Students use digitized images of onion root tips to identify different stages of the cell cycle. By counting the number of cells in each stage, they estimate how much time cells spend in interphase, prophase, metaphase, anaphase, and telophase.

1. Access digitized microscope images of onion root tips.
2. Review the five phases of the cell cycle: interphase, prophase, metaphase, anaphase, and telophase.
3. Examine the cells in the images, identifying which stage each cell is in.
4. Record the number of cells observed in each stage.
5. Calculate the percentage of cells in each phase.
6. Use these percentages to estimate the relative time cells spend in each stage of the cell cycle.

📄 Online Onion Root Tips - The Biology Project - Cell Biology: https://biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html

• Compare different regions of the root (e.g., tip vs. elongation zone) to see differences in mitotic activity.
• Use prepared slides of onion root tips under a classroom microscope to replicate the digital activity.
• Extend the activity to compare plant and animal cells undergoing mitosis.

• No safety concerns when using the online digital activity.
• If replicated in the lab with real onion roots, handle stains, sharp tools, and microscopes safely.

• Why are onion root tips good for studying the cell cycle? (They are regions of active growth, with many cells dividing.)
• Why do scientists divide the cell cycle into phases even though it is continuous? (It makes it easier to describe and study distinct events.)
• Which stage of the cell cycle usually takes the longest, and why? (Interphase, because the cell is growing and preparing for division.)
• How does the proportion of cells in each stage relate to the relative duration of that stage? (The more cells observed in a stage, the longer the cell spends in that stage.)