Astronauts have to wear special protective space suits filled with air when they go to the Moon. If they did not wear these space suits, the counter-pressure exerted by the body of the astronauts would make the blood vessels burst. The astronauts would bleed.

The air pressure is highest at sea level and decreases with height. In areas where temperature is high, the air gets heated and rises. This creates a low pressure area 
In areas having lower temperature, the air is cold. It is therefore heavy. Heavy air sinks and creates a  high pressure area. The air always moves from high pressure areas to low pressure areas.

Nitrogen is very important for plant's survival. They cannot take nitrogen directly from the air. Bacteria that live in the soil and roots of some plants take nitrogen from the air and change its form, so that plants can use it

Atmosphere consists of mainly nitrogen (78%), oxygen (21 %), argon (0.93%), carbon dioxide (0.03%) and other gases like helium, ozone and hydrogen (0.04%).

The pressure exerted by the weight of air on the Earth's surface is called air pressure.

1.Yes, global warming is a serious issues of contemporary world. Due to global warming, temperature on Earth is increasing. If it is not controlled, a day will come when all ice caps will melt and everything will get submerged into water.
2.Overburning of fuels like coal and oil causes the greenhouse effect.
3.Using bio-fuel and tree plantation make ways out of global warming.

The atmosphere is divided into five layers starting from the Earth's surface
(i) Troposphere Its average height is 13 km. The air we breathe exists here. Almost all the weather phenomena like rainfall, fog and hailstorm occur in this layer.
(ii) Stratosphere It lies above the troposphere which extends up to a height of 50 km. This layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aeroplanes. It contains a layer of ozone gas.
(iii) Mesosphere It lies above the stratosphere. It extends up to the height of 80 km. Meteorites burn up in this layer on entering from the space.
(iv) Thermosphere In thermosphere, temperature rises very rapidly with increasing height. Ionosphere is a part of this layer. It extends between 80-400 km. This layer helps in radio transmission. In fact, radio waves transmitted from the Earth are reflected back to the Earth by this layer.
(v) Exosphere This uppermost layer. This layer has very thin air. Light gases like helium and hydrogen float into the space from here.