Life Processes
What is tested
This domain tests nutrition, respiration, transportation and excretion in plants and humans. You should be able to explain photosynthesis, gas exchange, digestion, double circulation, nephron filtration and the need for a transport system.
Core rules
- Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2 in the presence of chlorophyll and sunlight. Stomata allow gas exchange and transpiration.
- Aerobic respiration releases more energy than anaerobic respiration. In muscles, anaerobic respiration produces lactic acid; in yeast, ethanol and CO2 are formed.
- Xylem transports water and minerals upward; phloem transports food in both directions.
- Human digestion involves mouth, stomach, small intestine and associated glands. Villi increase surface area for absorption.
- The heart has four chambers. Arteries carry blood away from the heart; veins carry blood toward it. The nephron filters blood and forms urine.
Worked example
Trace blood from the body: vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta → body. The right side handles deoxygenated blood and the left side oxygenated blood, so it is double circulation.
Traps
Arteries are not always oxygenated; the pulmonary artery carries deoxygenated blood. Xylem is not for food. Aerobic respiration gives more ATP than anaerobic. Do not confuse absorption in villi with assimilation.