The correct answer is letter A. The disk soaked in distilled water is the controlled variable because it is the only differential factor from all of the other variables which are all disinfectants. Controlled variables are elements that are not changed throughout the experiment. When something is unchanged it is better for scientists to analyze the relationships of other variables better.
Answer:
(Didn't list features so might be wrong)
distance away from organism to energy source(sun)
the amount of carbon dioxide
the amount of water
the concentration of energy (example; if you were conducting a lab and you use light bulbs as a energy source, higher wattage would be better then lower wattage.)
all of these need to be proportion to each other if you have too much of one thing and not even of the other then the organism will not preform photosynthesis efficiently.
Explanation:
Highschool biology lab
Macrophages (histiocytes) - are phagocytes - these cells 'eat' particles such as bacteria. These cells are derived from white blood cells called monocytes (see the section on blood).
:)
Hypotonic is transport :)
