Answer:
Experimental set up in the lab.are under the control of the scientist,therefore they can manoeuvre the the surrounding conditions to suit the experimental set up for best results. In addition the lab.environment does not involve the complex interactions or reaction between the set up and the lab. environments, compare to the natural environment.
Natural experimental set up gives accurate results from the interaction of the organisms(e.g animals) under investigation in the natural environments,thus the results obtained are natural interaction of the organisms based on the environmental factors the organism are exposed to.However, the number of organisms are usually large,and therefore great effort is needed to determine the actual cause and effects of the factors affecting the organisms under investigations in this natural environments.
