Biology (Holt)

http://www.scilinks.org

Topic:Cell Features

Keyword:HX4034

Common Features of Cells

Cells share common structural features, including an outer bound-

ary called the .The cell membrane encloses the cell

and separates the cell interior, called the (SITE oh plaz

uhm), from its surroundings. The cell membrane also regulates

what enters and leaves a cell—including gases, nutrients, and

wastes. Within the cytoplasm are many structures, often suspended

in a system of microscopic fibers called the .All cells

have ribosomes. (RIE buh sohmz)are the cellular struc-

tures on which proteins are made. All cells also have DNA, which

provides instructions for making proteins, regulates cellular activi-

ties, and enables cells to reproduce. Some specialized cells such as

red blood cells, however, later lose their DNA.

Ribosomes

cytoskeleton

cytoplasm

cell membrane

56 CHAPTER 3Cell Structure

Calculating Surface Area

and Volume

Background

You can improve your understanding of the relationship

between a cell’s surface area and its volume by practicing

with the large cube in Table 2.

x + 6x - 7 - 0^2 <

8

493

0

5

2

Paramecium(SEM)

Magnification: 230

1. Find the total surface area of the cube.
   
   
   • side length l4 mm
   
   
   • surface area of one sidelll^2
   
   
   • surface area of one side l^2  4 mm  4 mm  16 mm^2
   
   
   • total surface area  6 l^2  6  16 mm^2  96 mm^2
   
   
   
   


2. Calculate the volume of the cube.
   
   
   • height(h) l 4 mm
   
   
   • volume l^2 h  16 mm^2  4 mm 64 mm^3
   
   
   
   


3. Determine the surface area–to-volume ratio.A ratio compares two num-
   bers by dividing one number by the other. A ratio can be expressed in three ways:
   in words as a fraction with a colon
   xto y x_y x:y
   For the surface area–to-volume ratio, divide total surface area by volume.
   
   Divide both numbers by their greatest common factor:
   ^32

 96  32 

 64  32 

96

64

total surface area

volume

Analysis

1. Calculate the surface area–
   to-volume ratio of the cube
   with a side length of 2 mm
   in Table 2.
   2. Calculate the surface area–
   to-volume ratio of the cube
   with a side length of 1 mm
   in Table 2.

3.Critical Thinking

Relating ConceptsHow

does the flatness of the

single-celled Paramecium

shown above affect the cell’s

surface area–to-volume ratio?

2C