CCEA GCSE Biology 1.5 Respiratory System, Breathing and Respiration Exam Questions

About CCEA GCSE Biology 1.5 Respiratory System, Breathing and Respiration

This CCEA GCSE Biology Unit 1 topic deals with how air is moved into and out of the lungs, how gases are exchanged in the alveoli and how cells release energy by respiration. You need to name and locate the structures of the respiratory system, explain breathing in and out in terms of muscles, volume and pressure, and compare aerobic and anaerobic respiration. The prescribed practical investigates factors affecting respiration in yeast. The topic links to diffusion, the circulatory system and photosynthesis. Examiners often ask for step-by-step breathing mechanisms, the features of an efficient exchange surface and the products of anaerobic respiration in muscle and yeast.

What you need to know

• Structures Air passes through the trachea, which is kept open by rings of cartilage, into two bronchi, then bronchioles and finally the alveoli. The lungs are protected by the ribs, with intercostal muscles between them and the diaphragm below.
• Breathing in The external intercostal muscles contract, moving the ribs up and out, and the diaphragm contracts and flattens. The volume of the thorax increases, so the pressure inside falls below atmospheric pressure and air moves in.
• Breathing out The intercostal muscles relax so the ribs move down and in, and the diaphragm relaxes and domes upwards. The volume of the thorax decreases, the pressure increases above atmospheric pressure and air is forced out.
• Gas exchange surfaces Alveoli have a large surface area, walls one cell thick, a moist lining for gases to dissolve in and a good blood supply that maintains a concentration gradient. Oxygen diffuses into the blood and carbon dioxide diffuses out into the alveoli.
• Aerobic respiration Glucose + oxygen → carbon dioxide + water, releasing energy (C6H12O6 + 6O2 → 6CO2 + 6H2O). It happens in mitochondria and releases much more energy per glucose than anaerobic respiration. Energy is used for movement, growth, active processes and keeping warm.
• Anaerobic respiration In muscles during vigorous exercise: glucose → lactic acid, releasing a small amount of energy and causing an oxygen debt that is repaid by heavy breathing afterwards. In yeast: glucose → ethanol + carbon dioxide, used in brewing and bread making.
• Prescribed practical: yeast respiration Mix yeast with glucose solution and measure carbon dioxide production (for example bubbles counted per minute or gas collected) at different temperatures or sugar concentrations. Keep other variables such as volume and mass of yeast constant.

Common mistakes in 1.5 Respiratory System, Breathing and Respiration

• Saying that air rushing in makes the chest expand. The chest volume increases first, lowering the pressure, and then air moves in.
• Calling respiration breathing. Respiration is the chemical reaction that releases energy in cells; breathing is the movement of air.
• Stating that respiration produces energy. Energy cannot be made; respiration releases energy from glucose.
• Writing that anaerobic respiration in humans produces carbon dioxide or ethanol. In muscles it produces lactic acid only.
• Describing the diaphragm as moving up during inhalation. It contracts and flattens, moving down.

Try three 1.5 Respiratory System, Breathing and Respiration exam-style questions