Cell Lab for Introductory Biology

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This lesson follows a discussion on the parts of the cell.  There are many types of cells students can look at, and you can even order preserved cell slides from most biological supply companies.  For viewing cells I prefer to take real cells from common specimens.   I think this helps students to see the connection between what they are viewing on a slide and where it came from.

The easiest cell sources for an introductory lab are onion cells and anacharis cells.  I like to use both in a single lesson because both have specific characteristics of plants but they are distinctly different.  Students get the Plant Cell Lab Worksheet where they can look at the cells in the microscope.

Onions are an easy source for viewing cells, but you have to be careful to get the exact part.  Slice the onion and pull a ring from it.  The part you are looking for is a thin (almost skin-like) layer of cells on the inside of the ring.   Pull that carefully off and use a scalpel to cut it to a size that will conveniently sit on a slide.   You can also add iodine or other stains to make the cells look more dramatic.  If you want students to view the cells on high power you must add a coverslip.  I usually make one slide while the class is watching so they see the procedure but have slides already made for the students.   You can have them make their own slides, but this can get messy especially if you are limited on sinks and supplies.

The most obvious structures of the onion cell are the walls and the nuclei of individual cells.  Be sure to point out to students that they are not just looking at one cell, but looking at many cells lined up like a brick wall.   I’m always amazed at how many students don’t realize that they are looking at many cells and not one cell.

The procedure is similar for the anacharis leaf , though no staining is necessary.  Anacharis is a common aquarium plant that you can buy at most pet stores that sell fish and live plants.  The main difference between it and the onion is the obvious presence of chloroplasts.   Students have a great time watching the chloroplasts “march” around the central vacuole – cytoplasmic streaming.  Again, you may need to reinforce that they are looking at many cells, each having their own nucleus, cell wall and each having their own chloroplasts.

You can also do a cheek cell lab but I find with freshman this can be difficult.  You almost need another person to help students get a good focus and make sure they are not looking at air bubbles or other debris on the slide.  I usually save the cheek cell lab for older students in anatomy class or second year biology.
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Short video of elodea cells where you can view cytoplasmic streaming. Note how the chloroplasts move within the cell.

September 8, 2009 · smuskopf · Comments Closed
Posted in: Best Practices