Download Chapter 7: Cell Structure

Chapter 7: Cell Structure
Section 1: Introduction to Cells
Preview
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The Discovery of Cells
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Looking at Cells
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Cell Features
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Summary
The Discovery of Cells
• Microscope observations of organisms led to
the discovery of the basic characteristics
common to all living things.
• Scientists first discovered cells in the 1600s
using crude microscopes.
• Observations made by scientists using more
powerful microscopes in the 1800s led to the
formation of the cell theory.
Visual Concept: Cell Theory
Looking at Cells
• Cells vary greatly in their size and shape.
• A cell’s shape reflects its function. Cell size is
limited by a cell’s surface area-to-volume
ratio.
• Cells can be branched, flat, round, or
rectangular.
Looking at Cells, continued
• All substances that enter or leave a cell must
cross the surface of the cell.
• A cell’s ability to move substances across its
surface can be estimated by finding its surface
area-to-volume ratio.
• Cells with greater surface area-to-volume
ratios can exchange substances more
efficiently.
Relationship between Surface Area and
Volume
Looking at Cells, continued
• When comparing cells of the same shape,
small cells have greater surface area-tovolume ratios than large cells.
• So, small cells function more efficiently than
large cells.
Cell Features
• All cells share common structural features,
including a cell membrane, cytoplasm,
ribosomes, and DNA.
• The cell membrane is the outer layer that
covers a cell’s surface and acts as a barrier
between the outside environment and the
inside of the cell.
• The cytoplasm is the region of the cell within
the cell membrane. The cytoplasm includes
the fluid inside the cell called the cytosol.
Cell Features, continued
• A ribosome is a cellular structure that makes
proteins.
• The DNA of a cell provides instructions for
making proteins, regulates cellular activities,
and enables cells to reproduce.
Features of Prokaryotic and Eukaryotic
Cells
Cell Features, continued
Features of Prokaryotic Cells
• A prokaryote is an organism made of a single
prokaryotic cell.
• Prokaryotic cells do not have a nucleus or
other internal compartments. The genetic
material of a prokaryotic cell is a single loop of
DNA.
• For millions of years, prokaryotes were the
only organisms on Earth.
Cell Features, continued
Features of Eukaryotic Cells
• A eukaryote is an organism made up of one or more
eukaryotic cells. All multicellular organisms are made
of eukaryotic cells.
• The DNA of a eukaryotic cell is found in an internal
compartment of the cell called the nucleus.
• All eukaryotic cells have membrane-bound
organelles. An organelle is a small structure found in
the cytoplasm that carries out specific activities
inside the cell.
Cell Features, continued
• Each organelle in a eukaryotic cell performs
distinct functions.
• The complex organization of eukaryotic cells
enables them to carry out more specialized
functions than prokaryotic cells.
Visual Concept: Comparing
Prokaryotes and Eukaryotes
Comparing Prokaryotes and
Eukaryotes
Summary
• Microscope observations of organisms led to the
discovery of the basic characteristics common to all
living things.
• A cell’s shape reflects its function. Cell size is limited
by a cell’s surface area-to-volume ratio.
• The complex organization of eukaryotic cells enable
them to carry out more specialized functions than
prokaryotic cells.
Concept Check
• How were cells discovered?
• Why does cell shape vary?
• What enables eukaryotes to perform more
specialized functions than prokaryotes?
Test Prep
1. The discovery of cells is linked most directly with
A. the development of the microscope.
B. early investigations of causes of disease.
C. observations of large, unicellular organisms.
D.efforts to reproduce organisms in the laboratory.
2. Eukaryotic cells differ from prokaryotic cells in that
eukaryotic cells
A. have a nucleus.
B. lack organelles.
C. lack ribosomes.
D.have a cell wall.
3. The Dutch scientist Anton van Leewenhoek used a
microscope that made objects appear 300 times
larger than they were. If a cell appeared to be 6 mm
long under this microscope, how long was the cell in
real life?
A. 0.02 mm
B. 0.20 mm
C. 0.05 mm
D. 0.50 mm
Section 2: Inside the Eukaryotic
Cell
Preview
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The Framework of the Cell
Directing Cellular Activity
Protein Processing
Storage and Maintenance
Energy Production
Summary
The Framework of the Cell
• Eukaryotic cells have an intricate network of protein
fibers called the cytoskeleton which provides the
interior framework of the cell.
• The cytoskeleton helps the cell move, keep its shape,
and organize its parts.
• There are three different kinds of cytoskeleton
fibers: microfilaments, microtubules, and
intermediate fibers.
Cytoskeleton
Click to animate the image.
A
B
C
D
Directing Cellular Activity
• DNA contains instructions for making proteins which
control most of the activity of the cell.
• The DNA of eukaryotic cells is stored in the nucleus.
• DNA instructions are copied as RNA messages, which
leave the nucleus. In the cytoplasm, ribosomes use
the RNA messages to assemble proteins.
