Class 9 General Science Chapter 6 Question Answer

Complete Notes of Class 9 General Science Chapter 6 Question Answer Environment and Natural Resources in 9th Class General Science Urdu Medium by Sir Usman Lateef Suib. These computerized notes are very helpful in the preparation of the Environment and Natural Resources for students of the Class 9 General Science Chapter 6 Question Answer these are according to the new paper patterns of all Punjab boards.

• Important Multiple Choice Questions (MCQs) and Short Questions of Chapter No.6: Environment and Natural Resources in General Science 9th class Urdu Medium.
• Earth's atmosphere, its composition and layers
• Depletion of ozone layer and its effects on earth.
• Absorption and reflection of energy on earth and green house effect.
• Climatic changes due to human activities.
• Types of pollution and their impact on human life.
• Use and conservation of minerals and fossil fuels.
• Crops of Pakistan, mechanized farming and modern trends in agriculture.
• Development of dairy and poultry farming.
• Wildlife, national parks and conservation of wildlife.
• Effects of over population on environment, poverty and quality of life.
• Earth's Atmosphere: Atmosphere is an envelope of gases that covers earth from all sides. It is about the 200 km thick. The air we breathe in is part of the atmosphere. Photosynthesis and burning also occur in presence of air. Atmosphere maintains the temperature of the earth and protects from the harmful radiation coming from the sun.
• Composition of Atmosphere: The atmosphere is made up of about 78 percent nitrogen and 21 percent oxygen. The remaining one percent consists of water vapour and trace gases (carbon dioxide, hydrogen, argon, helium, ozone, etc).
• Our earth is the only planet of the solar system where free state oxygen and water vapour are present. Living organisms use oxygen in respiration. Although the proportion of carbon dioxide in air is only 0.04% but this gas is also very important for life on earth. Plants utilize carbon dioxide for preparation of food during photosynthesis. All other organisms, which cannot prepare their own food, also depend on this food. Carbon dioxide also helps in maintaining the earth's temperature. Carbon dioxide is produced during respiration and burning. The proportion of carbon dioxide is increasing in the air as a result of human activities. This may raise earth's temperature and lead to climatic change.
• Different Layers of Atmosphere: Atmosphere is divided into four parts or layers. Each layer has its own characteristic features. The four layers and their important characteristics are given below:
• 1. The Troposphere: The troposphere extends to a height of about 18 km above earth's surface. Most of the gas molecules and water vapour are in the troposphere. This is the layer where most. of the weather occurs.
• 2. The Stratosphere: This layer is above the troposphere. It reaches the height of 50 km from sea level. Most jet airplanes travel in lower stratosphere. The upper stratosphere contains a layer of a gas called ozone. The ozone layer is very important to living things because it filters out most of the ultra violet (UV) radiations given off by the sun.
• 3. The Mesosphere: Beyond the stratosphere is the mesosphere, which extends about 85 km above earth's surface. This is the coldest layer of the atmosphere. The temperature in the mesosphere can be as low as -100°C.
• 4. The Thermosphere: The thermosphere is the outermost layer of the atmosphere. It is the hottest layer, where temperature may be as high as 2000°C.
• Depletion of Ozone Layer: Ozone is a gas present in the upper stratosphere. It forms a protective covering around the earth, which prevents UV-radiations from reaching the earth. Certain chemicals are released from refrigerator, air conditioners, spray cans and factories manufacturing packing foams. These chemicals are called chlorofluorocarbons (CFCs). CFCs react with ozone causing its depletion and thinning of ozone layer.