4. Cell membranes and transport
A section of Biology, 9700
Listing 10 of 418 questions
A student carried out an investigation to estimate the water potential of potato tissue. The main steps in the procedure and in the analysis of results are outlined in . Six different concentrations of sucrose solution were prepared and an equal volume of each was placed in a labelled beaker. 0.0 0.1 0.2 0.3 0.4 0.5 beaker concentration of sucrose solution / mol dm–3 Six equal-sized blocks of potato tissue were cut out of the same potato, blotted dry and weighed. One potato block was immersed in the solution in each beaker for 30 minutes. After this time, the block was removed, blotted dry and reweighed. The experiment was repeated twice. The mean percentage change in mass of potato tissue was calculated for each concentration of sucrose used. A graph was drawn of mean percentage change in the mass of potato tissue against concentration of sucrose. Explain why the different concentrations of sucrose result in different mean percentage changes in mass of potato tissue. State how the graph is used to estimate the water potential of the potato tissue.
9700_s20_qp_23
THEORY
2020
Paper 2, Variant 3
View
Cloves are the aromatic flower buds of the tree Syzygium aromaticum. Eugenol is a drug extracted from cloves. Eugenol affects the movement of sodium ions through the cell surface membranes of sensory neurones. shows the effect of eugenol concentration on the percentage decrease in sodium ion movement. percentage decrease in sodium ion movement 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 eugenol concentration / mmol dm–3 Describe the effect of eugenol concentration on the percentage decrease in sodium ion movement. Using , determine the percentage decrease in sodium ion movement at a eugenol concentration of 0.5 mmol dm–3. percentage decrease % Eugenol can be used to relieve the pain of toothache by putting it onto the affected tooth and gum. Suggest and explain how the action of eugenol may reduce pain.
9700_w17_qp_42
THEORY
2017
Paper 4, Variant 2
View
A student set up an experiment to investigate diffusion. A block of agar, 1.0 cm  1.0 cm  1.0 cm, was stained uniformly with a water-soluble blue dye. The block of agar was put into a test-tube containing 10 cm3 of distilled water at 20 C. The intensity of the blue colour of the water after five minutes was measured. Four other experiments, A, B, C and D, were then carried out using different numbers of agar blocks, different sizes of agar blocks and different temperatures. All other variables were standardised. Which experiment would give a lighter blue colour in the water after five minutes compared to the first experiment?
9700_w21_qp_12
MCQ
2021
Paper 1, Variant 2
View
Paramecium is a ciliated, unicellular protoctist. The cilia are similar in structure to those found in the trachea of a human. The cilia beat to move Paramecium through the water in which it lives. shows Paramecium. Paramecium has anterior and posterior ends. Generally the cilia beat so that the organism is moved forwards. Sometimes reverse movement is needed, for example when the Paramecium meets an obstacle. • The direction of beating of the cilia is linked to the difference in concentration of calcium ions inside and outside the cell. • There is usually a higher concentration of calcium ions outside than inside the cell. • When Paramecium touches an object, its cell surface membrane becomes deformed. • The membrane potential becomes more positive inside the cell. • The organism moves backwards for a short time. Suggest the sequence of events that occurs to cause the Paramecium to move backwards when it touches an object. Suggest how Paramecium ensures that there is usually a higher concentration of calcium ions in the surrounding water than inside the cell. Paramecium has a contractile vacuole that fills up with water. When it is full, the contractile vacuole contracts to expel the water. The rate of contraction of the vacuole depends on the water potential of the surrounding water. Name the process by which water enters Paramecium. Suggest the relationship between the rate of contraction of the contractile vacuole and the water potential of the surrounding water. Describe how the DNA of Paramecium differs from that of a prokaryotic cell.
9700_m16_qp_42
THEORY
2016
Paper 4, Variant 2
View
Questions Discovered
418