Samacheer Class 6 Science - Air

Plants are essential for maintaining life on Earth through the process of photosynthesis. Plants require energy for their growth and development. To obtain this energy, plants manufacture food by a process called photosynthesis. During photosynthesis, plants take carbon dioxide from the atmosphere and use chlorophyll in the presence of sunlight to prepare their own food. As a result of this process, oxygen is released by plants into the atmosphere. This oxygen is available to animals and human beings for breathing and respiration. Interestingly, plants also take in oxygen and release carbon dioxide just as animals do, especially during the night when photosynthesis does not occur. This exchange of gases between plants and animals creates a balanced cycle that sustains life on our planet.

If we remove plants from the aquarium, several negative consequences will occur. The production of oxygen will be reduced significantly because plants are the primary producers of oxygen through photosynthesis. At the same time, the absorption of carbon dioxide and ammonia will be reduced, leading to an accumulation of these gases in the water, which can harm the fish. Plants provide shelter and hiding places for fish, making them feel secure. Without plants, fish will feel insecure and stressed. Additionally, algae growth will increase because there will be less competition for nutrients and light. The overall balance of the aquarium ecosystem will be disrupted, and the water quality will deteriorate, making it difficult for fish to survive.

Our earth is surrounded by a huge envelope of air called the atmosphere. The atmosphere is a mixture of gases, water vapor, and dust particles that extends from the surface of the Earth to a great height. It plays a crucial role in protecting life on Earth by filtering harmful solar radiation, regulating temperature, and providing oxygen for respiration. The atmosphere is divided into five distinct layers based on temperature and composition. The Troposphere is the lowest layer where weather occurs and where we live. The Stratosphere lies above it and contains the ozone layer which protects us from ultraviolet radiation. The Mesosphere is the third layer where temperatures decrease with altitude. The Ionosphere is the fourth layer containing ionized gases that reflect radio waves. The Exosphere is the outermost layer where the atmosphere gradually transitions into space.

If the clothes of a person catch fire accidentally, immediate action should be taken to extinguish the flames. The person should be covered with a rug, blanket, or any available cloth material and then rolled on the floor. This method works because covering the person cuts off the supply of oxygen to the fire, and since fire requires oxygen to burn, the flames will be extinguished. Rolling on the floor also helps to smother the flames and prevent them from spreading. Alternatively, a suitable fire extinguisher can be used if available nearby. It is important not to run around as this will fan the flames and make the fire worse. Quick action and keeping calm are essential in such emergency situations to minimize injuries and prevent the fire from spreading.

Traffic assistants wear masks on duty because they are continually exposed to smoke and pollutants emitted from vehicles on the road. Vehicle exhaust contains harmful gases such as carbon monoxide, nitrogen oxides, and particulate matter. Inhaling these pollutants over prolonged periods can cause serious breathing problems and lung diseases such as asthma, bronchitis, and other respiratory conditions. The mask acts as a protective barrier that filters out some of the harmful particles and gases from the air before they enter the respiratory system. By wearing a mask, traffic assistants reduce their exposure to these dangerous pollutants and protect their health. This is an important occupational safety measure for people who work in high-traffic areas where air pollution levels are significantly elevated.

Plants and animals maintain the balance of oxygen and carbon dioxide in the air through a continuous cycle of photosynthesis and respiration. During photosynthesis, plants use sunlight, water, and carbon dioxide to produce food and release oxygen as a byproduct. This oxygen is essential for animals to carry out respiration, during which they consume oxygen and release carbon dioxide back into the atmosphere. Animals release carbon dioxide through their respiratory processes, which plants then utilize during photosynthesis. In forests and other ecosystems with abundant vegetation, plants play a crucial role in consuming the carbon dioxide released by animals and replenishing the oxygen supply. This interdependent relationship between plants and animals creates a natural balance in the composition of atmospheric gases. Without this continuous exchange, the levels of oxygen and carbon dioxide would become imbalanced, making it difficult for life to sustain on Earth. The process occurs on a global scale, with forests acting as major contributors to maintaining atmospheric balance.

The atmosphere is essential for life on Earth because it performs several critical functions that make the planet habitable. The atmosphere maintains an appropriate climate by regulating temperature through various mechanisms. During the daytime, the atmosphere prevents a sudden and extreme increase in temperature by absorbing some of the incoming solar radiation and scattering it. This protective layer ensures that the surface does not become excessively hot. During the nighttime, the atmosphere plays an equally important role by slowing down the escape of heat from the Earth's surface into outer space. Gases like carbon dioxide and water vapor in the atmosphere trap heat through the greenhouse effect, keeping the average temperature of the Earth fairly constant. This temperature regulation is vital because it allows organisms to survive within a range of temperatures suitable for life. Additionally, the atmosphere contains oxygen necessary for respiration in most living organisms, protects us from harmful ultraviolet radiation through the ozone layer, and provides the air we breathe. Without the atmosphere's insulating and protective properties, Earth would be either too cold at night or too hot during the day, making it impossible for life as we know it to exist.

Fire extinguishers throw a stream of carbon dioxide (CO₂) while putting off fire because carbon dioxide does not support combustion. Fire requires three essential elements to burn, known as the fire triangle: fuel, oxygen, and heat. When carbon dioxide is sprayed on a burning object, it works in two ways to extinguish the fire. First, it stops the supply of oxygen by creating a blanket or layer around the burning material, preventing oxygen from reaching the fuel. Second, the carbon dioxide gas is denser than air and displaces the oxygen in the vicinity of the fire. Additionally, when carbon dioxide is released from the extinguisher, it expands rapidly and cools down, which helps reduce the temperature of the burning material. By removing oxygen and lowering temperature, carbon dioxide effectively breaks the fire triangle and controls the fire. This makes CO₂ an effective fire-suppressing agent, especially for fires involving electrical equipment and flammable liquids where water cannot be used safely.

Air is not an elementary substance but a composition because it is made up of a mixture of many different gases rather than being a single pure element. Air consists of nitrogen (N₂), oxygen (O₂), carbon dioxide (CO₂), and several other gases in varying proportions. Nitrogen makes up approximately 78 percent of air, oxygen about 21 percent, and the remaining 1 percent includes carbon dioxide, argon, neon, and other trace gases. Since air contains multiple gaseous components that can be separated from each other, it is classified as a mixture rather than an elementary substance. An elementary substance or element consists of only one type of atom or molecule, whereas air is a combination of different molecular gases. The proportions of these gases in air can also vary slightly depending on location and conditions. Because air is composed of distinct chemical substances mixed together in varying amounts, it is correctly described as a composite mixture of gases.