Chapter 5: Life Processes
Essential Life Processes in Organisms and the modes of Nutrition
Living organisms perform a range of vital functions such as nutrition, respiration, transport, and excretion to maintain their organized structures and sustain life. Nutrition provides energy and materials for growth. Autotrophs (like green plants) synthesize their food using sunlight through photosynthesis, while heterotrophs (like animals) consume other organisms. In humans, digestion begins in the mouth and continues through the alimentary canal, breaking down food into simpler substances absorbed and transported throughout the body for energy and repair.
Respiration and Transport Systems
Respiration is the biochemical process that releases energy from food. It can be aerobic (with oxygen) or anaerobic (without oxygen). Humans use aerobic respiration, producing energy in the form of ATP. Oxygen is transported by red blood cells containing haemoglobin, and carbon dioxide is mostly carried dissolved in blood. The human heart, with four chambers, ensures double circulation of blood—oxygenated and deoxygenated blood are kept separate for efficiency. Blood vessels (arteries, veins, and capillaries) and lymph form an extensive transport system. In plants, xylem carries water and minerals from roots, while phloem distributes food made during photosynthesis.
Excretion in Humans and Plants
Excretion is the process of removing metabolic wastes from the body. In humans, the kidneys filter nitrogenous wastes from the blood to form urine, which travels through ureters to the bladder and is eventually expelled. The functional unit of the kidney is the nephron, where filtration and selective reabsorption occur. Plants use different strategies like storing waste in vacuoles, shedding leaves, or releasing substances into the soil. Some waste products, like oxygen, are even useful by-products of photosynthesis.