Download Laboratory 4: Cell Structure and Function

Bio 120 Laboratory 4: Cells and Tissues
Cells are the basic structural and functional unit of all organisms. Cells differ
enormously in size, shape, and function; some are free living, independent organisms,
while others are immovably fixed as part of tissues of multicellular organisms.
All cells exchange materials with their immediate environment and therefore have a
plasma membrane that controls which substances are exchanged by allowing some
materials to pass through it while slowing or stopping others. The cytoplasm is protected
from the environment, yet still can exchange materials with it. Within the cytoplasm,
cells differ in the type and number of organelles.
Prokaryotic cells (bacteria) have the simplest structure with each independent cell
lacking any internal membrane organelles, including the lack of a nuclear membrane to
separate the genetic chromosome material from the rest of the cytoplasm.
More typical and more specialized are the eukaryotic cells, with a double nuclear
membrane and membrane organelles specialized to fit their function. Since no one cell
would have all organelles possible, observing a variety of animal cells will give you an
idea of the similarities and differences among cells.
Part 1: Eukaryotic Cells
A. Animal cells
We will examine a few examples of animal cells. All animal cells are eukaryotic,
therefore they, have a nucleus and other membrane bound organelles including
mitochondria.
Procedure 1: Examining Human Epithelial Cells
Step 1: Using the broad end of a toothpick, gently scrape the inside of your cheek, then
scrape the cells onto the slide
Step 2: Place one small drop of methylene blue dye on the microscope slide over the cells.
Step 3: Place cover slip, examine under compound microscope, going up to 400x
magnification
Step 4: Sketch the cells you see under 400x magnification
Questions:
What structures were visible in the stained slides?
_____________________________________________________________
What is the function of these structures?
____________________________________________________________
Procedure 2: Examining the effect of salt on blood cells
There are three terms describe the concentration of solutes outside of a cell:
Hypertonic: Concentration of solutes outside cell is greater than in side
Isotonic: Inside and outside have same conc.
Hypotonic: Outside the cell the concentration of solutes is lower than outside.
Step 1: Place one small drop of sheep’s blood onto a microscope slide
Step 2: Place one drop of saturated saline solution on top of the sheep’s blood
Step 3: Place coverslip on the slide, then observe under the microscope, going up to 400x
magnification
Step 4: Sketch the blood cells
Repeat this procedure using distilled water and then using the isotonic solution.
Questions:
1. When you added the saturated saline solution did you create a hypotonic, isotonic, or
hypertonic situation?
_______________________
2. Did the sheep’s blood cells swell up or shrink when the saturated saline solution was
applied to slide?.
_______________________
B. Elodea plant cells
Elodea is a flowering plant found in fresh water lakes and ponds. The leaves, unlike
those of many terrestrial plants, are only one or two cells layers thick, and therefore
enough light can penetrate the leaf for direct microscopic examination.
The most obvious organelles of the Elodea leaf cells are the numerous green chloroplasts.
These organelles perform photosynthesis for the plant. Photosynthesis is how the plant
creates sugar from water and carbon dioxide using the sun’s energy. The organells in the
cytoplasm are not stationary, they can move. The movement of organelles like
chloroplasts is cyclosis.
Procedure 3: Examining Elodea cells
Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
Place a leaf of Elodea on a clean slide.
Cover with one or two drops of isotonic water and add a coverslip.
Examine the cells under low and high power
Sketch the cells below, labeling any organelles seen.
Warm the slide up for about 10 minutes using high light intensity.
Now re-examine the slide, looking for cyclosis.
Questions:
1. What is the function of the cell wall?
_____________________________________________________________
2. Why do plant cells also need a plasma membrane?
_____________________________________________________________
3. Can you see signs of cyclosis?
_____________________________________________________________
Procedure 4: Examining Elodea cells in salt solution.
Step 1:
Step 2:
Step 3:
Step 4:
Place a leaf of Elodea on a clean slide.
Cover with one or two drops of saturated saline solution and add a coverslip.
Examine the cells under low and high power
Sketch the cells below, labeling any organelles seen.
Questions:
What has happened to the volume of cytoplasm within these cells? And Why?
_____________________________________________________________
Which of the three terms (hypotonic, isotonic, or hypertonic) best describes the
environment in relation to the Elodea cells after the salt solution was
added?___________________________
C. Plant cells -Potato Cells
Amyloplasts are organelles where starch is stored in plants. We will use iodine here to
stain the starch in the amyloplasts.
Procedure 5: Examining potato cells
Step 1: Cut a very thin a slice of potato using a scalpel.
Step 2: Place it on a slide and add a few drops of Lugol's iodine, then cover with a
coverslip.
Step 3: Using low power, examine the cells for dark-stained bodies within the cells of
the potato. These are amyloplasts that contain starch. The transparent membrane
and wall can faintly be seen.
Step 4: Sketch and label any organelles seen.
Question: Do you think potatoes are a good source of carbohydrates? _______________
Part 2: Tissues
There are four categories of tissues:
1.
2.
3.
4.
Connective tissue, - binds and supports the body.
Muscle tissue - moves the body and its parts.
Nervous tissue - receives stimuli and conducts nerve impulses.
Epithelial tissue - covers body surfaces and lines the cavities of the body.
We will be viewing prepared slides and drawing sketches of the tissue types. Be aware
that the prepared slides may contain more than one tissue type therefore you must search
around the slide until you find the correct tissue type. Tissues we will view in lab:
Epithelial:
1.
2.
3.
4.
Simple Squamous Epithelial - diffusion
Stratified Squamous Epithelial - protection
Simple Columnar Epithelial – absorption and secretion
Simple Cuboidal Epithelial - absorption and secretion
Connective:
5.
6.
7.
8.
Areolar connective tissue – bind and keep organs in place
Hyaline cartilage - cushion
Adipose – store energy, insulation, protect organs
Bone – structure, produce blood cells, with muscle - movement, store calcium
Muscle
9. Skeletal (Striated) muscle - movement
Nervous tissue
10. Neurons and Neuroglia – neurons transmit messages and glial cells support the
neurons
Identify each tissue types and know the following structures or features or cells:
1. Be able to identify the nucleus of all cells
2. In epithelial tissue: Basement membrane
3. In bone tissue: osteocytes, lacuna, canaliculi, central canal
4. In hyaline cartilage: chondrocytes, lacuna
5. In nervous tissue: both neurons and neuroglial cells
6. In areolar connective tissue: fibroblast nuclei, collagen fibers, elastic fibers