Directing Cellular Activity,
continued
Nucleus
• A double membrane called the nuclear envelope
surrounds the nucleus.
• Nuclear pores located on the nuclear envelope act as
channels to allow certain molecules to move in and
out of the nucleus.
• The nucleolus is a structure within the nucleus where
ribosome parts are made.
• These ribosome parts are transported out of the
nucleus into the cytoplasm where they are
assembled to form a complete ribosome.
The nucleus and the nuclear envelope
Click to animate the image.
The Nucleus
B
C
D
A
Directing Cellular Activity,
continued
Ribosomes
• Each ribosome in a cell is made of RNA and many
different proteins.
• Ribosomes that are suspended in the cytosol are
called “free” ribosomes.
• Free ribosomes make proteins that remain inside the
cell.
Directing Cellular Activity,
continued
Ribosomes
• Ribosomes that are attached to the membrane of
another organelle are called “bound” ribosomes.
• Bound ribosomes make proteins that are exported
from the cell.
• Ribosomes can switch between being bound or free,
depending on what proteins the cell needs to make.
Protein Processing
• Some proteins that a cell manufactures are needed
outside the cell that makes them.
• Proteins that are sent outside the cell are packaged
in vesicles. Vesicles are small, membrane-bound sacs
that enclose the proteins and keep them separate
from the rest of the cytoplasm.
• The endoplasmic reticulum and Golgi apparatus are
organelles involved in preparing proteins for
extracellular export.
Protein Processing, continued
Endoplasmic Reticulum
• The endoplasmic reticulum, or ER, is an extensive
system of internal membranes that moves proteins
and other substances through the cell.
• The membranes of the ER are connected to the
outer membrane of the nuclear envelope.
• The endoplasmic reticulum is divided into two
portions: rough ER and smooth ER.
Endoplasmic Reticulum (ER),
Protein Processing, continued
Endoplasmic Reticulum
• The portion of the ER with attached ribosomes is
called rough ER because it has a rough appearance
when viewed with an electron microscope.
• The portion of the ER with no attached ribosomes is
called smooth ER because it has a smooth appearance
when viewed with an electron microscope.
• The ribosomes on the rough ER make proteins that are
packaged into vesicles. Enzymes of the smooth ER
make lipids and break down toxic substances.
Visual Concept: Endoplasmic
Reticulum (ER) and Ribosomes
Protein Processing, continued
Golgi Apparatus
• The Golgi apparatus is a set of flattened,
membrane-bound sacs.
• The Golgi apparatus helps modify, sort, and
package cell products for distribution.
Golgi apparatus
Protein Processing, continued
Making and Exporting Proteins
• The ribosomes located on the rough ER make
proteins which then cross into the membranes of the
ER. The ER membrane then pinches off and forms a
vesicle around the proteins.
• Vesicles transport the proteins from the rough ER to
the Golgi apparatus, where they are modified by
enzymes and repackaged in new vesicles.
• These new vesicles transport the modified proteins
to the cell membrane to be released outside the
cell.
Storage and Maintenance
Lysosomes
• Vesicles help maintain homeostasis by storing and
releasing a variety of substances as the cell needs
them.
• A lysosome is a vesicle produced by the Golgi
apparatus that contains enzymes that break down
large molecules.
• Lysosomes recycle old or damaged organelles and
digest food particles to provide nutrients for the cell.
Visual Concept: Lysosomes
Storage and Maintenance,
continued
Vacuoles
• A vacuole is a fluid-filled vesicle found in the
cytoplasm of many plant cells.
• Plant cells contain a large compartment called the
central vacuole, which stores water, ions, nutrients,
and wastes.
• When water fills the central vacuole, the cell
becomes rigid, allowing the plant to stand up. When
the vacuole loses water, the cell shrinks, and the
plant wilts.
Visual Concept: Vacuoles
Storage and Maintenance,
continued
Other Vacuoles
• Some protists have contractile vacuoles which pump
excess water out of the cell in order to control the
concentration of salts and other substances.
• A food vacuole is another type of vacuole. It is
formed when the cell membrane surrounds food
particles outside the cell and pinches off to form a
vesicle inside the cell.
Energy Production
• Cells need a constant source of energy.
• The energy for cellular functions is produced
by chemical reactions that occur in the
mitochondria and chloroplasts.
• In both organelles, chemical reactions
produce adenosine triphosphate (ATP), the
form of energy that fuels almost all cell
processes.
Energy Production, continued
Chloroplasts
• A chloroplast is an organelle found in plant and algae
cells that uses light energy to make carbohydrates
from carbon dioxide and water.
• Chloroplasts are surrounded by two membranes and
have several stacks of flattened sacs where energy
production takes place.
• Plant cells may have several chloroplasts.
Energy Production, continued
Mitochondria
• Mitochondria are cell organelles that use energy
from organic compounds to make ATP.
• Most of the ATP needed by a cell is produced inside
mitochondria. Both animal and plant cells contain
mitochondria.
