Question

Why do you think these small, round structures (chloroplasts) were not present in the onion cells? What portion of the onion plant could you locate these structures? Why would you predict they would be found there? (hint: How does an onion grow?)

Answer 1

Chloroplasts are absent in onion cells examined from the bulb because it is not exposed to light and does not perform photosynthesis, unlike the green leaves or shoots which do contain chloroplasts to carry out photosynthesis.

Step-by-step explanation:

Chloroplasts were not present in the onion cells because the cells observed were likely from the onion bulb, which is generally not exposed to light. Photosynthesis is the main function of chloroplasts and occurs in areas of the plant that are exposed to light, primarily in the leaves. Thus, you would find chloroplasts in the green parts of the onion, such as its leaves, because these are the parts that can receive sunlight and carry out photosynthesis.

Onions grow by using energy stored in the bulb, which develops from the base of the leaves where chlorophyll-containing chloroplasts are not necessary. The cells in the onion bulb typically store nutrients in the form of carbohydrates and do not perform photosynthesis, thus they lack chloroplasts. However, the green shoots or leaves of an onion plant do contain chloroplasts, for this is where photosynthesis primarily occurs, utilizing sunlight to synthesize nutrients from carbon dioxide and water, with the production of oxygen as a byproduct.