Name the stage of cell cycle at which one of the following events occur:
(i) Chromosomes are moved to spindle equator
(ii) Centromere splits and chromatids separate
(iii) Pairing between homologous chromosomes takes place
(iv) Crossing over between homologous chromosomes takes place

Identify the meiotic stage in which the homologous chromosomes separate while the sister chromatids remain associated at their centromeres

Analyse the events during every stage of cell cycle and notice how the following two parameters change (i) Number of chromosomes (N) per cell (ii) Amount of DNA content (C) per cell Answer

Accourding to weismann prediction , every organism undergoes two kinds of cell divisions. In mitosis, there is no change in chromosomal number (2n) and in Meiosis, chromosomal number is reduced to half (n). (ii) In which cells, Meiosis takes place ?

Study the following statements and select the incorrect ones. (i) Pyramids of energy can never be inverted, since this would violate the laws of thermodynamics. (ii) Pyramids of standing crop and numbers can be inverted since the number of organisms at a time does not indicate the amount of energy flowing through the system. (iii) There are certain limitations of ecological pyramids such as they do not take into account the same species belonging to two or more trophic levels. (iv) Saprophytes are not given any place in ecological pyramids even though they play a vital role in the ecosystem.

Covalent molecules formed by heteroatoms bound to have some ionic character. The ionic character is due to shifting of the electron pair towards A or B in the molecule AB. Hence, atoms acquire small and equal charge but opposite in sign. Such a bond which has some ionic character is described as polar covalent bond. Polar covalent molecules can exhibit dipole moment. Dipole moment is equal to the product of charge separation, q and the bond length, d for the bond. The unit of dipole moment is Debye. One Debye is equal to 10^(-18) esu cm. Dipole moment is a vector quantity. It has both magnitude and direction. Hence, dipole moment of molecules depends upon the relative orientation of the bond dipoles, but not on the polarity of bonds alone. A symmetrical structure shows zero dipole moment. Thus, dipole moments help to predict the geometry of the molecules. Dipole moment values can be used to distinguish between cis-and traps-isomers, ortho-, meta-and para-forms of a substance, etc. The percentage of ionic character of a bond can be calculated by the application of the following formula : % " ionic character " = ("Experimental value of dipole moment ")/("Theoretical value of dipole moment ") xx 100 Arrange the following compounds in increasing order of dipole moments, toluene (I), o- dichlorobenzene (II), m-dicblorobenzene (III) and p dichlorobenzene (IV) :

Hydrogen bonding is said to be formed, -when sightly acidic hydrogen-atom attached to a strongly, electronegative fluorine, oxygen or nitrogen atom. is held with weak. electrostatic forces by the non-bonded pair of electrons of another atom. The co-ordination number of hydrogen in such cases is two. It acts as a bridge between two atoms, to one of which it is covalently bonded and to other attached through electrostatic forces, also called hydrogen bond. Though the hydrogen atoms in a methyl group are not polarised, if an electronegative group like chloro, carbonyl, nitro or cyano (in order to increase electronegativity) is attached to it, the C-H bond gets polarised due to the inductive effect and the hydrogen atom becomes slightly acidic resulting in the formation of weak hydrogen bonds. Though a weak bond the H-bond effects is large number of the physical properties of compounds some of which are - Boiling points of liquids - Solubility of polar compounds in polar solvents (containig H attached with strong electronegative atom) - Viscosity of liquids . Acidity Which of the following combinations can involve hydrogen bonding I) Mixture of KF and HF " " II) Mixture of CH_(3)COCH_(3) and CHCI_(3) III) Mixture of NH_(4) CI and H_(2)O" " IV) Mixture of CH_(3) and H_(2)O

Following are the events taking place to explain adsorption theory I : Desorption II : Diffusion of the reactants along the surface III : adsorption of the reactants IV : formation of the activated surface complex These events are taking place in the following order