Re: Why do plant roots contain Chloroplast ?

First, let me say that your reason for asking this question ("i just 
wanted to know")is one of the best reasons that you could possibly have 
for asking(although I must insist punctuation is important).  Curiosity, 
wanting to know something, has motivated generations of scientists.  Too 
often science is criticized for not being useful, as if satisfying our 
human curiosity and understanding nature is not worthwhile or useful.  So 
by all means, stay curious; keep asking questions.

Plants have chloroplasts in their roots because all the cells in 
multicellular organisms arise from a single cell via cell division.  The 
cellular contents including chloroplasts multiply and are apportioned to 
each daughter cell.  So all cells at the outset are basically identical 
although they develop to have different functions. Plants cannot 
manufacture new chloroplasts; chloroplasts can only come from other 
chloroplasts, which is one of the reasons scientists think chloroplasts 
were originally photosynthetic bacteria.  Chloroplasts have their own DNA 
and divide like other bacteria.  So root cells, stem cells, and leaf cells 
all start with the same complement of cell contents.  Actually what is 
present are plastids, which can develop to have one of several functions.  
Chloroplasts develop chlorophyll and function in photosynthesis.  Plastids 
in roots usually don't develop chlorophyll, but plastids in root cells 
function to store starch.  Starch grains are actually a type of plastid 
called amyloplasts (amylo- meaning starch).  Other plastids produce orange 
or red pigments and are called chromoplasts.  Such plastids produce some 
fruit and flower colors. The plastids in root cells of some plants like 
epiphytic (growing upon another plant) orchids develop chlorophyll making 
their roots green.  Some plants will make green roots if their roots are 
exposed to light.  All seedlings need light to stimulate chlorophyll 
production turning the plastids into chloroplasts.  Bean seeds germinated 
in the dark remain non-green until exposed to light.  Try it, you'll see.