Download Module Homework # 2 Smooth Endoplasmic Reticulum.

Module Homework # 2
1. Smooth Endoplasmic Reticulum.
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Function: It serves as a channel for the transport of proteins and other materials in and
out of the nucleus and provides some structural support for the cell. Sometimes the
endoplasmic reticulum will accumulate large masses of proteins and act as a storage
area.
2. Rough Endoplasmic Reticulum.
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Function: Rough endoplasmic reticulum has the ribosomes studding the outer
membrane, which gives it a course appearance.
3. Nucleolus
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Function: Nucleolus exists inside the nucleus. Each nucleolus is a small round dense
body. The nucleolus takes part in protein synthesis and manufactures ribosomes that
are made up of ribonucleic acid (RNA) and protein.
4. Nucleus
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Function: The nucleus is the most important structure within the cell. Usually located
near the center of the cell, it is the control center for most cell activity, and it is from
within the nucleus that cell division is initiated.
5. Chromatin
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Function: Chromatin is the complex combination of DNA and proteins that makes up
chromosomes. It is found inside the nuclei of eukaryotic cells. The functions of
chromatin are to package DNA into a smaller volume to fit in the cell, to strengthen
the DNA to allow mitosis and meiosis, and to serve as a mechanism to control
expression and DNA replication. Chromatin contains genetic material-instructions to
direct cell functions.
6. Ribosomes
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Function: Ribosomes move out to the cytoplasmic area, where they can be found
attached to the walls of the endoplasmic reticulum, floating freely in the cytoplasm,
or formed into clusters called polyribosomes. Ribosomes, among the smallest of cell
structures, are commonly referred to as the protein factories of the cell because their
function is one of the most important.
7. Cytoplasm
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Function: The cytoplasm, often thought of as the body of the cell, is a sticky
semifluid material found between the nucleus and the cell membrane. It may be
divided into two layers: an outer layer known as the ectoplasm, and an inner layer
known as the endoplasm. Chemical analysis of the cytoplasm shows that it is made up
of proteins, lipids, carbohydrates, minerals, salts, and a great deal of water (70% to
90%). Each of these substances varies greatly from one cell to the next and from one
organism to the next. The cytoplasm is the background for all the chemical reactions
that take place in a cell, such as protein synthesis and cellular respiration. Molecules
are transported around the cell by the circular motion of the cytoplasm (cyclosis).
Embedded in the cytoplasm are organelles, or cell structures, that help a cell to
function. These include the nucleus, mitochondria, ribosomes, Golgi apparatus,
endoplasmic reticulum, lysosomes, and the centriole.
8. Lysosome
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Function: Lysosomes are spherical bodies that originated in the Golgi apparatus and
are found in the cellular cytoplasm. They contain powerful digestive enzymes that
digest protein molecules. Their enzyme, Lysozyme, is capable of breaking down
foreign materials. The lysosome thus helps to digest old, worn – out cells, bacteria,
and foreign matter. Lysozyme can also digest old, broken down parts of the cell as
well as destroy the whole cell by a process known as autolysis. If a lysosome should
rupture, as sometimes happens, the lysosome will start digesting the cell’s proteins,
causing it to die. For this reason, lysosomes are sometimes also known as “suicide
bags.”
9. Vacuole
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A vacuole is a membrane organelle which is present in all plant and fungal cells and
some protist, animal and bacterial cells. The function and importance of vacuoles
varies greatly according to the type of cell in which they are present, having much
greater prominence in the cells of plants, fungi and certain protists than those of
animals and bacteria. In general, the functions of the vacuole include: Isolating
materials that might be harmful or a threat to the cell, containing waste products,
maintaining internal hydrostatic pressure or turgor within the cell, maintaining an
acidic internal pH, containing small molecules, exporting unwanted substances from
the cell, and allows plants to support structures such as leaves and flowers due to the
pressure of the central vacuole
10. Cell membrane
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Function: The cell membrane, sometimes called a plasma membrane, separates a
cell’s cytoplasm from its external environment and from the neighboring cells. It also
regulates the passage or transport of certain molecules into and out of the cell, while
preventing the passage of others. This is why the cell membrane is often called a
“selective semipermeable membrane.” The cell membrane is made up of a double
layer of phospholipid molecules (phospholipid bilayer) with protein molecules
embedded in the lipid layers. It is these molecules that regulate the passage of
nutrients and waste into and out of the cell.
