Question

1. list two factors that could affect the rate of diffusion.
2. temperature

2.

1. describe how structure is related to function for channel proteins.
2. what would happen to the transport of water across a membrane if the aquaporins were non - functional? would water still be able to cross, why or why not?
3. cisplatin is a chemotherapy medication used to treat several different cancers. cisplatin is administered through a vein as an infusion (iv). one of the side effects of cisplatin is kidney toxicity, which can potentially lead to renal (kidney) failure. the kidneys perform many crucial functions for the human body, one of them including maintaining water balance. kidney cells do this by absorbing water from urine before it is excreted from the body. researchers examined the urinary flow rate (the amount of urine produced per hour) of individuals after treatment with various concentrations of cisplatin. the results are in the table below.

	control	cisplatin (4mg/kg)	cisplatin (8 mg/kg)	cisplatin (12 mg/kg)
urinary flow rate (ml/hr)	103 ± 15	244 ± 14	357 ± 11	621 ± 17

a. describe the effect that cisplatin has on the urinary flow rate. what does this indicate about the composition of the urine?
b. using your knowledge of transport across membranes, identify which component(s) of the plasma membranes of kidney cells are most likely being affected by cisplatin. explain your reasoning.

Explanation:

1. Concentration gradient also affects diffusion rate. Higher the difference in concentration on either side of a membrane, faster the diffusion. Membrane permeability is another factor; more permeable membranes allow for faster diffusion.
2. Channel proteins have specific shapes and structures. Their pores or channels are sized and shaped to allow specific molecules or ions to pass through the cell - membrane, thus their structure directly determines their transport function.
3. Aquaporins are water - channel proteins that facilitate the rapid movement of water across the membrane. If non - functional, water can still cross the membrane by simple diffusion, but at a much slower rate because the lipid bilayer is less permeable to water.

11a. As the concentration of cisplatin increases, the urinary flow rate increases. This indicates that less water is being reabsorbed from the urine back into the body, so the urine is more dilute (has a higher water content).
11b. Aquaporins in the plasma membranes of kidney cells are most likely being affected. Reasoning: Since the main function of kidney cells in terms of water balance is reabsorbing water from urine, and an increase in cisplatin leads to increased urinary flow (less water reabsorption), it is likely that the proteins responsible for water transport (aquaporins) are being inhibited or damaged.

Answer:

1. Concentration gradient, Membrane permeability
2. Channel proteins' pores are specific for certain molecules/ions based on their structure, enabling transport.
3. Water can still cross by simple diffusion but at a slower rate as the lipid bilayer is less permeable to water.

11a. As cisplatin concentration increases, urinary flow rate increases, indicating more dilute urine (higher water content).
11b. Aquaporins are most likely affected. Kidney cells reabsorb water from urine via aquaporins, and increased cisplatin leads to less water reabsorption and higher urinary flow.