A. Kidneys removes extra salts and water from the blood
B. The urine is stored in Urinary bladder
C. Through urethra urine is excreted out of the body.
D. Ureter transfer urine from the kidneys to the urinary bladder.

A huge envelope of air surrounded the earth is called Atmosphere.
(i) This envelope is thicker near the earth's surface.
(ii) As we go higher up, the density and the availabillty of air gradually decreases.
(iii) Movement of wind, Presence of water vapours for cloud formation are the vital roles of atmosphere.
(iv) Troposphere is the responsible layer for the weather we experience on earth.
(v) Stratosphere has the Ozone layer which protects all life on earth from the harmful UV rays of the sun.

Conductors:
(i) The rate of flow of electric charges in a circuit is called electric current.
(ii) The materials which allow electric charges to pass through them are called conductors.
(iii) Examples: Copper, iron, aluminium, impure water, eafth etc.
Insulators (Non -Conductors) : 
(i) The material which do not allow electric charges to pass through them are called insulators or non- conductors.
(ii) Examples: plastic, glass, wood, rubber, chinna clav, ebonite etc.

We get electricity from thermal power, hydel power, tidal power wind power, solar power etc as sources of electricity
Thermal Power stations:
In thermal power stations, the thermal energy generated by burning coal, diesel or gas is used to produce steam. The steam is used to rotate the turbine. While the turbine rotates, the coil of wire kept between the electromagnet rotates. Due to electro magnetic induction electricity is produced. Here heat energy is converted into electrical energy.
Hydel power stations:
In hydel power stations, the turbine is made to rotate by the flow of water from dams to produce electricity. Here kinetic energy is converted into electrical energy. Hydel stations have long economic lives and low operating cost.
Atomic power stations:
In atomic power stations, nuclear energy is used to boil water. Here the steam is used to rotate the turbine. As a result, electricity is produced. Atomic power stations are also called as nuclear power stations. Here nuclear energy is converted into mechanical energy and then electrical energy.
Wind Mills:
In wind mills, wind energy is used to rotate the turbine to produce electricity. Here kinetic energy is converted into electrical energy.

The expansion of substance on heating is called, the thermal expansion of that substance 
(i) Gaps are left in between rails while laying railway track :
So that there is enough margin for the tracks to expand and contract due to the temperature changes. If that gap is not left then the tracks might have enormous stress in them while expanding due to heat, which can damage them.
(ii) Gaps are left in between two joints of a concrete bridge:
Thermal expansion takes place due to the increase in the kinetic energy of the constituent molecules as they are heated. Thermal expansion is the reason we leave some gaps between section of h concrete bridge.

While swallowing food if the food particles enter into respiratory tract leads to hiccup and cough to eject out the food particles from respiratory tract.

a) melting of wax and
d) Solidification of the molten wax can be reversed.
Burning of candle is a physical / reversible change. That is,
\(\text { Solid wax } \underset{\text { Cooling }}{\stackrel{\text { Heating }}{\rightleftarrows}} \text { molten wax }\)

Many of us expect that diameter of hole will decrease, but actually as the diameter of ring increases diameter of hole will also increase.

The heat is escaping from the room because the room temperature is higherthan atmosphere. Heat energy flows from higher temperature to lower temperature.