Download Unit 2 Section 3 Answer Key - WAHS

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Unit 2 Section 3: Structure and Function of Cells
Cell Organization
The eukaryotic cell can be divided into two major parts: the nucleus and the cytoplasm.
The cytoplasm is the fluid portion of the cell outside the nucleus. Prokaryotic cells have
cytoplasm as well, even though they do not have a nucleus.
Many cellular structures act as if they are specialized organs. These structures are
known as organelles, literally “little organs.” Understanding what each organelle does
helps us to understand the cell as a whole.
Comparing the Cell to a Factory
The eukaryotic cell is much like a living version of a modern factory. The specialized
machines and assembly lines of the factory can be compared to the different
organelles of the cell. Cells, like factories, follow instructions and produce products.
The Nucleus
In the same way that the main office controls a large
factory, the nucleus is the control center of the cell. The nucleus
contains nearly all the cell’s DNA and, with it, the coded instructions for making
proteins and other important molecules.
Chromosomes contain the genetic information that is passed from one generation of
cells to the next. Most of the time, the threadlike chromosomes are spread throughout
the nucleus in the form of chromatin—a complex of DNA bound to proteins.
The nucleus is surrounded by a nuclear envelope composed of two membranes. The
nuclear envelope is dotted with thousands of nuclear pores, which allow material to
move into and out of the nucleus.
Most nuclei also contain a small, dense region known as the nucleolus. The nucleolus is
where the assembly of ribosomes begins.
Organelles That Store, Clean-up, and Support
1. Vacuoles- storage
3. Lysosomes- clean up
2. Vesicles – storage and shipment
4. Cytoskeleton – support
Vacuoles and Vesicles
Many cells contain large, saclike, membrane-enclosed structures called vacuoles that
store materials such as water, salts, proteins, and carbohydrates.
Plant cells - single, large central vacuole filled with liquid. The pressure of the central
vacuole in these cells increases their rigidity.
Animals cells - unicellular organisms (ex. Paramecium) By contracting rhythmically, this
specialized vacuole pumps excess water out of the cell.
Nearly all eukaryotic cells contain smaller membrane-enclosed structures called
vesicles. Vesicles are used to store and move materials between cell organelles, as well
as to and from the cell surface.
Lysosomes
Lysosomes are small organelles filled with enzymes that function as the cell’s cleanup
crew. One function of lysosomes is the breakdown of lipids, carbohydrates, and
proteins into small molecules that can be used by the rest of the cell. Lysosomes are
also involved in breaking down organelles that have outlived their usefulness.
Cytoskeleton
Eukaryotic cells are given their shape and internal organization by a network of protein
filaments known as the cytoskeleton. Certain parts of the cytoskeleton also help to
transport materials between different parts of the cell, much like conveyer belts that
carry materials from one part of a factory to another.
Cytoskeleton creates cilia and flagella in cells that require movement.
Microtubules
In animal cells, structures known as centrioles are also formed from tubulins.
Centrioles are located near the nucleus and help to organize cell division.
Centrioles are not found in plant cells.
Organelles That Build Proteins
1. Ribosomes - assembly
2. Endoplasmic Reticulum - assembly with destination outside of the cell
3. Golgi Apparatus - modify, package, shipment
4. Nucleus - brains of the operation
 Cells need to build new molecules all the time, especially proteins, which catalyze
chemical reactions and make up important structures in the cell.
 Because proteins carry out so many of the essential functions of living things, a big
part of the cell is devoted to their production and distribution.
 Proteins are synthesized on ribosomes, sometimes in association with the rough
endoplasmic reticulum in eukaryotes.
Ribosomes
Ribosomes are small particles of RNA and protein found throughout the cytoplasm in
all cells. Ribosomes produce proteins by following coded instructions that come from
DNA. Each ribosome is like a small machine in a factory, turning out proteins on orders
that come from its DNA “boss.”
Endoplasmic Reticulum
Eukaryotic cells contain an internal membrane system known as the endoplasmic
reticulum, or ER. The endoplasmic reticulum is where lipid components of the cell
membrane are assembled, along with proteins and other materials that are exported
from the cell.
Rough ER
The portion of the ER involved in the synthesis of proteins is called rough endoplasmic
reticulum, or rough ER. It is given this name because of the ribosomes found on its
surface. Newly made proteins leave these ribosomes and are inserted into the rough
ER, where they may be chemically modified.
