Biology Lab
Which provides the largest field of view, the 10X or 40X objective?
10X low-power objective
How much more area can you see with the 4X objective than with the 40X objective?
About 100 times as much total area
In which solvent are liquids most soluble?
Acetone
How do shape and body consistency differ between Amoeba and Paramecium?
Amoeba body is more fluid; Paramecium body is rigid but somewhat flexible.
What structures visible in the stained preparation were invisible in the unstained preparation?
Amyloplasts especially; also nuclei are more visible; vacuoles
What is the approximate size of a nucleus?
Approximately 0.3-5.0 mm in diameter
Why is the granular-appearing cytoplasm more apparent at the sides of the cell rather than in the middle?
Because the vacuole occupies the center of the cell
Why is it more difficult to locate an object starting with the high-power objective than with the low-power objective?
Because you can only see part of the organism in the smaller field of view with high-power
What happens to the brightness of the view when you go from 4X to 10X?
Brightness decreases
What cellular structures of onion are more easily seen in stained as compared to unstained preparations?
Cell wall, nuclei, vacuoles
What organelles visible in Spirogyra are not visible in Amoeba and Paramecium?
Cell walls and chloroplasts
What are the functions of plasmodesmata?
Connects protoplasm of adjacent cells
Describe color changes in the two bags and their surrounding solutions.
Contents of starch bag appears blue, surrounding solution appears clear; phenolphthalein bag appears red, surrounding solution appears clear
What was the purpose of tube 7? (cell membrane)
Control
What are the functions of nuclei?
Control center of cell; storehouse of genetic information (DNA)
Approximately how long and wide is a brine shrimp?
Dimensions are about 0.2 mm or slightly more
What other differences are there between compound and dissecting microscopes?
Dissecting, three dimensional field vs. two dimensional field for compound. Dissecting larger working distance.
How does the direction of illumination differ in dissecting as opposed to compound microscopes?
Dissection illumination is reflective rather than transmitted.
Where are the pigments located in the cyanobacteria?
Distributed uniformly in cytoplasm
Use your results for tubes 4-7 to construct a line graph of Enzyme Activity versus Time on graph paper provided at the end of the exercise. Your graph will include four curves.
Each graph will be different according to results.
Which contains more protein (C-N bonds), egg albumen or honey? How can you tell?
Egg, because the Biuret reagent becomes purple
Why do Elodea and onion cells have more consistent shapes than human epithelial cells?
Elodea and onion cells function similarly, while human epithelial cells have more than one function depending on location.
In what shapes are the cells?
Elongate, rectangular boxes
What were the enzyme, substrate, and product of the enzymatic reaction
Enzyme = catechol oxidase; substrate = catechol; product = benzoquinone
What other solvents might be interesting to test in this experiment?
Ethanol, long chain alcohols, or other suggestions by students
Examine various layers of cells by focusing up and down through the layers. About how many cells thick is the leaf that you are observing?
Few cell layers, depends on leaf
Which of these two genera has the most prominent mucilaginous sheath?
Gloeocapsa
Which is a reducing sugar, sucrose or glucose? How do you know?
Glucose, because it reduces the Benedict's reagent to a green to reddish orange color
Which magnifications require the most illumination for best clarity and contrast?
High-power
The concentration of solvent affects its ability to dissolve lipids. Based on your results, did the highest concentration of both solvents cause the most damage?
Highest solvent concentration caused the most damage
How do the size and shape of a human epithelial cell differ from those of the Elodea and onion cells that you examined earlier?
Human cells are not a consistent shape.
How does the image move when the slide is moved to the right or left? Toward you or away from you?
In the opposite direction
How does the image through a dissecting microscope move when the specimen is moved to the right or left? Toward you or away from you?
In the same direction
Over what range of temperatures tested was catechol oxidase active? Should other temperatures be tested to more accurately determine the range of activity?
It varies with each group, but we have found at least some activity across all treatments except 100 C, and often have surprisingly high activity at very cold temperatures. A larger sample size with more tested temperatures would indeed plot a more accurate curve with less interpolation between points.
