Answer:
What happens when air is heated or cooled? ... So air, like most other substances, expands when heated and contracts when cooled. Because there is more space between the molecules, the air is less dense than the surrounding matter and the hot air floats upward. This is the concept used in the hot air balloons.
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The gel-filled space inside the chloroplast is called the stroma. The stroma surrounds the inner membrane of the chloroplast. Grana or stacks of thalakoid can also be found in the stroma.
To eliminate the possibility of hidden or unknown variables, the scientist must run an A) Control experiment
