The question
Name: ______________________ Date: ____________ Does shape affect how far a substance gets into a block? (4 points)
Experimental setup
Does shape affect how far a substance gets into a block?
A student has a tray of agar dyed with an indicator that is pink when basic and turns clear in acid, a beaker of dilute vinegar, a knife, a ruler and a timer. She wants to find out whether the shape of a cell, not just its size, affects how much of its volume a substance can reach by diffusion in a given time. She plans to cut blocks that all have a volume of 8 cm³ but different shapes: a 2 × 2 × 2 cm cube, a 4 × 2 × 1 cm block and an 8 × 2 × 0.5 cm slab.
(a) State the null hypothesis for this investigation. [1 point]
(b) Identify the independent variable and one variable that must be held constant, and justify holding that variable constant. [1 point]
(c) Describe how the student should measure the dependent variable, and explain why she should test several blocks of each shape. [1 point]
(d) Predict the results if the null hypothesis is rejected, and justify your prediction in terms of surface area and distance. [1 point]