AVERAGESOccasionally you will be required to find the average of data gatheredfrom an investigation. To find an average, add the items in the grouptogether and then divide the total by the number of items. Forexample, if there were five students of different ages—12,13,14,17,and 19—how would you find the average age of the group? Add thefive ages together and divide the total by 5, which is the number ofitems (students) in the group. What is the average age of this group ofstudents? Your answer should be 15 years old.

Figure 2

DRAWINGSLaboratory drawings can be made using several methods. Somedrawings are made in circles that represent the viewing field of amicroscope or another type of magnifier. When completing thesedrawings, be sure to include the magnification at which you viewedthe object. Other laboratory drawings represent organisms or parts oforganisms. These drawings show the relative size, shape, and locationof anatomical structures. When completing representative drawings,make the structures as clear and as accurate as possible.

Most laboratory drawings are labeled. Use the followingguidelines to help make your laboratory drawings.clear and legible:

•Use a ruler to draw label lines.

•Label lines should point to the center of the structure being labeled.

•Do not write on the label lines.

•Print all labels horizontally.

•Label the right-hand side of the drawing, if possible.

•Do not cross, label lines.

EXERCISE 3The following drawing was made without using the guidelines above.Circle those parts of the drawing that do not follow the guidelines.Then, on the lines provided, explain how the drawing should be done.

How Plant andAnimal Cells Differ

1. Place a drop of water on a clean slide. Obtain epithelial cells by gently scraping the inside of your cheek with a clean toothpick asshown in Figure 1. CAUTION: Never reuse a toothpick or put anything in your mouth which may not be clean. Stir the material fromthe toothpick in the drop of water on the slide. Then immediatelybreak the toothpick in half and throw it away.

PART I. HUMAN EP^THELIAL CELLS

Procedures and Observations III

waterin dropper bottle

methylene blue stainin dropper bottle

Lugol's iodine solutionforceps

oniolpipettetoothpickcover slipsslidesmicroscope

ObjectivesIn this activity you will:1.Observe human epithelial cells.2.Observe onion cells.

3.Describe the differences between animal cells and plant cells.

Materials

BackgroundAlthough plant and animal cells have many structures in common, •

they also have basic differences. Plant cells have a rigid cell wall, and ilthey are green, they also have chloroplasts. Animal cells lack both a cellwall and chloroplasts. They- also lack -the central uacuole common to

plant cells.

You will observe and compare animal cells and plant cells. You willfirst examine epithelial cells from the inside of your cheek. Epitheliumis a type of tissue that covers the surfaces of many organs and cavities

of the body.You will \\^o ohirpr^ oni'or\ epidci'iMO.! cells . TK^^c

Ure. fhe layfs of •^^e oi|on.

How Plant andAnimal Cells Differ

c. Describe the appearance of the cytoplasm.

b. What is the shape of the cells?

a. Make a^^rawing of two or three celb as they appear under highpower. Label the nucleus, nuclear membrane, cytoplasm, and cell

membrane of one of the cells, (use

Figure 1

2. Add a small drop of methylene blue stain to the slide. CAUTION:Stain can damage clothing and discolor skin. Use a clean toothpick tostir the cells on the slide, then immediately break the toothpick andthrow it away. Carefully place a cover slip on tKe slide. Examine the

slide under low power. When you find some cells that are separate

from each other, examine them under high power. Recall that you

may have to adjust the diaphragm to reduce the intensity of the

3. Explain that the cell membrane is immediately insidethe cell and is sometimes difficult to see.

Figure 2

3. Examine the wet mount under low power. Adjust the light to providethe best contrast,

a. What is the shape of the cells?

1.Cut an onion bulb into quarters.

2.-Take an inner layer of the onion and, with a razor blade, cut several

l/Z-cm squares through the paper-thin epidermis lining the leaf. Then,with a forceps, remove one of the squares of epidermal tissue. Place

it in a drop of water on a slide. Add a cover slip. This procedure isshown in Figure 2.

f. What structures do you see in the nucleus? Now many are there ineach nucleus?

Stain will enable you to see many cell structures In more detail.

5. Add a drop of Lugol's iodine solution to one side of the cover slip onyour onion slide. CAUTION: Stain can damage clothing and discolorskin. Take a strip of paper towel and touch it to the water at theopposite edge of the cover slip. See Figure 3. This should pull thestain under the cover slip. If more stain is needed, repeat the procedure. Carefully observe the slide under low power, then high power.

e. How many nuclei art present in each cell?

4. Carefully focus on the cytoplasm near the cell wall.

d. Describe the appearance of die cytoplasm and any motion that youobserve.

c What structure do you see that indicates these are plant cells?

Every plant cell is surrounded by a nonliving cell wall composed chieflyof cellulose. Pressed tightly against the cell wall is the cell membrane,which surrounds the granular cytoplasm. The central part of the cellconsists of the large, fluid-filled vacuole. The spherical nucleus appearsas a dense body in the cytoplasm near the cell wall. It is surrounded bya nuclear membrane. Within the nucleus are nucleolL

b. Make a diagram of a single cell. Label only the parts you see.A (use

Remind studentsto addwater to the edge of thecover slip if the specimendries out

g. How does the cytoplasm in the stained celt differ in appearancefrom the cytoplasm in the unstained cell?'

Onion Cells (continued)Observing

•Name.

Laboratory Investigation 5A 65

d. mitochondrion.

c nucleus _

b. cytosol.

5. Give the functions of the cell parts listed below,

a. plasma membrane

Plant cellAnimal cel

4. Typical Plant and Animal Cells

3. Describe hew stain is applied to a slide holding a wet mount preparation..

2. What is the purpose of staining the onion cells? .

1. What structures are found in plant cells but not in animal cells?.

. DATE .

NAME.

CLASS .Plant andAnimal Ceils

_Ab report