Observe Animal Cells and Identify their Components

Activity 3: Pre-Assessment

1. Answer the following question in your notebook: How do plant cells and animal cells differ? Why would these differences likely evolve in plant and animal cells?
2. Answer the following question in your notebook: What microscope techniques could help us see more structures within cells?
3. Discuss the answers to questions 1 and 2 with a partner and then the class.

Activity 3: Observe Animal Cells and Identify Their Components

Animal cells are eukaryotic and possess subcellular components in common with the plant cells you observed in Activity 2. Organelles that plant and animal cells share in common include the nucleus, Golgi apparatus, mitochondria, ribosomes, and the endoplasmic reticulum. These are all participants in protein synthesis. An illustration of an animal cell is shown in Figure 4.5. There are some exceptions to these general components. For example, mature red blood cells (RBC) which have ejected their nuclei to have more room for hemoglobin, the protein that carries oxygen around the body. One of the easiest eukaryotic cells to obtain in the lab is the squamous epithelial cell found in the tissue lining the internal surface of your cheek. These cells are arranged in a flat layer and are easy to remove and observe.

Safety Precautions

• Be careful when handling glass slides; the edges may be sharp.
• Dispose of used cover slips in a glass disposal box.
• Observe proper use of the microscope; avoid handling the electric cord with wet hands.
• Do not use the coarse adjustment knob of the microscope at high and oil immersion objectives.
• Inform your teacher immediately of any broken glassware as it could cause injuries.
• Used cotton swabs are considered biohazard; dispose of swabs in the biohazard trash container as soon as you have used them.
• Methylene blue is a dye; be cautious not to ingest methylene blue.
• Wash your hands with soap and water after handling live organisms.

For this activity, you will need the following:

• Prepared slide of red blood cells
• Light compound microscope
• Clean microscope slide, cover slip
• Clean cotton swab or toothpick
• 0.5–1 percent methylene blue solution
• Dropper or pipette
• Small squares of paper towels

For this activity, you will work in pairs.

Guided Inquiry

Step 1: Hypothesize/Predict: Predict the different features you expect to see in the animal cell versus the plant cell. Predict the differences you will see between animal cells and prokaryotic cells under low and high magnification. Include in your prediction the size differences between a cyanobacterium, plant cells, and animal cells. Create a table in your notebook to draw and label your predictions in your notebook.

Step 2: Student-led planning: Observe the red blood cell prepared slide. Record your observations (draw and label any visible parts, use color if visible, include magnification and size of cells) in your notebook. Both partners should view, draw, state the size and magnification, and label each sample.

Step 3: Prepare your cheek cell slides as shown in Figure 4.6 and Figure 4.7 and outlined below.

• Take a clean cotton swab or toothpick and gently scrape the inside of your mouth.
• Smear the cotton swab or toothpick on the center of the microscope slide for 2 to 3 seconds.
• Add a small drop of methylene blue solution (a dye) and place a coverslip on top.
• Remove any excess solution by allowing a paper towel to touch one side of the coverslip.
• View the slide at all magnifications.
• Record your observations as drawings. Use color if present, label the magnification, and estimate the size of the cells in your notebook. Record your observations (drawings, color if present, labels, magnification, and size of cell) in your notebook.

Step 4: Critical Analysis: Were differences observed between the RBC and the cheek cell? What does the methylene blue stain reveal in the cheek cell? There should be small blue dots visible on the cheek cells much smaller than the nuclei.

Hypothesize what those blue dots might be. How does the animal cell compare to the plant cells in Activity 2 and the cyanobacteria in Activity 1? Record the answers to these questions in your notebook.

Assessments

1. Based on the staining technique you performed in this activity, how could you distinguish stained prokaryotic cells from stained eukaryotic cells?
2. What do all cells have in common, whether prokaryotic or eukaryotic? What major differences would you expect to find?
3. Identify whether the following images (Figure 4.9a, Figure 4.9b, and Figure 4.9c) show an animal cell, a plant cell, or a prokaryote cell. Explain how you know the difference.