Smooth ER
The other portion of the ER is known as smooth endoplasmic reticulum (smooth ER)
because ribosomes are not found on its surface. In many cells, the smooth ER contains
collections of enzymes that perform specialized tasks, including the synthesis of
membrane lipids and the detoxification of drugs.
Golgi Apparatus
Proteins produced in the rough ER move next into the Golgi apparatus, which appears
as a stack of flattened membranes. The proteins are bundled into tiny vesicles that bud
from the ER and carry them to the Golgi apparatus.
The Golgi apparatus modifies, sorts, and packages proteins and other materials from
the ER for storage in the cell or release outside the cell. It is somewhat like a
customization shop, where the finishing touches are put on proteins before they are
ready to leave the “factory.” From the Golgi apparatus, proteins are “shipped” to their
final destination inside or outside the cell.
Organelles That Capture and Release Energy
1. Chloroplast - solar panels and cafeteria
2. Mitochondria – power houses
Chloroplast
Plants and some other organisms contain chloroplasts. Chloroplasts are the biological
equivalents of solar power plants. They capture the energy from sunlight and convert it
into food that contains chemical energy in a process called photosynthesis.
*NOTE: Chloroplasts DO NOT MAKE ENERGY- they make sugar which is used by the
mitochondria to make chemical energy.
Mitochondria
Nearly all eukaryotic cells, including plants, contain
mitochondria. Mitochondria are the power plants of
the cell. They convert the chemical energy stored in
food into energy-rich compounds that are more convenient for the cell to use. This is
called: cellular respiration!
Cell Boundaries
Similarly, cells are surrounded by a barrier known as the cell membrane. Many cells,
including most prokaryotes and plant cells, also produce a strong supporting layer
around the membrane known as a cell wall.
Cell Walls
The main function of the cell wall is to provide support and protection for the cell.
Prokaryotes, plants, algae, and fungi have cell walls. Animal cells do not have cell walls.
Cell walls lie outside the cell membrane and most are porous enough to allow water,
oxygen, carbon dioxide, and certain other substances to pass through easily.
Cell Membranes
All cells contain a cell membrane that regulates what enters and leaves the cell and
also protects and supports the cell. A double-layered sheet called a lipid bilayer, a
flexible structure and forms a strong barrier between the cell and its surroundings.
The Properties of Lipids
Many lipids have oily fatty acid chains attached to chemical groups that interact
strongly with water. The fatty acid portions of such a lipid are hydrophobic, or “waterhating,” while the opposite end of the molecule is hydrophilic, or “water-loving.”
The head groups of lipids in a bilayer are exposed to water, while the fatty acid tails
form an oily layer inside the membrane from which water is excluded.
The Fluid Mosaic Model
Most cell membranes contain protein molecules that are embedded in the lipid bilayer.
Carbohydrate molecules are attached to many of these proteins.
Because the proteins embedded in the lipid bilayer can move around and “float”
among the lipids, and because so many different kinds of molecules make up the cell
membrane, scientists describe the cell membrane as a “fluid mosaic.”
Some of the proteins form channels and pumps that help to move material across the
cell membrane. Many of the carbohydrate molecules act like chemical identification
cards, allowing individual cells to identify one another.
 Although many substances can cross biological membranes, some are too large
or too strongly charged to cross the lipid bilayer.
 If a substance is able to cross a membrane, the membrane is said to be
permeable to it.
 A membrane is impermeable to substances that cannot pass across it.
 Most biological membranes are selectively permeable, meaning that some
substances can pass across them and others cannot. Selectively permeable
membranes are also called semipermeable membranes.
Add these too:
centrioles
lysosomes
endoplasmic reticulum (ER)
golgi apparatus
flagella/cilia
cytoskeleton
Answer Key
Cells and Their Organelles
The cell is the basic unit of life. The following is a glossary of animal cell terms. All cells are
surrounded by a cell membrane. The cell membrane is semipermeable, allowing some
substances to pass into the cell and blocking others. It is composed of a double layer of
phospholipids and embedded proteins. Plant cells have an additional layer surrounding them
called the cell wall. The cell wall is made of nonliving materials called cellulose. The
centrosome (also called the :microtubule organizing center”) is a small body located near the
nucleus. The centrosome is where microtubules are made. During cell division (mitosis), the
centrosome divides and the two parts move to opposite sides of the dividing cell. The centriole
is the dense center of the centrosome. Only animal cells have centrosomes. Microtubules are
shaped like soda straws and give the nucleus its shape.
