13. Excretion in Humans (Cambridge IGCSE Biology 0610 for exams in 2023, 2024 and 2025)

Recent questions

• What is excretion in the human body?

  Excretion is a vital biological process that involves the removal of toxic materials and excess substances from the body. This process primarily occurs through the lungs, which expel carbon dioxide, and the kidneys, which eliminate urea, excess water, and ions. By effectively managing these waste products, excretion helps maintain the body's internal balance, ensuring that harmful substances do not accumulate to levels that could disrupt normal physiological functions.

• How do kidneys filter blood?

  The kidneys filter blood through a complex structure known as nephrons, which are the functional units of the kidney. Each nephron consists of several components, including the glomerulus, Bowman's capsule, and various tubules. Blood enters the nephron at the glomerulus, where it undergoes a process called ultrafiltration, allowing water, ions, and small molecules to pass into Bowman's capsule while retaining larger molecules like proteins. The filtered fluid then travels through the tubules, where selective reabsorption occurs, ensuring that essential substances are returned to the bloodstream while waste products are excreted as urine.

• What role does the liver play in excretion?

  The liver plays a crucial role in the excretion process by converting excess amino acids into urea through a process known as deamination. This transformation is essential because it prevents the buildup of toxic ammonia in the body, which can be harmful. Once urea is formed, it is transported via the bloodstream to the kidneys, where it is filtered out and ultimately excreted from the body. This function of the liver is vital for maintaining metabolic balance and ensuring that potentially harmful substances are efficiently removed from the body.

• What are the components of the urinary system?

  The urinary system is composed of several key structures that work together to filter blood and excrete waste. These components include the kidneys, ureters, bladder, and urethra. The kidneys are responsible for filtering blood and producing urine, which then travels through the ureters to the bladder, where it is stored until excretion. The urethra serves as the final passageway for urine to exit the body. This coordinated system is essential for regulating fluid balance, electrolytes, and waste removal, contributing to overall health and homeostasis.

• Why is maintaining balance in the body important?

  Maintaining balance in the body, often referred to as homeostasis, is crucial for overall health and proper functioning of physiological processes. The body must regulate various factors, such as temperature, pH levels, and the concentration of ions and nutrients, to ensure that all systems operate optimally. Excretion plays a significant role in this balance by removing waste products and excess substances that could disrupt normal bodily functions. If homeostasis is not maintained, it can lead to various health issues, including toxicity, dehydration, and organ dysfunction, highlighting the importance of effective excretory processes.