Notes to Instructors
Chapter 6 A Tour of the Cell
What is the focus of this activity?
Students sometimes think that introductory biology texts and courses spend too much
time dealing with cellular structure and function. It helps to remind them that many
What is the particular activity designed to do?
Activity 6.1 What makes a cell a living organism?
The specific questions in this activity are designed to help students review and
understand:
What misconceptions or difficulties can this activity reveal?
Activity 6.1
Question 2: In general, students understand that animal cells contain mitochondria. Yet,
many think that plant cells differ from animal cells because they contain chloroplasts
instead of mitochondria. It helps to remind students that plant cells contain both
Question 3: Most students understand that a micrometer is one-millionth of a meter and a
nanometer is one-billionth of a meter. However, they still may not have a good feel for the
relative sizes of molecules and organelles in the cell. This question is designed to give
students a better understanding of these relative sizes and help them understand how so
many different chemical reactions can occur simultaneously inside a cell.
Answers
Activity 6.1 What makes a cell a living organism?
1. Single-celled organisms and individual cells within multicellular organisms can vary
greatly in appearance as well as in the functions they perform. Nonetheless, each of
these cells is alive and therefore must have some common characteristics.
24 Activity 6.1
a. At a minimum, what structures or
components must a cell contain to be
alive?
b. What is the function of each structure
or component listed in part a?
1. Plasma or cell membrane 1. A selectively permeable cell
c. If you consider the types of single-celled organisms that exist today, which, if
any, have a structure similar to your description in part a?
2. What would you need to add to or change about the cell you described in question 1
to make it:
Activity 6.1 25
a. A eukaryotic animal cell? b. A eukaryotic plant cell?
1. Double-membrane-bound nucleus
containing chromosomes
complexed with histone proteins.
1. Double-membrane-bound nucleus
containing chromosomes complexed
with histone proteins.
3. To get an idea of the different sizes of various cellular components, do the following
calculations: Assume that the cell, its nucleus, and a globular protein—for example,
an enzyme—are spherical. In addition, assume the diameter of the protein is
5 nm, the diameter of the cell is 100 m (micrometers), and the diameter of the
nucleus is 40 m.
26 Activity 6.1
If you draw the globular protein as a sphere with a diameter of 2 cm (approximately
the diameter of a U.S. penny), what size would each of the following measurements
of the cell be if drawn to the same scale (5 nm real length ⫽2 cm)?
g. The volume of the Empire State Building is 1.05 ⫻106 m3. How many of your
scaled nuclei could fit into the Empire State Building? How many of your scaled
cells could fit?
The volume of the scaled nucleus is almost 2 times the volume of the Empire
h. Do the results of these calculations help you to understand how so much can be
going on inside a cell at once? Explain.
The calculations give a clearer idea of dimension relationships inside cells. For