Figure 16 shows the urinary system of a human - Edexcel - GCSE Biology - Question 7 - 2018 - Paper 1

The concentration of protein in the blood plasma is 47 g per dm³, while in the filtrate within the nephron it is 0 g per dm³. This difference is because there is no protein present in the filtrate. This occurs due to the size of protein molecules, which are too large to pass through the selectively permeable membrane during ultrafiltration.

Glucose moves from the blood plasma into the nephron through a process called active transport. Glucose is reabsorbed in the proximal convoluted tubule of the nephron. Due to a higher concentration of glucose in the blood plasma compared to the filtrate, glucose molecules move across the partially permeable membrane into the nephron actively. This process requires energy, as glucose is transported against its concentration gradient.

Dialysis is a medical treatment used when kidneys are damaged and can no longer effectively remove waste products from the blood. During dialysis, blood is taken from the patient and passed into a dialysis machine. Here, it is separated from a dialysis solution by a partially permeable membrane. This membrane allows small unwanted substances, such as urea and other toxic substances, to diffuse into the dialysis fluid due to a concentration gradient. As the blood moves through the machine, it is cleansed by removing these unwanted substances, and the cleaned blood is then returned to the body.