How does the size of Lactobacillus cells compare with that of Oscillatoria and Gloeocapsa?
Lactobacillus is smaller than Oscillatoria and Gloeocapsa.
Use an ocular micrometer or the dimensions of the field of view (FOV) calculated in Exercise 3 to measure the dimensions of an onion epidermal cell. Are these cells larger or smaller than the Elodea cells you examined in Procedure 4.3?
Larger
What do you conclude about the solubility of lipids in polar solvents such as water? In nonpolar solvents such as acetone?
Lipids are insoluble in polar solvents. Lipids are soluble in nonpolar solvents.
Which objective, high or low power, provides the greatest depth of field?
Low power
Which objective should you use to initially locate the specimen? Why?
Low-power objective because the field of view is much larger with low power
What structures in Amoeba and Paramecium also occur in plant cells? What structures in Amoeba and Parameciumdo not occur in plant cells?
Mitochondria, nuclei, and endoplasmic reticulum occur in plant cells. A contractile vacuole and pellicle do not occur in plant cells.
Write a hypothesis and a null hypothesis for the effect of temperature on catechol oxidase activity.
My hypothesis for the effect of temperature on catechol oxidase activity is that the activity of the catalase decreases in response to a change in the optimal pH. On the other hand, my null hypothesis is that the catalase activity will not be affected at any pH range.
Are any cellular structures other than amyloplasts stained intensely by iodine
No
Are nuclei visible in cyanobacterial cells?
No
Do free amino acids have peptide bonds?
No
Is salad oil soluble in water?
No
Is the image always best with highest illumination?
No
Is the same level of illumination best for all magnifications?
No
Can all three threads be in focus at the same time using the high-power objective?
No, because high-power has a very thin (narrow) depth of field
Do onion cells have chloroplasts? Explain.
No, because the function of these cells is not photosynthesis; it is food storage
Does Amoeba have a cell wall? How can you tell?
No; rapidly changing shape would be impossible with cell wall
Are all cellular components moving in the same direction and rate during cytoplasmic streaming?
Not necessarily
What do you conclude about the uniformity of cytoplasmic streaming?
Not necessarily uniform
Which are larger, chloroplasts or nuclei?
Nuclei
How do you explain the differences in the apparent shapes and positions of the nuclei in different cells?
Nuclei are mobile and move in the three dimensions of the cytoplasm.
How many times is the image of the e magnified when viewed through the high-power objective?
Ocular (usually 10X) times objective lens (usually 40X) = 400X
Were mitochondria as abundant in human epithelial cells as in onion epidermal cells (procedure 4.6)? Explain.
Onion epidermal had more mitochondria. Human epithelium is far less metabolically active.
Which contains more reducing sugars, potato juice or onion juice? How do you know?
Onion, because the reaction with Benedict's is more intense
What does this tell you about how sugars are stored in onions and potatoes?
Onions store reducing sugars, while potatoes store non-reducing sugars in addition to their starch.
How does movement of Paramecium compare to that of Amoeba?
Paramecium move faster, smoother
List the organelles found in plant cells, in Amoeba, and common to both.
Plant: nucleus, vacuole, plastids, cell wall, mitochondria, cytoplasm Animal: nucleus, cytoplasm, mitochondria Shared: nucleus, cytoplasm, mitochondria
Which of the solutions is a positive control? Negative control?
Positive is tube 6, reducing sugar; negative is tube 5, distilled water, and tube 7, starch.
Why are potatoes a good source of carbohydrates?
Potatoes store large amounts of starch in the edible, underground tuber for the rest of the plant.
Which colors more intensely, onion juice or potato juice? Why?
Potatoes, Potatoes store much starch; onions store less starch.
How do the appearances of Amoeba differ in live cells and preserved cells?
Preserved cells are stained; live cells may be contracted; cilia are less visible in preserved specimens.
What are the functions of carbohydrates in living organisms?
Primarily rapidly-accessible energy storage (glycogen, starch, sugars), and strong structural polysaccharides (cellulose)
What are the functions of the cell wall?
Protection; support; prevents cell from bursting when placed in hypotonic environment
What are the functions of proteins in living organisms?
