is held constant throughout the experiment.
the control group is used as a foundation for your experiment so you know what changes what and how to manipulate the independent variable.
Answer:
Brain is the main organ of this system- nervous system.
Produces hormone- Endocrine System
Breaks food down for body's use Digestive System
Sends nutrient to all the body cells circulatory system.
Provides structure for the body and
provides support and movement- Skeletal system
Kidneys are the main organs of this system- Excretory system
lungs are the primary organs of this system Respiratory system
Um...they become contaminated too, it's just a matter of determining the amount of contamination in the water in ppm & rate of absorption in the organism.
i think its b. People can’t digest cellulose.
hoped this helped