Question 1
Paper 2Medium16 marksA researcher used four model membranes, each consisting of a phospholipid bilayer separating a donor compartment from a receiving compartment. Each donor initially contained one substance at 10.0 mmol dm⁻³; each receiver initially contained none. The donor volume was 20 times the receiver volume. Membrane area and temperature were the same in all four setups. Figure 1 shows the concentration of each substance in the receiving compartment during the experiment.
At 4 min, identify the substance with the highest concentration in the receiving compartment and state that concentration.
Compare the changes in receiving-compartment concentrations of O₂ and CO₂ with those of Na⁺ and glucose over the 8 min. Quote data from Figure 1.
Calculate the mean rate of increase in CO₂ concentration in the receiving compartment from 0 to 4 min. Include a unit.
Using Figure 1, explain how the structure of the phospholipid bilayer accounts for the pattern of movement of the four substances.
A student states: “The bilayer completely blocks Na⁺ and glucose, but allows O₂ and CO₂ to cross.” Assess this statement using Figure 1.
The measurements stop at 8 min. Identify one limitation this creates for assessing the movement of Na⁺ and glucose, and suggest a further measurement.