Short Summary

Chapter 6, Life Processes, outlines the essential physiological mechanisms required to maintain life and prevent damage or breakdown in living organisms. Maintenance functions require energy obtained from outside the body through nutrition. Autotrophs, such as green plants, use simple inorganic substances like carbon dioxide and water in the presence of sunlight and chlorophyll to synthesise complex, high-energy organic substances, which are stored as starch, through photosynthesis while releasing oxygen as a by-product. Heterotrophs depend on complex food sources that are broken down with the help of biological catalysts called enzymes. During respiration, organisms break down carbon-based food sources to obtain cellular energy. Glucose is first converted into pyruvate in the cytoplasm, which is then oxidised aerobically in the mitochondria or broken down anaerobically to produce substances such as ethanol or lactic acid, while generating ATP to power cellular activities. In human beings, the circulatory system uses blood, which consists of plasma, red blood cells, white blood cells, and platelets, and is pumped by a four-chambered heart through arteries, veins, and capillaries to transport oxygen, nutrients, and metabolic wastes throughout the body. Plants use specialised vascular tissues, with xylem transporting water and minerals through processes influenced by transpiration, while phloem carries photosynthetic products to different parts of the plant. Excretion involves the removal of harmful metabolic waste products from the body through specialised structures, such as the nephrons in human kidneys, which filter the blood, reabsorb essential substances, and ultimately produce urine.