429_p01-14_MSS05_RE 8/16/04 3:27 PM Page 1 impos06 301:goscanc:Reading Essentials - LS:layouts:
chapter
23
Cells
1
section ●
Cell Structure
Before You Read
What You’ll Learn
■
the names and
functions of cell parts
■ the importance of a
nucleus in a cell
■ about tissues, organs,
and organ systems
Think about the different jobs people have in a restaurant.
List three of those jobs on the lines below. Then explain
how these people work together to provide food to customers.
Read to Learn
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Common Cell Traits
Living cells have many things in common. A cell is the
smallest unit that can perform life functions. All cells have
an outer covering called a cell membrane. Inside every cell
is a gelatinlike material called cytoplasm (SI tuh pla zum).
Cytoplasm contains hereditary material that controls the life
of the cell.
Identify Important
Words As you read the
section, circle all the words you
do not understand. Highlight
the part of the text that helps
you define those words.
How do cells differ?
Cells come in different sizes and shapes. A cell’s shape
might tell you something about its function. A nerve cell
has many branches that send and receive messages to and
from other cells. A nerve cell in your leg could be a meter
long. A human egg cell is no bigger than the dot on this i. A
human blood cell is much smaller than the egg cell. A
bacterium is even smaller—8,000 of the smallest bacteria
can fit inside one red blood cell.
A nerve cell cannot change its shape. Muscle cells and
some blood cells can change shape. Some cells in plant
stems are long and hollow and have openings at their ends.
These cells carry food and water throughout the plant.
1.
Infer Why are cells in
plant stems hollow with
openings at both ends?
Reading Essentials
19
429_p01-14_MSS05_RE 8/16/04 3:27 PM Page 2 impos06 301:goscanc:Reading Essentials - LS:layouts:
Picture This
2.
What types of cells are there?
Identify Circle the
features that are the same
in both types of cells.
Scientists separate cells into two groups, as shown in the
figure below. A prokaryotic (proh KAYR ee yah tihk) cell
does not have membrane-bound structures inside the cell. A
cell with membrane-bound structures inside the cell is called
a eukaryotic (yew KAYR ee yah tihk) cell.
Prokaryotic
Eukaryotic
Cell
membrane
Gel-like capsule
Cell wall
Nucleolus
Cell membrane
Nucleus with
hereditary
material
Flagellum
Hereditary
material
Ribosomes
Organelles
Ribosomes
Just as restaurant workers have specific jobs, each cell in
your body has a certain job to do. Cells take in nutrients,
release and store chemicals, and break down substances
24 hours a day.
What protects a cell and gives it shape?
3.
List three things found in
the cell wall of a plant.
20
Cells
A cell wall is a tough, rigid outer covering that protects the
cell and gives it shape. The cells of plants, algae, fungi, and
most bacteria are enclosed in a cell wall.
A plant cell wall is mostly made up of a carbohydrate
called cellulose. The long, threadlike fibers of cellulose form
a thick mesh. The mesh allows water and dissolved materials
to pass through the cell wall.
Cell walls may contain pectin, which is used to thicken
jams and jellies. Cell walls also contain lignin. Lignin is a
compound that makes cell walls rigid. Plant cells responsible
for support have large amounts of lignin in their walls.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Cell Organization
429_p01-14_MSS05_RE 8/16/04 3:27 PM Page 3 impos06 301:goscanc:Reading Essentials - LS:layouts:
What is the function of the cell membrane?
The protective layer around all cells is the cell membrane. If
a cell has a cell wall, the cell membrane is inside the cell wall.
The cell membrane controls what happens between a cell and
its environment. Water and some food particles move freely
into and out of a cell through the cell membrane. Waste
products leave through the cell membrane.
What is cytoplasm?
Cytoplasm is a gelatinlike material in the cell. Many
important chemical reactions occur within the cytoplasm.
Cytoplasm has a framework called the cytoskeleton, which
helps the cell keep or change its shape. The cytoskeleton helps
some cells to move. The cytoskeleton is made up of thin,
hollow tubes of protein and thin, solid protein fibers.
What are the functions of organelles?
4.
Describe What is the
cytoskeleton?
5.
Explain the function of
Most of a cell’s life processes happen in the cytoplasm.
Within the cytoplasm of eukaryotic cells are structures
called organelles. Some organelles process energy. Others
make materials needed by the cell or other cells. Some
organelles move materials. Others store materials. Most
organelles are surrounded by membranes.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Why is the nucleus important?
The nucleus (NEW klee us) directs all cell activities. The
nucleus usually is the largest organelle in a cell. It is separated
from the cytoplasm by a membrane. Materials enter and
leave the nucleus through openings in the membrane. The
nucleus contains DNA. DNA is the chemical that contains
the code for the cell’s structure and activities.
Which organelles process energy?
Cells need energy to do their work. In plant cells, food
is made in green organelles called chloroplasts
(KLOR uh plasts). Chloroplasts contain chlorophyll
(KLOR uh fihl), which captures light energy that is used to
make a sugar called glucose. Animal cells and some other
cells do not have chloroplasts. Animals must get food from
their environment.
The energy in food is stored until it is released by
organelles called mitochondria (mi tuh KAHN dree uh).
Mitochondria release energy by breaking down food into
carbon dioxide and water. Some types of cells, such as
muscle cells, are more active than other types of cells. These
cells have large numbers of mitochondria.
the nucleus.
