Cell size calculations

Developed by: John Merrill
Modifications: Jon Stoltzfus

Surface to Volume Ratios

Campbell's Biology, 9th ed. Chapter 6.

Introduction to cellular structure and function. This activity was developed to reinforce the concept that metabolic requirements impose an upper limit to cell size. In addition, it reinforces the key concept of the plasma membrane as a selective barrier and the concept that the cell must exchange/interact with its environment. Use of the glucose transporter allows solid linkage to the chapter on membranes and membrane transport.

Connection to Vision and Change

Core Concepts

2.  Structure and Function

Basic units of structure define the function of all living things.  The plasma membrane as a selective barrier.  

Core Competencies and Disciplinary Practice

2. Ability to use quantitative reasoning.  Students should understand that biology is often analyzed through quantitative approaches.  Applying basic quantitative skills to a biological problem.


Learning Objectives:            

1.  Explain how metabolic requirements impact cell size. 

2.  Explain why the ratio of surface area to volume is critical.



This exercise begins by having the students calculate the surface to volume ratios of cells with different diameters.  The final activity has them calculate the number of Glucose transporters needed to support metabolism for cells of a set size.  

The original activity was developed by John Merrill, with arbitrary numbers, mostly chosen for ease of calculations.  The final version was modified by Jon Stoltzfus using more realistic numbers. Jon also developed a Handout that has the students do a number of calculations that pose some interesting thought questions.  Both Powerpoints (JM and JS) are posted, so you can see how two different instructors use this activity.

Handout with problems for students378.83 KB
Calculation key for instructor659.47 KB
Background information for instructor about numbers used4.43 MB
Original lecture slides and clicker questions - JM1.99 MB
Modified lecture slides and clicker questions - JS520.86 KB

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This material is based upon work supported by the National Science Foundation (DUE grants: 1438739, 1323162, 1347740, 0736952 and 1022653). Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF.