IGCSE Biology glossary
Ultrafiltration
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Definition
The process in the kidney where blood is filtered under high pressure in the glomerulus. Small molecules (water, glucose, urea, amino acids, ions) are forced through the capillary walls and Bowman's capsule into the nephron, while large molecules (proteins) and blood cells are retained in the blood.
What to include in an exam answer
Ultrafiltration is a passive process driven by blood pressure, not active transport. The 'filter' is the capillary wall and the Bowman's capsule wall. If protein appears in the urine, it indicates damage to this filter.
Example in context
Explain how ultrafiltration occurs in the kidney (3 marks): Blood enters the glomerulus under high pressure from the afferent arteriole. Small molecules such as water, glucose, urea and ions are forced through the walls of the glomerular capillaries into the Bowman's capsule. Large molecules like proteins and blood cells are too large to pass through and remain in the blood.
Related syllabus topic
Excretion in humans