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 higher compared to that in the nephron filtrate. This difference arises because there is no protein in the filtrate as protein molecules are too large to pass through the glomerular membrane. Thus, proteins remain in the blood plasma while smaller molecules may be filtered into the nephron.

Glucose moves into the nephron through a process called active transport. Initially, the concentration of glucose is higher in the blood plasma compared to the filtrate. As blood passes through the glomerulus, glucose is filtered into the Bowman’s capsule. From there, glucose is actively transported back into blood capillaries surrounding the nephron, which ensures that glucose is reabsorbed efficiently.

Dialysis is a process used when the kidneys are unable to remove waste products from the blood effectively. Blood is drawn from the patient and passed into a dialysis machine, where it flows through a dialysis membrane. This membrane allows for the diffusion of unwanted substances from the blood into a dialysis solution while retaining larger molecules like proteins and blood cells. Unwanted substances removed include urea, excess salts, and other toxic compounds. The fresh dialysis solution is continuously replaced to maintain a concentration gradient that promotes the removal of these waste materials.