WJEC GCSE Biology 1.2 Respiration and the Respiratory System in Humans Exam Questions

About WJEC GCSE Biology 1.2 Respiration and the Respiratory System in Humans

This Unit 1 topic links the chemistry of respiration inside cells to the organ system that supplies oxygen and removes carbon dioxide. You need word equations for aerobic and anaerobic respiration in humans, the idea of oxygen debt, and the labelled structure of the breathing system from nasal cavity to alveoli. You must explain inspiration and expiration in terms of changes in volume and pressure in the thorax, including the bell jar model and its limitations. Examiners often ask about adaptations of the alveoli for gas exchange, the composition of inhaled and exhaled air, and how smoking damages cilia and leads to lung cancer and emphysema.

What you need to know

• Aerobic respiration glucose + oxygen → carbon dioxide + water, releasing energy as ATP. It is a series of enzyme-controlled reactions in cells and releases much more energy per glucose than anaerobic respiration.
• Anaerobic respiration In human muscle cells: glucose → lactic acid. It releases less energy (less ATP) because glucose is only partly broken down. After exercise, extra oxygen (the oxygen debt) is needed to break down the lactic acid.
• Breathing system Label the nasal cavity, trachea, bronchi, bronchioles, alveoli, lungs, diaphragm, ribs and intercostal muscles. Mucus traps dust and microbes and cilia sweep it up and out of the airways.
• Ventilation Inspiration: intercostal muscles contract to move the ribs up and out, the diaphragm contracts and flattens, thoracic volume increases, pressure falls below atmospheric and air flows in. Expiration is the reverse. The bell jar model shows this but cannot model the movement of the ribs.
• Alveoli and gas exchange Alveoli have a large surface area, thin walls (one cell thick), a moist lining and a rich capillary supply, keeping a steep concentration gradient. Oxygen diffuses into the blood and carbon dioxide diffuses out. Exhaled air has less oxygen and more carbon dioxide and water vapour than inhaled air.
• Smoking Tar and smoke damage cilia, so mucus builds up and causes coughing and infections. Smoking is linked to lung cancer and emphysema, where alveolar walls break down and the surface area for gas exchange falls.

Common mistakes in 1.2 Respiration and the Respiratory System in Humans

• Saying respiration produces energy. Energy cannot be made; respiration releases energy from glucose, transferred to ATP.
• Including carbon dioxide in the human anaerobic word equation. In human cells the only product is lactic acid.
• Confusing breathing with respiration. Breathing (ventilation) moves air in and out of the lungs; respiration is a chemical process in every living cell.
• Saying the lungs suck air in. Air moves in because volume in the thorax increases, pressure falls below atmospheric pressure, and air is pushed in by the higher pressure outside.

Try three 1.2 Respiration and the Respiratory System in Humans exam-style questions