CIE iGCSE Co-Ordinated Science B3.1 Diffusion Exam Style Questions Paper 4
Question
(a) A student investigates the effect of temperature on the rate of diffusion of red dye into agar jelly cubes.
The student prepares three cubes of agar jelly A, B and C.
- Each cube is equal in size.
- A is kept at 30 °C, B is kept at 25 °C, C is kept at 20 °C.
- Three separate containers of red dye are also kept at 30 °C, 25 °C and 20 °C.
- Each cube is immersed in red dye equal to its temperature for 10 minutes.
- The cubes are then removed from the dye and cut in half.
Fig. 7.1 shows the cubes cut in half.
Table 7.1 shows the results.
(i) Calculate the rate of diffusion for cube A.
▶️Answer/Explanation
0.10 cm per min
Calculation: Rate = Diffusion distance/Time = 1.0 cm/10 min = 0.10 cm/min
Experimental observation: The higher temperature (30°C) shows fastest diffusion, consistent with kinetic theory.
(ii) Use the results in Table 7.1 to describe the relationship between temperature and the rate of diffusion.
▶️Answer/Explanation
As temperature increases, the rate of diffusion increases (positive correlation).
Scientific explanation: 1. Higher temperature → greater kinetic energy of dye molecules
2. More frequent and energetic collisions
3. Faster net movement from high to low concentration
(iii) State one variable, other than the size of the cubes, that should be kept constant in this investigation.
▶️Answer/Explanation
Possible answers: • Concentration of red dye
• Immersion time (10 minutes)
• Type of agar jelly
• pH of the solution
Control importance: Keeping these constant ensures only temperature affects results (fair test).
(b) Explain why the red dye diffuses into the agar jelly.
▶️Answer/Explanation
1. Concentration gradient exists (high dye concentration outside → low inside jelly)
2. Dye molecules move randomly (Brownian motion)
3. Net movement down concentration gradient until equilibrium
Molecular level: Dye particles collide with agar pores and gradually spread through available spaces.
(c) Materials diffuse in and out of living cells. Name the gas produced by respiration that diffuses out of cells.
▶️Answer/Explanation
Carbon dioxide (CO2)
Biological context: This waste product of aerobic respiration moves from high concentration in cells to lower concentration in blood/capillaries.