Shikshakendra

Mendel's Experimentation  After obtaining plants pure for their characters Mendel started his experiments. Mendel did not consider a number of characters at the same time. He first conducted experiment by considering only a single character. This cross dealing with only a single character at a time is termed as monohybrid cross. Similarly he conducted experiments by taking two characters at a time. This was termed as dihybird cross. Mendel's Monohybrid Cross  In one of his experiments Mendel selected plants having contrasting characters for height, i.e. he selected long plants (above six feet) and dwarf plants (about one foot). Being pure for their characters, the plants were homozygous long and and homozygous dwarf. These plants represented the parental  (P) generation. He cross-pollinated the long and dwarf plants. He collected the seeds obtained from this cross and grew them. The plants obtained from this cross were long, none of them was dwarf or of intermediate size....

~ HEREDITY  The transmission of traits from parents to offsprings is termed as heredity. This transmission takes place by the process of reproduction. The reproductive process generates the individuals of similar design. The transmission or inheritance of characteristics from parents to offsprings is governed by certain well defined rules called the rules of heredity.  INHERITED TRAITS   The traits (characteristics) obtained from parents are termed as inherited traits. You must have seen a number of children similar to their parent (s). This is because of the traits which they inherited from their parents. Body design, shape, colour, etc. are all inherited from parents. Though all human beings are similar, still they possess variations. For example, free and attached earlobes are two variants found in human populations.  Rules for the Inheritance of Traits : Mendel ' s Contributions Every human individual has two copies of genetic material, i.e. DNA. The gametes...

~ INTRODUCTION  In the last chapter you have studied how organisms reproduce to produce new individuals. The offsprings produced as a result of reproduction are similar to their parents as well as other individuals of the species. For example, man resembles man in body shape size etc. Similarly dogs resemble dogs,  cows resemble cows, and so on. Similarly the plant obtain from the seed of a mustard plant is similar to its parent. The offspring plant is similar to other mustard plants as well. But how is it that the offsprings are similar to other members of the species as well as to Parents. All this happens because of the presence of genes in parent/parents which are transferred to the next generation via  gametes or other means. These genes transfer the biological information of parents to offsprings which gives rise to various characteristics in the offspring thereby making them similar to parents or other members of species.  These differences in characteristics ...

Clearly, chlorine requires one more electron to acquire the stable noble gas electronic configuration. In order to become stable, hydrogen and chlorine will share one electron with each other. This allows hydrogen atom to attain its duplet and chlorine to attain its octet. The electron dot structure of hydrogen chloride molecule is shown in fig. 4.3. Further, since chlorine atom and hydrogen atom share one electron to form HCL molecule, thus, valency of HCL is 1. That is, HCL is also monovalent.    (iv) Formation of Ammonia Molecule, NH3:  Atomic number of nitrogen = 7         Electronic configuration = K  L                                                       2  5 Clearly, nitrogen has 5 electrons in its outermost shell, i.e., l  shell and thus, requires one more electron to atta...

  ~ Types of Covalent Bonds  The covalent bonds are of three types :  (i) If each atom contributes one electron then the covalent bond formed is called a single  covalent bond which is represented by a single  line (-). (ii) If each atom contributes two electrons, then the covalent bond formed is called a  double bond which is represented by a double  line. (iii) If each atom contributes three electrons, then the covalent bond formed is called a    triple bond which is represented by a triple  line.  ~ Formation of Covalent Bonds  We shall now discuss formation of some simple molecules formed by sharing of valence electrons (i) Formation of Hydrogen Molecules, H2 : The atomic number of hydrogen is 1. Hence, Hydrogen has one electron in its K shell and it requires one more electron to fill the K shell. So the two hydrogen atoms share their electrons to form a molecule of hydrogen, H2. This allows each hydrogen atom to attain the...

  ~ INTRODUCTION  Carbon is a unique element. It is a non-metal with symbol C. Carbon gets its name from the Latin word Carbo , which means a black rock that can burn. Carbon exists in nature in many forms.  The carbon compounds are also known as organic compounds.  Besides this, a large number of things we use or consume in our everyday life are made up of carbon compounds. For example, our food materials like grain, pulses, fats, sugar, coffee, fruits and vegetables, etc., are made up of carbon compounds. The fuels such as wood, coal, kerosene, LPG (liquefied Petroleum gas), natural gas, CNG (compressed natural gas), petrol and diesel, etc., which we used to cook our food and to run vehicles are made up of carbon compounds.  The carbon is a versatile element. The amount of carbon present in the earth's crust and in the atmosphere is quite meagre. The earth's crust has only 0.02% carbon in the form of minerals (like carbonates, hydrogencarbonates, coal, petrole...