To study food preservation, four blocks of firm tofu of different shapes and sizes are completely submerged in an acidic marinade containing a pH indicator. The marinade must diffuse fully to the center of each block to ensure complete preservation. Assuming the rate of diffusion is constant and identical for all blocks, which of the following blocks will be the first to be completely penetrated by the marinade?
a cube with edges of 5.0 cm5.0\text{ cm}5.0 cm each
a sphere with a diameter of 6.2 cm6.2\text{ cm}6.2 cm
a cuboid with dimensions 4.0 cm×8.0 cm×12.0 cm4.0\text{ cm} \times 8.0\text{ cm} \times 12.0\text{ cm}4.0 cm×8.0 cm×12.0 cm
a cuboid with dimensions 5.4 cm×6.0 cm×6.0 cm5.4\text{ cm} \times 6.0\text{ cm} \times 6.0\text{ cm}5.4 cm×6.0 cm×6.0 cm
34 exam-style questions on OCR A A Level Biology Exchange surfaces. Each one has a worked solution and a mark scheme showing where the marks go.