Onion Root Tips & Meristem


The onion root is used in lab experiments to see how cell division occurs in plants.

The onion root is commonly chosen because the chromosomes are larger than in most plants and stain dark making them easy to view under the microscope.

The onion has specific sections where cells divide. These sections aid in how you can learn more about how plants grown.

Root Cap and Meristem

  • The root cap is an area at the very bottom of the tip, which protects cells that are growing and dividing. The root cap contains cells that protect the actively growing cells in the meristem from abrasion and damage as the root pushes through the soil.

    The meristem, located just above the root cap, is a specific part of the root tip; this area of the root tip is where the cells multiply the fastest. The cells are dividing but not increasing in size, but different stages of cell division can be viewed.

Cell Elongation

  • Above the meristem is a region known as the "cell elongation"; this is where cells are becoming larger and stretched out as the root grows. The cells get larger but do not divide in this region. This is where the cells are sensitive to gravity and respond to gravitropism, which means the cells grow longer downwards towards the root tip.

Stages of Cell Division

  • Plant cells go through different stages of growth in a process known as "mitosis." Before mitosis occurs, the plant cells are actively dividing but not growing yet in a stage known as "interphase."

    When the cells reach mitosis where DNA replication occurs, they go through six stages. These stages are prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis. Two new separate cells are formed when cytokinesis occurs.

Viewing Plant Cells

  • The plant cells in onion root tips can be easily viewed under the microscope as they grow and divide. This is because the chromosomes are supercoiled into a dense, compacted form. The cells are also easier to view when they are stained which makes them darker. A particular stain known as the "Feulgen stain" is used to determine if DNA is present. The root tips of cells are flattened on microscope slides which makes it easier to view individual chromosomes of individual cells.

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