(Copy the title, problem, and summarized background neatly in your lab
notebook)
AP Biology: Cellular Processes
Investigation 4: Diffusion and Osmosis
______Big Idea 2
Problem:
What causes my plants to wilt if I forget to water them?
Background:
(Read the background and understanding water potential on the packet and
summarize both for your lab notebook)

Understanding Water Potential
(Copy the big idea, enduring understandings and learning objective codes in your
lab notebook)
Big Idea 2: Biological systems utilize free energy and molecular
building blocks to grow, to reproduce and to maintain dynamic
homeostasis.
Enduring Understandings
 2B Growth, reproduction, and dynamic homeostasis require that cells
create and maintain internal environments that are different from their
external environments.
 2B1: Cell membranes are selectively permeable due to their structure.
 2B2: Growth and dynamic homeostasis are maintained by the constant
movement of molecules across membranes.
Learning Objectives: 2.6, 2.7, 2.10, 2.11, 2,12
 2.6 The student is able to use calculated surface area-to-volume ratios to
predict which cell(s) might eliminate wastes or procure nutrients faster by
diffusion (2A3 & SP 2.2, SP 2.6).
 2.7 The student is able to explain how cell size and shape affect the
overall rate of nutrient uptake and the rate of waste elimination (2A3 & SP
2.2, SP 6.2).
 2.10 The student is able to use representations and models to pose
scientific questions about the properties of cell membranes and selective
permeability based on molecular structure (2B1 & SP 1.4, SP 3.1, SP 4.2,
SP 4.3, SP 4.4).
 2.11 The student is able to construct models that connect the movement
of molecules across membranes with membrane structure and function
(2B2 & SP 1.1, SP 2.1, SP 2.2, SP 5.1, SP 7.1, SP 7.2).
 2.12 The student is able to use representations and models to analyze
situations or solve problems qualitatively and quantitatively to investigate
whether dynamic homeostasis is maintained by the active movement of
molecules across membranes (2B1 & 2B2 & SP 1.4, SP 2.2, SP 5.2, SP
5.3)
(Copy the general safety precautions, investigations and getting started headings
in your lab notebooks)
General Safety Precautions:
(Summarize the safety concerns and precautions in your lab notebook)
The Investigations:
(Read and summarize the three parts of the investigation into your lab notebook)
Getting Started:
(Answer all the getting started questions in your lab notebooks. Make sure your
responses are full sentence answers that would make sense to you and the
reader)
Procedure 1: Surface Area and Cell Size:
(Read and answer the questions in your lab notebook. Make sure your responses
are full sentence answers that would make sense to you and the reader)
Step 1:
(Record the in-class table “Phenolphthalein Color Indicator” and answer the
questions listed).
Step 2:
(Make a prediction on the relationship of surface area to volume and the
diffusion rate)
Designing and Conducting Your Investigation
(List the procedures for your experiment, also create a data table that includes
the cube size (cm), SA (cm2), V (cm3), SA:V ratio, rate of diffusion (cm/min) and
the extent of diffusion for each cell.)
(Create two graphs 1. the rate of diffusion relative to SA:V and 2. the extent of
diffusion relative to SA:V)
Data Analysis: (Summarize the results, do your results support your
predictions?)
(Copy the procedure heading in your lab notebook)
Procedure 2: Modeling Diffusion and Osmosis
(Answer the 6 bulleted questions and summarize the purpose of the experiment)
Step 1: Predictions: (include pictoral predictions of your cells and arrows to
show direction of diffusion/osmosis)
Step 2-3: Create a data table that includes the cell contents, extracellular
solution type, cell weight before (g) and cell weight after (g), percent change of
weight
Step 4: (Finish data table calculations summarize the results, do your results
support your predictions? Also answer all the bulleted questions)
Designing and Conducting Your Investigation
We will not be conducting this portion of the lab.
(Copy the procedure heading in your lab notebook)
Procedure 3: Observing Osmosis in Living Cells
(Summarize the paragraph and answer the bulleted questions. Make sure your
responses are full sentence answers that would make sense to you and the
reader)
Step 1:
(Create a wet mount of Elodea cells and view/sketch under high power. Answer
all the bulleted questions.)
Step 2:
(Test one of the solutions from Procedure 2. Make a prediction of what you think
will happen. Record your procedure, a sketch and other observations in your lab
notebook.)
(Copy the heading and purpose in your lab notebook)
Designing and Conducting Your Investigation
Purpose: Identify the concentrations of the sucrose solutions and use the
solutions to determine the water potential of the plant tissues.
(Do the following in your lab notebook:
Answer the first two bulleted questions
Create your procedures
Set up the cores to run for 30 minutes.
Create a data table to contain the following information: solution type, initial
mass(g), final mass(g), change in mass(g), and % change in mass.
% change of mass =final mass(g) – initial mass(g)/ final mass(g) then X 100
Analysis
Answer the following questions in your lab notebook:
1.Which mystery color solution had the highest concentration of sucrose? How
do you know this?
2. Knowing that the mystery solutions were composed of sucrose at various
concentrations (0.2M, 0.4M, 0.6M, 0.8M, and 1.0M). Determine which color
solution is each molarity by creating a graph showing the relationship between
the solute concentration and the % change of mass.
3. What is the molarity of the potato core (use the graph to determine this)?
4. What is the water potential of the potato core? Use the formulas. Show the
formulas, all your calculations and reasoning in your lab notebook.
5. Which solution had a water potential
5. If you looked at your potato cores under the microscope what would you see?
6. What would your results be if the potato were placed in a dry area for several
days before your experiment?
7. When potatoes are in the ground, do they swell with water when it rains? If
not, how do you explain that, and if so, what would be the advantage or
disadvantage?