Reading Essentials
21
429_p01-14_MSS05_RE 8/16/04 3:27 PM Page 4 impos06 301:goscanc:Reading Essentials - LS:layouts:
What organelle makes proteins?
6.
Identify Where are
ribosomes made?
Protein takes part is almost every cell activity. Cells make
their own proteins on structures called ribosomes, which
are shown below. Ribosomes are considered organelles, even
though they are not membrane bound. Hereditary material
in the nucleus tells ribosomes how, when, and in what order
to make proteins. Ribosomes are made in the nucleolus
(new klee OHL us) and move out into the cytoplasm. Some
ribosomes are free-floating in the cytoplasm and some attach
to the endoplasmic reticulum.
Animal Cell
Rough endoplasmic
reticulum (RER)
Smooth endoplasmic
reticulum (SER)
Ribosome
Nucleus
Nucleolus
Picture This
7.
Golgi bodies
Compare Circle the
organelles that direct cell
activities in each cell.
Highlight the organelle that
contains chlorophyll.
Free ribosome
Lysosome
Plant Cell
Central vacuole
Chloroplast
Free ribosome
Cell wall of
adjacent cell
Nucleus
Smooth endoplasmic
reticulum (SER)
Nucleolus
Ribosome
Rough endoplasmic
reticulum (RER)
Golgi bodies
Mitochondrion
Cell wall
Cell membrane
22
Cells
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Mitochondrion
Cytoskeleton
Cell membrane
429_p01-14_MSS05_RE 8/16/04 3:27 PM Page 5 impos06 301:goscanc:Reading Essentials - LS:layouts:
What is the endoplasmic reticulum?
The endoplasmic reticulum (en duh PLAZ mihk •
rih TIHK yuh lum), or ER, is a series of folded membranes
in which materials can be processed and moved around inside
the cell. Smooth ER processes materials such as lipids that
store energy. Rough ER has ribosomes that make proteins. The
proteins are used within the cell or moved out of the cell.
What types of organelles transport or
store materials?
The Golgi (GAWL jee) bodies sort proteins and other
cellular materials and put them into structures called
vesicles. Vesicles deliver the cellular materials to areas inside
the cell and to the cell membrane where they are released.
Cells have membrane-bound spaces called vacuoles. Vacuoles
store cellular materials, such as water, wastes, and food.
A Describe Make a
●
three-tab Foldable, as shown
below. Use the Foldable to
describe how cells are organized
to work together.
How does a cell recycle its materials?
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Active cells break down and recycle materials. An
organelle called a lysosome (LI suh sohm) contains digestive
chemicals that help break down materials in the cell. The
lysosome’s membrane stops the digestive chemicals from
leaking into the cytoplasm and destroying the cell. When a
cell dies, a lysosome’s membrane breaks down. The released
digestive chemicals destroy the cell’s contents.
Tissue
Organ
Organ
System
From Cell to Organism
The figure below shows how a many-celled organism is
organized. A cell in a many-celled organism performs its own
work and depends on other cells in the organism. Similar
cells grouped together to do one job form a tissue. Each cell
works to keep the tissue alive. Tissues are organized into
organs. An organ is made up of two or more different types
of tissue that work together. For example, your heart is an
organ that is made up of cardiac tissue, nerve tissue, and
blood tissues. An organ system is a group of organs that work
together to perform a function. Your cardiovascular system
is made up of your heart, arteries, veins, and capillaries.
Organ systems work together to keep an organism alive.
Cell
Tissue
Organ
Organism
Organ
system
Picture This
8.
Sequence Write a
number from 1 to 5 beside
each label on the diagram.
A 1 is the simplest level of
organization and a 5 is the
most complex level of
organization.
Reading Essentials
23
429_p01-14_MSS05_RE 8/16/04 3:27 PM Page 6 impos06 301:goscanc:Reading Essentials - LS:layouts:
After You Read
Mini Glossary
cell membrane: the protective layer around a cell, which
controls what happens between a cell and its environment
cell wall: a tough, rigid outer covering that protects the cell
and gives it shape
chloroplast (KLOR uh plast): a green organelle that makes
food in plant cells
cytoplasm (SI tuh pla zum): gelatinlike material inside
every cell where hereditary material is contained
endoplasmic reticulum: a series of folded membranes in
which materials can be processed and moved around
inside the cell
Golgi (GAWL jee) bodies: organelles that sort proteins and
other cellular materials and put them into structures
called vesicles
mitochondria: organelles that release energy by breaking
down food into carbon dioxide and water
nucleus (NEW klee us): directs all cell activities
organ: a structure made up of two or more different types of
tissues that work together
organelle: a structure within a eukaryotic cell; some process
energy and others make substances needed by the cell
or other cells
ribosome: a small structure where a cell makes its
own protein
tissue: a group of similar cells that work together to do one job
2. Complete the diagram below to show the organization of many-celled organism.
Tissue
Organism
3. Beside each organelle listed below, write Plant, Animal, or Both to show where the
organelle is found.
a. Nucleus
d. Ribosome
b. Chloroplast
e. Lysosome
c. Golgi bodies
f. Mitochondrion
End of
Section
24
Cells
Visit life.msscience.com to access your textbook, interactive
games, and projects to help you learn more about cell structure.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
1. Review the terms and their definitions in the Mini Glossary. Choose one term that
describes a cell structure and write a sentence to explain its function.