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Learning Objectives

At the end of this lab, students should know...

What are the common features of all cells?

All cells share common features such as having a plasma membrane, a cytoplasm, DNA, and ribosomes. A plasma membrane is a phospholipid bilayer that surrounds the cell. Inside the plasma membrane, the cell is filled with a gel-like fluid called cytoplasm that contains organic molecules, salts, and other materials that are vital for the cell’s functions. All cells use DNA as the genetic material, which is the hereditary blueprint to construct cellular structures and products. Finally, all cells use ribosomes to synthesize their protein products.

What are the two main types of cells? How do ecologists calculate the biodiversity in a local community?

There are two types of cells based on the location of their genetic material: prokaryotic and eukaryotic.

What are the main differences between prokaryotic and eukaryotic cells?

Prokaryotic cells are small in size and lack a distinct nucleus and organelles. Eukaryotic cells are relatively larger, contain a distinct nucleus, and various organelles with specialized functions.

What are the differences between plant and animal cells?

Plant cells have chloroplasts, which are used for photosynthesis and often contain the green pigment chlorophyll. Additionally, they are surrounded by cell walls, which are rigid outer layers made of cellulose to support growth and water retention. Because they need to store large amounts of water to maintain the water pressure in the cell, they have larger vacuoles than animal cells. In addition, plant cells also have another type of specialized storage organelles called plastids, which contain pigments and photosynthetic products, such as starch.

How do we visualize cells?

Most cells are too small to see with the naked eye and can only be observed with a microscope. However, most cells are also transparent, therefore they first need to be stained selectively based on their molecular composition. Next, they are mounted on glass slides to be observed with a microscope.

List of Materials

  • Microscope Slides
    10
  • Glass coverslips
    10
  • Toothpicks
    10
  • Forceps
    10
  • Glass droppers
    15
  • Petri dishes
    10
  • Stop watch
    5
  • Blotting paper
    1 roll/station
  • Safranin O Solution
    1 bottle/station
  • Methylene blue solution
    1 bottle/station
  • Glycerol
    1 bottle/station
  • Immersion oil
    1 bottle/station
  • Lens cleaning paper
    1 bottle/station
  • Onion bulbs
    Dependent on the lab size
  • Compound Microscopes (with 100x Oil Immersion Objective)
    Dependent on the lab size

Lab Prep

  1. Visualizing Onion and Cheek Cells
    • Immediately before the experiment, wash and peel onion bulbs for the class.
    • Remove the entire brown outer skin and cut the onion in half with a knife. Pull apart the layers of the onion. The thin, nearly transparent film layers within the onion will be used by the students.
    • Place the onion film into a Petri dish and then place this into the refrigerator until the students arrive.
    • Bring out the microscopes and set them on the lab bench.
    • Set the microscopes to the lowest magnification and plug them into an electrical outlet.
    • Clean the lenses with lens paper or laboratory wipes and test the knobs to make sure the lenses focus properly.
    • Make sure that the stage can be moved.

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