Cracking the AP Biology Exam

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Laboratory

LAB 3: MITOSIS AND MEIOSIS

This lab highlighted the differences between mitosis and meiosis. There were two parts to this lab.

EXERCISE 3A

In lab 3A, slides of onion root tips were prepared to study plant mitosis while slides of a whitefish blastula were prepared to study animal mitosis.

What are the general concepts you really need to know?

Be familiar with the concept of mitosis in both plants and animals. In plants, primary growth is limited to dividing cells in the tips of roots and stems. In animals, however, mitosis occurs in all growing cells, especially those in dividing embryos.

EXERCISE 3B

In lab 3B, the sexual life cycle of the fungus Sordaria fimicola was examined. Sexual reproduction in this fungus involves the fusion of two nuclei—a plus strain and a minus strain—to form a diploid zygote. The zygote immediately undergoes meiosis, and haploid cells called ascosporesare produced. These ascospores are found in tiny, sac-like structures called asci.

What are the general concepts you really need to know?

• Know the concept of meiosis. Meiosis involves crossing-over of chromosomes to create genetic variability. Crossing-over and recombination in fungi results in a particular arrangement of these ascospores within asci. If crossing-over occurs, you’ll see different genetic combinations in the offspring compared to the parent strain. If, however, crossing-over does not occur, each ascospore will be identical to the parent strain.