Respiration

Correct answer: A. To obtain energy

Respiration is a vital life process in which food molecules such as glucose are broken down, with or without oxygen, to release usable energy. Cells use this energy for movement, growth, repair, transport and other activities. Thus option A is correct. Colouring the body, removing undigested food and sleeping are not the main purposes of respiration.

Correct answer: A. Aerobic respiration

Respiration that takes place in the presence of oxygen is called aerobic respiration. During this process, glucose is broken down, generally producing carbon dioxide, water and a relatively large amount of usable energy. Therefore, option A is correct. Anaerobic respiration occurs without oxygen, photosynthesis makes food in suitable cells, and excretion removes wastes rather than releasing energy from food.

Correct answer: B. Anaerobic respiration

Respiration carried out without oxygen is called anaerobic respiration. In this process, glucose is only partially broken down, so less energy is released than in aerobic respiration; the products may include alcohol and carbon dioxide in yeast or lactic acid in muscles during strenuous activity. Hence option B is correct, while aerobic respiration requires oxygen.

Correct answer: A. Aerobic respiration

The governing distinction is whether oxygen participates in the breakdown of food. Respiration carried out in the presence of oxygen is called aerobic respiration. It generally allows a more complete breakdown of glucose and releases more energy than anaerobic respiration. Photosynthesis makes food using light, while excretion removes metabolic wastes. Hence option A correctly names oxygen-dependent respiration.

Correct answer: A. Anaerobic respiration

Anaerobic respiration is the release of energy from food without using oxygen. Because glucose is not completely broken down in this pathway, it usually produces less energy than aerobic respiration; yeast may form alcohol and carbon dioxide, while muscle cells may form lactic acid during oxygen shortage. Aerobic respiration requires oxygen, transportation moves materials, and photosynthesis makes food, so option A is correct.

Correct answer: A. To release energy from food

Respiration is a life process in which food molecules, especially glucose, are broken down to release usable energy. In aerobic respiration, glucose reacts with oxygen and produces carbon dioxide, water and energy; in anaerobic respiration, breakdown is incomplete and less energy is released. This energy supports movement, growth, repair and other cellular activities. The other options are unrelated functions, so option A is correct.

Correct answer: A. Oxygen

Aerobic respiration is defined as the breakdown of food in the presence of oxygen. Oxygen acts as the final electron acceptor in the cellular process, allowing glucose to be oxidised more completely and releasing a comparatively large amount of energy. Carbon dioxide is mainly a product, while nitrogen and helium do not support this energy-releasing reaction. Therefore, option A is the required gas.

Correct answer: A. In lack of oxygen

Anaerobic respiration occurs when cells obtain energy without using oxygen, commonly when oxygen is absent or insufficient. Because glucose is then broken down incompletely, the products may include lactic acid in human muscles or alcohol and carbon dioxide in yeast, and the energy yield is lower than in aerobic respiration. Light, excess water and salt do not define this process; hence, option A is correct.

Correct answer: A. Mitochondria

Cellular respiration involves the controlled breakdown of glucose and the production of ATP, the cell’s usable energy currency. In eukaryotic cells, glycolysis begins in the cytoplasm, but most aerobic respiration and ATP production occur in the mitochondria through the Krebs cycle and electron transport chain. Thus option A is the expected answer. The nucleus stores genetic material, the cell wall provides support, and the vacuole mainly stores substances.

Correct answer: A. It is a waste product of cellular respiration

During cellular respiration, cells break down food molecules to release energy, and carbon dioxide is produced as a waste product, especially during aerobic respiration. If it accumulates, it can disturb the internal chemical balance and harm cells. It is transported in the blood to the lungs and removed during exhalation. Thus option A correctly states the reason; the other options confuse carbon dioxide with food, clotting factors, or digestive enzymes.

Correct answer: A. ATP

During cellular respiration, energy released as glucose is broken down is transferred to ATP (adenosine triphosphate). ATP supplies usable energy for many cellular activities. Glucose is the fuel being broken down, while DNA and RNA are involved in genetic information, so ATP is the correct answer.

Correct answer: A. Alveoli

Gas exchange occurs in the alveoli, the tiny air sacs of the lungs. Their very thin walls and dense surrounding capillary network allow oxygen to diffuse into the blood and carbon dioxide to diffuse from the blood into the alveoli. The trachea and bronchi mainly conduct air; they are not the main sites of gas exchange. Exam tip: associate gas exchange with alveoli.

Correct answer: A. Oxygen

Oxygen is used in cellular respiration for the complete oxidation of food such as glucose, releasing energy in the form of ATP. Although nitrogen is abundant in air, human cells do not use it for cellular respiration. Carbon dioxide is a waste product of respiration and is exhaled. Exam tip: For the gas required in respiration, choose oxygen; carbon dioxide is a product.

Correct answer: A. Oxygen

Humans take in oxygen-rich air, and oxygen is used by cells during aerobic respiration to help release energy from food. Thus, option A is correct. Carbon dioxide is mainly produced as a waste product and exhaled, not taken in for cellular energy release. Nitrogen is abundant in air but is not used directly in ordinary human respiration, while hydrogen is not the required respiratory gas.