IB Biology HL B2.1 Membranes and membrane transport questions

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Question 1

Paper 2Medium16 marks

A researcher investigated the movement of different solutes across a model phospholipid bilayer. The same apparatus was used for separate trials, one solute per trial. Figure 1 shows the initial conditions for each trial. After 30.0 minutes, the amount of solute detected in chamber B was measured.

Avolume = 1.00 cm³initially: 20.0 nmolof one soluteBvolume = 1.00 cm³initially: no solutephospholipid headshydrocarbon chains
Solute testedDescriptionAmount detected in chamber B after 30.0 min / nmol
SteroidNon-polar molecule15.2
GlucosePolar molecule1.6
Sodium ionsIons0.8
PolymerLarge, hydrophilic molecule0.2
(a)

State the independent variable, the dependent variable and one variable controlled in the investigation.

[3]
(b)

Calculate the percentage of the initial amount of steroid detected in chamber B after 30.0 minutes.

[2]
(c)

Compare the amounts detected in chamber B for the four solutes.

[3]
(d)

Explain how the structure of the phospholipid bilayer accounts for the results for the steroid and the other three solutes.

[4]
(e)

A student concludes that the bilayer is an effective barrier to every solute tested. Evaluate this conclusion using the data.

[4]

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