The amount of light entering the eye cap be controlled by the pupil. If the intensity of outside light is low, then the pupil expands to allow more light to enter the eye. Gn the other hand, if outside intensity of light is high, then the pupil contracts so that less light enters the eye.
If the ozone layer in the atmosphere depletes then the extremely harmful ultraviolet radiations coming from the Sim would reach the earth. These uv-radiations would cause skin cancer and other ailments in men, animals and plants.
A basic event in reproduction is the creation of a DNA copy. This is necessary to produce organisms which are similar to their parents. DNA copying is accompanied by the creation of an additional cellular apparatus. When two DNA copies separate, each with its own cellular apparatus by cellular division, so from one cell, two cells are produced. The process of copying of DNA brings some variations each time. Thus the surviving cells are similar to but subtly different from each other. This inbuilt tendency for variation during reproduction brings variations among the individuals of the same species.
In MgO , valency of Mg is 2 and of O is also 2 (Mg1O1) Similarly, valency of Ba is 2 and of NO3(nitrate) is 1 so, for neutralizing the chemical formula we must take 2 unit of NO3 with 1 unit of Ba so, the chemical formula of barium nitrate will be Ba(NO3)2 Similarly in barium sulphate,valency of SO4 is also 2 so the chemical formula of barium sulphate will be BaSO4.
A male has one X-chromosome and one Y-chromosome. Thus half the male gametes have X-chromosomes and the other half have Y-chromosomes. A female has two X-chromosomes. Thus all female gametes have only X- chromosomes. If a sperm carrying Y-chromosome fertilises an ovum carrying X-chromosome, then the child bom will be a boy. If a sperm carrying X-chromosome fertilises an ovum carrying X-chromosome, then the child bom will be a girl. Therefore it is the sperm from the father which determines the sex of the child.
All the elements of a group of the periodic table have the same number of valence electrons. Group number of an element upto 2 Valance Electrons (VE). is equal to the number of valence electrons and group number of an element having Valance Electrons (VE) more than 2 is equal to (10 + V.E.). (ii)
All the elements of a period of the periodic table have same number of shells. The period number of an element is equal to the number of electron shells in its atom. (b)
As we go down in a group, a new shell of electrons is added to the atoms at every step. On moving from left to right in a period, the number of valence electrons increases from 1 to 8. On moving from left to right in a period the atomic radius of elements decreases due to the large positive charge on the nucleus, the electrons are pulled in more close to the nucleus. On going down in a group, the size of the atoms increases as a new shell of electrons is added to the atoms at every step.
