7th Cell Organization
Cellular Organization
Investigation One
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Microscope:
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The total magnification used to view a slide can be calculated by multiplying the
power of the microscope’s eyepiece (10x) and the power of the objective used to
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view the specimen (either 4x, 10x, or 40x).
An oil immersion x100 lenses helps improve the image it produces by increasing the
amount of light it captures and sends up to the eyepiece for further magnification.
You are to use only the “fine focus” knob when using the 100x oil immersion lens.
Cells:
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Basic building blocks of life.
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Discovered by Robert Hooke
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Cells are the smallest structure of living things that can perform the functions
necessary for life. Living things are made of cells. Cells come from other living cells.
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Prokaryotic Cell
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Single Cell units that survive independently of each other.
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Prokaryotes have no distinct, membrane-bound nucleus. In prokaryotes, a DNAcontaining chromosome is loose in the cytoplasm.
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Prokaryotes have no distinct, membrane-bound organelles, which are functionally
distinct sub-compartments in the cytoplasm of eukaryotes.
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Prokaryotes are generally much smaller and harder to see in the microscope than
eukaryotes.
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Example: Bacteria, algae, amoeba,
Eukaryotic Cell
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Cells that are a part of plant or animal tissue
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Eukaryotes have a distinct, membrane-bound nucleus.
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Eukaryotes have distinct, membrane-bound organelles, which are functionally distinct
sub-compartments in the cytoplasm.
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Two Types of Eukaryotic Cells
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Plant Cells- usually square or rectangular shaped; when looking at in a
microscope can look similar to a brick wall
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Rigid Cell Wall, Chloroplasts, Large Central Vacuole
Animal Cells- usually spherical; contain no cell wall or chloroplasts, contains
small vacuoles
7th Cell Organization
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Organization- when multiple cells are organized together they begin to form tissues:
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Cell  Tissues  Organ  Organ System  Organisms
Focus Questions
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Can you identify the type of organism a cell comes from through observation? Explain
your answer.
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You were most likely unable to identify what type of organism a cell comes from
through observation. Without a significant amount of prior knowledge, a person may
have difficulty drawing conclusions based on what cell structures can or cannot be
viewed under a microscope. Most likely you were not able to differentiate between
unicellular and multicellular organisms.
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You need to have more information and an understanding of cells in order to
correctly identify specific cells.
Additional Post-Lab Information
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Why did you need to use a microscope? Cells are so small, they are impossible to see
without powerful magnification.
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At what magnification were you able to view cells? At a total magnification of 100X we
were able to view cells. When looking through a microscope, you look through two lenses, one
in the eyepiece and one in the objective. In order to calculate total magnification, the
magnification of the eyepiece must be multiplied by the magnification of the objective. For
example, when using the 10X objective on a microscope with a 10X eyepiece, the total
magnification is 100X.
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At what total magnification were you able to view cells with the greatest detail? Our
microscopes were able to enlarge the image of the cells to a magnification of 1000X, enabling
us to view the cells with the greatest detail.
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How did your view of the cells differ when different objectives were used? Each objective
offered a different field of view and resolution. The field of view is the total area observed
when viewing the specimen. The resolution is the ability to see fine details in the specimen. As
the objectives increased in their refractive power (4X, 10X, 40X, 100X) the field of view
decreased, but the resolution of the specimens increased.
7th Cell Organization
Investigation Two
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Through a light microscope the parts of the cell that are able to be seen are
 Nucleus
 Organelles
 Cell membrane
Wet Mount slide
1. Place small drop of solution on the specimen on a dry clean slide
2. Slowly place a clean coverslip over the specimen eliminating any bubbles
3. Gently tap coverslip to make sure that all bubbles are removed
Cross- Sectioning (Think of cutting in half)
Cross- Sectioning
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Longitudinal Sectioning (Think of peeling a thin layer off)
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Importance of Sectioning
 Knowing how the specimen was sectioned is
important because changing the sectioning can
change the appearance of the cell
 Observation of size, shape, and arrangement of cells
can be affected by the sectioning
 Cross section of celery reveals small holes
 Longitudinal sectioning will reveal long strips across the specimen
Staining
 Staining a specimen allows for various structures to be seen more easily
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Longitudinal
Specimens from the lab
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Did your cheek cells appear different from the prepared cheek cell slide? If so, in what
way? Cheek cell slide contained fewer cells or that the cells from their slide were a different
size than the cells on the prepared slide. Notice a distinct difference in the color of the cells.
The cells in their own slide were clear and did not contain much color. However, the cells
observed on the prepared slide were stained dark pink, with purple nuclei.
7th Cell Organization
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The prepared slide was stained. How did the staining affect your observations of the
cheek cells? The staining allowed students to observe the cheek cells more easily. The cells
were easier to locate on the slide, and students could easily observe the cells’ nuclei on the
prepared slide.
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Did the celery appear different depending on the way it was cut, or sectioned? Yes. When
a cross section of the celery was made, the celery was crescent-shaped. We were able to view
small circles scattered across the specimen where the string-like fibers were cut. When a
longitudinal section of the celery was made, it was long and rectangular. No small circles were
visible. Rather, long stripes stretched across the specimen.
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Did the longitudinal section slide appear different from the cross section slide of the corn
stem? How did this compare to the celery sectioning? Just as the celery appeared different
depending on the way it was sectioned, so the corn stem appeared differently.
Focus Questions
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How does staining affect the appearance of a specimen? Student answers will vary.
