2.1. Testing for biological molecules
A subsection of Biology, 9700, through 2. Biological molecules
Listing 10 of 108 questions
A student carried out the Benedict’s test on four different concentrations of glucose solution and then recorded the time taken for the first appearance of a colour change (the end-point). The student found it difficult to identify the first appearance of a colour change and consistently timed each solution for two seconds after the colour change first appeared. This introduced a source of error into the experiment. Which statements about this error are correct?
9700_w23_qp_12
MCQ
2023
Paper 1, Variant 2
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A mixture of glucose and starch solutions was placed in a length of dialysis (Visking) tubing and the tubing sealed. The tubing was then placed in a boiling tube containing distilled water. Two samples were immediately removed from this water (time 0 minutes) and tested with either iodine solution or Benedict’s solution. This was repeated at 10 minute intervals for 30 minutes. The iodine solution gave an orange-brown colour each time. The table shows the results of the Benedict’s test. time / minutes colour produced by Benedict’s test blue green yellow red What may be concluded from these results?
9700_w24_qp_12
MCQ
2024
Paper 1, Variant 2
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Human prolactin (hPRL) is a globular protein. It is a single polypeptide composed of 199 amino acids. The protein is transported in the bloodstream and has an effect only on cells that have a cell surface membrane protein known as PRLR. One effect of hPRL is to stimulate cells in the mammary glands to produce breast milk. Cells that have been stimulated by hPRL need more glucose and therefore the passive uptake of glucose increases. State one reason why the cells in the mammary glands that have been stimulated by hPRL need more glucose. An experiment was carried out to investigate the movement of glucose and hPRL across Visking tubing membrane. • A short section of Visking tubing, tied at both ends and containing distilled water, was placed into a beaker containing a solution of glucose and hPRL. • After 20 minutes, separate samples of the solution in the Visking tubing and the solution in the beaker were each tested for the presence of protein and reducing sugar. A summary of the methods used, the experimental results and the deductions made are shown in Table 5.1. Table 5.1 sample method used colour obtained after testing deduction solution in Visking tubing biuret solution added to sample protein absent from solution in Visking tubing solution in beaker protein present in solution in beaker solution in Visking tubing Benedict’s solution added to sample and mixture heated in a water-bath reducing sugar present in solution in Visking tubing solution in beaker reducing sugar present in solution in beaker Complete the column in Table 5.1 headed colour obtained after testing. With reference to the deductions made in Table 5.1, explain the movement of hPRL and reducing sugar across Visking tubing membrane. Outline how glucose crosses the cell surface membranes of the cells of the mammary glands. The production of milk by the cells of the mammary glands involves the action of several different enzymes. The cell surface membranes of these cells contain the membrane protein PRLR. shows an outline summary of hPRL involvement in the production of breast milk. anterior pituitary cells at the base of the brain synthesis and release of hPRL membrane protein PRLR milk not to scale milk mammary gland cells capillary hPRL Explain why the production of breast milk can be described as an example of a cell signalling process.
9700_m19_qp_22
THEORY
2019
Paper 2, Variant 2
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To estimate the concentration of glucose in an unknown solution, equal volumes of a range of known concentrations of glucose were each mixed with the same excess volume of Benedict’s solution. After mixing, the solutions were placed in a thermostatically controlled water-bath at 90 C for three minutes. The unknown solution was then treated in the same way and the colours of the known and unknown solutions compared. What is the independent variable in this procedure?
9700_m23_qp_12
MCQ
2023
Paper 1, Variant 2
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Questions Discovered
108