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5.1 All organisms are
composed of cells.
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• The
cell is the smallest unit of life. All living things are made of cells.
• The cell is composed of a nuclear region, which holds
the hereditary apparatus, enclosed within the cytoplasm.
• In all cells, the cytoplasm is bounded by a membrane
composed of phospholipid and protein.
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1. What are
the three principles of the cell theory?
2. How does the surface area-to-volume ratio of cells limit the
size that cells can attain?
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5.2 Eukaryotic cells
are far more complex than bacterial cells.
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• Bacteria,
which have prokaryotic cell structure, do not have membrane-bounded organelles
within their cells. Their DNA molecule is circular.
• The eukaryotic cell is larger and more complex, with
many internal compartments.
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3. How are
prokaryotes different from eukaryotes in terms of their cell walls, interior
organization, and flagella?
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5.3 Take a tour of
a eukaryotic cell.
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• A
eukaryotic cell is organized into three principal zones: the nucleus,
the cytoplasm, and the plasma membrane. Located in the cytoplasm are numerous
organelles, which perform specific functions for the cell.
• Many of these organelles, such as the endoplasmic
reticulum, Golgi apparatus (which gives rise to lysosomes), and nucleus,
are part of a complex endomembrane system.
• Mitochondria and chloroplasts are part of the energy-processing
system of the cell.
• The cytoskeleton encompasses a variety of fibrous
proteins that provide structural support and perform other functions for
the cell.
• Many eukaryotic cells possess flagella or cilia having
a 9 + 2 arrangement of microtubules; sliding of the microtubules past
one another bends these cellular appendages.
• Cells transport materials long distances within the
cytoplasm by packaging them into vesicles that are pulled by motor proteins
along microtubule tracks.
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4. What is
the endoplasmic reticulum? What is its function? How does rough ER differ
from smooth ER?
5. What is the function of the Golgi apparatus? How do the substances
released by the Golgi apparatus make their way to other locations in the
cell?
6. What types of eukaryotic cells contain mitochondria? What function
do mitochondria perform?
7. What unique metabolic activity occurs in chloroplasts?
8. What cellular functions do centrioles participate in?
9. What kinds of cytoskeleton fibers are stable and which are changeable?
10. How do cilia compare with eukaryotic flagella?
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5.4 Symbiosis played
a key role in the origin of some eukaryotic organelles.
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• Present-day
mitochondria and chloroplasts probably evolved as a consequence of early
endosymbiosis: the ancestor of the eukaryotic cell engulfed a bacterium,
and the bacterium continued to function within the host cell.
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11.
What is the endosymbiont theory? What is the evidence supporting this
theory?
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