is controlled by the Luteinising hormone. Ovaries also secrete estrogens and progesterone hormones. ,

→ Fallopian tubes (oviducts) are differentiated into infundibulum, ampulla, isthmus, and uterine part. Fallopian tubes conduct the ovum towards the uterus.

→ The uterus is the site of fetal growth during pregnancy. The uterus (womb) is differentiated into the fundus, body, and cervix. The vagina acts as the birth canal. Vulva is the external genitalia. It comprises of vestibule, labiaminora, labia majora and clitoris. Breasts are accessory sex organs of females. Their size depends upon the estrogen of the ovary at puberty and lactogenic hormone after parturition.

→ Puberty is the period of sexual maturity. It is characterized by the development of secondary sexual characters. It comes between 13 to 16 years in the male and between 10 to 14 years in the female. It is controlled by testosterone in male and estrogens in the female.

→ Gametogenesis is the process of formation of haploid gametes (sperms and ova) in the primary sex organs, gonads (testes and ovaries).

→ Spermatogenesis occurs in seminiferous tubules of the testes. In it, diploid spermatogonium undergoes growth phase to form diploid primary spermatocyte which undergoes meiosis and form 4 haploid spermatids. Each spermatid transforms into sperm by a process called spermiogenesis. A mature sperm consists of a head, a neck, a middle piece, and a tail.

→ Oogenesis occurs in the ovary. A diploid oogonium undergoes a growth phase and forms a diploid primary oocyte which undergoes meiosis and forms a haploid ovum in 2 or 3 polar bodies. The human ovum is alecithal and is surrounded by many egg envelopes.

→ The menstrual cycle is cyclic changes in the ovaries and the reproductive tracts of primate females which culminate into the period vaginal bleeding called menstruation. It takes 28 days. It consists of four phases: Proliferative, ovulatory, luteal, and menstrual. The proliferative phase involves the growth and proliferation of the uterine endometrium, fallopian tubes, and vagina.

→ Ovulation occurs in the ovulatory phase. In the luteal phase, empty Graafian follicle changes into corpus luteum which secretes progesterone, further proliferation of the endometrium, and secretion of uterine milk. This is followed by menstruation if the ovum remains unfertilized. If fertilization occurs it is followed by implantation and normal growth of the fetus.

→ Menopause is the period when ovulation and the menstrual cycle stops. It generally occurs between 45 to 55 years.

→ The primate females show the menstrual cycle, the females of most of the mammals become sexually responsive during the heat period, they have an estrous cycle.

→ Asexual reproduction: Reproduction which involves no formation and fusion of gametes.

→ Binary fission: Type of asexual reproduction in which parent divides into two daughters.

→ Conjugation: Type of sexual reproduction found in ciliate protozoans. e.g. Paramecium.

→ Copulation: the sexual union of male and fèrnale. Also called coition.

→ Cytokinesis: Division of cytoplasm during cell division.

→ Epididymis: Secondary sex organs of males, which store sperms.

→ Gametogenesis: The formation of haploid gametes in the gonads.

→ Gestation period: The period of embryonic development between fertilization and delivery.

→ Hermaphrodite: Organisms with both testes and ovaries.

→ Isogamy: When two fusing gametes are morphologically and physiologically similar.

→ Karyokinesis: Division of the nucleus during the cell division.

→ Menopause: Period when ovulation and menstruation stop in the female.

→ Oogenesis: Formation of the ovum in the ovary.

→ Parthenogenesis: Development of an unfertilized ovum.

→ Reproduction: Method of producing progeny by the existing individuals for the continuation of the race.

→ Sexual reproduction: Method of reproduction that involves fusion of the gametes.

→ Spermatogenesis: Formation of haploid sperms in the testes.

→ Vitellogenesis: Formation of the yolk in the ovum.