why the onion cell do not have a chroplast?

Answer 1

Because the onion bulb is not the photosynthetic portion of the onion plant, the cells will not have visible chloroplasts.
In truth the practical answer
to this is that they don't need chloroplasts. Think of where an onion
lives and how much light it normally receives. Chloroplasts only function
in the presence of light. Because it costs energy to develop chloroplasts,
it is not useful for the plant to put develop them if they won't function.
However accurate, this answer is a little simplified compared to what
really happens.

Chloroplasts are only one type of plastid, along with chromoplasts (causing
the red color of peppers and tomatoes) and amyloplasts (storing starch in
potatoes and corn). None of these plastids can be assembled from raw
materials within the cell of a plant. Rather they all develop from another
type of plastid called a proplastid. Proplastids are small and clear.
They divide at the same time the cells divide, so every cell in a plant has
proplastids. However, they are difficult to see in most plants because of
their size.

One piece of evidence that the proplastids exist in onion cells is easily
seen. Leave an onion exposed to light for several days or weeks. It will
begin to grow new green leaves. Also, some of the outer layers of the bulb
(actually leaves, too), will begin to green up, as their proplastids
develop into chloroplasts.

According to Eames and MacDaniels (1925, p 12)
Plastids may be found in all living cells of a plant, and probably are
present in every cell in the early stages of development. Later they
become restricted to certain cells, and are abundant only in those which
have specialized functions, such as photosynthesis, storage, and color
manifestation. Plastids do not occur in the fungia, bacteria, �
�Plastids multiply freely by division, and in this way the large numbers
present in some cells are in part secured. Plastids are present in the
very young meristematic dells where they are very minute, the smallest
being at the limit of [light, not electron] microscopic visibility.
Light is needed for the development of chloroplasts. There are many types
of plastids found in plant cells but, not all plant cells have all the
different types of plastids. Some plastids can contain pigments other
than chlorophyll and are called chromoplasts and plastids that store
starch are amyloplasts. It is thought that all plastids arise from a pro-
plastids. Since onion bulbs are below ground they do not get the light
necessary for chloroplast development. There are lots of web sites
available that have information on this subject. Try a google search
using the words "chloroplasts and onions" or "onion chloroplasts". If you
are interested in learning more about cells, onions are a good
experimental organism. Onion root tips are great to study mitosis and
meiosis and the thin membranous epidermis between the onion rings are
perfect for observing plasmolysis

References:

Eames, A.J. and L.H.MacDaniels. 1925. An Introduction to Plant Anatomy.
McGraw-Hill Book Company, Inc:NY.

Esau, K. 1953. Plant Anatomy. John Wiley And Sons, Inc:NY.

Esau, K. 1977. Anatomy of Seed Plants, 2nd ed. John Wiley and Sons,
Inc:NY.

Answer 2

Onion Cell

Answer 3

because it is a underground part of the onion plant.. if i m not wrong u r talking abt the onion bulb. Chloroplast is needed for trapping sunlight and is found in aerial parts of the plants friend.

Answer 4

they do not get the light necessary for chloroplast development during the growth underground...