Exercise Solutions

1. Fill in the blanks.

   a. The layer of gases on the Earth is called the atmosphere.

   b. Water is available in liquid, solid, and gaseous states.

   c. The solid part of the Earth's surface is called land.

   d. Nitrogen gas is used for protein synthesis in plants by nitrogen fixation.

   e. The ozone layer protects the Earth from harmful ultraviolet rays.

2. Match the pairs.

   Group A	Group B
   a. Carbon dioxide	i. Photosynthesis
   b. Oxygen	ii. Respiration
   c. Nitrogen	iii. Protein synthesis
   d. Ozone layer	iv. Protection from UV rays
   e. Argon	v. Electric bulbs

3. True or False. If false, correct the statement.

   a. The Earth's surface is covered by 97% fresh water.

   Answer: False. The Earth's surface is covered by approximately 97% saline (salty) water in oceans and seas, and only about 3% is fresh water.

   b. Land is a source of minerals and oil.

   Answer: True.

   c. Deforestation helps in controlling air pollution.

   Answer: False. Deforestation increases air pollution because fewer trees mean less absorption of carbon dioxide, and it can also lead to more dust and smoke in the atmosphere. Tree plantation helps in controlling air pollution.

   d. Water pollution can spread diseases like cholera.

   Answer: True.

4. Give reasons.

   a. The ozone layer is important for living organisms.

   Answer: The ozone layer is crucial because it absorbs most of the harmful ultraviolet (UV) radiation coming from the sun. If these UV rays reached the Earth's surface in full intensity, they would cause severe damage to living organisms, such as skin cancer, cataracts, and harm to plants and aquatic life. Thus, the ozone layer acts as a protective shield for life on Earth.

   b. It is important to conserve water.

   Answer: It is important to conserve water because freshwater, which is essential for human survival, agriculture, and industry, is a limited resource. Although Earth has a lot of water, most of it is salty ocean water, and only a small percentage is available as freshwater. With increasing population and pollution, the availability of clean freshwater is decreasing. Conserving water ensures that enough water is available for current and future generations, prevents water scarcity, and protects aquatic ecosystems.

   c. We should prevent air pollution.

   Answer: We should prevent air pollution because polluted air contains harmful substances that can cause serious health problems in humans, such as respiratory diseases (asthma, bronchitis) and heart conditions. It also damages plants, buildings, and contributes to environmental issues like acid rain and global warming. Preventing air pollution ensures cleaner air for breathing, protects public health, and preserves the environment.

   d. Soil is an important natural resource.

   Answer: Soil is an important natural resource because it provides the necessary nutrients and support for plant growth, which forms the basis of almost all food chains. Most of our food crops, fruits, and vegetables grow in soil. It also acts as a habitat for many small organisms and plays a vital role in the water cycle by filtering water. Without fertile soil, agriculture would not be possible, leading to food scarcity and affecting entire ecosystems.

5. Answer the following questions in your own words.

   a. What are natural resources? Give examples.

   Answer: Natural resources are materials or substances that occur naturally in the environment and are essential or useful to humans and other living organisms. They are found in nature and are not man-made. They include everything from the air we breathe and the water we drink to the land we live on and the minerals found beneath it.

   Examples of natural resources include:

   • Air: Oxygen, Nitrogen, Carbon dioxide.
   • Water: Rivers, lakes, oceans, groundwater, rain.
   • Land: Soil, mountains, plains, forests.
   • Minerals: Iron, coal, petroleum, gold, silver.
   • Sunlight
   • Wildlife

   b. Explain the composition of air.

   Answer: Air is a mixture of several gases, along with water vapor and dust particles, that forms the Earth's atmosphere. The main components of air are:

   • Nitrogen ($\text{N}_2$): Makes up about 78% of the air. It is the most abundant gas.
   • Oxygen ($\text{O}_2$): Accounts for approximately 21% of the air. It is vital for breathing and burning.
   • Argon (Ar): About 0.9% of the air. It is an inert gas.
   • Carbon Dioxide ($\text{CO}_2$): Present in a small amount, about 0.03%. It is essential for plants during photosynthesis.
   • Other gases: Very small amounts of noble gases like Neon (Ne), Helium (He), Krypton (Kr), Xenon (Xe), as well as Methane ($\text{CH}_4$), etc.
   • Water vapor ($\text{H}_2\text{O}$): The amount varies depending on location and weather.
   • Dust particles: Tiny solid particles suspended in the air.

   c. How is the water cycle important?

