Student _______________________________________________ Class __________ Date _______________
CONCEPT 6-1:
All Organisms Are Made of Cells
Cells are as basic to biology as atoms are to chemistry.
All organisms are made of cells. Organisms are either
unicellular (single-celled), such as most bacteria and protists,
or multicellular (many-celled), such as plants, animals, and
most fungi. Because most 1_____ cannot be seen without
magnification, people’s understanding of cells and their
importance is relatively recent.
1. a) cells
c) protists
b) organisms
d) animals
e) atoms
THE CELL THEORY
Human understanding of nature often follows the
invention and improvement of instruments that extend
human senses. The development of microscopes
provided increasingly clear windows to the world of
cells.
Light microscopes, the kind used in your classroom,
were first developed and used by scientists around 1600.
In a light 2_____, visible light passes through an object,
such as a thin slice of muscle tissue, and glass lenses
then enlarge the image and project it into the human eye
or a camera.
In 1665, an English scientist named Robert Hooke
observed “compartments” in a thin slice of cork (oak
bark) using a light microscope. He named the
compartments cells. Actually, Hooke was observing the
walls of dead plant 3_____. Many more observations by
many other scientists were needed to understand the
importance of Hooke’s discovery. By 1700, Dutch
amateur scientist Anton van Leeuwenhoek (LAY vun
hook) had developed simple light microscopes with highquality lenses to observe tiny living 4_____, such as
those in pond water. He described what he called
“animalcules” in letters to Hooke and his colleagues.
For the next two centuries, scientists, using
microscopes, found cells in every organism they
examined. By the mid-1800s, this evidence led to the
cell theory—the generalization that all living things are
composed of 5_____, and that cells are the basic unit of
structure and function in living things. Later, the cell
theory was extended to include the concept that all cells
come from pre-existing cells.
2. a) camera
c) image
b) lens
d) classroom
e) microscope
3. a) organisms
c) corks
b) cells
d) walls
e) seeds
4. a) microscopes c) individuals
b) lights
d) models
e) organisms
5. a) cells
b) atoms
c) matter
d) particles
e) molecules
MICROSCOPES AS WINDOWS TO CELLS
Light microscopes (abbreviated LM) are useful for
magnifying objects up to about 1000 times their actual
size. This type of microscope works for viewing objects
about the size of a bacterium or larger. But much of a
cell’s structure is so small that even magnifying it 1000
times is not enough to see it. Knowledge of cell
structure took a giant leap forward as biologists began
using electron microscopes in the 1950s. Instead of
light, the electron microscope uses a beam of 6_____.
Certain electron microscopes can magnify objects as
much as a million (1,000,000) times, enough to reveal
details of the structures inside a cell.
Biologists use the scanning electron microscope
(SEM) to study the surface structures of cells. The
transmission electron microscope (TEM) is used to
explore their internal structure. Specimens for both types
of electron microscopes must be killed and preserved
before they can be examined. For this reason, light
microscopes are still useful for observing living cells.
A photograph of the view through a microscope is
called a micrograph. Throughout your textbook, most
7_____ have a notation alongside the image that
indicates the kind of microscope used to view the object
and its final magnification. For example, the notation
“LM 200X” indicates that the micrograph is an image
made with a light microscope and shown here at a
8_____ of 200X, or 200 times its actual size. (You may
notice that some light micrographs in your book have
magnifications listed of more than 1000X. That is
because the photographs have been further enlarged from
the originals.)
6. a) quarks
b) atoms
c) protons
d) neutrons
e) electrons
7. a) micrographs c) drawings
b) illustrations d) diagrams
e) photographs
8. a) decrease
c) magnification
b) reduction
d) augmentation
e) growth
As you tour the parts of a cell in this chapter, you will
encounter comparisons to a scale model of a cell
enlarged to the size of your classroom. At this
magnification, the “classroom cell” is over 300,000 times
larger than a normal cell.
AN OVERVIEW OF ANIMAL AND PLANT CELLS
Each part of a cell with a specific job to do is called
an organelle, meaning “mini-organ.” Cutaway diagrams
of a generalized animal cell (Figure 6-4) and plant cell
(Figure 6-5) show the 9_____ in each kind of cell. For
now, the cell parts labeled in the figures are just words
and structures, but these organelles will come to life as
you take a closer look at how each of them works, here
and later in the chapter.