• A smooth outer membrane and a folded inner
membrane surround a mitochondrion. ATP is
produced by enzymes on the folds of the inner
membrane.
Mitochondrion
Summary
• The cytoskeleton helps the cell move, keep its shape,
and organize its parts
• DNA instructions are copied as RNA messages, which
leave the nucleus. In the cytoplasm, ribosomes use
the RNA messages to assemble proteins.
• The endoplasmic reticulum and Golgi apparatus are
organelles involved in preparing proteins for
extracellular export.
Summary, continued
• Vesicles help maintain homeostasis by storing and
releasing a variety of substances as the cell needs
them.
• The energy for cellular functions is produced by
chemical reactions that occur in the mitochondria
and chloroplasts.
Concept Check
• What does the cytoskeleton do?
• How does DNA direct activity in the cytoplasm?
• What organelles are involved in protein production?
• What are vesicles and vacuoles?
• How does the cell get energy?
Test Prep
4. Which organelle produces proteins that are exported
from the cell?
A. nucleolus
B. rough ER
C. free ribosome
D.bound ribosome
5.
A.
B.
C.
D.
Which structure helps a plant stand upright?
lysosome
chloroplast
central vacuole
contractile vacuole
6.
A.
B.
C.
D.
Ribosome : protein synthesis :: mitochondria :
cell support
energy release
nutrient storage
protein transport
The graph shows the amount of ATP in the
muscles of a squid after it had been
exposed to low oxygen concentrations.
7. At what time during the
experiment were the
mitochondria in the
squid’s muscles
producing the most
energy?
A. 0 minutes
B. 15 minutes
C. 30 minutes
D. 45 minutes
Section 3: From Cell to Organism
Preview
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Diversity in Cells
Levels of Organization
Body Types
Summary
Diversity in Cells
• Both prokaryotic and eukaryotic cells can have
a variety of shapes and structures.
• The function of a cell is determined by its
shape and the organelles found in the cell.
• The different organelles and features of cells
enable organisms to function in unique ways
in different environments.
Diversity in Cells, continued
Diversity in Prokaryotes
• Prokaryotes can vary in shape, the way they obtain
and use energy, and their ability to move.
• Many prokaryotes have a flagellum, a long, hair-like
structure that grows out of the cell and enables the
cell to move through its environment.
• Prokaryotes may also have pili, short outgrowths
that allow the cell to attach to surfaces or other cells.
Flagella On Prokaryotic Cells
B
Click to animate the image.
C
D
A
E
F
Diversity in Cells, continued
Eukaryotic Cell Specialization
• Eukaryotic cells can vary in shape and external
features.
• Depending on their function, eukaryotic cells can
also vary in their internal organelles. For example,
muscle cells, which use large amounts of energy,
contain many mitochondria.
• Animal and plant cells are two types of eukaryotic
cells. Both have many of the same organelles, but
plant cells also have chloroplasts, a large central
vacuole, and a cell wall.
Eukaryotic Click
Cells
to animate the image.
I
J
C
D
A
B
E
A
M
L
J
G
E
F
H
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D
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B
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K
Levels of Organization
• Plants and animals have many highly specialized cells
that are arranged into tissues, organs, and organ
systems.
• A tissue is a distinct group of similar cells that
perform a common function.
• An organ is a collection of tissues that work together
to form a structure which performs a specific
function.
• An organ system is composed of a group of organs
that work together to perform major body functions.
Body Types
• Unicellular organisms can thrive independently or live
together in groups.
• Cells that are permanently associated but do not work
together or integrate cell activities are called colonial
organisms.
• A multicellular organism is composed of many individual,
permanently associated cells that coordinate their activities
with each other. True multicellularity occurs only in
eukaryotes.
Visual Concept: Comparing
Organisms that are Unicellular
and Multicellular
Body Types, continued
• In a multicellular body, cells are interdependent.
Distinct types of cells have specialized functions to
help the organism survive.
• The individual cells in a multicellular organism
cannot survive alone and are dependent on the
other cells of the organism.
• Must multicellular organisms begin as a single cell,
which divides to form more cells. These cells then
grow and become specialized in a process called
differentiation.
Visual Concept: Differentiation
Summary
• The different organelles and features of cells enable
organisms to function in unique ways in different
environments.
• Plants and animals have many highly specialized cells
that are arranged into tissues, organs, and organ
systems.
• A multicellular organism is composed of many
individual, permanently associated cells that
coordinate their activities with each other.
Concept Check
• What makes cells and organisms different?
• How are cells organized in a complex multicellular organism?
• What makes an organism truly multicellular?
Test Prep
8. The process by which cells become specialized in
form and function during development is called
A. association.
B. aggregation.
C. coordination.
D.differentiation.
Use the figure shown below to answer
the next two questions.
9. What is Structure 1?
A. pilum
B. cilium
C. flagellum
D.mitochondrion
10. What is the function of
Structure 1?
A. to make ATP
B. to grab food
C. to store energy
D.to move the cell