Biology, Answering the Big Questions of Life/Mitosis

Mitosis and Meiosis Laboratory

Mitosis

To do the Mitosis lab, you must have access to microscopes and have a set of mitosis slides.

Students should observe and draw diagrams of the slides, labeling each by phase.

Recommended slides are:

Animal Mitosis: Whitefish Blastula

Plant Mitosis: Onion Root Tip(Allum)

Mitosis in Onion Root Tip

Mitosis phases visible in onion root tip slide

Students should make drawings of the steps of mitosis observed

These are the standard slides that have been used to teach mitosis and meiosis for decades.

Onion Root tip has large cells with clear easy to see chromosomes. Whitefish Blastula, when dyed properly, clearly shows the spindle.

Use the two to point out the differences between Animal and Plant cell division.

• Animals have visible centromeres and plants do not.
• Animal cytokinesis involves pinching off. Plant cells form a cell plate.
• In animal embryos all of the cells are dividing at once, in plants they divide only in certain regions at the tips called meristems.

Remind the students that although the slides are frozen in place, the cells are constantly moving. If possible show a slide of living cells dividing.

Meiosis

It is not usually possible to see all of the steps of meiosis under the microscope, for this reason, it is recommended that you only ask the students to observe tissues of organs containing cells dividing by meiosis.

Recommended slides:

Grasshopper testis
Human ovaries

For Grasshopper testis, point out that you can clearly see chromosomes in many of the cells showing that the cells are dividing.

Also point out the tails of sperm which are clearly visible in testis samples.

In the ovary samples, point out the large egg cells surrounded by many small follicle cells. Tell the students that egg cells result from uneven division of the cytoplasm during meiosis so that one cell gets almost all of the cytoplasm, and the other cells are very small structures called polar bodies.

Point out that Meiosis is necessary to keep the number of chromosomes from rising every time diploid organisms reproduce.

Advanced options

If possible, you can try to obtain live dividing cells. Please note that cell division takes from about 20 minutes in bacteria to several hours in some animals.

Good candidates include,

• Bacterial cells - If your microscope is big enough you can observe cells dividing by binary fission. You will not however be able to see the chromosomes.
• Yeast cells - Yeast samples will easily grow under the microscope, but it is sometimes difficult to locate a budding cell among the thousands of non-budding ones. Try to get living cells in the log stage of growth.
• Although I have never done it, it is theoretically possible to make slides of living root cells. The hard part will be to dye the chromosomes in a way that will not fix the cell.