Biology Class 12

 c 9 Animal Husbandry Introduction ● The practice of breeding and raising livestock is called animal husbandry. ● It includes breeding of livestock (cows, buffaloes, pigs, etc.), poultry farming, and fisheries. Farm Management ● Dairy Farm Management ○ Milk yield is dependent upon the quality of breed selected. Quality encompasses yielding potential and disease resistance. ○ Care of cattle − Proper accommodation, adequate water, feeding in a scientific manner (quality of fodder), hygiene, visits by a veterinary doctor ○ All these processes nowadays have become mechanised and proper record keeping is followed. ● Dairy Farm Management ○ Poultry includes meat from birds such as chicken, ducks, and turkey. ○ The main emphasis in poultry farming is selection of a disease-free and healthy breed. ○ Safe farm conditions, proper feed, water, and hygiene are also necessary. Animal Breeding ● Breed − A group of animals related by descent and similar in most characters such as general appear...

 c 7 Origin of Life Urey and Miller experiment ● Primitive atmosphere had high temperature, volcanic storms, and reducing atmosphere, containing CH4, NH3, H2, etc. ● Urey and Miller took the same compounds in a closed flask along with water vapour at 800ºC and created an electric discharge. ● Formation of biomolecules such as amino acids, simple sugars, fats, etc. was observed in the flask. Theories of Evolution ● The theory of special creation or divine intervention was challenged by Charles Darwin. ● He made observations on his sea-trip around the world aboard H.M.S. Beagle and concluded that all existing living forms share similarities among themselves and also with other life forms, which existed millions of years ago of which many are extinct. ● The evolution of life forms has been gradual and those life forms better fit in environments that leave more progeny. This is called natural selection and is a mechanism of evolution. ● Alfred Wallace working in the Malay Archepelago a...

 c 6 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 model for DNA based on X-ray diffraction data ○...

 c 5 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: ● True breeding pea lines were obtained by continuous self pollination for several generations. ● Fourteen true breeding pea lines were selected as pairs, which were similar except for one character with contrasting traits. ● Artificial cross pollination (hybridisation) was performed on such varieties to obtain first hybrid generation known as the first filial proge...