1. At what level of organization does life begin? cellular
2. What surrounds all cells? Cell membrane
3. What is meant by semipermeable? Some substances are able to pass into the cell, but
not everything.
4. What 2 things make up the cell membrane? Phospholipids and embedded proteins
5. The cell membrane is also called the __p___ ___l__ ___a__ __s___ __m___ ___a__ membrane.
6. Centrioles are found inside of what type of cell? animal
7. What additional layer is found around the outside of plant cells and bacteria? Cell wall
8. Centrioles are found at the center of the
___c__ __e___ __n___ __t___ __r___ __o___ ___s__ __o___ __m___ __e___.
The nucleus in the center of a cell is a spherical body containing the nucleolus that makes
ribosomes. The nucleus controls many of the functions of the cell (by controlling protein
synthesis). It also contains DNA assembled into chromosomes. The nucleus is surrounded by
the nuclear membrane. Materials can move from the nucleus to the cytoplasm through nuclear
pores in the membrane around the nucleus. Cytoplasm is the jellylike material outside the cell
nucleus in which the organelles are located. All cells, even prokaryotes contain small bodies
called ribosomes. Proteins are made here by a process called protein synthesis.
9. Where is DNA found inside a cell? nucleus
10. What cell process is controlled by the nucleus? Protein synthesis
11. DNA coils tightly during division and assembles into visible
___c__ __h___ _r____ __o___ __m___ __o___ __s___ __o___ __m___ ___e__ ___s__
12. Where are organelles located? cytoplasm
13. Where are proteins made in a cell? ribosomes
14. Do all cells need ribosomes? yes
15. The process of making proteins is called. Protein synthesis
Rough endoplasmic reticulum (rough ER) is a vast system of interconnected, membranous,
infolded and convoluted sacks that are located in the cell’s cytoplasm. The ER is continuous with
the outer nuclear membrane. Rough ER is covered with ribosomes that give it a rough
appearance. Rough ER transports materials through the cell and produces proteins in sacks
called cristern which are sent to the Golgi body, or inserted into the layered, sac-like organelle
that looks like a stack of pancakes. The Golgi body modifies and packages proetins and
carbohydrates into membrane-bound vesicles for “export” from the cell. Smooth ER does NOT
have ribosomes on its surface. It makes proteins and lipids that will be exported by the cell. It
also controls the calcium level in muscles and detoxifies poisons, alcohol, and drugs.
16. How does rough ER differ from smooth ER? The rough ER is covered with ribosomes
and the smooth ER does not have ribosomes on it.
17. Rough ER is connected to the___nuclear________________________ membrane and to the
________smooth__________________ ER.
18. Proteins made by rough ER travel to the Golgi in sacks called
________vesicles___________________. Golgi ____modifies_________________ and
_packages_______________________ proteins for export out of the cell.
19. Give 3 jobs of the smooth ER.
a. __make lipids____________________________________
b. _______________makes proteins_______________________
c. _controls the calcium level in muscles and detoxifies poisins, alcohol and
drugs_____________________________________
Chloroplasts are elongated or disc- shaped organelles containing chlorophyll that trop sunlight
for energy. Photosynthesis (in which energy from sunlight is converted into chemical energyfood) takes place in the chloroplasts. Only plant cell, not animal cells, can make their own food.
Cells also contain fluid-filled sacs called vacuoles. The vacuole fills with food being digested and
waste material that is on its way out of the cell. In plant cells, a large central vacuole takes up
most of the space in the cell. Mitochondria are spherical to rod-shaped organelles with a double
membrane. The inner membrane is infolded many times, forming a series of projections called
cristae. The mitochondrion converts the energy stored in glucose into ATP (adenosine
triphosphate) for the cell. Both plant and animal cells have double membranes and their own
DNA. Cells also contain spherical organelles called lysosomes that contain digestive enzymes.
Nutrients are digested by the cell here, as well as, old cell organelles that are going to be recycled.
20. What process takes place inside chloroplasts? photosynthesis
21. What is the energy for this process? sunlight
22. What pigments traps the energy? chlorophyll
23. Chloroplasts are found in what type of cell(s)? plant
24. Both chloroplasts and mitochrondria are lake in that they both have
__double________________________ membranes and their own DNA.
25. Food, water, and wastes are stored inside _vacuoles________________________________.
26. Digestion takes place inside ____lysosmes_______________________________ containing
__digestive enzymes_____________________________________________.
27. The largest organelle in plants is the ______central vacuole__________
28. What organelle breaks down and recycles worn out cells? ________lysosome_______