Respiration

The governing concept is coordination between gas exchange and transport. In the alveoli of the lungs, oxygen from inhaled air diffuses into the blood, while carbon dioxide diffuses out. The circulatory system then carries oxygen, mainly bound to haemoglobin, to body cells. Cells use it to release energy from food during aerobic respiration, and the blood carries carbon dioxide back toward the lungs. Therefore option A is correct.

Aerobic respiration requires a continuous supply of oxygen to cells. In humans, the respiratory system brings air to the alveoli, where oxygen diffuses into the blood. Haemoglobin in red blood cells then transports that oxygen through the circulatory system to body tissues. Therefore option A correctly combines gas exchange and blood transport; digestion, bile production, and urine storage do not deliver oxygen to cells.

Aerobic respiration uses oxygen to oxidise glucose through a series of controlled cellular reactions. Glucose is broken down much more completely into carbon dioxide and water, so considerably more ATP is produced than in anaerobic respiration, where breakdown is incomplete. Hence option A gives the governing reason. The other choices describe storage, absence of oxygen, or urine and cannot explain energy release.

In yeast fermentation, glucose is broken down without oxygen. This anaerobic pathway produces ethanol and carbon dioxide, so carbon dioxide bubbles are released in processes such as bread making. Therefore option B is correct. Oxygen is used in aerobic respiration rather than produced by ordinary yeast fermentation, while nitrogen, hydrogen, photosynthesis, and excretion do not describe this reaction.

Breathing is the physical exchange or movement of air: inhalation brings oxygen into the respiratory system and exhalation removes carbon dioxide. Respiration is a chemical process occurring in cells, in which glucose is broken down to release usable energy, usually with oxygen and sometimes without it. Breathing supplies gases needed for aerobic respiration, but the two terms are not identical. Hence option A is correct; the other choices confuse or restrict the processes incorrectly.

Mitochondria are the main sites of aerobic cellular respiration in eukaryotic cells. They use products of glucose breakdown and oxygen to produce ATP, the immediately usable energy required for active transport, movement, synthesis, growth, and repair. If mitochondria stopped functioning, ATP production would fall sharply; although some limited energy could come from glycolysis, it would not support normal activity for long. Therefore option A is correct, while the other choices concern unrelated plant or digestive functions.

Cellular respiration continuously produces carbon dioxide as a waste product when food molecules are oxidised for energy. The lungs remove this gas during exhalation, making its elimination an excretory function as well. If removal fails, carbon dioxide accumulates and disturbs respiration and internal balance. Therefore option A is correct; photosynthesis, ingestion, and transpiration are not the relevant human processes here.

The governing concept is the completeness of glucose oxidation. In anaerobic respiration, oxygen is unavailable or insufficient, so glucose is only partially broken down into products such as lactic acid in muscles or alcohol and carbon dioxide in yeast. Much of the chemical energy remains in these products, so less ATP is obtained than in aerobic respiration. Therefore A is correct; excess oxygen and light production are false, and carbon dioxide entry is not the cause.

The governing concept is anaerobic respiration in muscle cells. During intense or rapid running, the demand for oxygen and ATP can temporarily exceed the oxygen supply. Muscle cells then obtain some energy by partially breaking down glucose, producing lactic acid. Its accumulation is associated with fatigue, pain, or cramps after strenuous activity. Thus A is correct; muscles do not form starch, haemoglobin does not become bile, and digestion does not occur in lungs.

The governing concept is oxygen transport by haemoglobin. Haemoglobin in red blood cells binds oxygen in the lungs and carries it to tissues. Cellular aerobic respiration uses that oxygen to release energy from glucose. If haemoglobin levels fall greatly, the oxygen-carrying capacity of blood decreases, so cells may receive less oxygen and produce less energy aerobically. Therefore A is correct; the remaining choices involve starch, bile, or plant transport and are unrelated.

The governing concept is coordination among life processes. Digestion supplies glucose, breathing supplies oxygen, and the transport system carries these substances through blood to body cells. In cellular respiration, glucose is oxidised in the presence of oxygen and energy is released for cellular activities. Therefore option A correctly connects transport with respiration. Transport does not chew food or make urine, and respiration does not send blood to leaves; those distractors assign incorrect functions.

The governing concept is cellular respiration and ATP production. Mitochondria contain enzymes and internal membranes where most aerobic stages of respiration occur. Energy stored in glucose is released in a controlled series of reactions and captured largely in ATP, the molecule used to power cellular activities such as movement, growth and active transport. Thus option A explains the term power house. Starch testing, stomatal opening and urine formation belong to different structures or systems.

Cellular respiration breaks down glucose and transfers the released energy into ATP, or adenosine triphosphate. ATP stores energy in its phosphate bonds and supplies usable energy for cellular activities, so it is called the cell’s energy currency. DNA and RNA store or use genetic information, while glucose is the fuel being broken down rather than the immediate energy-carrying molecule produced for cell work.

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.

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.

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.