brain is the organ which does play a role in mechanical or chemical digestion
<u>Answer</u>: c. a and b
Trees play vital roles in the production of oxygen as well as the fixation of carbon from 
. As trees use nitrogen, phosphorus and water as nutrients for growth, their diminishing numbers would change the balance between these three elements significantly.
Thus, during rains, the water level will rise much faster and higher in the absence of trees. These could possibly lead to increasing cases of devastating landslides.
Answer:
Because they don't have fertilizer.
Explanation:
Well, if this was a long time ago, then farmers did not have fertilizer. So, there are bacteria on the roots of plants that convert nitrogen into a usable form. It's very important for growing, and when farmers harvest the crop, not much of the nitrogen is returned to the land, so it is not as fertile. Fertilizer is largely consisted of nitrogen, so that is why farmers use fertilizers today. But "a long time ago," farmers did not have fertilizer.
Answer:
Scientists know that any response during an experiment is associated only with that cell type.
Explanation:
A cell culture is a group of cells that develops from a single original cell. Biologists can use cell cultures to test cell responses under controlled environmental conditions in order to study interactions between cells, and different processes occurs in it. Cell culture is one of the major tools used in the study of physiology and effect of toxic substances on the cells.
