Science PMR By M Smkdmscience

A volcano is a correct answer because it is a natural source of heat. Volcanoes are formed when molten rock called magma rises to the surface of the Earth. This magma is extremely hot and can reach temperatures of several thousand degrees Celsius. When the magma erupts from the volcano, it releases heat energy in the form of lava, ash, and gases. This heat can be intense enough to melt rocks and cause widespread destruction in the surrounding area. Therefore, a volcano is a significant source of heat.

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Temperature can be measured in Kelvin, Celsius, and Fahrenheit. Joules is not a unit of temperature measurement, but rather a unit of energy measurement. Therefore, the correct answer is II, III and IV only.

The correct answer is I and II only. This is because inhaled air contains a higher percentage of oxygen (21%) compared to exhaled air (16%). Additionally, inhaled air contains a lower percentage of carbon dioxide (0.03%) compared to exhaled air (4%). This information aligns with our understanding of the respiratory system, where oxygen is taken in during inhalation and carbon dioxide is expelled during exhalation.

Smoking cigarettes can cause lung cancer, emphysema, and bronchitis. Lung cancer is a type of cancer that starts in the lungs and is strongly associated with smoking. Emphysema is a chronic lung disease that is caused by damage to the air sacs in the lungs, often due to smoking. Bronchitis is an inflammation of the bronchial tubes, which carry air to and from the lungs, and smoking is a common cause of chronic bronchitis. Hepatitis, on the other hand, is a viral infection that affects the liver and is not directly caused by smoking cigarettes.

When we exhale, the rib cage moves down, which is represented by statement I. This movement helps in reducing the volume of the thoracic cavity. Additionally, the outer intercostal muscles relax, as mentioned in statement II. This relaxation allows the rib cage to move down and aids in the exhalation process. However, there is no mention of the thoracic cavity becoming bigger or air flowing from the atmosphere into the lungs, so statements III and IV are not correct. Therefore, the correct answer is I and II only.

When we inhale, the muscles in the diaphragm contract and move downwards, causing the volume of the chest cavity to increase. This increase in volume results in a decrease in air pressure within the lungs. As a result, air from the atmosphere rushes into the lungs to equalize the pressure, filling them with fresh oxygen.

The pulmonary artery is not part of the human respiratory system. It is a blood vessel that carries deoxygenated blood from the heart to the lungs for oxygenation. The respiratory system is responsible for the exchange of gases, particularly oxygen and carbon dioxide, between the body and the environment. The trachea, ribs, and intercostal muscles are all directly involved in the process of breathing and are essential components of the respiratory system.

Cigarette smoke contains harmful chemicals that can damage the lungs and airways. When smokers inhale cigarette smoke, these chemicals can irritate and inflame the airways, causing them to become narrow and blocked. This can lead to a decrease in the amount of oxygen that can enter the bloodstream, resulting in shortness of breath. Additionally, smoking can also lead to the development of chronic obstructive pulmonary disease (COPD), a progressive lung disease that can further contribute to breathing difficulties.

Tar is the correct answer because it contains numerous toxic chemicals, including polycyclic aromatic hydrocarbons (PAHs), which are known to be carcinogenic. When tar is inhaled, it can cause damage to the respiratory system and increase the risk of developing lung cancer. Additionally, tar is commonly found in tobacco smoke, making it a significant contributor to the development of various types of cancer, including lung, throat, and mouth cancer.