OCR GCSE Biology Practice Exam 2025 – Comprehensive All-in-One Guide to Exam Success

Anti-diuretic hormone (ADH), also known as vasopressin, plays a crucial role in regulating the body's water balance. It specifically affects the permeability of the kidney tubules, particularly in the collecting ducts of the nephron. When ADH is released into the bloodstream, it binds to receptors in the kidney, leading to an increase in the permeability of the tubules to water. This allows more water to be reabsorbed back into the bloodstream, reducing urine volume and helping to concentrate the urine.

This process helps the body retain water when it is needed, thereby playing a vital role in maintaining proper hydration and electrolyte balance. The presence of ADH is critical in situations when the body is dehydrated or when there is an increase in blood osmolarity, ensuring that the kidneys conserve water efficiently.

In contrast, while heart rate regulation, blood sugar level regulation, and nutrient absorption are important physiological processes, they are not directly influenced by ADH. Heart rate is primarily regulated by the autonomic nervous system and hormones like adrenaline. Blood sugar levels are managed by insulin and glucagon, not ADH. Nutrient absorption is regulated by various factors including digestive hormones and conditions in the intestine, which do not involve ADH's mechanisms