Respiration - Year 8 Science IGCSE Free MCQ Test with solutions

Respiration is the process by which energy is released from food (glucose) within cells through chemical reactions. It occurs in every cell, not just the lungs, and is essential for providing energy for cellular functions. Options A, C, and D are incorrect as they do not accurately describe the primary purpose of respiration.

Aerobic respiration requires oxygen to break down glucose, producing energy, carbon dioxide, and water. Oxygen is absorbed from inhaled air and transported to cells via the bloodstream. Nitrogen, carbon dioxide, and hydrogen are not required for this process, making options A, B, and D incorrect.

The trachea (windpipe) serves as a passageway for air, connecting the mouth and nose to the lungs. It is supported by cartilage rings to remain open. Gas exchange occurs in the alveoli (not the trachea), mucus production is a secondary function, and the trachea does not store oxygen, making options A, C, and D incorrect.

Gas exchange, where oxygen enters the bloodstream and carbon dioxide is removed, occurs in the alveoli (air sacs). The thin walls of the alveoli and surrounding capillaries facilitate this diffusion. The trachea, bronchi, and bronchioles are primarily air passageways, not sites of gas exchange, making options A, B, and D incorrect.

During inhalation, the diaphragm muscles contract, pulling the diaphragm downward. This increases the chest cavity volume, reducing pressure and drawing air into the lungs. Relaxation occurs during exhalation, and the diaphragm does not remain stationary or move upward during inhalation, making options B, C, and D incorrect.

Carbohydrates, broken down into glucose during digestion, are the primary source of energy for cellular respiration. Glucose is used in the mitochondria during aerobic respiration to produce energy. While fats and proteins can also provide energy, carbohydrates are the main source, and vitamins do not directly provide energy, making options A, C, and B incorrect.

Red blood cells contain hemoglobin, which binds oxygen in the lungs and transports it to tissues. They also carry carbon dioxide back to the lungs. White blood cells fight infections, platelets aid in clotting, and plasma transports nutrients and waste, making options A, B, and D incorrect for oxygen transport.

Mitochondria are the site of aerobic respiration, where glucose is broken down with oxygen to release energy in a controlled manner. While carbon dioxide is a by-product, the primary role is energy release. Mitochondria do not store glucose or transport oxygen, making options A, C, and D incorrect.

Neutrophils are the most abundant white blood cells and are the first responders to bacterial infections, engulfing and digesting bacteria. Lymphocytes are involved in immune regulation, monocytes become macrophages, and eosinophils combat parasitic infections, making options A, C, and B incorrect for bacterial infections.

During exhalation, the intercostal muscles and diaphragm relax, causing the ribs to drop and the diaphragm to return to its dome shape. This reduces the chest cavity volume, increasing pressure and pushing air out of the lungs. An increase or unchanged volume occurs during inhalation, making options B, C, and D incorrect.