1. Write in brief about the earth’s lithosphere and hydrosphere.     A large portion of the earth’s surface covered by the oceans and seas including rivers, lakes, etc is known as the Hydrosphere. On the other hand, another part of the earth’s surface formed by land slightly above sea-level is called the Lithosphere. The hydrosphere and lithosphere are penetrating within each other through fragmentation of both the units. The lithosphere is divided into four divisions. The first part of the lithosphere is formed by the continents of Asia, Europe and Africa; the second part is formed by the continents of North America and South America; the third part by Australia including a large number of islands constituting the continent of Oceania; and the fourth part by the continent of Antarctica. A large proportion of the hydrosphere (57per cent) is confined to the southern hemisphere. On the other hand, among the five oceans of the earth, which are all interli...

Chapter 12     Electricity Page 200 1.       What does an electric circuit mean? An electric means a closed and continuous pathway for the passage of electric current.   2.       Define the unit of current. The SI unit of current is ampere (A)       1 ampere is defined as the amount of current that is constituted by the flow of 1 coulomb of charge through any point of a wire for every 1 second.   3.       Calculate the number of electrons constituting one coulomb of charge. One coulomb of charge is constituted by a total of 6 x 10 18 electrons.   Page 202 1.       Name a device that helps to maintain a potential difference across a conductor. A cell or a battery is a device that helps to maintain a potential difference across as conductor.   2.       What is meant by saying...

                  Chapter 7   Control and Coordination                     Textual Question and Answers   Page 119   1.   The differences are a)   A reflex action is fast and spontaneous while walking is a slower action. b) A reflex action does not require thinking while walking requires thinking. c)   A reflex action is generally controlled by the spinal cord while walking is controlled by the brain. 2.   The gap between the axon of a neuron and the dendrite of the next neuron is called as the synapse. It allows the transmission of an impulse in one direction only. Any impulse brought by the axon terminates at the synapse but releases chemical neuro-transmitters that cross the synapse and generate a similar impulse at the dendrite of the next neuron. 3.   C...