Proteins are necessary for maintenance of body tissue, including development and repair. Works a major source of energy and is involved in the synthesis of hormones.
What shape are the chloroplasts? What is their function?
Rather spherical, or squashed, irregular spheres; to store starch
What three-dimensional shape are Elodea cells?
Rectangular boxes
Use your results to argue for or against the statement, "Catechol oxidase functions equally and efficiently at various temperatures."
Results should show that enzymes do not function equally well at different temperatures as demonstrated by the different amounts of benzoquinone produced in each treatment.
Place a microscope slide of the letter e on the stage as you view the letter e, how is it oriented?
Right-side up
What similarities and differences are there between plant and animal cells?
Similarities: cell membrane, nuclei, basic organelles Differences: cell wall, vacuole, plastids
What characteristic distinguishes those molecules and ions passing through the membrane from those that do not pass through the membrane?
Size of the molecule
Why was each tube left undisturbed for 5 minutes in step 6 of procedure 11.1?
So the liquid in the tube could equilibrate to the proper temperature
For which molecules and ions (phenolphthalein, iodine, starch, Na+, OH-) does your experiment give evidence for passage through the semipermeable membrane?
Sodium ion, hydroxyl ion, and iodine pass through
What can you conclude about the location of starch in storage cells of potato
Starch is in amyloplasts.
In what parts of a plant is the most starch typically stored?
Stems, roots and fruit
What are the functions of amyloplasts in potatoes?
Storage of starch
Examine figure 6.8. What are the reactive groups of the fatty acids?
The OH of the carboxyl group
Use an ocular micrometer or refer to the dimensions of the field of view calculated in Exercise 3 to measure the dimensions of an Elodea cell. What are the cell's approximate dimensions?
The cells are approximately 30 mm wide and 70 mm long.
Which of the solutions is a positive control? Which is a negative control? (egg albumen and honey)
The solution in Tube 5, the protein solution, is the positive control. The solution in Tube 4, the distilled water, is the negative control.
Which of the solutions is a positive control? Which is a negative control? (onion juice and potato juice)
The solution in Tube 7, the starch solution, is the positive control. The solution in Tube 5, the distilled water, is the negative control.
Why do you suspect that there are so many plasmodesmata connecting the cells in this fruit?
There are a lot of nutritive cells in this plant and the plasmodesmata connect all cells within the plant.
Based on your results, which damages membranes more: 50% methanol or 25% acetone?
These two treatments often haven similar results
How many cells are held within one sheath of Gloeocapsa
Three or four
Why is it important to put a coverslip over the drop of water when you prepare a wet mount?
To protect the objective lens
Explain the results observed for tubes 1-3. What was the purpose of these tubes?
Tube 1 was a control for any changes that might occur in only distilled water; tube 2 was a control for any changes that might occur spontaneously in catechol; tube 3 was a control for any changes that might occur spontaneously by the enzyme in the potato extract even without its substrate (catechol) present.
How accurate were your hypothesized rankings for the temperature treatments?
Typically the predictions are quite accurate.
Is Spirogyra branched or unbranched?
Unbranched
As you view the letter e, how is it oriented? Upside down or right side up?
Upside-down if "e" was placed on the stage right-side up
Which of the available stains enhanced your observations the most?
Usually methylene blue
Where are the chloroplasts located within the Elodea cell—toward the perimeter or center of the cell?
Usually toward the perimeter
What is the area of the field of view when you use the lowest magnification of your dissecting microscope?
Varies among microscope oculars and objectives
What is the area when you use the highest magnification?
Varies among microscopes oculars and objectives
Does your data support or refute your hypotheses?
Various answer choices
Are all three colored threads in focus at low power?
Yes
Based on your results, are lipids soluble in both acetone and methanol?
Yes
Can you see nuclei in the Elodea cells?
Yes
Do the cells have a cell wall? If so, how can you tell?
Yes, the outer edges are noticeable thickened
If you didn't already know what you were looking at, could you determine at this magnification that you were looking at a letter e? How?
Yes, with difficulty. You could move the slide and view one piece at a time and deduce its overall shape.
