Comparing Plant And Animal Cells Lab (1)

Comparing Plant and Animal Cells Lab Objectives: In this lab you will observe cell structures, compare and contrast animal and plant cells and relate the structure of a cell to its function. Materials: glass slides, coverslips, pipette, water, microscope, toothpick, onion, Elodea plant in water, methylene blue, iodine solution, papertowel Procedure: Part 1: Plant Cells Onion bulbs are organized tissue that, under appropriate conditions, will give rise to an entire plant. The curved pieces that flake away from an slice of onion are called scales. On the underside of each scale is a thin membrane called the epidermis. 1. Obtain a piece of onion and remove one of the scales from it. Use forceps (tweezers) to pull away the epidermis from the inner surface. Be careful not to wrinkle the membrane. Place a drop of water on the center of a microscope slide and cut a very small square piece of onion membrane. Using a toothpick to straighten out any wrinkles, place the membrane sample in the drop of water. Take a coverslip and carefully place it over the sample, lowering it at an angle to the slide. 2 Examine the epidermis under low and high power. Unstained specimens are often seen with less light so try turning down the amount of light using your diaphragm. Draw (TO SCALE) what you see under low and high power. Be sure to label the magnification of each drawing.

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Question 1 – How many layers thick does the onion epidermis appear to be?

Question 2 – What is the general shape of a typical cell? 3. To stain your specimen, remove your slide from the microscope. Place a drop of iodine on the side of the coverslip so that the drop is just touching the edge of the coverslip. Draw the water from underneath the cover slip with a piece of paper towel placed edge to the opposite side of the coverslip from the iodine drop. The stain will be drawn under the coverslip to replace the water and stain the cells. Draw the cells again as you did before.

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QUESTION 3 – Within an individual cell, where are the cytoplasm and nucleus found? QUESTION 4 – Label the following structures in the cell drawings above: nucleus, cell Wall, central vacuole, cytoplasm

5. Obtain a single leaf of Elodea (from the young leaves at the tip) and prepare a wet mount as you did before. Again, draw the specimens under low and high power. Also, take notice of the way it looks under medium power as well.

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QUESTION 5 – Draw a single chloroplast using color!

QUESTION 6 – Are the chloroplasts moving or stationary? QUESTION 7 – In what ways are the cells of onion epidermis and Elodea similar? Different?

QUESTION 8 – What observable characteristics can be used as evidence for classifying a specimen as a plant? Use information from your textbook to help you with this question.

Part 2: Animal Cells 6. Prepare a slide of epithelial cells from your oral cavity, by the following procedure. Place a drop of methylene blue on a glass slide. Take a flat toothpick ( a NEW one ) and using the large end, gently scrape the inside of your cheek 3 or 4 times. Gently mix the end of the toothpick with the methylene blue dye. Take a coverslip and carefully place it over the sample, lowering it at an angle to the slide. 7. Examine and draw the cells under low and high power. Be sure to draw the cells to scale as you see them in the microscope’s field of view.

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QUESTION 9 – Inside the mouth, these cells are joined together in a sheet. Why are they scattered here?

QUESTION 10 – How are these animal cells different from the plant cells you observed?

QUESTION 11 – Label the cell membrane, nucleus, and cytoplasm in the cells you drew above.

QUESTION 12 – What is the relationship between plant cell structure and the ability of plants to stand upright? 8. Wash and DRY your microscope slide and place it back in the box. Return coverslips and any staining solutions. Your microscope should be put away properly and your lab table should be wiped down even if it does not look dirty!