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Blood is filtered in the kidney - Edexcel - GCSE Biology - Question 10 - 2023 - Paper 2
Question 10
Blood is filtered in the kidney. Figure 17 shows the diameter of some molecules found in human blood. | molecule | diameter in nanometres (nm) | |----------|-------... show full transcript
Worked Solution & Example Answer:Blood is filtered in the kidney - Edexcel - GCSE Biology - Question 10 - 2023 - Paper 2
Step 1
Which part of the nephron is the site of ultrafiltration?
Answer
The site of ultrafiltration in the nephron is the glomerulus (Option C). The glomerulus is a network of capillaries that filters blood, allowing small molecules, such as water, ions, and small solutes to pass into the Bowman’s capsule while retaining larger molecules like proteins and blood cells.
Step 2
Explain why protein is not usually found in urine.
Answer
Proteins are generally not found in urine because of their large size compared to the filtration barrier in the glomerulus. The glomerular filtration membrane is designed to allow the passage of small molecules and ions while restricting larger molecules. Proteins, being significantly larger than the pores, are retained in the bloodstream and typically do not enter the filtrate. Additionally, the kidney has mechanisms for reabsorbing any small amounts of protein that might escape filtration.