9. a) organelles
c) cells
b) jobs
d) divisions
e) compartments
Figure 6-4
This diagram provides an overview of a generalized animal cell. Later in the chapter,
watch for miniature versions of the diagram with “you-are-here” highlights. They will
serve as road maps on your tour of cells.
There are more similarities between animal and plant
cells than there are differences. Both kinds of 10_____
have a thin outer covering, called the plasma membrane,
which defines the boundary of the cell and regulates the
traffic of chemicals between the cell and its
surroundings. Each cell also has a prominent nucleus
(plural, nuclei), which houses the cell’s genetic material
in the form of DNA. In the classroom-cell scale model,
the nucleus would be the size of a small car in the middle
of your classroom.
10. a) atoms
c) organisms
b) organelles
d) animalcules
e) cells
Figure 6-5
A plant cell has many of the same structures as an animal cell. Miniature versions of this
generalized plant cell diagram will appear in parts of the chapter where its unique
organelles are discussed.
The entire region of the cell between the nucleus and
the plasma membrane is called the cytoplasm (SYT oh
plaz um), which consists of various organelles suspended
in a fluid. Many of these organelles are enclosed by their
own membranes. These 11_____ help to maintain
chemical environments inside the organelles that are
different from the environment of the rest of the cell. If
you compare Figures 6-4 and 6-5, you will see that there
are a few key differences in cell structure between plants
and animals. One difference is the presence of
chloroplasts in some plant cells, but not in animal cells.
A chloroplast is the organelle in which photosynthesis
occurs. 12_____ converts light energy to the chemical
energy stored in molecules of sugars and other organic
compounds. Also, a plant cell is encased by a strong
cell wall outside its plasma membrane. The cell wall
protects the plant cell and maintains its shape. Animal
cells do not have cell walls.
TWO MAJOR CLASSES OF CELLS
There are two basic kinds of cells. One kind—a
prokaryotic cell (pro KAR ee oh tik)— lacks a nucleus
and most other organelles. Bacteria and another group of
organisms called the archaea are prokaryotic cells.
Prokaryotic organisms appear earliest in Earth’s fossil
record. In contrast, a eukaryotic cell (yoo KAR ee oh
tik) has a nucleus surrounded by its own membrane, and
has other internal organelles bounded by membranes.
Protists, fungi, plants, and animals consist of 13_____
cells. Organisms with eukaryotic cells appeared later in
Earth’s history.
The major difference between these two main classes
of cells is indicated by their names. The word eukaryotic
is from the Greek eu meaning “true,” and karyon meaning
“kernel.” The kernel refers to the nucleus that eukaryotic
cells have and prokaryotic cells lack. In a eukaryotic
cell, the 14_____ is the largest organelle. There are
many other types of organelles outside the nucleus,
surrounded by membranes of their own.
A bacterium is an example of a prokaryotic cell (pro
means “earlier than”). Without a true nucleus and the
organelles of eukaryotic cells, prokaryotic cells are much
simpler in structure (Figure 6-6). The DNA in a
15_____ cell is concentrated in an area called the
nucleoid region, which is not separated from the rest of
the cell by a membrane, as is the case in a eukaryotic
11. a) organisms
c) beings
b) fluids
d) membranes
e) environments
12. a) Respiration c) Reproduction
b) Oxidation
d) Transpiration
e) Photosynthesis
13. a) ancient
c) eukaryotic
b) simpler
d) bacterial
e) prokaryotic
14. a) kernel
b) seed
c) cell
d) nucleus
e) organelle
13. a) prokaryotic c) complex
b) complicated d) multifaceted
e) eukaryotic
cell. Most bacteria are 1 to 10 micrometers in diameter,
whereas eukaryotic cells are typically 10 to 100
micrometers in diameter. You’ll examine prokaryotic
cells in more detail in Chapter 16. Eukaryotic cells are
the main focus of this chapter.
Figure 6-6
A cutaway diagram reveals the structure of a generalized prokaryotic cell.
CONCEPT CHECK 6.1
Answer the following questions in the space provided
1. What evidence led to the development of the cell theory?
2. What is the cell theory?
3. How do the various kinds of microscopes differ as tools in the study of cells?
4. What is the main advantage compound light microscopes have over electron microscopes?
What is the main disadvantage?
5. Identify two similarities and two differences between plant and animal cells. Create a Venn
diagram if necessary.
6. How is a eukaryotic cell different from a prokaryotic cell?
7. What is the function of the plasma membrane?