Biological fluids are liquids found within living organisms that play essential roles in various physiological processes. Examples include blood, saliva, urine, and lymph. These fluids help transport nutrients, remove waste, and facilitate communication between cells. Each type of biological fluid has specific functions. For instance, blood carries oxygen and nutrients to tissues, while urine helps eliminate waste products from the body. Saliva aids in digestion and keeps the mouth moist, and lymph is involved in immune responses. Understanding these fluids is crucial for studying health and disease.