Download AP Biology Rate of Diffusion/Cell Size Pre-Lab Questions 11-20-12

AP Biology Rate of Diffusion/Cell Size Pre-Lab Questions 11-20-12
Pre-Lab Questions: Before you start the lab today answer the following questions:
1. Look up the acid-base properties of the phenolphthalein indicator we are using in
today’s lab, including its expected color changes and the pH range for each color
form.
2. The phenolphthalein-agar model cells we are using are initially pink.
a. Predict the observations when these cells are placed in dilute hydrochloric
acid assuming H3O+ ions are able to diffuse into the agar.
b. How can these observations be used to measure the rate of diffusion?
3. Calculate the volume and surface area of the 2-cm cubic unit we are using in
today’s lab. (you should already know the formulas for volume and surface area
from math class)
4. Take a look at the diagram at the bottom of page 2 of the lab packet you have and
read the scenario that is set up in the diagram provided for you. Answer the
following questions:
- Which solute (s) will diffuse into the cell? Explain
- Which solute (s) will diffuse out of the cell? Explain
- With respect to glucose….is the surrounding environment hyper
or hypotonic to the cell? Explain
Post-Lab Questions: After completing the baseling activity answer the following
questions:
1. Calculate the rate of diffusion of HCl into the agar-phenolphthalein cube and
compare the surface area-to-volume ration of this agar ‘model cell.’
2. Why are most cells so small? Why aren’t they larger?
3. How doe the rate of diffusion influence the ability of a cell to obtain needed
nutrients?
4. Calculate the expected surface area-to-volume rations for 4cc and 8cc model cells.
5. Predict how the surface area-to-volume ratio might affect the rate of diffusion into
a cell.
6. Many cells or organelles that play a key role in nutrient absorption or energy
transfer have highly ‘convoluted’ membranes with many folds. How does this
affect the surface area of the cell or organelle and the rate of diffusion?
*Inquiry Experimental design
1. Design a controlled experiment to investigate the effects of surface area and cell
volume on the rate of diffusion in agar model cells. Identify the following:
a. focusing question
b. hypothesis
c. control group
d. independent variable
e. dependent variable
f. variables to be controlled
g. data collection method
h. data analysis method
2. Review the above with your instructor prior to doing the experiment. (if we have
enough time and materials)
3. Analyze and explain your results in terms of the metabolic requirements of cells
in both larger organisms and in specialized tissues such as the small intestine.