MadSci Network: Cell Biology

Re: What is the reasoning why the onion skin is not green?

Date: Tue Oct 9 09:58:18 2001
Posted By: Cynthia Galloway, Faculty Biology
Area of science: Cell Biology
ID: 1001267095.Cb

While most plant cells are typically green, the epidermal cells are rarely 
green.  Plant cells are green because of the presence of chloroplasts and 
the only epidermal cells having chloroplasts are the guard cells of the 
stomatal apparatus. The cells beneath the epidermis are green and you can 
see them through the colorless epidermis.  Plant cells not exposed to 
light, such as root cells, do not develop chloroplasts. While an onion bulb 
is not a root, it shares a similar environment with roots. The rings of an 
onion are actually modified leaves.  They are surrounding the stem so, when 
you slice an onion you may notice a green spot in the center. This green 
spot is the stem.  The main function of the onion bulb is food storage for 
the plant. The food being stored comes from photosynthesis.

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