Using Fig. 6.1, complete the table by entering the correct letter for each description: • region in which no aquaporins are found in the tubule wall cells; • region in which aquaporins and glucose transport proteins are found in tubule wall cells; • region in which aquaporins are always present in the tubule wall cells but glucose transport proteins are absent; • region in which tubule wall cells are altered to form filtration slits.
Urine from people on different diets was analysed. Those on a low protein diet had a mean urea concentration of $2.40\,\text{g dm}^{-3}$. Those on a high protein diet had a mean urea concentration of $14.76\,\text{g dm}^{-3}$. Calculate the percentage increase in urea concentration from the low to the high protein diet. Show your working.
Explain why a greater amount of protein in the diet causes the urea concentration in the urine to rise.