For the past two weeks, I have been in a group of 3 studying how different lights affect plant growth. So we growth two chickpeas plants and put one in white light and the other in blue light.

These are the results:

Days    Blue light    White light
           (cm)          (cm)
 1          6.6           8.2
 2          8.5           9.9
 3         11.0          11.6
 6         15.8          16.0
 7         17.2          17.6
 8         18.0          18.2
 9         19.6          18.7

The blue-light plant didn't really branch out a lot whereas the white-light plant branched out a lot.

My question is:

What caused the white light plant to not grow as fast like blue; Why did the white light plant branch out?

What I read about the second question:

Experiments with blue light resulted in plants that are wider than usual. This can be explained by reference to the fact that more flowering buds (more branches) could form by reason of diminished apical dominance at the growth point. http://www.canna.com.au/influence_of_colours

I don't understand why the blue lights plant did not branch out a lot like the white light ones?

  • 3
    $\begingroup$ Hi and welcome to Bio.SE. There are a lot of factors that need to be considered here; temperature, time exposed to light, moisture, earth/fertiliser used, size of potting etc. In order to somewhat account for the variation that will be introduced even if all those factors are controlled, you will need to repeat the experiment and see if any trends emerge. For example, could we be sure of the conclusion (blue lit plants grow more than white lit plants) if we re-ran the experiment and it showed exactly the opposite was true? $\endgroup$
    – James
    Nov 29, 2016 at 7:11

1 Answer 1


With all the research I did this is my understand of why the plant that was exposed to blue light grew taller than the plant that was exposed to white light.

The results of this experiment proves the hypothesis that the plant that was exposed to the blue light will grow taller than the plant that was exposed to white light. Chlorophyll is a green photosynthetic pigment that is found in most plants. The chlorophylls are found around pigments in the photosystem, chlorophyll helps the plant to get the right wavelength of light. There are two types of chlorophyll a and b. Chlorophyll a absorbs red and violet wavelength best, but it absorbs very little blue light. Chlorophyll b absorbs a lot of blue light. Understanding chlorophyll b will explain why the blue plant grew taller than the white plant. It grew taller because in both of the photosystems there were more chlorophyll b then a, therefore there was a lot of pigments that absorbed the blue light and the plant was able to use the energy to produce more ATP which in the end resulted in more growth. There were many factors that we could not control temperature, time exposed to light, moisture, earth/fertilizer used, size of potting. In order to get an accurate result of different light affecting the growth of plants some of these factors must be implemented.

Sources: http://scienceline.ucsb.edu/getkey.php?key=3155

Can someone Confirm if this is right?


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