Staining of specimens may add artificial color to the cells to allow various structures to be
more easily viewed. For instance, the staining of the prepared cheek cell slide allowed
students to observe the cheek cells more easily. The cells were easier to locate on the slide,
and students could observe more detail in the cells on the prepared slide.
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How does sectioning affect the appearance of a specimen? Student answers will vary.
Observations of the size, shape, and arrangement of cells can be affected by the sectioning of
the specimen. Observations of the size, shape, and arrangement of cells were possibly
affected by the sectioning of the specimen. In order to conclusively answer this question,
students would need to compare each type of tissue sectioned in several different ways.
7th Cell Organization
Investigation Three
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Organelles- a cellular structure which has a specific function
Plant and animal cells share many of the same organelles with the exception of a few.
o Plant cells have additional organelles of cell wall, chloroplast, and a large central
vacuole
7th Cell Organization
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Models of plant and animal cells
7th Cell Organization
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Comparison of plant and animal cell organelles
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How are the structures in plant and animal cells similar to and different from each
other? Plant cells generally contain a nucleus, a cell wall, a cell membrane, chloroplasts and
cytoplasm. However, under a magnification of 1000X it is not possible to differentiate
between the cell wall and the cell membrane. In addition, not all plant cells contain
chloroplasts. Animal cells generally contain a nucleus, a cell membrane, and cytoplasm.
However, some animal cells, such as red blood cells, do not contain nuclei.
Are all cells from the same organism the same? No. Based on our observations of different
cells from the Elodea plant and human tissue, the cells in an organism may differ from tissue
to tissue.
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7th Cell Organization
Investigation Four
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Semipermeable Membrane- allows water molecules to freely pass through it. Solute
molecules, on the other hand, are not able to pass through the semipermeable membrane.
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The cell membrane of both plant and animal cells are semipermeable membranes.
o They separate the cell from its surrounding environment.
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The cell has a certain amount of dissolved solute in its cytoplasm.
o Depending on the concentration of solutes in the environment, water will either
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enter the cell from the outside or leave the cell.
Diffusion- moving from an area of high concentration to an area of lower concentration
until both areas are equal.
Osmosis- diffusion of water across a semipermeable membrane.
o High conc. to lower conc.
There are three different types of solutions based on the amount of solutes they contain.
o An isotonic solution has the same amount of dissolved solutes as found inside the
cell.
o A hypertonic solution has a higher concentration of dissolved solutes outside the
cell than inside the cell.
o A hypotonic solution contains a lower concentration of dissolved solutes outside
than inside the cell.
Osmosis causes water to move into or out of the cell depending on which of the three
types of solutions the cell is surrounded by.
o Isotonic Solution - Since there is the same amount of dissolved solute outside
and inside the cell there is no net movement of water into or out of the cell.
o Hypertonic Solution, there is more dissolved solute outside the cell than inside,
so water will leave the cell. It is as if the cell is trying to dilute the external solute
solution.
o Hypotonic Solution, there is less dissolved solute outside the cell than on the
inside. Therefore, water will begin to enter the cell.
Plant Cell Osmosis
7th Cell Organization
o Isotonic Conditions- no net water movement occurs. The arrows show that water
may move across the semipermeable cell membrane, but as much water that enters
the cell, the same amount exits.
o Hypertonic solution- water leaves the cell. As it does, the membrane pulls away
from the cell wall and “shrivels” up. This is because the cellular volume decreases
as the water leaves.
o Hypotonic solution- water begins to enter the plant cell. However, since the plant
cell has a ridge and strong cell wall, the amount of water that can enter is
counteracted by the force of the cell wall pushing against the further expansion of the
semipermeable cell membrane. This pressure is referred to as turgor pressure and
stops the plant cell from exploding in hypotonic solutions.
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Animal Cell Osmosis
o Isotonic conditions- no net movement. The arrows show that water may move across
the semipermeable cell membrane, but as much water that enters the cell, the same
amount exits.
o Hypertonic solution- water leaves the animal cell through its semipermeable
membrane. As cell volume decrease with water loss, the entire cell may shrivel.
Shifting the cell to an isotonic environment may reverse this process.
o Hypotonic solution- water from the environment rushes into the cell. The cell
membrane will expand and stretch to a limit and then, if the solute concentration
outside the cell is low enough, will eventually burst. This is sometimes referred to as
cell lysis. Once the cell lyses, returning to an isotonic solution cannot reverse the
damage.
7th Cell Organization
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Is the cell membrane of a plant cell permeable to salt? The cell membrane of a plant cell
is not permeable to salt. This was evidenced by the shrinking of cells. To balance the
concentration of salt within and outside the cell, water flowed from the cells into the
surrounding environment. If the cell membrane was permeable to salt, water and salt could
have both flowed back and forth through the cell membrane until both environments
contained equal concentrations of salt.
Are the cell wall and the cell membrane of a plant cell permeable to water? The cell wall
and cell membrane are permeable to water. This was also evidenced by the shrinking of cells.
To balance the concentration of salt inside and outside the cells, water flowed from the cells
into the surrounding environment. If the cell membrane were not permeable to water, the
cells would not have shrunk.
How does the structure of the cell wall and cell membrane affect the movement of
substances in and out of a cell? The structure of the cell wall and cell membrane determines
whether or not each structure is permeable to salt and water. The permeability of each
structure determines whether or not salt moves in a out, which in turn affects whether or not
water moves in and out of the cell.