11. Mitochondrion
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Function: This is where all of the cells energy comes from. Mitochondria (singular,
mitochondrion; mito means “thread,” chondrion means “granule”). These
mitochondria vary in shape and number. There can be as few as a single one in each
cell or as many as a thousand or more. Cells that need the most energy have the
greatest number of mitochondria. Energy, in the form of adenosine triphosphate
(ATP), is organized in the mitochondria and released to all parts of the cell as needed.
Because they supply the cell’s energy, mitochondria are also known as the
“powerhouse” of the cell.
12. Lysosomes
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Function: Lysosomes are oval or spherical bodies that originated in the Golgi
apparatus and are found in the cellular cytoplasm. They contain powerful digestive
enzymes that digest protein molecules.
13. Golgi apparatus
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The Golgi apparatus was discovered in 1898 by the Italian scientist, Camillo Golgi. It
is also called the Golgi bodies or the Golgi complex. It is an arrangement of layers of
membranes resembling a “stack of pancakes.” Scientists believe that this organelle
synthesizes carbohydrates and combines them with protein molecules as they pass
through the Golgi apparatus. In this way, the Golgi apparatus stores and packages
secretions for discharge from the cell. It follows logically that these organelles are
abundant in the cells of gastric glands, salivary glands, and pancreatic glands.
14. Pinocytic vesicle
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Function: Large molecules such as protein and lipids, which cannot pass through the
cell membrane, will enter a cell by way of the Pinocytic vesicles. The Pinocytic
vesicles form by having the cell membrane fold inward to form a pocket. Some of the
fluid surrounding the cell flows into this pocket. The fluid contains large molecules in
solution. The edges of the pocket then close and pinch away from the cell membrane,
forming a bubble or vacuole in the cytoplasm. The contents of the vacuole are
separated from the cytoplasm by a cell membrane. This process by which a cell forms
Pinocytic vesicles to take in large molecules is called pinocytosis or “cell drinking.”
15. Centrioles
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A centriole is a barrel-shaped cell structure found in most animal eukaryotic cells,
though absent in higher plants and most fungi. Centrioles are involved in the
organization of the mitotic spindle and in the completion of cytokinesis.
16. Diffusion
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Diffusion is a physical process whereby molecules of gases, liquids, or solid particles
spread or scatter themselves evenly through a medium. When solid particles are
dissolved within a fluid, they are known as solutes. Diffusion also applies to a slightly
different process, in which solutes and water pass across a membrane to distribute
themselves evenly throughout the two fluids, which remain separated by the
membrane. Generally, molecules move from an area in which they are greatly
concentrated to an area in which they are less concentrated. The molecules will,
finally, distribute themselves evenly within the space available; when this happens,
the molecules are said to be in a state of equilibrium. Molecules will diffuse more
quickly in gases and more slowly in solids. Diffusion occurs due to the heat energy of
molecules. As a result, molecules are always in constant motion, except at absolute
zero (-273*C). In all cases, the movement of molecules increases with an increase in
temperature. The diffusion rate of molecules in the various media (gas, liquid, and
solid) depends upon the distances between each molecule and how freely they can
move. In a gas, molecules can move more freely and quickly; within a liquid,
molecules are more tightly held together. Diffusion plays a vital role in permitting
molecules to enter and leave a cell. Oxygen diffuses from the bloodstream, where it
dwells in greater concentration. From the blood stream, the oxygen enters the fluid
surrounding a cell, then into the cell itself, where it is far less concentrated. In this
manner, the flow of blood through the lungs and bloodstream provides a continuous
supply of oxygen to the cells. Once oxygen has entered a cell, it is utilized in
metabolic activities.
