Reflection: Developing a Conceptual Understanding Modeling Mitosis - Section 6: Putting It All Together: How Models are Developed


In this lesson, I stress the importance of incorporating certain sampling techniques with my students. Students are encouraged to avoid false replication, collect from the proper location of the root, and ensure reliability.  

First, I stress that one sample is defined as all the cells counted on one root from one onion bulb. Students are required to count a large number of cells (100) on a single root. If they need to use multiple fields of view as part of their count, they may.  However, they can only count one experimental sample.  Students, also, cannot take multiple roots from the same onion. In fact, each student group is encouraged to use  a different onion for their counting.  This is too avoid pseudoreplication. All root samples from a single onion bulb have the same genetic makeup so they must be considered the same sample.  By counting cells from root squashes from different onion bulbs, onions with potentially different genetic variation are considered. 

Also, it is important that students obtain their sample from the apical meristem of the onion root and not the end of the onion root tip . The root tip cap is a protective area and cell are not actively grow.  The most mitotic grow occurs right above the root tip cap.  For students to obtain the best chromosomal squash, they need to use cells from that area.  

Onion roots can grow at different rates so it is important that students not rely on counts from only one plant.  That is true even with high cell counts (200, 500, or 1000).  Instead, it would be better to count 100 cells from 200 plants to obtain the variation between individual plants.  It will give more reliability to the sampling.  


  The Importance of Sample Size
  Developing a Conceptual Understanding: The Importance of Sample Size
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Modeling Mitosis

Unit 9: The Cell Cycle
Lesson 1 of 2

Objective: Students will create a stop motion video that shows a healthy cell cycle and the behavior of chromosomes during mitosis.

Big Idea: Today students learn how scientists first determined how cells divide.

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3 teachers like this lesson
Growth and Development, mitosis, Science, Developing and Using Models, Systems and System Models, cell cycle
  86 minutes
mitosis  261 14  pressed  root meristem of onion  cells in prophase  anaphase
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