Scientists measured the concentration of sodium ions and potassium ions in the red blood cells and in the blood plasma of a group of people. The results are shown in Table 1.1. Table 1.1 mean concentration of sodium ions /mmol dm⁻³ red blood cells 10 blood plasma 100 mean concentration of potassium ions /mmol dm⁻³ 100 4

1. (a)(i)Use the information in Table 1.1 to identify and describe the process by which potassium ions enter red blood cells from the blood plasma.[3]
2. (a)(ii)Sodium ions and oxygen molecules enter red blood cells. State one similarity and one difference between the processes used by sodium ions and oxygen molecules to enter red blood cells. similarity difference[2]
3. (a)(iii)Chloride ions move across the membrane of human red blood cells in a process called the chloride shift. Explain why the chloride shift is important in the transport of carbon dioxide from respiring tissues.[2]
4. (b)Scientists studied the uptake of a substance, F, by human red blood cells. The red blood cells were immersed in a solution of substance F for 30 minutes. After this time the scientists recorded two observations: - the cell surface membrane of the red blood cells showed infoldings (invaginations) - an increase in the number of vesicles in the cytoplasm. Identify the process by which substance F entered the red blood cells.[1]