Biology 9700 · AS & A Level · Transport mechanisms
Transport mechanisms — practice question
A student carried out an investigation into how altering the surface area to volume ratio affects diffusion. Two agar blocks of different sizes, X and Y, were prepared. The agar included Universal Indicator solution. Universal Indicator solution changes colour when acid is added. The blocks were then put into dilute hydrochloric acid at the same temperature. The student recorded how long each block took to become completely colour-changed. Blocks X and Y are shown in Fig. 6.1. All dimensions are in cm.
(a(i))[2]
Block X has a surface area to volume ratio of 5:1. Calculate the surface area to volume ratio of block Y. Show your working.
(a(ii))[2]
The student saw that block X became completely colour-changed far more quickly than block Y. Explain why.
(a(iii))[2]
Suggest how the results from this investigation help to explain why plants need a transport system.
(b)[1]
A student carried out an experiment to see whether reducing sugars can diffuse through Visking tubing. Fig. 6.2 shows the apparatus used. At the beginning of the experiment, the solution outside the tubing contained no reducing sugars. At set intervals, the student tested for reducing sugars both inside the Visking tubing and in the external solution. Name the reagent used to test for the presence of reducing sugars.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Surface area to volume ratio for block Y = 1.67:1” …