   Answer: The water cycle, also known as the hydrological cycle, is extremely important because it ensures the continuous circulation and availability of fresh water on Earth. It is a natural process where water evaporates from bodies of water and land, forms clouds through condensation, and returns to Earth as precipitation (rain, snow). This cycle:

   • Replenishes freshwater sources like rivers, lakes, and groundwater.
   • Distributes water across different regions, supporting various ecosystems.
   • Regulates Earth's temperature by moving heat around.
   • Cleans and purifies water naturally.

   Without the water cycle, freshwater sources would dry up, making life impossible.

   d. List some measures to conserve natural resources.

   Answer: To conserve natural resources for present and future generations, we can adopt several measures:

   • Reduce, Reuse, Recycle: Minimize consumption, find new uses for old items, and process waste materials into new products.
   • Plant more trees: Reforestation and afforestation help improve air quality, prevent soil erosion, and conserve biodiversity.
   • Save water: Turn off taps while brushing, fix leaky pipes, use buckets for washing vehicles, and practice rainwater harvesting.
   • Use public transport or cycle: Reduce vehicle emissions to control air pollution.
   • Proper waste management: Dispose of garbage correctly, separate biodegradable and non-biodegradable waste, and avoid littering.
   • Use renewable energy: Promote solar, wind, and hydroelectric power instead of fossil fuels.
   • Educate others: Raise awareness about the importance of conservation and encourage sustainable practices.
6. Identify the relation.

   Resource	Use/Characteristic
   Air	Respiration, combustion
   Water	Drinking, agriculture
   Land	Agriculture, minerals
   Ozone layer	Protects from UV rays
   Nitrogen	Protein synthesis in plants

7. Find the odd one out.

   a. Oxygen, Nitrogen, Hydrogen, Carbon dioxide

   Answer: Hydrogen (Hydrogen is not a major component of air, while Oxygen, Nitrogen, and Carbon dioxide are.)

   b. River, Lake, Glacier, Well

   Answer: Glacier (Glaciers are large masses of ice, while rivers, lakes, and wells are forms of liquid freshwater bodies or sources.)

   c. Mountain, Plain, Plateaus, Ocean

   Answer: Ocean (Ocean is a large body of saltwater, while mountain, plain, and plateau are types of landforms.)

   d. Deforestation, Air pollution, Water pollution, Soil erosion

   Answer: Soil erosion (Air pollution, water pollution, and soil erosion are direct consequences of environmental degradation, while deforestation is an activity that *leads* to degradation and can exacerbate pollution and erosion. Or, deforestation, air pollution, and water pollution are types of pollution, whereas soil erosion is a process that affects land.)

8. What will happen if...

   a. ...the ozone layer completely disappears?

   Answer: If the ozone layer completely disappears, the Earth would be exposed to extremely high levels of harmful ultraviolet (UV) radiation from the sun. This would have devastating consequences:

   • Increased rates of skin cancer, cataracts, and weakened immune systems in humans and animals.
   • Damage to plant life, leading to reduced crop yields and disruption of ecosystems.
   • Harm to marine life, especially plankton, which are at the base of the ocean food chain.
   • Overall severe impact on the entire planet's biodiversity and climate, making life as we know it very difficult to sustain.

   b. ...all the fresh water on Earth dries up?

   Answer: If all the freshwater on Earth dries up, it would lead to a catastrophic global crisis:

   • All land-based living organisms, including humans, animals, and plants, would die due to lack of drinking water.
   • Agriculture would cease, leading to massive food shortages and starvation.
   • Industries that rely on freshwater for production would shut down.
   • The entire terrestrial ecosystem would collapse, affecting the climate and ultimately rendering the planet uninhabitable for most current life forms.

   c. ...human activities continue to cause excessive pollution of air, water, and land?

   Answer: If human activities continue to cause excessive pollution of air, water, and land, the quality of our natural environment will degrade significantly, leading to severe consequences:

   • Health crisis: Increased respiratory diseases, water-borne illnesses, and other health problems in humans due to contaminated air, water, and food.
   • Ecosystem collapse: Destruction of habitats, loss of biodiversity, and extinction of many plant and animal species.
   • Resource scarcity: Clean drinking water would become extremely scarce, fertile land would become barren, and breathable air would diminish.
   • Climate change: Worsening of global warming, more extreme weather events, and disruption of natural cycles.
   • Ultimately, the planet would become increasingly unsuitable for sustaining human life and many other species.
9. Projects/Activities.

   a. Prepare a chart showing the composition of air and its uses.

   b. Conduct a water audit at your home and identify ways to reduce water consumption.

   c. Visit a local park or garden and observe the different layers of soil. Draw and label them.

   (Note: These are practical activities for students to perform.)