Human beings are an important part of the environment. But some human activities change the environment and the changes in the environment affect life on earth. For example: An environmental problem caused by human activities is depletion of ozone layer. If the ozone layer in the atmosphere disappears completely, then all the extremely harmful ultraviolet radiations coming from the Sun would reach the earth surface and would cause skin cancer and other ailments. Therefore it is necessary to conserve our environment.
Biodegradable wastes- (i)-Wastes which can be broken down into non-poisonous substances in nature in due course of time by the action of micro-organisms(bacteria, fungi) are called bio-degradable wastes. (ii) Sewage, peals of fruits and vegetables, etc. Non-biodegradable wastes- (i)-Wastes which cannot be broken down into non-poisonous substances in nature are called non-biodegradable wastes. (ii)Plastic, glass, etc.
Disadvantages of fossil fuels: 1- Fossil fuels are non-renewable source of energy. 2- The burning of fossil fuels produces acidic gases such as sulphur dioxide and nitrogen oxides. These acidic gases cause acid rain. 3-The burning of fossil fuels produces smoke which pollutes the enviornment air. 4-The burning of fossil fuels, especially coal, leaves behind a lot of ash.
Various stages of evolution: 1-Complex organs may have evolved because of the survival advantages of the intermediate stage. 2-Complex organ like eyes are created bid by bid over generation. 3-The structure of the eye in all organisms is different enough to have separate evolutionary origin. 4-Organs may be adapted to new functions during the course of evolution, e.g., feathers are thought to have evolved for warmth and later adapted for flight. 5-Some dissimilar looking structures also evolved from common anscestor, e.g., different vegetation like cauliflower, cabbage, broccoli, kale, etc. are generated by artificial selection from wild cabbage. 6-Changes in DNA during reproduction are the basic events of evolution.
(a) On moving from left to right in a period the metallic character of elements decreases. This is because on moving from left to right in a period of the periodic table, the nuclear charge increases due to gradual increase in the number of protons. Due to the increase in nuclear charge, the valence electrons are pulled in more strongly by the nuclear and it becomes more and more difficult for the atoms to lose electrons therefore on moving from left to right in a period thus metallic character decreases from left to right in a period.” (b) On moving from left to right in a period the size of the atom decreases because number of energy shells remains same in a period but nuclear charge increases from left to right and thus the force of attraction between the nucleus and the electrons increases which reduces the size of the atoms on moving from left to right in a period.
-The splitting up of white light into seven colours on passing through a transparent medium like a glass prism is called dispersion of light. -We get different colours of light when , white light is passed through a glass prism because white light is a mixture of lights of seven colours: red, orange, yellow, green, blue, indigo and violet. The dispersion of light occurs because the angle of refraction (or angle of bending) of lights of different colours is different when passing through the glass prism. https://padhaaiweb.s3.ap-south-1.amazonaws.com/gurucool-admin/30449757776_84f4d76a21_o_e883b5eff8/30449757776_84f4d76a21_o
(a) The ability of an eye to focus the distant objects as well as the nearby objects on the retina by changing the focal length or converging power of its lens is called accommodation. A normal eye has a power of accommodation which enables objects as far as infinity and as close as 25 cm to be focussed on the retina. (b) Myopic eye, v= -1.2 m , u= infinite ,f=? applying lens formula, 1/f=1/v-1/u 1/f=1/-1.2 - 1/ infinite=1/-1.2 f=-1.2 m =-120 cm. P=1/f=1/-1.2= -0.83 D. negative sign shows that the lens is concave.Hence, corrected lens must be a concave lens of 0.83 D.
The presence of feathers in dinosaurs and birds indicates that they are evolutionarily related. Dinosaurs had feathers not for flying but instead these feathers provided insulation to these warm-blooded animals. However, the feathers in birds are used for flight. This proves that reptiles and birds are closely related and that the evolution of wings started in reptiles.