CHAPTER 4 A TOUR OF THE CELL
Scientific Skills Exercise
Teaching objective: This exercise is designed to give students practice using a scale bar to
measure the size of a cell in a micrograph and to use the measurement to calculate volume and
surface area of the cell.
Teaching tips: A version of this Scientific Skills Exercise can be assigned in MasteringBiology.
Most students have difficulty grasping the relationship between the scale bar and the size of the
object shown in the image. It may help to sketch (or photocopy) the picture at one size, then
have changed, the cell remains the same size. There will be some variation in measurements
using the scale bar, according to where students delineate the edges of the cells in the image. As
long as they are consistent between the two cells, the relationships will hold.
Answers:
1. If the 1-µm scale bar is 5 mm long, and the diameter of the image of the parent cell is 20 mm;
dividing 20 by 5 yields a cell diameter of 4 µm. Since the diameter of the image of the new cell
Suggested Answers for End-of-Chapter Essay Questions
See the general information on grading short-answer essays and the suggested rubric at the
beginning of this document.
9. Scientific Inquiry
You could start by examining the organism and especially its mystery organelle by TEM at high
magnification, looking closely for structural similarities with known organelles. Then, starting
with a suspension of the organism in an aqueous solution, you could carry out cell fractionation:
10. Focus on Evolution
(a) Unity is best revealed by cell structures that are shared. Almost all biological membranes are
phospholipid bilayers. This feature arose early in the evolution of life on Earth and has been
11. Focus on Organization
Sample key points:
Life emerges from the integration of the functions performed by individual cell components.
Although the nucleus contains instructions for all cell components, other cell components are
required to carry them out.
Sample top-scoring answer:
ges from the integration of all the functions performed by
12. Synthesize Your Knowledge
Epithelial cells in the small intestine function both in the absorption of nutrients from partially
digested food and as a barrier between the substances in the small intestine and the blood supply.