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ISC Biology, Class 12 Biology Click on the links given alongside the chapters for important questions along with the answers:- Happy Studying ☺️ 1. Reproduction in Organisms :  http://novakidhs.blogspot.com/2022/02/reproduction-in-organisms-class-12.html 2. Sexual Reproduction in Flowering Plants:  http://novakidhs.blogspot.com/2022/02/sexual-reproduction-in-flowering-plants.html 3. Human Reproduction:  http://novakidhs.blogspot.com/2022/02/human-reproduction-class-12-biology-isc.html 4. Reproductive Health:  http://novakidhs.blogspot.com/2022/02/reproductive-health-class-12-biology.html 5. Principles of Inheritance and Variation:  http://novakidhs.blogspot.com/2022/02/principles-of-inheritance-and-variation.html 6. Molecular Basis of Inheritance:  http://novakidhs.blogspot.com/2022/02/molecular-basis-of-inheritance-class-12.html

MOLECULAR BASIS OF INHERITANCE DNA : Structure of Polynucleotide Chain DNA − Polymer of deoxyribonucleotides Nucleoside = Nitrogenous base + Pentose sugar (linked through N − glycosidic bond) Example − adenosine, deoxyadenosine, cytidine, etc. Nucleotide = Nucleoside + Phosphate group (linked through phosphodiester bond) Many nucleotides link together through 3′ − 5′ phosphodiester bond to form polynucleotide chain (as in DNA and RNA). In course of formation of polynucleotide chain, a phosphate moiety remains free at 5′ end of ribose sugar (5′ end of polymer chain) and one -OH group remains free at 3′ end of ribose (3′ end of polymer chain). Double Helix Model for the Structure of DNA Scientists involved Friedrich Meischer − First identified DNA as an acidic substance present in nucleus and named it as ‘Nuclein’ Wilkins and Franklin − Produced X-ray diffraction data for DNA structure Watson and Crick − Proposed double helix structure mod...

PRINCIPLES OF INHERITANCE AND VARIATION   Genetics Genetics is a branch of biology dealing with inheritance and variation of characters from parents of offspring. Inheritance Process by which characters are passed on from parent to progeny Variation Degree by which the progeny differs from its parents Mendel’s Experiments Gregor Johann Mendel known as the father of genetics proposed the laws of inheritance. He used garden pea as his sample. Large sampling size gave credibility to his collected data. Garden pea plant possessed certain completely opposite traits. Example − tall and dwarf plants He worked on the following seven traits of garden pea: S. No. Character Dominant Recessive 1 Stem height Tall Dwarf 2 Flower colour Violet White 3 Flower position Axial Terminal 4 Pod shape Inflated Constricted 5 Pod colour Green Yellow 6 Seed shape Round Wrinkled 7 Seed colour Yellow Green True breeding pea lines were obtained by continuous self pollination for several generations. ...

Reproductive Health Reproductive Health   It is defined as the total well being in all aspects of reproduction. India as a country ensures reproductive health to all, and since 1951, successive governments have introduced a number of programmes to ensure this, e.g., family planning and RCH (Reproductive and Child Healthcare) programmes. The aim of these programmes is to create awareness among people about the various aspects of reproductive health. Several audio-visual aids and pamphlets have been developed by both governmental and non-governmental organisations. Awareness is being created among school children by introducing sex education in schools. It is essential to provide medical assistance to people with problems related to STDs, pregnancy, contraception and infertility, especially in villages. Amniocentesis (foetal sex determination based on chromosomal pattern) has been banned to check female foeticide. Population Explosion Improvement in the quality of life due to al...

Human Reproduction Male and Female Reproductive Systems Human beings reproduce sexually and are viviparous. In humans, the reproductive phase starts after puberty. It involves: Gametogenesis Insemination Fertilisation Implantation Gestation Parturition The Male Reproductive System It is located in the pelvic region. It consists of: A pair of testes Accessory glands and ducts External genitalia Testes Situated within the scrotum, which protects the testes and also helps in maintaining the temperature. Each testis is 4 to 5 cm in length, and 2 to 3 cm in width, and has about 250 compartments called testicular lobules. Testicular lobules have seminiferous tubules which are the sites of sperm formation. Seminiferous tubules are lined by two types of cells: Male germ cells − They undergo meiosis to form sperms. Sertoli cells − They provide nourishment to the germ cells. Region outside the seminiferous tubules is called the interstitial space, which contains...

CH 2 Sexual Reproduction in Flowering Plants Pre-Fertilisation Events Several hormonal and structural changes result in the development of a flower. Inflorescences bear the flower buds, and then the flowers. Flowers are the reproductive parts of a plant. In the flowers, the androecium (male reproductive part) and the gynoecium (female reproductive part) develop. Androecium The androecium consists of whorls of stamen. The stamen consists of the filament (long and slender stalk) and anther (bilobed structure). Filament is attached to the thalamus or to the petal. Anther: A typical anther is bilobed and each lobe is dithecous (consists of two theca). Theca are separated by a longitudinal groove running lengthwise. The microsporangia are located at the corners, two in each theca. They further develop to form pollen sacs, which contain the pollen grains. Structure of microsporangium The microsporangium is surrounded by four wall layers (epidermis, endothecium, middle laye...