Biology Questions: Basic Cell Structure

Introduction: All living things are composed of cells. The person credited with the discovery of the cell was Robert Hooke in the 17th century. He viewed cork through a microscope that he invented and he named the small, rectangular units “cells.” Biologists divide cells into two types based on the complexity of their internal structure. Prokaryotes are simpler cells. The DNA is found in the cytoplasm and not within a nucleus. They also do not have large, membrane bound organelles inside their cytoplasm. Examples of prokaryotes include bacteria, cyanobacteria, and archaea. Eukaryotes are more highly organized. They contain membrane-bound organelles such as lysosomes, Golgi bodies, mitochondria, and chloroplasts. Eukaryotes also house their DNA within a membrane bound nucleus. Protists, fungi, plants and animals are examples of eukaryotes. In the early part of the 19th century, the German biologists Schleiden and Schwann realized that all living things – plants and animals, are made up of cells. This understanding eventually established the cell theory. Purpose: To observe and describe basic cell structures and to compare and contrast plant and animal cells. PROCEDURES: Activity 1-Prokaryote cells 1. Observe the slides that demonstrate the three different shapes of bacteria. 2. In the circles provided, sketch the shapes of spirilla, coccus, and bacillus. 3. Answer the questions for Activity 1 on the data page. Activity 2-Plant cell; ONION 1. Remove a thick scale and peel the transparent tissue from the inner surface. 2. Cut a square of the tissue and mount it on a slide and add a drop of iodine stain onto the onion tissue. (NOTE: avoid wrinkling the tissue) 3. Add a coverslip to your mount and examine the onion cells under low power (100X). 4. Select one cell that shows the contents clearly and examine it carefully under high power. 5. In the space provided, draw the cell under high power and label the following cellular structures: nucleus, cell wall, cell membrane (not visible but you should label where it should be) and cytoplasm. 6. Answer questions c-g. Activity 3-Plant Cell; ELODEA 1. Prepare a wet mount of a single Elodea leaf. (Break one of the younger leaflets near the tip of the branch) 2. Examine the leaf on scanning power, center, focus and switch to low power. 3. Center, focus and switch to high power. 4. Using the fine adjustment knob focus on the layer of cells that have moving chloroplasts. (You may need to look very closely to see them moving. In some samples they will be moving faster than others.) 5. Draw 5 cells and label the following cellular structures in ONE of your drawn cells: cell wall, cell membrane (not visible but you should label where it should be), chloroplasts, and cytoplasm. 6. Answer questions h-m. 7. Wash and dry your slide and coverslip for activity 4. Activity 4-Animal cell; CHEEK 1. Place one drop of iodine on the surface of your microscope slide. ** Remember iodine will stain clothing and skin. 2. Use a clean toothpick to gently scrape the inside of your cheek. 3. Smear the toothpick that now has your cheek cells on it, in the drop of iodine. You may not see much on the toothpick; however there will be hundreds of cells. 4. Throw your used toothpick in the biohazard bucket! 5. Place the coverslip over the smear as you would with a regular wet mount. Following the proper procedure, examine the slide under high power. 5. Draw and label the following structures of the cheek cell: cell membrane, nucleus and cytoplasm. 6. Answer questions n-s. 7. REMEMBER to put your used cheek cell slide in the sharps container! Be sure you spray and wipe down your lab station so that it is clean and dry!!! DATA Page Activity 1: Bacteria. In the spaces below, draw the 3 different shapes of bacteria. a. Name two differences between prokaryotic and eukaryotic cells. 1.___________________________ 2.___________________________ b. If you were to look at your skin under a microscope would there be bacteria on it? _____________ Activity 2: Onion Cell. In the space below, draw and label an onion cell observed under high power. 450x c. What is the shape of the cells? ________________________________________________ d. Are all the cells similar in shape? _____________________________________________ e. What is the appearance of the cytoplasm? __________________________________ f. What is the appearance of the nuclei? ____________________________________ g. Are the nuclei always in the same position in the cell? ____________________ Explain your answer. ____________________________________________________ Spirilla Coccus Bacillus Activity 3: Elodea leaf. 450x h. How many cell layers thick is the leaf? *Focus up and down to determine this. You’re approximating here so this is just an estimate. __________________________________________ i. Describe the color and shape of the chloroplast. ________________________________ j. What is the function of the chloroplasts? ______________________________________ k. Why is it beneficial for the chloroplasts to move rather than remain stationary in the cell? _________________________________________________________________________________ l. What cell structures are responsible for this movement of chloroplasts? ___________________________________________________________________________ m. Why didn’t the onion cells have chloroplasts like this Elodea plant? Explain.__________________________________________________________________________ Activity 4: Cheek cell. 450x n. Why did you use iodine? __________________________________________________ o. Why are cheek cells all different shapes compared to the box-like shape of plant cells? __________________________________________________________________________ p. The light microscope used in the lab is not powerful enough to view other organelles in the cheek cell. What parts of the cell were visible? _________________________________________________________________ q. List 2 organelles that were NOT visible but should have been in the cheek cell. __________________________________________________________________ r. Is the cheek cell eukaryotic or prokaryotic? How do you know? __________________________________________________________________ s. The mouth is the first site of chemical digestion (chemical reactions) in a human. Your saliva starts the process of breaking down the food you eat. Keeping this in mind, what kind of protein do you think would be present in your saliva? _______________________________ Conclusion l. Based on your observations from this lab, not from the textbook, list at least three observable differences between prokaryotic, plant, and animal cells. 2. Animal Cell Organelle Identification: Without looking at your book, label as many organelles as possible on this animal cell. Once you are finished labeling, consult your book or notes for those that you missed. 3. Name three organelles that you would find in a plant that you do not find in the above animal cell. 4. Name a least one organelle that is found in an animal cell that is not found in a plant cell. 5. Name three different ways that a cell can move.