17. Osmosis
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Osmosis is the diffusion of water through a selective permeable membrane (such as
the cell membrane) from an area of greater concentration of water to an area of lesser
concentration. A selective permeable membrane is any membrane through which
some solutes can diffuse, but others cannot. Osmotic pressure, which is the pressure
exerted by water molecules within a casing at equilibrium, is dependent upon the
number of molecules of solute dissolved in a solution. The higher the osmotic
pressure (osmolality) of a solution, the greater the number of molecules in that
solution; and the greater the concentration of molecules, the stronger the “pull” or
attraction for water molecules. Therefore, water molecules move toward the area of
greater osmolality. In physiology, the osmotic characteristics of solutions are
determined by the manner in which they affect red blood cells. In other words, the
osmolality of a given solution is compared with that of blood plasma.
18. Filtration
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Filtration is the movement of solutes and water across a semipermeable membrane,
resulting from some mechanical force such as blood pressure or gravity. The solutes
and water move from an area of higher pressure to an area of lower pressure. The size
of the membrane pores determines which molecules are to be filtered. Thus, filtration
allows for the separation of large and small molecules. Such filtration takes place in
the kidneys. The process allows for the separation of large and small molecules to
remain within the body and smaller ones to be excreted as waste.
19. Active Transport
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Active Transport is a process in which molecules move across the cell membrane
from an area of lower concentration, against a concentration gradient, to an area of
higher concentration. This process requires the high – energy compound ATP. The
ATP is supplied by the cell membrane. One theory of the process of active transport
suggests that a molecule is picked up from the outside of the cell membrane and
brought inside by a carrier molecule. Both molecule and carrier are bound together,
forming a temporary carrier – molecule complex. This carrier – molecule complex
shuttles across the cell membrane; the molecule is released at the inner surface of the
membrane. From here it enters the cytoplasm. At this point, the carrier acquires
energy at the inner surface of the cell membrane. Then it returns to the outer surface
of the cell membrane to pick up another molecule for transport. Accordingly, the
carrier can also convey molecules in the opposite direction from the inside to the
outside.
20. You are trying to explain to a fellow student the information in Figure # 5.7 on page 91
of your textbook. Why does the water move in the direction indicated in Figures A & C?
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The figure illustrates the process of osmosis. Before the explanation of this
experiment begins, it is important to understand 3 of the terms that will be used in the
explanation of the illustration.
a. Hypertonic Solution
A hypertonic solution contains a greater concentration of impermeable
solutes than the solution on the other side of the membrane. When a cell’s
cytoplasm is bathed in a hypertonic solution the water will be drawn into the
solution and out of the cell by osmosis. If water molecules continue to
diffuse out of the cell, it will cause the cell to shrink.
b. Hypotonic Solution
A hypotonic solution contains a lesser concentration of impermeable solutes
than the solution on the other side of the membrane. When a cell’s cytoplasm
is bathed in a hypotonic solution the water will be drawn out of the solution
and into the cell by osmosis. If water molecules continue to diffuse into the
cell, it will cause the cell to swell and possibly burst.
c. Isotonic Solution
Isotonic solutions contain equal concentrations of impermeable solutes on
both sides of the membrane.
We have 3 red blood cells in three solutions. In jar A, we have a 0.1% saline hypotonic
solution, in jar B we have a 0.85% saline isotonic solution, and in jar 1.0% we have
saline hypertonic solution. The red blood cell in jar A has a greater concentration of
salt in the red blood cells, thus water moves into the red blood cells to try to equalize
the salt concentrations on both sides of the red – cell membrane. The red cell swells
with the added water and it will eventually burst, releasing the contents of the cell
into the water.
In the hypertonic solution, because the salt concentration is greater in the saline solution,
water rushes out of the red cell, causing it to shrivel up and become crenated.
Therefore, in a hypotonic solution, the osmolality is lower than that of blood plasma, and
the red blood cell will swell and burst. This is caused by water molecules moving into
the cell. However, a red blood cell placed inside a hypertonic solution, such as
seawater (with a higher osmolality than that of blood plasma, will shrink and wrinkle
up because of the water moving out of the cell.